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Socioemotional selectivity theory (SST; developed by Stanford psychologist Laura L. Carstensen) is a life-span theory of motivation. The theory maintains that as time horizons shrink, as they typically do with age, people become increasingly selective, investing greater resources in emotionally meaningful goals and activities. According to the theory, motivational shifts also influence cognitive processing. Aging is associated with a relative preference for positive over negative information in individuals who have had rewarding relationships. This selective narrowing of social interaction maximizes positive emotional experiences and minimizes emotional risks as individuals become older. According to this theory, older adults systematically hone their social networks so that available social partners satisfy their emotional needs.
The theory also focuses on the types of goals that individuals are motivated to achieve. Knowledge-related goals aim at knowledge acquisition, career planning, the development of new social relationships and other endeavors that will pay off in the future. Emotion-related goals are aimed at emotion regulation, the pursuit of emotionally gratifying interactions with social partners and other pursuits whose benefits can be realized in the present.
When people perceive their future as open ended, they tend to focus on future-oriented and development- or knowledge-related goals, but when they feel that time is running out and the opportunity to reap rewards from future-oriented goals' realization is dwindling, their focus tends to shift towards present-oriented and emotion- or pleasure-related goals. Research on this theory often compares age groups (e.g., young adulthood vs. old adulthood), but the shift in goal priorities is a gradual process that begins in early adulthood. Importantly, the theory contends that the cause of these goal shifts is not age itself, i.e., not the passage of time itself, but rather an age-associated shift in time perspective.
This justified shift in perspective is the rational equivalent of the psychological perceptual disorder known as "foreshortened future," in which an individual, usually a young and physically healthy individual, unreasonably believes (either consciously or unconsciously) that their time horizons are more limited than they actually are, with the effect that the individual undervalues long-term goals and long-run pleasure and instead disproportionately pursues short-term goals and pleasure, thereby diverting resources from investment for the future and often even actively reducing their long-term prospects.
The thought of nearing “the end” leads to an increased orientation toward social and emotional targets. Here, “the end” signifies death, which is generally associated with chronological old age. However, it would be inaccurate to limit old age to chronological aging because one’s chronological age does not reveal any information about one’s health, personality, cognitive development, role in social life, and social status. Evaluating old age within the framework of various biological, psychological, and sociological factors makes it easier for researchers to obtain more detailed and specific results. Regardless of the characteristics selected to assess old age, it is possible to say that aging has biological, physiological, psychological, and sociological impacts on individuals, either positive or negative.
== Cross-cultural incidence ==
Researchers have found that across diverse samples – ranging from Norwegians to Catholic nuns to African-Americans to Chinese Americans to European-Americans – older adults report better control of their emotions and fewer negative emotions than do younger adults. At the same time, culture seems to color how aging-related effects impact one's emotional life: Whereas older Americans were shown to de-emphasize negative experiences more than younger Americans, no such effect has been observed in Japan. Instead, older Japanese were shown to assign a greater value to positive aspects of otherwise negative experiences than younger Japanese, whereas no such effect has been observed in the U.S.
== Positivity effect in older adults ==
=== In perception ===
Studies have found that older adults are more likely than younger adults to pay more attention to positive than to negative stimuli (as assessed by the dot-probe paradigm and eye-tracking methods). However, the effect also differs across cultures. For example, Hong Kong Chinese looked away from happy stimuli and more towards fearful stimuli, and the difference in attention pattern was related to differences in self-construal.
=== In recall ===
The term positivity effect also refers to age differences in emotional attention and memory. As people get older, they experience fewer negative emotions and they tend to look to the past in a positive light. In addition, compared with younger adults' memories, older adults' memories are more likely to consist of positive than negative information and more likely to be distorted in a positive direction. This version of the positivity effect was coined by Laura L. Carstensen's research team. There is a debate about the cross-cultural generalizability of the aging-related positivity effect, with some evidence for different types of emotional processing among Americans as compared to Japanese.
==== Hypothesized causes ====
One theory of the positivity effect in older adults' memories is that it is produced by cognitive control mechanisms that improve and decrease negative information due to older adults' greater focus on emotional regulation. Research shows an age-related reversal in the valence of information processed within the medial prefrontal cortex (MPFC). In younger adults, more MPFC activity was found in the presence of negative stimuli compared to positive stimuli whereas in older adults this was reversed.
However, the positivity effect may be different for stimuli processed automatically (pictures) and stimuli processed in a more controlled manner (words). Compared to words, pictures tend to be processed more rapidly and they engage emotion processing centres earlier. Automatic stimuli are processed in the amygdala and dorsal MPFC, whereas controlled stimuli are processed in the temporal pole and ventral MPFC. Compared to younger adults, older adults showed less amygdala activation and more MPFC activation for negative than positive pictures. Increased motivation to regulate emotion leads older adults to actively engage the mPFC differently from younger adults, which in turn yields diverging amygdala activation patterns. The opposite pattern was observed for words. Although older adults showed a positivity effect in memory for words, they did not display one for pictures. Thus, the positivity effect may arise from ageing differences in MPFC use during encoding.
Recent study by Helene Fung's group in China University in Hong Kong and Deep Longevity utilized artificial intelligence to show that people who are unhappy and lonely have accelerated biological age.
== See also ==
Aging and memory
Negativity bias
Positivity effect
== References ==
== Sources ==
Carstensen, L. L. (1992). "Motivation for social contact across the life span: A theory of socioemotional selectivity". Nebraska Symposium on Motivation. 40: 209–54. PMID 1340521.
Carstensen, Laura L.; Isaacowitz, Derek M.; Charles, Susan T. (1999). "Taking time seriously: A theory of socioemotional selectivity". American Psychologist. 54 (3): 165–81. doi:10.1037/0003-066X.54.3.165. PMID 10199217.
Lockenhoff, Corinna E.; Carstensen, Laura L. (2004). "Socioemotional Selectivity Theory, Aging, and Health: The Increasingly Delicate Balance Between Regulating Emotions and Making Tough Choices". Journal of Personality. 72 (6): 1395–424. CiteSeerX 10.1.1.319.121. doi:10.1111/j.1467-6494.2004.00301.x. PMID 15509287.
Fung, Helene H.; Carstensen, Laura L. (2004). "Motivational Changes in Response to Blocked Goals and Foreshortened Time: Testing Alternatives to Socioemotional Selectivity Theory". Psychology and Aging. 19 (1): 68–78. doi:10.1037/0882-7974.19.1.68. PMID 15065932.
Pruzan, Katherine; Isaacowitz, Derek M. (2006). "An Attentional Application of Socioemotional Selectivity Theory in College Students". Social Development. 15 (2): 326. doi:10.1046/j.1467-9507.2006.00344.x.
Carstensen, Laura L.; Mikels, Joseph A. (2005). "At the Intersection of Emotion and Cognition. Aging and the Positivity Effect". Current Directions in Psychological Science. 14 (3): 117. CiteSeerX 10.1.1.551.1460. doi:10.1111/j.0963-7214.2005.00348.x. S2CID 59067078.
Reed, A. E.; Carstensen, L. L. (2012). "The Theory Behind the Age-Related Positivity Effect". Frontiers in Psychology. 3: 339. doi:10.3389/fpsyg.2012.00339. PMC 3459016. PMID 23060825.
== External links ==
https://web.archive.org/web/20060926170243/http://www.nrpa.org/content/default.aspx?documentId=1974
Positivity effect and cognitive control in aging
List of papers related to aging and positivity effect | Wikipedia/Socioemotional_selectivity_theory |
The PAD emotional state model is a psychological model developed by Albert Mehrabian and James A. Russell (1974 and after) to describe and measure emotional states. PAD uses three numerical dimensions, Pleasure, Arousal and Dominance to represent all emotions. Its initial use was in a theory of environmental psychology, the core idea being that physical environments influence people through their emotional impact. It was subsequently used by Peter Lang and colleagues to propose a physiological theory of emotion. It was also used by James A. Russell to develop a theory of emotional episodes (relatively brief emotionally charged events). The PA part of PAD was developed into a circumplex model of emotion experience, and those two dimensions were termed "core affect". The D part of PAD was re-conceptualized as part of the appraisal process in an emotional episode (a cold cognitive assessment of the situation eliciting the emotion). A more fully developed version of this approach is termed the psychological construction theory of emotion.
The PAD (Pleasure, Arousal, Dominance) model has been used to study nonverbal communication such as body language in psychology. It has also been applied to consumer marketing and the construction of animated characters that express emotions in virtual worlds.
== The dimensional structure ==
PAD uses three-dimensional scales which in theory could have any numerical values. The dimensional structure is reminiscent of the 19th century work of Wilhelm Wundt who also used a three-dimensional system and also the 20th century work of Charles E. Osgood.
The Pleasure-Displeasure Scale measures how pleasant or unpleasant one feels about something. For instance, both anger and fear are unpleasant emotions, and both score on the displeasure side. However, joy is a pleasant emotion.
The Arousal-Nonarousal Scale measures how energized or soporific one feels. It is not the intensity of the emotion -- for grief and depression can be low arousal intense feelings. While both anger and rage are unpleasant emotions, rage has a higher intensity or a higher arousal state. However boredom, which is also an unpleasant state, has a low arousal value.
The Dominance-Submissiveness Scale represents the controlling and dominant versus controlled or submissive one feels. For instance, while both fear and anger are unpleasant emotions, anger is a dominant emotion, while fear is a submissive emotion.
A more abbreviated version of the model uses just 4 values for each dimension, providing only 64 values for possible emotions. For instance, anger is a quite unpleasant, quite aroused, and moderately dominant emotion, while boredom is slightly unpleasant, quite unaroused, and mostly non-dominant.
== Applications ==
=== Marketing ===
The abbreviated model has also been used in organizational studies where the emotions towards specific entities or products marketed by the respective organisations are measured.
The PAD model has been used in studying consumer behavior in stores, to determine the effects of pleasure and arousal on issues such as extra time spent in the store and unplanned spending.
=== Virtual emotional characters ===
The PAD model, and the corresponding PAD Space have been used in the construction of animated agents that exhibit emotions. For instance, Becker et al. describes how primary and secondary emotions can be mapped via the PAD space to features in the faces of animated characters to reflect happiness, boredom, frustration or annoyance. Lance et al. discuss how the PAD model can be used to study gaze behavior in animated agents.
Zhang et al. describes how the PAD model can be used to assign specific emotions to the faces of avatars. In this approach the PAD model is used as a high-level emotional space, and the lower-level space is the MPEG-4 Facial Animation Parameters (FAP). A mid-level Partial Expression Parameters (PEP) space is then used in a two-level structure: the PAD-PEP mapping and the PEP-FAP translation model.
== See also ==
Affect measures
== References ==
== Further reading ==
Valdez, P.; Mehrabian, A. (1994). "Effects of color on emotions". Journal of Experimental Psychology. 123 (4): 394–409. doi:10.1037/0096-3445.123.4.394. PMID 7996122. | Wikipedia/PAD_emotional_state_model |
The main concepts of the Cannon–Bard theory are that emotional expression results from the function of hypothalamic structures, and emotional feeling results from stimulations of the dorsal thalamus. The physiological changes and subjective feeling of an emotion in response to a stimulus are separate and independent; arousal does not have to occur before the emotion. Thus, the thalamic region is attributed a major role in this theory of emotion. The theory is therefore also referred to as the thalamic theory of emotion.
== Origins ==
Walter Bradford Cannon (1871–1945) was a physiologist at Harvard University, who is perhaps best known for his classic treatise on homeostasis. Philip Bard (1898–1977) was a doctoral student of Cannon's, and together they developed a model of emotion called the Cannon–Bard Theory. Cannon was an experimenter who relied on studies of animal physiology. Through these studies, Cannon and Bard highlighted the role of the brain in generating physiological responses and feelings; a role that is important in their explanation of emotion experience and production.
A dominant theory of emotion of Cannon's time was the James–Lange theory of emotion, and Cannon recognized that to test this theory, an examination of emotional expression with no visceral afferent feedback was required. This was necessary because the link between visceral changes and the feedback required to stimulate cerebral manifestations of an emotion would no longer be present. To do so, Cannon experimented with severing afferent nerves of the sympathetic branch of the autonomic nervous system in cats. Cannon compiled his experimental results in 1915, then refined and expanded them, and finally proposed his model of emotion as a challenge and alternative to the James–Lange theory of emotion.
The James–Lange theory relies on the backflow of impulses from the periphery to account for unique emotional experiences; impulses that William James assumed to come from all parts of the organism, including the muscles, skin, and the viscera. The viscera were attributed a major role by James. The viscera are composed of smooth muscle and glands. Cannon identified and outlined five issues with the James–Lange theory's notion of the vasomotor center as the explanation of emotional experience.
Total separation of the viscera from the central nervous system does not alter emotional behaviour.
In an experiment, cats were kept alive and healthy after having their sympathetic nervous systems completely removed. Removal of this system resulted in the abolishment of all the reactions under control of the vasomotor center, the region that the James–Lange theory purported to be responsible for emotional experiences. However, it was found that destroying these functions had little or no effect on the animals' emotional responses. The cats displayed the typical signs of rage in response to a barking dog, and the animals displayed full emotional expression in all organs that had not had their connections to the brain destroyed.
The same visceral changes occur in very different emotional states and in non-emotional states.
The sympathetic nervous system functions as a single unit. Visceral changes brought on/caused by sympathetic nervous system action include: increased heart rate; contraction of arterioles; dilatation of bronchioles; increased levels of blood sugar; sweating; widening of the pupils and erection of hairs; and discharge of adrenaline. These physiological changes can be seen in great excitement under any circumstances, including in distinguishable emotional states such as fear and rage, as well as situations of fever, asphyxia, and exposure to cold temperatures. Cannon articulated that these responses of the viscera are too uniform to offer a means of distinguishing emotions that have varying subjective qualities. He postulated that if emotions were the result of impulses from the viscera, we could expect fear, rage, chilliness, asphyxia, and fever to feel similarly, which is not the case.
The viscera are relatively insensitive structures.
Cannon wrote that there is a common belief that the more deeply the body is penetrated, the more sensitive it becomes; however, this is not the case. In the nerves distributed to the viscera the afferent sensory fibers may be only 1/10th as numerous as the efferent sensory fibers. For example, in the case of the viscera, we are unaware of the contractions and relaxations of the digestive processes. Such processes are undemonstrative and beyond our physical awareness, even when marked changes are induced in them.
Visceral changes are too slow to be a source of emotional feeling.
As previously stated, the viscera are composed of smooth muscle and glands, which are typically sluggish in their responses. It has been found that the latent period of the psychogalvanic response in man is approximately 3 seconds. However, it has also been noted that the latent period of affective responses to photos of men and women can end within 0.8 seconds. The James–Lange theory contends that such affective responses result from reverberations from the viscera. Cannon pointed out that the time required for nerve impulses to travel from the brain to the periphery and back to the brain again could not occur quickly enough to be the cause of such emotional responses.
Artificial induction of the visceral changes typical of strong emotions does not produce them.
When adrenaline is injected it induces the physiological responses typical of sympathetic nervous system activity previously discussed (dilation of bronchioles, constriction of blood vessels, increased blood sugar etc.). These changes are typical of intense emotional states. Therefore, if these visceral changes were artificially induced by the injection of adrenaline, one would expect the emotions to follow, as articulated by the James–Lange theory of emotion. When this experiment was done, participants experienced no specific emotions. However, it was found that an emotional response may develop only when the adrenaline as injected subsequent to discussing with patients their sick children or their dead parents. Thus, injection of adrenaline had an effect when an emotional mood already existed in participants.
== Further criticisms of the James–Lange theory ==
William James argued that there were either special centers for cerebral processes that accompany emotion, or they occurred in the ordinary motor and sensory centers of the cortex. Cannon responded by positing that there may not be one or the other, that there may be cortical processes and special centers that accompany emotional responses. He outlined two ideas regarding the existence of two sources of cerebral processes of emotions.
=== Emotional expression results from action of subcortical centers ===
Cannon summarized research done by Bechterev regarding emotional expression. In this research, it was argued that emotional expression must be independent of the cortex because the expression of emotions cannot always be inhibited or controlled (e.g. laughing from being tickled) because visceral changes occur independent of our control, and because these responses, which cannot be inhibited, are seen soon after birth before cortical management is developed. Furthermore, after cerebral hemispheres were removed from animal test subjects, correct affective responses could be elicited by appropriate stimulations. These emotional effects were no longer present when the optic thalamus was removed from the animals; thus, it was concluded that this region plays a significant role in the expression of emotions.
To further support the assertion that emotional expression results from action of subcortical centers, Cannon and Britton performed further experimental research with cats. Cats were decorticated, and after a period of recovery they spontaneously displayed the behaviours characteristic of intense fury. This response, referred to as sham rage, continued to be displayed after ablation of all brain regions anterior to the diencephalon. However, once the lower posterior portion of the thalamic region was removed, the display of sham rage by the cats subsided. Based on this finding, it was concluded that the thalamus was a region from which, in the absence of cortical control, impulses are discharged which evoke an extreme degree of "emotional" activity, both muscular and visceral.
Based on these findings and observations, Cannon asserts that the optic thalamus is a region in the brain responsible for the neural organization for the different emotional expressions.
=== Thalamic processes are a source of affective experience ===
There are numerous reported and cited cases of patients with unilateral lesions in the thalamus region who have a tendency to react excessively to affective stimuli. For example, pin pricks, painful pressure, and excessive heat or cold all cause more distress on the damaged side of the body as compared to the normal side. Similar results can be observed from agreeable stimuli: warmth stimuli may cause intense pleasure, demonstrated by facial expressions of enjoyment and exclamations of delight by the individual. The increased influence of stimuli resulting in excessive responses was attributed to the release of the thalamus from cortical inhibition. When the thalamus is released from cortical control, the affective states and responses are increased; thus, it was concluded that the thalamic region is occupied with the affective component of sensation.
== The Cannon–Bard theory ==
According to Cannon, an external stimulus activates receptors and this excitation starts impulses toward the cortex. Upon arriving in the cortex, the impulses are associated with conditioned processes that determine the direction of the subsequent response. It is this response that stimulates the thalamic processes. Once the thalamic processes are activated, they are ready to discharge. The thalamic neurons fire in a special combination in a given emotional expression. These neurons then discharge precipitately and intensely. Cannon wrote that within and near the thalamus, the neurons responsible for an emotional expression lie close to the relay in the sensory path from the periphery to the cortex, and when these neurons fire in a particular combination they innervate muscles and viscera and excite afferent paths to the cortex by direct connection or irradiation.
The key component of the Cannon–Bard theory of emotion is that when the thalamic discharge occurs, the bodily changes occur almost simultaneously with the emotional experience. The bodily changes and emotional experience occur separately and independently of one another; physiological arousal does not have to precede emotional expression or experience. The theory asserts that the thalamic region is the brain area responsible for emotional responses to experienced stimuli.
Cannon summarises the observations that serve as the basis for his theory of emotion which claims the thalamic region is the coordinating center for emotional reactions. First, after the removal of the cerebrum anterior to the thalamus in animal test subjects, the animals continue to display rage-like emotional responses. These reactions cease when the thalamus is then removed. Secondly, a tumor on one side of the thalamus can result in unilateral laughter or grimace under the appropriate conditions, although cortical and voluntary control of the same muscles is bilateral. Lastly, temporary impairment of cortical control of lower centers from light amnesia or permanent impairment by disease (e.g. tumor or lesion) can cause uncontrollable and prolonged weeping or laughing.
== Additional theories of emotion ==
The Cannon–Bard theory of emotion was formulated as a challenge and alternative to James–Lange theory. The Papez-Maclean theory is another influential theory of emotion that differs from the Cannon–Bard theory in terms of the area that is considered to be responsible for emotion expression. James Papez initially suggested that the interconnections among structures of the limbic system were ideally constituted to handle the long-lasting, intense aspects of experience that are typically associated with emotion.
The circuit originally proposed by Papez consisted of the hippocampus, the ipsilateral mammillary body, the anterior nucleus of the thalamus, the cingulate cortex, the parahippocampal gyrus, and the entorhinal cortex, returning to the hippocampus. MacLean elaborated on Papez's earlier work, adding the prefrontal cortex, the septum, and the amygdala, and named this group of structures the limbic system.
There is also the two-factor theory of emotion, as proposed by Stanley Schachter and Jerome E. Singer.
== References == | Wikipedia/Cannon-Bard_theory |
The two-factor theory of emotion posits when an emotion is felt, a physiological arousal occurs and the person uses the immediate environment to search for emotional cues to label the physiological arousal.
The theory was put forth by researchers Stanley Schachter and Jerome E. Singer in a 1962 article.
According to the theory, emotions may be misinterpreted based on the body's physiological state.
== Empirical support ==
In 1962, Stanley Schachter and Jerome E. Singer performed a study that tested how people use clues in their environment to explain physiological changes. They had three hypotheses going into the experiment. First, that if a person experiences a state of arousal for which they have no immediate explanation, they will label this state and describe their feelings in terms of the cognitions available to them at the time. Second, that if a person experiences a state of arousal for which they have an appropriate explanation, then they will be unlikely to label their feelings in terms of the alternative cognitions available. Third, that if a person is put in a situation that in the past could have made them feel an emotion, they will react emotionally or experience emotions only if they are in a state of physiological arousal.
Participants were told they were being injected with a new drug called "Suproxin" to test their eyesight. The participants were actually injected either with epinephrine (which causes an increase in blood pressure, heart rate, and breathing) or a placebo. There were four conditions that participants were randomly placed in: epinephrine informed (where participants were told they would feel effects similar to epinephrine), epinephrine ignorant (where participants were not told about side effects), epinephrine misinformed (where participants were told wrong side effects), and a control group (where participants were injected with a placebo and not told about any side effects).
After the injection, a confederate, acting either as angry or euphoric, interacted with the students. The experimenters watched through a one way mirror and rated the participants' state on a three category scale. The participants were then given a questionnaire and their heart rate was checked. Participants in the epinephrine misinformed group experienced the highest euphoria, followed by the ignorant, placebo, and informed group. In contrast, participants in the ignorant group experienced the most anger, followed by the placebo and informed group. The results show that those participants who had no explanation of why their body felt as it did were more susceptible to the confederate, supporting the three hypotheses.
=== Misattribution of arousal ===
The misattribution of arousal study tested Schachter and Singer's two-factor theory of emotion. Psychologists Donald G. Dutton and Arthur P. Aron wanted to use a natural setting that would induce physiological arousal. In this experiment, they had male participants walk across two different styles of bridges. One bridge was a very scary (arousing) suspension bridge, which was very narrow and suspended above a deep ravine. The second bridge was much safer and more stable than the first.
At the end of each bridge an attractive female experimenter met the [male] participants. She gave the participants a questionnaire which included an ambiguous picture to describe and her number to call if they had any further questions. The idea of this study was to find which group of males were more likely to call the female experimenter and to measure the sexual content of the stories the men wrote after crossing one of the bridges. They found that the men who walked across the scary bridge were more likely to call the woman to follow up on the study, and that their stories had more sexual content.
The two-factor theory would say that this is because they had transferred (misattributed) their arousal from fear or anxiety on the suspension bridge to higher levels of sexual feeling towards the female experimenter.
=== Schachter & Wheeler ===
In the Schachter & Wheeler (1962) study the subjects were injected with epinephrine, chlorpromazine, or a placebo (chlorpromazine is a neuroleptic, i.e., an antipsychotic). None of the subjects had any information about the injection. After receiving the injection, the subjects watched a short comical movie. While watching the movie, the subjects were monitored for signs of humor. After the movie was watched, the subjects rated how funny the movie was and if they enjoyed. The results concluded that the epinephrine subjects demonstrated the most signs of humor. The placebo subjects demonstrated fewer reactions of humor but more than the chlorpromazine subjects.
== Criticisms ==
Criticism of the theory has come from attempted replications of the Schachter and Singer (1962) study. Marshall and Zimbardo (1979, and Marshall 1976) tried to replicate the Schachter and Singer’s euphoria conditions. Just as Schachter and Singer did, the subjects were injected with epinephrine or a placebo, except the administrator told the subjects that they will be experiencing non-arousal symptoms. Then the subjects were put into four different conditions: subjects injected epinephrine and were exposed to a neutral confederate, another in which they received the placebo and were told to expect arousal symptoms, and two conditions in which the dosage of epinephrine was determined by body weight rather than being fixed. The results found that euphoria confederate had little impact on the subjects. Also, that the euphoric confederate didn’t produce anymore euphoria than the neutral confederate did. Concluding that the subjects who were injected with epinephrine were not more susceptible to emotional manipulations than the non-aroused placebo subjects.
Maslach (1979) designed a study to try to replicate and extend on the Schachter and Singer study. Instead of being injected with epinephrine, the administrators used hypnotic suggestions for the source of arousal. Either the subjects were hypnotized or were used as a control (same as the placebo effect in the Schachter and Singer study). Subjects that were hypnotized were given a suggestion to become aroused at the presentation of a cue and were instructed not to remember the source of this arousal. Right after the subjects had been hypnotized, a confederate began acting either in a euphoric or angry condition. Later on in the study the subjects were exposed to two more euphoric confederates. One confederate was to keep aware the source of the arousal, while the other confederates told the subjects to expect different arousal symptoms.
The results found that all the subjects both on self-reports and on observation found that unexplained arousal causes negative conditions. Subjects still showed angry emotions regardless of the euphoric confederate. Maslach concluded that when there is a lack of explanation for an arousal it will cause a negative emotion, which will evoke either anger or fear. However, Maslach did mention a limitation that there might have been more negative emotion self-reported because there are more terms referring to negative emotions than to positive ones.
There are also criticisms of the two-factor theory that come from a theoretical standpoint. One of these criticisms is that the Schachter-Singer Theory centers primarily on the autonomic nervous system and provides no account of the emotional process within the central nervous system aside from signaling the role of cognitive factors. This is important considering the heavy implication of certain brain centers in mitigating emotional experience (e.g., fear and the amygdala).
It can also be noted that Gregorio Marañon also had early studies in the development of cognitive theories of emotion and should be recognized for making contributions to this concept.
== See also ==
Cannon–Bard theory
James–Lange theory
Misattribution of arousal
== Notes ==
== References ==
Cotton, J. L. (1981). "A review of research on Schachter's theory of emotion and the misattribution of Arousal". European Journal of Social Psychology. 11 (4): 365–397. doi:10.1002/ejsp.2420110403.
Dutton, D. G.; Aron, A. P. (1974). "Some evidence for heightened sexual attraction under conditions of high anxiety". Journal of Personality and Social Psychology. 30 (4): 510–517. CiteSeerX 10.1.1.335.100. doi:10.1037/h0037031. PMID 4455773.
Erdmann, G.; Janke, W. (1978). "Interaction between physiological and cognitive determinants of emotions: Experimental studies on Schachter's theory of emotions". Biological Psychology. 6 (1): 61–74. doi:10.1016/0301-0511(78)90007-8. PMID 623859. S2CID 597601.
Izard, C. E. The face of emotion. New York: Appleton-Century-Crofts, 1971.
LeDoux, J. E. (1995). "Emotion: Clues from the brain". Annual Review of Psychology. 46: 209–235. doi:10.1146/annurev.ps.46.020195.001233. PMID 7872730.
Marshall, G. D. (1976). The affective consequences of "inadequately explained" physiological arousal. Unpublished doctoral dissertation, Stanford University.
Marshall, G. D.; Zimbardo, P.G. (1979). "Affective consequences of inadequately explained physiological arousal". Journal of Personality and Social Psychology. 37 (6): 970–988. doi:10.1037/0022-3514.37.6.970.
Maslach, C (1979). "Negative emotional biasing of unexplained arousal". Journal of Personality and Social Psychology. 37 (6): 953–969. doi:10.1037/0022-3514.37.6.953.
Pruett, C (2011). "Two-factor theory of emotion displayed by video games". Game Developer. 18 (2): 33.
Schachter, S.; Singer, J. (1962). "Cognitive, Social, and Physiological Determinants of Emotional State". Psychological Review. 69 (5): 379–399. doi:10.1037/h0046234. PMID 14497895.
Schachter, S.; Wheeler, L. (1962). "Epinephrine, chlorpromazine, and amusement". Journal of Abnormal and Social Psychology. 65 (2): 121–128. doi:10.1037/h0040391. PMID 14497896.
== External links ==
A Powerpoint presentation describing Schachter & Singer's experiment
A Powerpoint presentation describing Dutton & Aron's experiment | Wikipedia/Two-factor_theory_of_emotion |
Affect theory is a theory that seeks to organize affects, sometimes used interchangeably with emotions or subjectively experienced feelings, into discrete categories and to typify their physiological, social, interpersonal, and internalized manifestations. The conversation about affect theory has been taken up in psychology, psychoanalysis, neuroscience, medicine, interpersonal communication, literary theory, critical theory, media studies, and gender studies, among other fields. Hence, affect theory is defined in different ways, depending on the discipline.
Affect theory is originally attributed to the psychologist Silvan Tomkins, introduced in the first two volumes of his book Affect Imagery Consciousness (1962). Tomkins uses the concept of affect to refer to the "biological portion of emotion," defined as the "hard-wired, preprogrammed, genetically transmitted mechanisms that exist in each of us," which, when triggered, precipitate a "known pattern of biological events". However, it is also acknowledged that, in adults, the affective experience is a result of interactions between the innate mechanism and a "complex matrix of nested and interacting ideo-affective formations."
== Affect theory in psychology ==
=== Silvan Tomkins's nine affects ===
According to the psychologist Silvan Tomkins, there are nine primary affects. Tomkins characterized affects by low/high intensity labels and by their physiological expression:
Positive:
Enjoyment/Joy (reaction to success/impulse to share) – smiling, lips wide and out
Interest/Excitement (reaction to new situation/impulse to attend) – eyebrows down, eyes tracking, eyes looking, closer listening
Neutral:
Surprise/Startle (reaction to sudden change/resets impulses) – eyebrows up, eyes blinking
Negative:
Anger/Rage (reaction to threat/impulse to attack) – frowning, a clenched jaw, a red face
Disgust (reaction to bad taste/impulse to discard) – the lower lip raised and protruded, head forward and down
Dissmell (reaction to bad smell/impulse to avoid – similar to distaste) – upper lip raised, head pulled back
Distress/Anguish (reaction to loss/impulse to mourn) – crying, rhythmic sobbing, arched eyebrows, mouth lowered
Fear/Terror (reaction to danger/impulse to run or hide) – a frozen stare, a pale face, coldness, sweat, erect hair
Shame/Humiliation (reaction to failure/impulse to review behaviour) – eyes lowered, the head down and averted, blushing
=== Prescriptive applications ===
According to Tomkins, optimal mental health involves maximizing positive affects and minimizing negative affects. Affect should also be properly expressed so to make the identification of affect possible to others.
Affect theory is also used prescriptively in investigations about intimacy and intimate relationships. Kelly describes relationships as agreements to work collaboratively toward maximizing positive affect and minimizing negative affect. Like the "optimal mental health" blueprint, this blueprint requires that members of the relationship express affect to one another in order to identify progress.
These blueprints can also describe natural and implicit goals. For example, Donald Nathanson uses the "affect" to create a narrative for one of his patients:
I suspect that the reason he refuses to watch movies is the sturdy fear of enmeshment in the affect depicted on the screen; the affect mutualization for which most of us frequent the movie theater is only another source of discomfort for him. ... His refusal to risk the range of positive and negative affect associated with sexuality robs any possible relationship of one of its best opportunities to work on the first two rules of either the Kelly or the Tomkins blueprint. Thus, his problems with intimacy may be understood in one aspect as an overly substantial empathic wall, and in another aspect as a purely internal problem with the expression and management of his own affect.
Tomkins claims that "Christianity became a powerful universal religion in part because of its more general solution to the problem of anger, violence, and suffering versus love, enjoyment, and peace.".
Affect theory is also referenced heavily in Tomkins's script theory.
=== Attempts to typify affects in psychology ===
Humor is a subject of debate in affect theory. In studies of humor's physiological manifestations, humor provokes highly characteristic facial expressions. Some research has shown evidence that humor may be a response to a conflict between negative and positive affects, such as fear and enjoyment, which results in spasmodic contractions of parts of the body, mainly in the stomach and diaphragm area, as well as contractions in the upper cheek muscles. Further affects that seem to be missing for Tomkins's taxonomy include relief, resignation, and confusion, among many others.
The affect joy is observed through the display of smiling. These affects can be identified through immediate facial reactions that people have to a stimulus, typically well before they could process any real response to the stimulus.
The findings from a study on negative affect arousal and white noise by Stanley S. Seidner "support the existence of a negative affect arousal mechanism through observations regarding the devaluation of speakers from other Spanish ethnic origins".
== Critical theory ==
Emotion theory organizes emotions into distinct categories, sometimes used interchangeably with emotions and subjectively experienced emotions, and typifies their physiological, social, interpersonal, and internalized symptoms. Conversations about emotion theory are addressed in fields such as psychology, psychoanalysis, neuroscience, medicine, interpersonal communication, literary theory, critical theory, media studies, and gender studies. Emotion theory is therefore defined in different ways depending on the field. Emotion theory was originally written by psychologist Silvan Tomkins and was introduced in the first two volumes of his book Effects on Image Consciousness (1962). Tomkins uses the concept of emotion to refer to the "biological part of emotion." This part is defined as "a wired, pre-programmed, genetically transmitted mechanism that exists within each of us" and causes "known biological patterns" when triggered. . event". However, it is also accepted that in adults, emotional experience is the result of interactions between innate mechanisms and "a complex matrix of nested and interacting thought-feeling formations".
Affect theory is explored in philosophy, psychoanalytic theory, gender studies, and art theory. Eve Sedgwick and Lauren Berlant have been called "affect theorists" who write from critical theory perspectives. Many other critical theorists have relied heavily on affect theory, including Elizabeth Povinelli. Affect theory is drawn from by Marxist autonomists including Franco Berardi, Michael Hardt and Antonio Negri, as well as Marxist feminists such as Selma James and Silvia Federici, who consider the cognitive and material manifestations of particularized gendered, performed roles including caregiving. Critical theorist Sara Ahmed describes affect as "sticky" in her essay "Happy Objects" to explain the sustained connection between "ideas, values, and objects."
In line with these theorists, many scholars identify the role of affect in shaping social values, gender ideals, and collective groups. Affect is seen as instrumental for events and symbols that produce shared identities, and is therefore central in contemporary politics. Affect is also treated as central in capitalist systems, including people's attachment to commodities and "dreams" of class mobility. In addition, the non-discursive and non-deliberative attributes of affect may produce social interactions and experiences that are non-reducible to specific endpoints, and at times may allow people to experience new modes of existence separated from their main life goals.
Scholars who explored affect theory as an approach to art include Ruth Leys and Charles Altieri. In “The Turn to Affect”, Leys explained how the shift to the “neuroscience of emotions” based on the affect theory has a deleterious effect of equating precognitive, nonrational responses to critical and reflective insights. She maintained that there are no precognitive insights, nothing that acts as inhuman, presubjective, visceral forces, and intensities that shape our thoughts and judgments. Affect theory is part of Altieri's critique of contemporary literary criticism, which he believes is obsessed with historical and socio-political critiques. For him, this focus leads to “over-readings” of meaning. Instead, he focused on affect in relation to aesthetic experience. In his conceptualization, Altieri used the term “rapture” to explain the aesthetics of effects. He also drew from cognitive and neuroscience studies to distinguish “affect” or “feeling” and “emotion”.
== Interpersonal communication ==
This nonverbal mode of conveying feelings and influence is held to play a central role in intimate relationships. The Emotional Safety model of couples therapy seeks to identify the affective messages that occur within the couple's emotional relationship (the partners' feelings about themselves, each other, and their relationship); most importantly, messages regarding (a) the security of the attachment and (b) how each individual is valued.
One practical application of affect theory has been its incorporation into couples therapy. Two characteristics of affects have powerful implications for intimate relationships:
According to Tomkins, a central characteristic of affects is affective resonance, which refers to a person's tendency to resonate and experience the same affect in response to viewing a display of that affect by another person, sometimes thought to be "contagion". Affective resonance is considered to be the original basis for all human communication (before there were words, there was a smile and a nod).
Also according to Tomkins, affects provide a sense of urgency to the less powerful drives. Thus, affects are powerful sources of motivation. In Tomkins' words, affects make good things better and bad things worse.
== Criticism ==
Some scholars have taken issue with the claims and methodologies of affect theorists. Ruth Leys has objected to affect theory's implications for artistic and literary criticism, as well as to its appropriation in some forms of trauma theory.
Aubrey Anable has also criticised affect theory for its imprecision, claiming that its "language of intensity, becoming, and in-betweenness and its emphasis on the unpresentable give it a maddening incoherence, or shade too easily into purely subjective responses to the world". Jason Josephson Storm, a professor of religious studies, argued that affect theory in the humanities has failed to distinguish itself from poststructuralism and ignores empirical evidence that affects are culturally constructed.
== See also ==
Selective exposure theory
Mood management theory
Affect consciousness
== References ==
== External links ==
Tomkins Institute | Wikipedia/Affect_theory |
The neurocircuitry that underlies executive function processes and emotional and motivational processes are known to be distinct in the brain. However, there are brain regions that show overlap in function between the two cognitive systems. Brain regions that exist in both systems are interesting mainly for studies on how one system affects the other. Examples of such cross-modal functions are emotional regulation strategies such as emotional suppression and emotional reappraisal, the effect of mood on cognitive tasks, and the effect of emotional stimulation of cognitive tasks.
A variety of methods can be used to examine the relationship between executive function and emotion, including behavioural studies, functional brain activity, and neuroanatomy. Some of the most prominent results are listed here.
== Behavioural studies ==
=== Mood affects style of information processing ===
A large body of research has looked at the effects of positive or negative mood manipulations on performance in tasks of executive function. In most cases, positive mood inductions impair executive function, whereas negative mood has little effect. Overall, the best supported explanation for the observed effects is that mood affects processing style, with positive mood facilitating more heuristic methods of solving problems, and negative mood facilitating more algorithmic methods. Research in this area is incomplete, as negative mood inductions are less thoroughly studied.
=== Effects of mood on working memory and planning ===
In word span tasks, positive mood caused greater deficits in complex tasks compared to simpler tasks, where negative mood had no effect. In a Tower of London planning task, positive mood caused poorer planning performance compared to neutral mood. Researchers in both cases suggested that lack of effect could be explained by insufficient mood manipulation methods.
=== Effects of mood on fluency and creativity ===
In word fluency tasks, one study has shown that positive mood results in better fluency over negative mood, while another has shown that negative mood results in higher word production. A third study did not find any effect of either mood manipulation. However, there is some evidence that positive mood can result in increased performance in some tasks requiring creative thinking. No evidence of negative mood on creative thinking is available.
=== Effects of mood on inhibition and switching ===
In the Stroop task, a near significant trend was found for Stroop costs in positive mood conditions. In two tasks of switching, it was found that positive mood results in impaired switching compared to a neutral condition. Little evidence is found for the effect of negative mood.
=== Interpretation ===
Taken together positive mood impairs tasks of working memory, planning, word production, inhibition and switching, and facilitates word fluency. Negative mood impairs fluency, but facilitates planning tasks, word production, and has not shown any effect for tasks of working memory, creativity, inhibition, or switching. The results, while incomplete, would be consistent with the interpretation that mood influences style of processing.
== Prefrontal cortex regions involved in emotional regulation ==
Some of the more significant cortical areas involved in emotional regulation include the ventrolateral prefrontal cortex, medial prefrontal cortex, dorsolateral prefrontal cortex and dorsomedial prefrontal cortex.
=== Ventrolateral prefrontal cortex (vlPFC) ===
The ventrolateral prefrontal cortex (vlPFC) is a subdivision of the prefrontal cortex. Its involvement in modulating existing behavior and emotional output given contextual demands has been studied extensively using cognitive reappraisal studies and emotion-attention tasks. Cognitive reappraisal studies indicate the vlFPC's role in reinterpreting stimuli, and reducing or augmenting responses. Studies using emotion-attention tasks demonstrate the vlFPC's function in ignoring emotional distractions while the brain is engaged in performing other tasks.
=== Medial prefrontal cortex (mPFC) ===
The medial prefrontal cortex (mPFC) is a subdivision of the prefrontal cortex. It encodes expected outcomes, both positive and negative, and signals when the expected outcomes do not occur. The mPFC, mediated by the amygdala, is also involved in the extinction and modulation of conditioned responses, including emotional ones, and the augmentation of emotional states. The function of the mPFC in higher order emotional processing is still unclear.
=== Dorsal prefrontal cortex ===
The dorsolateral prefrontal cortex (dlPFC) and the dorsomedial prefrontal cortex (dmPFC) are implicated in the enhancement of representations of stimuli relevant to current decisions, behaviors or tasks. These areas also play a role in modulating emotions and dealing with emotional distractions during demanding tasks, and are also implicated in facilitating decision/resolve perceptual or conflict making by augmenting representations of stimuli relevant to decision or behavior. The dmPFC's role in human emotional regulation decision making (decision conflict perspective – levels of indecision) e.g. Picking between similar items, acting in novel situations. There is also evidence of an inverse relationship between activation in the dPFC areas and activation in emotionally activated brain areas.
== Ventral and dorsal streams ==
=== Ventral stream ===
The ventral stream primarily involves the vlPFC and mPFC. Signals of expected outcomes trigger the mPFC to update stimulus associations through exchanges with the amygdala and the nucleus accumbens. When a response change is needed, the mPFC interacts with the vlPFC. Then, the vlPFC modulates the emotional response to stimuli through interactions with the dorsal striatum. Preliminary findings indicate that the vlPFC may also modulate activity in the nucleus accumbens, temporal cortex, anterior insula and amygdala.
=== Dorsal stream ===
The dorsal stream activates by the presence of response conflict. The dmPFC relays information on past reinforcement to the dlPFC, which initiates selective attention. dlPFC influences action and emotion by weighing the importance of competing goals/representations in the temporal cortex. Representations opposite to what the stimulus originally elicited are rendered more salient and compete with the original representations. These competitions influence the modulation of activity in the amygdala and the mPFC.
== Adolescent development ==
An imbalance between the relative influence between the emotional and executive systems is posited to be responsible for the heightened levels of risk-taking and emotionality observed in adolescents. Specifically, dopamine-rich regions related to motivation, including the ventral striatum which has been shown to represent the appetitive value of a stimulus, show increased signaling in adolescent years. This is suggested to be indicative of maturation in this region. In contrast, it is known that regions of the brain known to be involved with modulation of emotional effect on executive function, including the vlPFC, as well as the entire ventrolateral frontostriatal network, do not fully mature until late adolescence to early adulthood. Recent research has shown that adolescents are less capable of inhibiting responses to pre-potent stimuli. Additionally, the ventral striatum and frontolateral prefrontal cortex showed patterns of activity that are more connected with each other during adolescence than early adulthood. While it is accepted that adolescents are less able to inhibit responding to tempting stimuli, it is unclear the specific neural mechanism that modulates this phenomenon.
== Other research ==
The emotional-oddball paradigm is a variation on the traditional oddball paradigm used in neuroscience. Studies show emotionally enhanced memory during trials depicting negative imagery when people participate in visual, simultaneous attention-emotional tasks. Emotional arousal has also been shown to cause augmentation in memory, and enhanced processing and information consolidation when paired with stimuli. This effect has been explained by the arousal-biased competition (ABC) model, which postulates that bottom-up sensory preference to arousing stimuli and top-down relevance to current activity or goal pursuit both influence how priority is determined for an event. More simply, if an event is paired with a particularly emotionally arousing stimulus, it will be more salient to processing and have greater resources devoted to it.
== References == | Wikipedia/Interactions_between_the_emotional_and_executive_brain_systems |
A functional account of emotions posits that emotions facilitate adaptive responses to environmental challenges. In other words, emotions are systems that respond to environmental input, such as a social or physical challenge, and produce adaptive output, such as a particular behavior. Under such accounts, emotions can manifest in maladaptive feelings and behaviors, but they are largely beneficial insofar as they inform and prepare individuals to respond to environmental challenges, and play a crucial role in structuring social interactions and relationships.
Researchers who subscribe to a functional perspective of emotions disagree as to whether to define emotions and their respective functions in terms of evolutionary adaptation or in terms of socially constructed concepts. However, the goal of a functional account of emotions is to describe why humans have specific emotions, rather than to explain what exactly constitutes an emotion. Thus, functionalists generally agree that in order to infer the functions of specific emotions, researchers should examine the causes, or input, and consequences, or output, of those emotions.
The events that elicit specific emotions and the behavioral manifestations of those emotions can vary significantly based on individual and cultural context. Thus, researchers claim that a functional account of emotions should not be understood as a rigid input and output system, but rather as a flexible and dynamic system that interacts with an individual's goals, experiences, and environment to adaptively shape individuals’ emotional processing and responding.
== History ==
Historically, emotions were primarily understood and studied in terms of their maladaptive consequences. For example, Stoicism, an Ancient Greek tradition of philosophy, described how most emotions, particularly negative emotions like anger, are irrational and prevent people from achieving inner peace. Early psychologists followed this approach, often describing how emotions interfere with rational deliberation and can lead to reckless behaviors that risk well-being or relationships.
Around the 1960s, however, the focus of emotions research began shifting towards the beneficial consequences of emotions, and a growing body of psychological research contributed to understanding emotions as functional. For example, emotions structure relationships by facilitating bonding that promotes survival. Additionally, the expression of emotions can coordinate group behavior, thus promoting cooperation and collaboration. Interdisciplinary research in fields such as cultural psychology, sociology, and anthropology found that sociocultural norms often interact with and even emerge from individual and collective emotional experiences, providing further support for the role of emotions in organizing social life. While some researchers retained that emotions may have once been functional but are no longer necessary in the present environment, many researchers began to adopt the now-dominant view that emotions are systems that aim to provide solutions to problems in the present-day environment.
== Emotion functions ==
A functional account of any system assesses its specific function in terms of the factors that elicit the activation of that system, and the changes that follow the activation of that system. Importantly, not every cause and consequence of a system pertains to its primary function; the primary function is the specific purpose that the system fulfills. For example, tools have specific functions that are defined in terms of why the tool has certain features and the problem that it typically solves. So, while a pair of scissors can be used as a weapon, or a paper-weight, the sharp blades of scissors were designed to cut, and the problem that scissors typically solve is the need to cut something. Thus, the primary function of scissors is to cut.
Functional accounts of emotion similarly define the functions of specific emotions in terms of why those emotions are associated with certain features, such as particular bodily and cognitive changes, as well as the environmental problem that the emotion helps to solve. For example, why is anger typically associated with an increase in heart rate and the desire to approach the source of anger. When people become angry in response to an environmental problem, how does it help them change their environment in a way that benefits them? Emotion researchers attempt to answer such questions in relation to various prominent emotions, including negative emotions such as sadness, embarrassment, and fear, and positive emotions such as love, amusement, and awe. In order to identify the primary function of each emotion, researchers investigate its intrapersonal functions, or how emotions function at the level of the individual to help them navigate their surroundings, and interpersonal functions, or how emotions function at the group level to facilitate efficient communication, cooperation, and collaboration.
=== Intrapersonal functions ===
In investigating the intrapersonal functions of emotions, or how emotions help individuals navigate and respond to their environments, researchers typically document the physiological changes, subjective experiences, and behavioral motivations associated with different emotions. For example, anger is associated with high arousal, feelings of disapproval or dissatisfaction with some event, and the motivation to express that disapproval or take action against the source of dissatisfaction.
Given how emotional responses affect individual experience and behavior, researchers describe the intrapersonal function of specific emotions in terms of how they inform and prepare individuals to respond to a particular environmental challenge. For example, feeling anger usually informs individuals of something unjust in the environment, such as betrayal from a loved one, threats of physical violence from a bully, or corruption. Anger is associated with blood flow in the body shifting away from internal organs towards the limbs, physiologically preparing individuals for movement towards the cause of anger. Even when locomotion or physical confrontation is not required to address an unjust actor or event, the high arousal and emotional sensitivity associated with anger tend to motivate individuals to confront the issue. Emotional responses tend to diminish once the emotion elicitor, or the environmental cause of the emotion, changes, suggesting that emotions at the individual level function to evoke some sort of action or behavior to address the elicitor. For example, anger typically diminishes following an apology or the perception that justice has been restored.
=== Interpersonal functions ===
A crucial aspect of how emotions help individuals adaptively navigate the world is tied to their interpersonal functions, or how they influence social interactions and relationships. Emotional expressions, such as a smile or a frown, are relatively involuntary, so they can provide a fairly reliable source of information about a person's emotions, beliefs, and intentions to those around them. The communication of such information is crucial for structuring social relationships, and for negotiation and cooperation within groups, because it conveys not only how people are thinking and feeling, but also how they are likely to behave. This information can in turn guide how other people think, feel, and behave towards those expressing their emotions. For example, emotional expressions can evoke complementary emotional responses, such as fear in response to anger, or guilt in response to disappointment. They can also evoke reciprocal emotions, such as empathy or love. Thus, emotions play a crucial role in conveying valuable information in social interactions that can rapidly coordinate group behavior even in the absence of explicit verbal communication.
Given this communicative role of emotions, emotions facilitate learning by serving as incentives or deterrents for certain kinds of actions or behaviors. For example, when children see how their parents or friends emotionally respond to things they do, they learn what types of actions and behaviors are likely to lead to desirable outcomes, including positive emotional responses from those around them. This communicative role is important in informing how people behave in both professional and intimate adult human relationships as well, since emotions can convey how a particular relationship or interaction is evolving in positive or negative directions. For example, anger can signal that an individual or group has reached its limit within a negotiation, and can immediately structure the behavioral responses from the opposite party. Meanwhile, sadness can communicate the readiness to disengage from a goal, and the potential for social withdrawal from a person or group, thereby conveying that a potentially valuable relationship is at risk.
Emotions have also been found to play a role in organizing group identity insofar as shared emotional experiences tend to strengthen communal identity, in-group solidarity, and cultural identity. Furthermore, emotions play a role in defining and identifying an individual's role within a group, such that the specific role that an individual assumes (ex. nurturing, protecting, leading) is associated with the expression of particular emotions, such as sympathy, anger, fear, or embarrassment.
=== Negative and positive emotion ===
Researchers who adopt a functional perspective of emotions have devoted attention to several prevalent emotions. For example, research suggests that the function of anger is to correct injustice, the function of sadness is to disengage from an unattainable goal, the function of embarrassment is to appease others, and the function of fear is to avoid danger. The focus of emotions research for some time was on negative emotions, with positive emotions primarily being understood as “undoing” the arousing effects of negative emotion. In other words, while negative emotions increase arousal to help individuals address an environmental problem, positive emotions quell that arousal to return an individual to baseline.
While positive emotions can return individuals to baseline following a negative emotional experience, for example joy after an angering event has been addressed, or amusement that distracts from sadness, positive emotions themselves can increase arousal from baseline. Thus, a growing body of literature describes the distinct functions of positive emotions. For example, research suggests that the function of romantic love is to facilitate mating, the function of amusement is to facilitate play, which encourages learning, and the function of awe is to accommodate new information.
== Variability ==
Emotions are highly personal insofar as they play a critical role in defining an individual's subjective experiences and interact with how individuals think about and judge the world around them. Since individuals differ in their personal goals and past experiences, individuals within one society or group can vary greatly in how they experience and express specific emotions.
Emotions are also highly social insofar as they facilitate communication and often arise in response to the actions or feelings of other people. Given their highly social nature, the ways that emotions are experienced and expressed, and the specific roles that they play in structuring interactions and relationships, can vary significantly according to social and cultural context. For example, research investigating cultural differences in facial expressions found that East Asian models of anger show characteristic early signs of emotional intensity with the eyes, which are under less voluntary control than the mouth, as compared with Western Caucasian models. Such findings suggest that contextual factors such as a particular society's display rules may directly modulate both how an emotion is expressed, and how it is perceived and responded to by others. Furthermore, some emotions are generally experienced less in certain societies. For example, anger is not frequently reported amongst Utku Eskimos.
Given this immense variation in how individuals experience and express emotions, functionalists emphasize the dynamic quality of emotion systems. Under a functional account, emotion systems process feedback from the environment about when and how various emotions are likely to serve adaptive functions in a specific environment. In other words, emotion systems are flexible and can incorporate information that an individual learns across their lifespan to modify how the system operates. Furthermore, emotions interact with cognition such that how an individual learns and thinks about their own emotions can affect how they experience and express emotions.
== Relation to mental illness ==
There are cases when an emotion, for example a constantly excessive level of anxiety, actually inhibits life functions rather than facilitating them. This is sometimes regarded as part of a mental illness.
== References == | Wikipedia/Functional_accounts_of_emotion |
Constant false alarm rate (CFAR) detection is a common form of adaptive algorithm used in radar systems to detect target returns against a background of noise, clutter and interference.
== Principle ==
In the radar receiver, the returning echoes are typically received by the antenna, amplified, down-converted to an intermediate frequency, and then passed through detector circuitry that extracts the envelope of the signal, known as the video signal. This video signal is proportional to the power of the received echo. It comprises the desired echo signal as well as the unwanted signals from internal receiver noise and external clutter and interference. The term video refers to the resulting signal being appropriate for display on a cathode ray tube, or "video screen".
The role of the constant false alarm rate circuitry is to determine the power threshold above which any return can be considered to probably originate from a target as opposed to one of the spurious sources. If this threshold is too low, more real targets will be detected, but at the expense of increased numbers of false alarms. Conversely, fewer targets will be detected if the threshold is too high, but the number of false alarms will also be low. In most radar detectors, the threshold is set to achieve a required probability of false alarm (equivalently, false alarm rate or time between false alarms).
Suppose the background against which targets are to be detected is constant with time and space. In that case, a fixed threshold level can be chosen that provides a specified probability of false alarm, governed by the probability density function of the noise, which is usually assumed to be Gaussian. The probability of detection is then a function of the signal-to-noise ratio of the target return. However, in most fielded systems, unwanted clutter and interference sources mean that the noise level changes both spatially and temporally. In this case, a changing threshold can be used, where the threshold level is raised and lowered to maintain a constant probability of false alarm. This is known as constant false alarm rate (CFAR) detection.
== Cell-averaging CFAR ==
Detection occurs when the cell under test exceeds the threshold. In most simple CFAR detection schemes, the threshold level is calculated by estimating the noise floor level around the cell under test (CUT). This can be found by taking a block of cells around the CUT and calculating the average power level. Cells immediately adjacent to the CUT are normally ignored to avoid corrupting this estimate with power from the CUT itself (and referred to as "guard cells"). A target is declared present in the CUT if it is greater than all its adjacent cells and greater than the local average power level. The estimate of the local power level may sometimes be increased slightly to allow for the limited sample size. This simple approach is called a cell-averaging CFAR (CA-CFAR).
Other related approaches calculate separate averages for the cells to the left and right of the CUT, and then use the greatest-of or least-of these two power levels to define the local power level. These are referred to as greatest-of CFAR (GO-CFAR) and least-of CFAR (LO-CFAR), respectively, and can improve detection when immediately adjacent to areas of clutter.
== Sophisticated CFAR approaches ==
More sophisticated CFAR algorithms can adaptively select a threshold level by taking a rigorous account of the statistics of the background in which targets are to be detected. This is particularly common in maritime surveillance (radar) applications, where the background of sea clutter is particularly spikey and not well approximated by additive white Gaussian noise. This is a difficult detection problem, as it is difficult to differentiate between spikes due to the sea surface returns and spikes due to valid returns from, for example, submarine periscopes. The K-distribution is a popular distribution for modelling sea clutter characteristics.
== See also ==
Detection theory
False alarm
Pulse-Doppler signal processing
Receiver operating characteristic
== References == | Wikipedia/Constant_false_alarm_rate |
Ablative brain surgery (also known as brain lesioning) is the surgical ablation by various methods of brain tissue to treat neurological or psychological disorders. The word "Ablation" stems from the Latin word Ablatus meaning "carried away". In most cases, however, ablative brain surgery does not involve removing brain tissue, but rather destroying tissue and leaving it in place. The lesions it causes are irreversible. There are some target nuclei for ablative surgery and deep brain stimulation. Those nuclei are the motor thalamus, the globus pallidus, and the subthalamic nucleus.
Ablative brain surgery was first introduced by Pierre Flourens (1794–1867), a French physiologist. He removed different parts of the nervous system from animals and observed what effects were caused by the removal of certain parts. For example, if an animal could not move its arm after a certain part was removed, it was assumed that the region would control arm movements. The method of removal of part of the brain was termed "experimental ablation". With the use of experimental ablation, Flourens claimed to find the area of the brain that controlled heart rate and breathing.
Ablative brain surgery is also often used as a research tool in neurobiology. For example, by ablating specific brain regions and observing differences in animals subjected to behavioral tests, the functions of all the removed areas may be inferred.
Experimental ablation is used in research on animals. Such research is considered unethical on humans due to the irreversible effects and damages caused by the lesion and by the ablation of brain tissues. However, the effects of brain lesions (caused by accidents or diseases) on behavior can be observed to draw conclusions on the functions of different parts of the brain.
== Uses ==
=== Parkinson's disease ===
Parkinson's disease (PD) is a progressive degenerative disease of the basal ganglia, characterized by the loss of dopaminergic cells of the substantia nigra, pars compacta (SNc). Surgical ablation has been used to treat Parkinson's disease. In the 1990s, the pallidum was a common surgical target. Unilateral pallidotomy improves tremor and dyskinesia on one side of the body (opposite the side of the brain surgery), but bilateral pallidotomy was found to cause irreversible deterioration in speech and cognition.
Two other rapidly evolving or potential surgical approaches to Parkinson's disease are deep brain stimulation (DBS) and restorative therapies.
Deep brain stimulation is a surgical treatment involving the implantation of a neurostimulator medical device, sometimes called a 'brain pacemaker', which sends electrical impulses to specific parts of the brain. Generally, deep brain stimulation surgery is considered preferable to ablation because it has the same effect and is adjustable and reversible.
The advent of deep brain stimulation has been an important advance in the treatment of Parkinson's disease. DBS may be employed in the management of medication-refractory tremor or treatment-related motor complications, and may benefit between 4.5% and 20% of patients at some stage of their disease course. DBS at high frequency often has behavioral effects that are similar to those of lesioning.
In Australia, patients with PD are reviewed by specialized DBS teams who assess the likely benefits and risks associated with DBS for each individual. The aim of these guidelines is to assist neurologists and general physicians identify patients who may benefit from referral to a DBS team. Common indications for referral are motor fluctuations and/or dyskinesias that are not adequately controlled with optimised medical therapy, medication-refractory tremor, and intolerance to medical therapy. Early referral for consideration of DBS is recommended as soon as optimised medical therapy fails to offer satisfactory motor control.
The thalamus is another potential target for treating a tremor; in some countries, so is the subthalamic nucleus, although not in the United States due to its severe side effects. Stimulation of portions of the thalamus or lesioning has been used for various psychiatric and neurological conditions, and when practiced for movement disorders the target is in the motor nuclei of the thalamus. Thalamotomy is another surgical option in the treatment of Parkinson's disease. However, rigidity is not fully controlled after successful thalamotomy, it is replaced by hypotonia. Furthermore, significant complications can occur, for example, left ventral-lateral thalamotomy in a right-handed patient results in verbal deterioration while right thalamotomy causes visual-spatial defects. However, for patients for whom DBS is not feasible, ablation of the subthalamic nucleus has been shown to be safe and effective. DBS is not suitable for certain patients. Patients with immunodeficiencies are an example of a situation in which DBS is not a suitable procedure. However, a major reason as to why DBS is not often performed is the cost. Because of its high cost, DBS cannot be performed in regions of the world that are not wealthy. In the case of such circumstances, a permanent lesion in the subthalamic nucleus (STN) is created as it is a more favourable surgical procedure. The surgical procedure is going to be done on the non-dominant side of the brain; a lesion might be favored to evade numerous pacemaker replacements. More so, patients who gain relief from stimulation devoid of any side effects and need a pacemaker change may have a lesion performed on them in the same position. The stimulation parameters act as a guide for the preferred size of the lesion. In order to identify the part of the brain that is to be destroyed, new techniques such as micro electrode mapping have been developed.
=== Cluster headaches ===
Cluster headaches occur in cyclical patterns or clusters—which gives the condition of its name. Cluster headache is one of the most painful types of headache. Bouts of frequent cluster headaches may last from weeks to months. Attempts have been made to treat cluster headaches via ablation of the trigeminal nerve, but have not been very effective. Other surgical treatments for cluster headaches are currently under investigation.
=== Psychiatric disorders ===
Ablative psychosurgery continues to be used in a few centres in various countries. In the US there are a few centres including Massachusetts General Hospital that carry out ablative psychosurgical procedures. Belgium, the United Kingdom, and Venezuela are other examples of countries where the technique is still used.
In the People's Republic of China, surgical ablation was used to treat psychological and neurological disorders, particularly schizophrenia, but also including clinical depression, and obsessive-compulsive disorder. The official Xinhua News Agency has since reported that China's Ministry of Health has banned the procedure for schizophrenia and severely restricted the practice for other conditions. In recent studies, Deep Brain Stimulation (DBS) is beginning to replace Ablative Brain Surgery for severe psychiatric conditions that are generally treatment resistant, such as obsessive-compulsive disorder.
== Methods ==
Experimental ablation involves the drilling of holes in the skull of an animal and inserting an electrode or a small tube called a cannula into the brain using a stereotactic apparatus. A brain lesion can be created by conducting electricity through the electrode which damages the targeted area of the brain. likewise, chemicals can be inserted in the cannula which could possibly damages the area of interest. By comparing the prior behavior of the animal to after the lesion, the researcher can predict the function of damaged brain segment. Recently, lasers have been shown to be effective in ablation of both cerebral and cerebellar tissue. A laser technology called MRI-guided laser ablation, for example, allows great precision in location and size of the lesion and the causes little to no thermal damage to adjacent tissue. The Texas Children's Hospital is one of the first to use this MRI guided method to destroy and treat brain lesions effectively and precisely. A prime example is a patient at this hospital who now no longer undergoes frequent seizures because of the success of this treatment. MRI-guided laser ablation is also used for ablating brain, prostate and liver tumors. Heating or freezing are also alternative methods to ablative brain surgery.
=== Sham lesions ===
A sham lesion is a way for researchers to give a placebo lesion to animals involved in experimental ablation. Whenever a cannula or electrode is placed into brain tissue, unintended additional damage is caused by the instrument itself. A sham lesion is simply the placement of the lesioning instrument into the same spot it would be placed in a regular lesion, only there is no chemical or electrical process. This technique allows researchers to properly compare to an appropriate control group by controlling for the damage done separate from the intended lesion.
=== Excitotoxic lesions ===
An excitotoxic lesion is the process of an excitatory amino acid being injected into the brain using a cannula. The amino acid is used to kill neurons by essentially stimulating them to death. Kainic acid is an example of an excitatory amino acid used in this type of lesion. One crucial benefit to this lesion is its specificity. The chemicals are selective in that they do not damage the surrounding axons of nearby neurons, but only the target neurons.
=== Radio frequency lesions ===
Radio frequency (RF) lesions are produced by electrodes placed in the brain tissue. RF current is an alternating current of very high frequency. The process during which the current passes through tissue produces heat that kills cells in the surrounding area. Unlike excitotoxic lesions, RF lesions destroy everything in the nearby vicinity of the electrode tip.
The use of ablative brain surgery on the nucleus accumbens is the wrong method to treat addictions according to Dr. Charles O'Brien. Dr. John Adler, however, believes ablation can provide valuable information about how the nucleus accumbens works.
== See also ==
Ablation (artificial intelligence), analogous process used in artificial neural networks
== References ==
== Further reading ==
Bain, P (1 November 2003). "Surgical treatment of Parkinson's disease and other movement disorders". Journal of Neurology, Neurosurgery & Psychiatry. 74 (11): 1601. doi:10.1136/jnnp.74.11.1601-a. PMC 1738211. ProQuest 1781234131.
Eric, M. Gabriel; Blaine, S. Nashold (March 1998). "Evolution of Neuroablative Surgery for Involuntary Movement Disorders: An Historical Review". Neurosurgery. 42 (3): 575–591. doi:10.1097/00006123-199803000-00027. PMID 9526992. | Wikipedia/Ablative_surgery |
Oral and maxillofacial surgery (OMFS) is a surgical specialty focusing on reconstructive surgery of the face, facial trauma surgery, the mouth, head and neck, and jaws, as well as facial plastic surgery including cleft lip and cleft palate surgery.
== Specialty ==
An oral and maxillofacial surgeon is a specialist surgeon who treats the entire craniomaxillofacial complex: anatomical area of the mouth, jaws, face, and skull, head and neck as well as associated structures. Depending upon the national jurisdiction, oral and maxillofacial surgery may require a degree in medicine, dentistry or both.
=== United States ===
In the U.S., oral and maxillofacial surgeons, whether possessing a single or dual degree, may further specialise after residency, undergoing additional one or two year sub-specialty oral and maxillofacial surgery fellowship training in the following areas:
Cosmetic facial surgery, including eyelid (blepharoplasty), nose (rhinoplasty), facial lift, brow lift, and laser resurfacing
Cranio-maxillofacial trauma, including zygomatic (cheek bone), orbital (eye socket), mandibular and nasal fractures as well as facial soft tissue lacerations and penetrating neck injuries
Craniofacial surgery/paediatric maxillofacial surgery, including cleft lip and palate surgery and trans-cranial craniofacial surgery including Fronto-Orbital Advancement and Remodelling (FOAR) and total vault remodelling
Head and neck cancer and microvascular reconstruction free flap surgery
Maxillofacial regeneration, which is re-formation of the facial region by advanced stem cell technique
=== United Kingdom and Europe ===
In countries such as the UK and most of Europe, it is recognised as a specialty of medicine with a degree in medicine and an additional degree in dentistry being compulsory. The scope of practice is mainly head and neck cancer, microvascular reconstruction, craniofacial surgery and cranio-maxillofacial trauma, skin cancer, facial deformity, cleft lip and palate, craniofacial surgery, TMJ surgery and cosmetic facial surgery.
In the UK, maxillofacial surgery is a specialty of the Royal College of Surgeons of England, Royal College of Surgeons of Edinburgh. Intercollegiate Board Certification is provided through the JCIE, and is the same as plastic surgery, ENT, general surgery, orthopaedics, paediatric surgery, neurosurgery and cardiothoracic surgery.
The FRCS (Fellowship of the Royal College of Surgeons) is the specialist exam at the end of surgical training, and is required to work as a Consultant Surgeon in maxillofacial surgery.
In the EU, OMFS is defined within Directive 2005/36 on professional qualifications (updated 2021). The two OMFS specialties are 'dual degree' dental, oral, and maxillofacial surgery (DOMFS) and 'single medical degree' maxillofacial surgery (MFS). In some cases a dental degree may be required to enter specialty training but in all cases the medical degree must be obtained before starting OMFS specialty training.
In Poland, maxillofacial surgery has always been dominated by dentists and still the majority of current OMFS trainees are dental graduates.
Since 2019, Norway switched from dual degree requirement for maxillofacial surgery to medical degree only. Similarly, Sweden has started several maxillofacial surgery training programs for medical graduates.
=== Canada and Asia ===
In Asia, oral and maxillofacial surgery is also recognized as a dental specialty and requires a degree in dentistry prior to surgical residency training. The Canadian model is the same as the model used in the United States of America.
=== Pakistan ===
In Pakistan, OMFS is recognized as a specialty of dentistry which requires FCPS from CPSP after 4 years BDS degree and a one-year housejob. The candidate has to pass FCPS-1 in order to commence their training followed by PGMI Exam (not in all cases).
=== India ===
Oral and maxillofacial surgery, also known as OMFS, is a branch recognized by DCI (Dental Council of India). Becoming a maxillofacial surgeon requires a five-year dental degree followed by three years of post-graduate specialisation. Oral and maxillofacial surgery includes the treatment of complex dental surgery, including wisdom tooth removal, dental implant, craniomaxillofacial trauma, orofacial pain (trigeminal neuralgia) and jaw joint pain (temporomandibular disorder) management, jaw joint replacement for ankylosis and deformed jaw joint cases, Lefort-3 distraction for craniosynostosis case, jaw tumour and cyst removal surgery, head and neck cancer, facial aesthetic like rhinoplasty, eye and ear plastic surgery, facial cosmetic surgery, microvascular surgery, and cleft and craniomaxillofacial surgery. A maxillofacial surgeon is considered one of the required members of an emergency team. Almost 20-25% of trauma patients usually have sustained facial trauma, and that needs urgent opinion and primary management that can be better managed by maxillofacial experts.
=== Australia and New Zealand ===
In Australia and New Zealand, oral and maxillofacial surgery is recognised as both a specialty of medicine and dentistry. Degrees in both medicine and dentistry are compulsory prior to being accepted for surgical training. The scope of practice is broad and there is the ability to undertake subspecialty fellowships in areas such as head and neck surgery and microvascular reconstruction.
=== Globally ===
In other countries, oral and maxillofacial surgery as a specialty exists but under different forms, as the work is sometimes performed by a single or dual qualified specialist depending on each country's regulations and training opportunities available. In several countries, oral and maxillofacial surgery is a specialty recognized by a professional association, as is the case with the Dental Council of India, American Dental Association, Royal College of Surgeons of England, Royal College of Surgeons of Edinburgh, Royal College of Dentists of Canada, Royal Australasian College of Surgeons and Brazilian Federal Council of Odontology (CFO).
== Regulation in the United States ==
Oral and maxillofacial surgery is an internationally recognized surgical specialty. Oral and maxillofacial surgery is formally designated as either a medical, dental or dual (medical and dental) specialty.
In the United States, oral and maxillofacial surgery is a recognised surgical specialty, formally designated as a dental specialty. A professional dental degree is required, a qualification in medicine may be undertaken optionally during residency training. In this respect, oral and maxillofacial surgery is sui generis among surgical specialties. Board certification in the U.S. is governed by the American Board of Oral and Maxillofacial Surgery (ABOMS). Oral and maxillofacial surgery is among the fourteen surgical specialties recognized by the American College of Surgeons. Oral and maxillofacial surgeons in the United States, whether single or dual degree, may become Fellows of the American College of Surgeons, "FACS" (Fellow, American College of Surgeons).
The American Association of Oral and Maxillofacial Surgeons (AAOMS) is the chief professional organization representing the roughly 9,000 oral and maxillofacial surgeons in the United States. The American Association of Oral and Maxillofacial Surgeons publishes the peer-reviewed Journal of Oral and Maxillofacial Surgery.
== Surgical procedures ==
Globally, treatments may be performed on the craniomaxillofacial complex: mouth, jaws, face, neck, and skull, and include:
Cosmetic surgery of the head and neck: (rhytidectomy/facelift, browlift, blepharoplasty/Asian blepharoplasty, otoplasty, rhinoplasty, septoplasty, cheek augmentation, chin augmentation, genioplasty, oculoplastics, neck liposuction, hair transplantation, lip enhancement, injectable cosmetic treatments like botox, fillers, platelet rich plasma, stem cells, chemical peel, mesotherapy.
Orthognathic surgery, surgical treatment/correction of dentofacial deformity as well as management of facial trauma, and sleep apnea
Oncology head and neck surgery with free flap microvascular reconstruction
Cutanous malignancy/skin cancer surgery of head and neck surgery skin grafts and local flaps
Diagnosis and treatment of:
benign pathology (cysts, tumors etc.)
malignant pathology (oral & head and neck cancer) with (ablative and reconstructive surgery, microsurgery)
cutaneous malignancy (skin cancer), lip reconstruction
congenital craniofacial malformations such as cleft lip and palate and cranial vault malformations such as craniosynostosis, (craniofacial surgery)
chronic facial pain disorders
temporomandibular joint (TMJ) disorders
Orthognathic (literally "straight jaw") reconstructive surgery, orthognathic surgery, maxillomandibular advancement, surgical correction of facial asymmetry.
soft and hard tissue trauma of the oral and maxillofacial region (jaw fractures, cheek bone fractures, nasal fractures, LeFort fracture, skull fractures and eye socket fractures).
Dentoalveolar surgery (surgery to remove impacted teeth, difficult tooth extractions, extractions on medically compromised patients, bone grafting or preprosthetic surgery to provide better anatomy for the placement of implants, dentures, or other dental prostheses)
Surgery to insert osseointegrated (bone fused) dental implants and maxillofacial implants for attaching craniofacial prostheses and bone anchored hearing aids.
== Occupation ==
Oral and maxillofacial surgery is intellectually and physically demanding and is among the most highly compensated surgical specialties in the United States with a 2008 average annual income of $568,968.
The popularity of oral and maxillofacial surgery as a career for persons whose first degree was medicine, not dentistry, seems to be increasing. At least one program (University of Alabama at Birmingham) exists that allows highly qualified candidates whose first degree is in medicine to earn the required dental degree, so as to qualify for entrance into oral and maxillofacial residency training programs and ultimately achieve board eligibility and certification in the surgical specialty.
== Education and training ==
In the UK, oral and maxillofacial surgery is one of the ten medical specialties, requiring MRCS and FRCS examinations.
In mainland Europe, its status, including whether or not oral surgery, maxillofacial surgery, and stomatology are considered separate specialties, varies by country. The required qualifications (medical degree, dental degree, or both, as well as the required internship and residency programs) also vary.
In the US, Australia and South Africa, oral and maxillofacial surgery is one of the ten dental specialties recognised by the American Dental Association, Royal College of Dentists of Canada, and the Royal Australasian College of Dental Surgeons. Oral and maxillofacial surgery requires four to six years of further formal university training after dental school (i.e., DDS, BDent, DMD, or BDS).
Residency training programs are either four or six years in duration. In the United States, four-year residency programs grant a certificate of specialty training in oral and maxillofacial surgery. Six-year programs granting an optional MD degree emerged in the early 1990s in the United States. Typically, six-year residency programs grant the specialty certificate and an additional degree such as a medical degree (e.g., MD, DO, MBBS, MBChB) or research degree (e.g., MS, MSc, MPhil, MDS, MSD, MDSc, DClinDent, DSc, DMSc, PhD). Both four– and six–year graduates are designated US "board eligible" and those who earn "board certification" are diplomats. Approximately 50% of the training programs in the US and 66% of Canadian training programs are "dual-degree." The typical length of education and training, in post-secondary school is 12 to 14 years. Beyond these years, some sub-specialise, adding an additional 1-2 year fellowship.
The typical training program for an oral and maxillofacial surgeon is:
2–4 years of undergraduate study (BS, BA, or equivalent degrees)
4 years dental study (DMD, BDent, DDS or BDS)
4–6 years residency training – Some programs integrate an additional degree such as a master's degree (MS, MDS, MSc, MClinDent, MScDent, MDent), doctoral degree (PhD, DMSc, DClinDent, DSc), or medical degree (e.g., MBBS, MD, DO, MBChB, MDCM)
After completion of surgical training most undertake final specialty examinations: US: "Board Certified (ABOMS)", Australia/NZ: FRACDS, or Canada: "FRCDC"
Some colleges offer membership or fellowships in oral/maxillofacial surgery: MOralSurg RCS, M(OMS) RCPS, FFD RCSI, FEBOS, FACOMS, FFD RCS, FAMS, FCDSHK, FCMFOS (SA)
Both single and dual qualified oral and maxillofacial surgeons may obtain fellowship with the American College of Surgeons (FACS).
=== Surgical sub-specialty fellowship training ===
In addition, single and dual-qualified graduates of oral and maxillofacial surgery training programs can pursue post-residency sub-specialty fellowships, typically 1–2 years in length, in the following areas:
Head and neck cancer – microvascular reconstruction
Cosmetic facial surgery (facelift, rhinoplasty, etc.)
Craniofacial surgery and pediatric maxillofacial surgery (cleft lip and palate repair, surgery for craniosynostosis, etc.)
Cranio-maxillofacial trauma (soft tissue and skeletal injuries to the face, head and neck)
== Charities ==
Several notable philanthropic organizations provide humanitarian oral and maxillofacial surgery globally. Smile Train was created in 1998 by Charles Wang focusing on childhood facial deformity. Operation Smile focuses on correcting cleft lips and palates in children. AboutFace, created by Paul Stanley, of the rock band KISS, who was born with a facial deformity, focuses on craniofacial disfiguration.
== See also ==
== References ==
== External links ==
International Association of Oral and Maxillofacial Surgeons
British Association of Oral and Maxillofacial Surgeons
American College of Surgeons
American Association of Oral and Maxillofacial Surgeons
American Board of Oral and Maxillofacial Surgeons
Journal of Oral and Maxillofacial Surgery | Wikipedia/Oral_and_maxillofacial_surgery |
Reconstructive surgery is surgery performed to restore normal appearance and function to body parts malformed by a disease or medical condition.
== Description ==
Reconstructive surgery is a term with training, clinical, and reimbursement implications. It has historically been referred to as synonymous with plastic surgery. In regard to training, plastic surgery is a recognized medical specialty and a surgeon can be a "board-certified" plastic surgeon by the American Board of Plastic Surgery. However, reconstructive surgery is not a specialty and there are no board-certified reconstructive surgeons.
More accurately, reconstructive surgery should be contrasted with cosmetic surgery. Reconstructive surgery is performed to
Improve/restore to normal function.
Restore to a normal appearance of "abnormal" or "malformed" body parts caused by the disease or condition and/or
Improve the patient's quality of life.
Separately, the patient must be healthy enough so that the benefits of the procedure outweigh the risks of complications or death. A procedure could be considered reconstructive but not medically necessary due to the risk to the patient.
In addition, Section 1862(a) (1) (A) of the Social Security Act directs the following:
"No payment may be made under Part A or Part B for any expenses incurred for items or services not reasonable and necessary for the diagnosis or treatment of illness or injury or to improve the functioning of a malformed body member." Therefore, outside clinical interpretation and carrier guidelines, there is a federal statute that "improving functionality and restoring appearance" are covered as reconstructive and medically necessary.
This definition is contrasted with cosmetic surgery performed to improve aesthetics or the appearance of a body part. A plastic surgeon can perform both reconstructive and cosmetic procedures. Some procedures, such as a panniculectomy (aka tummy tuck) can be considered as cosmetic by one insurance company and reconstructive by another. The surgeon may not be using the Medicare or reimbursement criteria when referring to a procedure as reconstructive or cosmetic. Plastic surgeons, maxillo-facial surgeons and otolaryngologists do reconstructive surgery on faces to correct congenital defects, after trauma and to reconstruct the head and neck after cancer.
Another good example is repair of a cleft palate, or cheiloplasty, which surgically corrects abnormal development, restores function to the lips and mouth and produces a more normal appearance. This meets the definition of reconstructive surgery and is mandated by state laws in at least 31 states, but could be denied as cosmetic by individual insurance companies in the remaining states.
Other branches of surgery (e.g., general surgery, gynecological surgery, pediatric surgery, plastic surgery, podiatric surgery) also perform some reconstructive procedures.
Reconstructive surgery represents a small but critical component of the comprehensive care of cancer patients. Its primary role in the treatment of cancer patients is to extend the ability of other surgeons and specialists to more radically treat cancer, offering patients the best opportunity for cure.
Reconstructive surgeons use the concept of a reconstructive ladder to manage increasingly complex wounds. This ranges from very simple techniques such as primary closure and dressings to more complex skin grafts, tissue expansion, and free flaps.
Reconstructive surgery procedures include breast implant removal, reduction mammoplasty, breast reconstruction, surgical correction of birth anomalies, congenital nevi surgery, and liposuction for lipedema.
Cosmetic surgery procedures include breast enhancement, reduction and lift, face lift, forehead lift, upper and lower eyelid surgery (blepharoplasty), laser skin resurfacing (laser resurfacing), chemical peel, nose reshaping (rhinoplasty), reconstruction liposuction, Nasal reconstruction using a paramedian forehead flap, as well as tummy tuck (abdominoplasty).
=== Facial plastic and reconstructive surgery ===
Facial plastic and reconstructive surgery (FPRS) is a surgical subspecialty focused on improving both the functional and aesthetic aspects of the face, head, and neck.
== Use of implants and biomaterials ==
Recent literature in medline also has noted implementation of barbed suture in these procedures.
Biomaterials are, in their simplest form, plastic implants used to correct or replace damaged body parts. Biomaterials were not used for reconstructive purposes until after World War II due to the new and improved technology and the tremendous need for the correction of damaged body parts that could replace transplantation. The process involves scientific and medical research to ensure that the biomaterials are biocompatible and that they can assume the mechanical and functioning roles of the components they are replacing.
A successful implantation can best be achieved by a team that understands not only the anatomical, physiological, biochemical, and pathological aspects of the problem, but also comprehends bioengineering. Cellular and tissue engineering is crucial to know for reconstructive procedures.
An overview of the standardization and control of biomedical devices has recently been gathered by D. G. Singleton. Papers have covered in depth the U.S. Food and Drug Administration (FDA) Premarket Approval Process (J. L. Ely) and FDA regulations governing Class III devices. Two papers have described how the National Institute of Standards and Technology, American Dental Association, National Institute of Dental and Craniofacial Research, and private dental companies have collaborated in a number of important advances in dental materials, devices, and analytical systems.
== References == | Wikipedia/Reconstructive_surgery |
A Bachelor of Medicine, Bachelor of Surgery (Latin: Medicinae Baccalaureus, Baccalaureus Chirurgiae; MBBS, also abbreviated as BM BS, MB ChB, MB BCh, or MB BChir) is a medical degree granted by medical schools or universities in countries that adhere to the United Kingdom's higher education tradition. Despite the historical distinction in nomenclature, these degrees are typically combined and conferred together. This degree is usually awarded as an undergraduate degree, but it can also be awarded at graduate-level medical institutions. The typical duration for completion is five to six years.
A Bachelor of Medicine (BMed, BM, or MB) is an undergraduate medical degree awarded by medical schools in countries following the tradition of China. The completion period for this degree is generally five to six years. The term 'Medicine' in this context encompasses the broader field of medical science and practice, rather than specifically internal medicine. Consequently, graduates with a BMed degree are qualified to practise surgery. The BMed degree serves as the primary medical qualification, and individuals holding it may pursue further professional education, such as a Master of Medical Science or a Doctor of Medical Science (equivalent to a PhD).
Both degrees are considered equivalent to the Doctor of Medicine degree typically conferred by universities in North America. In the United States, doctors trained in some osteopathic medicine programs receive the Doctor of Osteopathic Medicine degree. For practical purposes, all these degrees (MBBS/BMed/MD/DO) are considered to be equivalent.
== History and nature ==
The degree is currently awarded in institutions in the United Kingdom and countries formerly part of the British Empire.
Historically, Bachelor of Medicine was also the primary medical degree conferred by institutions in the United States and Canada, such as the University of Pennsylvania, Harvard University, the University of Toronto, the University of Maryland, and Columbia University. Several early North American medical schools were (for the most part) founded by physicians and surgeons who had trained in England and Scotland. University medical education in England culminated with the Bachelor of Medicine qualification and in Scotland the Doctor of Medicine. In the mid-19th century, the public bodies that regulated medical practice required practitioners in Scotland and England to hold the dual Bachelor of Medicine and Bachelor of Surgery degrees. Over the course of the 19th century, North American medical schools switched to the tradition of the ancient universities of Scotland and began conferring Doctor of Medicine rather than Bachelor of Medicine.
In the countries that award bachelor's degrees in medicine, however, Doctor of Medicine denotes a holder of a junior doctorate and is reserved for medical practitioners who undertake research and submit a thesis in the field of medicine. Nevertheless, those holding Bachelor of Medicine, Bachelor of Surgery are usually referred to by the courtesy title of "Doctor" and use the prefix "Dr.", whether or not they also hold a Ph.D. or DSc.
In many countries, the degrees are awarded after an undergraduate course lasting five or six years. For example, most Chinese universities offering medical degrees provide undergraduate courses lasting six years. In some cases, a graduate in another discipline may subsequently enter a special graduate-entry medical course, reduced in duration to account for relevant material covered or learning skills acquired during the first degree. In some cases the old first-year courses (for six-year degrees) in the basic sciences of physics, chemistry, and biology have been abolished: that standard has to be reached by school examinations before entry. However, in most countries, a newly graduated Bachelor of Medicine and Surgery must spend a specified period in internship before he or she can obtain full registration as a licensed medical practitioner.
== Naming ==
The names and abbreviations given to these degrees depend on the institution, awarding body or country, and vary widely. This is mostly for reasons of tradition rather than to indicate any difference between the relative levels of the degrees. They are considered equivalent.
If the awarding body titles the degrees in Latin, the degrees are commonly named Medicinae Baccalaureus, Chirurgiae Baccalaureus; Medicinae Baccalaureus et Chirurgiae Baccalaureus; or Baccalaureus in Medicina et in Chirurgia; abbreviated as MB ChB, MB BCh or otherwise. If titled in English, they are named Bachelor of Medicine, Bachelor of Surgery; Bachelor of Medicine and Bachelor of Surgery; or Bachelor of Medicine and Surgery; usually abbreviated as MB BS, and sometimes as BM BS, even though most MB BS-awarding institutions do not use Latin to name their degrees.
Below are described the specific names used, arranged by country.
=== Australia ===
Historically, Australian medical schools have followed the British tradition by conferring the degrees of Bachelor of Medicine and Bachelor of Surgery (MBBS) to its graduates whilst reserving the title of Doctor of Medicine (MD) for their research training degree, analogous to the PhD, or for their honorary doctorates. Although the majority of Australian MBBS degrees have been graduate programs since the 1990s, under the previous Australian Qualifications Framework (AQF) they remained categorised as Level 7 Bachelor's degrees together with other undergraduate programs.
The latest version of the AQF includes the new category of Level 9 Master's (Extended) degrees which permits the use of the term 'Doctor' in the styling of the degree title of relevant professional programs. As a result, most undergraduate Australian medical schools have replaced their MBBS degrees with a combined degree that ends with the MD (e.g. the Bachelor of Medical Studies / Doctor of Medicine at The University of New South Wales or the Bachelor of Medical Science and Doctor of Medicine at Monash University) or switched to graduate only MD pathways, to resolve the previous anomalous nomenclature. Even still, Curtin University and James Cook University both still offer the MBBS degree. With the introduction of the Master's level MD, universities have also renamed their previous medical research doctorates. The University of Melbourne was the first to introduce the MD in 2011 as a basic medical degree, and has renamed its research degree to Doctor of Medical Science (DMedSc).
=== Bahrain ===
The Medical University of Bahrain or RCSI-Bahrain is a constituent university of the Royal College of Surgeons in Ireland (RCSI) and awards its graduates the MB, BCh, BAO (Hons), the same degree awarded to graduates at RCSI.
=== Bangladesh ===
All medical schools in Bangladesh award MBBS.
=== Barbados ===
The Bridgetown International University, Victoria University of Barbados, American University of Barbados School of Medicine, and University of the West Indies Faculty of Medicine all award the MBBS.
=== China ===
In China, medical undergraduates are awarded a Bachelor of Medicine (MB, also BMed, and BM) in Clinical Medicine for a course of study lasting five years for native Chinese students and six years for international/foreign students, including internship. International students may take the program in English or Chinese. Some medical schools also award MBBS degrees, but only for the international students. In total, 247 universities are authorized to award medical degrees. All 247 universities are recognized by most of the medical councils around the world and by ECFMG. By August 2022, 136 universities have passed the process of Accreditation of Medical Education from the Ministry of Education of China. The universities awarding MB and MBBS degrees are at the list of medical schools in China.
=== Egypt ===
All Egyptian medical schools, public and private, award an MB BCh as the basic medical degree after completion of five academic and clinical study years followed by two years of obligatory clinical rotations (the MB BCh is issued only after the completion of the clinical rotations) with total of seven years both academic, clinical study and clinical rotations.
=== France ===
French students get permitted access to medical studies when succeeding the competitive examination occurring at the end of their first year of studies. They spend their second and third year at their medical school where they learn physiology, semiology and the basics of medical examination. From their fourth year, they begin their rotations in teaching hospitals where they assist junior and senior physicians and learn their art. At the end of their sixth year, they undertake a competitive examination to match with their medical specialty and city of practice. Students are then full-time physicians practising under supervision and will be called "doctors" only when graduating at the end of their residency.
After 9 years (or 3 cycles including successfully defending a Practical (or Exercise) thesis (Le Doctorat en Medecine) on an area of interest), they are awarded : Diplôme d'État de docteur en médecine (State diploma of Doctor of Medicine) and Diplôme d'études spécialisées (DES) which are both needed for full registration on the National Council of the Order of Physicians (l'Ordre des médecins) and can practise medicine
=== Ghana ===
All Ghanaian medical schools award an MBChB as the basic medical degree after 6 academic years. These seven medical schools are Kwame Nkrumah University of Science and Technology, University of Ghana, University for Development Studies, University of Cape Coast, University of Health and Allied Sciences and the private Accra College of Medicine, and Family Health Medical School, another private medical school.
=== Guyana ===
The University of Guyana awards MB BS. Other "offshore" United-States-linked schools in the country award the North American MD, such as Texila American University, Lincoln American University.
=== Hong Kong ===
The awarding of qualifications in Hong Kong follows the British tradition.
The dual degree is awarded as:
MBBS at the University of Hong Kong
MBChB at the Chinese University of Hong Kong
=== India ===
In India the MBBS is generally a 5+1⁄2-year course including one year of mandatory internship and an additional year of mandatory rural posting. Some institutes like the All India Institutes of Medical Sciences and other Deemed Medical Colleges do not have the 1 year of mandatory rural posting. During internship, medical students are paid a stipend. Registration as MBBS doctor is granted after completion of these postings. MBBS in India comes under purview of the National Medical Commission which has the power to recognize or de-recognize medical colleges which provide MBBS education.
Over the last decade, a number of medical colleges have been opened in India, to cater to the huge Indian population. The National Medical Commission mentions 704 medical colleges, which teach MBBS in the country, as in July 2023. There are both government run as well as private medical colleges in India. Admission to MBBS program in government colleges can be highly competitive because of subsidized education and extensive hands-on experience. Every year, millions of students appear for the national competitive examination National Eligibility cum Entrance Test (Undergraduate) for a total of 107,798 MBBS seats in the country, as of July 2023.
The MBBS course starts with the basic pre and para-clinical subjects such as biochemistry, physiology, anatomy, microbiology, pathology, forensic medicine including toxicology and pharmacology. The students simultaneously obtain hands-on training in the wards and out-patient departments, where they interact with real patients for five years. The curriculum aims to inculcate standard protocols of history taking, examination, differential diagnosis and complete patient Management. The student is taught to determine what investigations will be useful for a patient and what are the best treatment options. The curriculum also contains a thorough practical knowledge and practice of performing standard clinical procedures. The course also contains a 12-month-long internship, in which an intern is rotated across various specialties. Besides standard clinical care, one also gets a thorough experience of ward management, staff management, and thorough counselling skills. After 1 year of rotatory internship, additional years of rural internship is mandatory in many states, which can be skipped by paying a huge fine to the government, for obtaining permanent registration as a medical practitioner.
MBBS curriculum in India is going through changes with incorporation of modern teaching methods and introduction of National Exit Test (NExT) as the exit test for obtaining MBBS degree, notified on 30 June 2023.
=== Indonesia ===
In Indonesia, graduating students are awarded the academic degree of Sarjana Kedokteran / Bachelor of Medicine (written as suffix "S.Ked") after completing their pre-clinical studies. At this point, the graduate is not yet a practising doctor, but may choose to work directly as a medical scientist or other non-clinician professions (usually health-related). However, most graduates will pursue the conventional path, which is to enroll in the clinical clerkship program (Program Pendidikan Profesi Dokter) for another 1.5 to 2 years. During this program, students are required to rotate through different medical/surgical specialties in a teaching hospital, actively involved in diagnoses and treatment of patients under the direct supervision of residents and consultants/attending physicians. After completing a clinical clerkship, students take the national medical licensing examination (Ujian Kompetensi Mahasiswa Program Profesi Dokter/UKMPPD) and will be awarded the title Dokter (written as prefix "dr.") as their first professional title if they pass the examination.
=== Iraq ===
All medical schools in Iraq award MB ChB, with the exception of the University of Kurdistan-Hewlêr which awards the MBBS degree.
=== Ireland ===
The medical schools in both the Republic of Ireland and Northern Ireland – Queen's University Belfast, Trinity College Dublin, some constituent institutions of the National University of Ireland (University College Dublin, University College Cork and University of Galway), and the Royal College of Surgeons in Ireland — award the degrees of MB BCh BAO. The letters BAO stand for Baccalaureus in Arte Obstetricia (Bachelor of Obstetrics), a degree unique to Ireland which the Irish universities added in the 19th century as the legislation at the time insisted on a final examination in obstetrics. This third degree is not registerable with the Irish Medical Council nor the British General Medical Council (GMC). The only exception is the newly established University of Limerick graduate entry school of medicine which awards BM BS for Bachelor of Medicine and Bachelor of Surgery.
At Trinity College Dublin, the preclinical course leads to an additional Bachelor of Arts (BA) degree (upgradable after three or four years to Master of Arts); as originally after this most students used to go elsewhere to complete clinical training.
LRCPI LRCSI, or simply LRCP&SI, denotes a holder of the historical non-university qualifying licentiates awarded jointly by the Royal College of Physicians of Ireland and the Royal College of Surgeons in Ireland to students of the RCSI's medical school under the Irish Conjoint Scheme. Unlike the corresponding licentiates awarded by the Royal Colleges in Scotland and England (which were external qualifications), these qualifications are still registerable with the Irish Medical Council, but not with the British GMC. Students at RCSI still receive these licences but now also receive the degrees MB BCh BAO, due to RCSI's status as a recognised college of the National University of Ireland. The RCSI students received a Licence in Midwifery (LM) from each college, in the same way that the Irish universities granted BAO degrees, so their qualifications were sometimes expressed as L & LM, RCPI, L & LM, RCSI or more misleadingly as LLM, LRCPI LRCSI, or simply LRCP&SI.
LAH formerly denoted a licentiate of the Apothecaries' Hall of Ireland, and is no longer awarded.
=== Japan ===
In Japan, medical undergraduates are awarded a Bachelor of Medicine, a course of study lasting six years. It is awarded by 42 national, 8 public and 31 private universities.
=== Jordan ===
The Bachelor of Medicine and Surgery (MBBS) degree is awarded in Jordan.
=== Kenya ===
The national universities with medical faculties in Kenya, namely Jomo Kenyatta University of Agriculture and Technology, University of Nairobi, Aga Khan University, Moi University, Kenyatta University, Egerton University, Maseno University and Kenya Methodist University award MB ChB.
Mount Kenya University and Egerton University also award the four-year BSc. Clinical Medicine degree in addition to the six-year MBChB.
=== Liberia ===
The AM. Dogliotti College of Medicine (University of Libeira) awards the MD degree.
=== Libya ===
There are three major public medical universities in Libya, University of Tripoli (Tripoli), University of Benghazi (formerly Garyounis) (Benghazi), and University of Alzaweyah. The schools award the MBBCh.
The Libyan International Medical University is an accredited private medical university that awards an MBChB to its graduates.
=== Malaysia ===
The MBBS is awarded by five public and 17 private universities.
=== Mexico ===
In Mexico, the National Autonomous University of Mexico, the Monterrey Institute of Technology and Higher Education, the National Polytechnic Institute, the Metropolitan Autonomous University, among others, grant the title of "Médico cirujano" (Physician-surgeon) after five or six years of post-high school education, plus one year of internship and one year of social service depending on each institution.
=== Myanmar ===
All five medical schools (UM1, UM 2, DSMA, UMM, UMMG) in Myanmar award the MB BS.
=== Namibia ===
The University of Namibia UNAM School of Medicine, the only medical school in the country, awards the MBChB degree.
=== Nepal ===
There are 18 medical schools in Nepal that award the MBBS degree. Medical education commission, Nepal (MEC) organizes the work related to establishment and operation of medical institutions all over Nepal and bears the sole responsibility to maintain quality, professionalism, institutional accountability and social justice in medical education. There is another entity called Nepal Medical Council (NMC) which major functions are quality control of medical education of the country, establish ethical health care practice, establish standardization of medical practice as well as responsible for giving license to practise medicine within the country's border.
=== Netherlands ===
In the Netherlands, students follow a period of 6 academic years. After three years, students obtain the title Bachelor Geneeskunde (translates to Bachelor of Medicine). After a further three years of study and internships, students obtain the Master Geneeskunde (translates to Master of Medicine) title. After the completion of the master's degree, the students are recognized as medical doctors.
=== New Zealand ===
The two New Zealand medical schools, Auckland and Otago, style their degrees as "MBChB" and "MB ChB" respectively.
=== Nigeria ===
The MBBS/MB ChB is awarded by many public and private universities in Nigeria, after a period of 6 academic years.
=== Pakistan ===
In Pakistan, a medical school is more often referred to as a medical college. The full-form of MBBS is Bachelor of Medicine, Bachelor of Surgery. It is a 5-year course plus one-year internship in affiliated hospital that can be completed from a college recognized by the Pakistan Medical and Dental Council, to receive a degree titled MBBS (Medical colleges in Pakistan). Medical colleges may also teach Post Graduate courses such as FCPS and diplomas. A medical college is affiliated with a university as a department which usually has a separate campus. Currently, a total of 127 medical colleges are listed in World Directory of Medical Schools in Pakistan.
All medical colleges and universities are regulated by the respective provincial department of health. They, however, have to be recognised after meeting criteria set by a central regulatory authority called Pakistan Medical and Dental Council (PMDC). Entrance into the medical colleges is based on merit under the guidelines of PMDC. Both the academic performance at the HSSC (grades 11–12) and a centralized entrance test like NMDCAT, are taken into consideration for the eligibility to enter most of the medical colleges.
To get admission into any government medical college, the weightage is determined by the provincial or federal government. In order to get admission into any private medical college, the following weightage is used:
50% to Marks of entrance test like Medical and Dental College Admission Test (MDCAT).
40% to Marks of Higher Secondary School Certificate (HSSC) Pre-Medical.
10% to Marks of Secondary School Certificate (SSC) Pre-Medical.
=== Rwanda ===
All Rwandan medical schools, public and private, award an MBBS as the basic medical degree after completion of five or six academic years.
=== Saudi Arabia ===
Medical schools in Saudi Arabia award the MBBS.
=== Singapore ===
The Yong Loo Lin School of Medicine at the National University of Singapore and the Lee Kong Chian School of Medicine at Nanyang Technological University confer MB BS. The American Duke University has a medical programme based in Singapore (Duke-NUS Graduate Medical School), but it follows the North American model of styling its degree Doctor of Medicine (MD) at master's degree level.
=== Somalia ===
Somali National University, Amoud University, Benadir University Salaam University and Hargeisa University award the MB ChB, East Africa University awards MMBS.
=== South Africa ===
The University of Pretoria, University of Cape Town, University of the Free State, University of Stellenbosch, University of KwaZulu-Natal, Walter Sisulu University and MEDUNSA all award MBChB, whereas the University of the Witwatersrand styles its degree as MBBCh.
=== South Sudan ===
The University of Juba, University of Bahr El-Ghazal and Upper Nile University in South Sudan awards the MBBS degree after the successful completion of six academic years.
=== Sri Lanka ===
In 1942, the University of Ceylon was established through legislation and the MBBS degree was recognised for registration of doctors in place of the Licentiate in Medicine and Surgery (LMS).
=== Sudan ===
The medical degree in Sudan is a six-year program that includes both classroom and clinical training. Students who successfully complete the program are awarded the Bachelor of Medicine, Bachelor of Surgery (MBBS) degree, which is recognized internationally.
=== Syria ===
The higher education in Syria provides training to a Diploma, Bachelor, Master, and Doctorate levels (see European Education, Audiovisual and Culture Executive Agency on Higher Education: Syria).
=== Tunisia ===
Medical education in Tunisia is solely administered by the government Ministry of Higher Education and Ministry of Public Health. Students get permitted access to medical studies when succeeding their national baccalauréat exam and obtaining a competitive score that allows them admission to medical schools (usually in the 95% percentile).
The curriculum spans six years, two years of fundamental medicine, followed by three years of clinical medicine, culminating in a final year of internship. Upon the completion of this comprehensive training, students are awarded a certificate equivalent to a bachelor's degree, known as the "Diplome de Fin des Etudes Cliniques en Médecine." Subsequently, a national exam is undertaken, and students are ranked based on their performance. Specialization in medicine then follows, ranging from an additional three years for family medicine to five years for most medical and surgical specialties.
During the initial two years at medical school, students focus on foundational subjects such as physiology, semiology, and the fundamentals of medical examination. From the fourth year onwards, they engage in rotations at teaching hospitals, where they actively participate under the guidance of junior and senior physicians, honing their practical skills. At the conclusion of the fifth year, students undergo a competitive examination to determine their medical specialty and city of practice. Following this, they transition to full-time physicians, practising under supervision, and earn the title of "doctors" upon successful completion of their residency.
=== Uganda ===
The nine universities in Uganda that have medical schools that teach undergraduate courses, namely; Makerere University, Mbarara University, Gulu University, Kampala International University, Busitema University, Kabale University, Habib Medical School, St. Augustine International University, and Uganda Christian University all award the MBChB degree, after five years of study.
=== Ukraine ===
In Ukraine, the full-form of MBBS is Bachelor of Medicine and Bachelor of Surgery. It is generally a 5.8 year course including one year compulsory internship, that can be completed from a college accredited by the National Medical Commission. At present, Ukraine is ranked at the fourth position in Europe for having the largest number of post graduates in fields of medicine. Ukraine has a number of Top Government Medical Universities offering MBBS, MD and other degrees in medicine to the local students as well as international students.
The MBBS course starts with the basic pre and para-clinical subjects such as biochemistry, physiology, anatomy, microbiology, pathology, forensic medicine including toxicology and pharmacology. The students simultaneously obtain hands-on training in the wards and out-patient departments, where they interact with real patients for six years. The curriculum aims to inculcate standard protocols of history taking, examination, differential diagnosis and complete patient Management. The student is taught to determine what investigations will be useful for a patient and what are the best treatment options. The curriculum also contains a thorough practical knowledge and practice of performing standard clinical procedures. The course also contains a 12-month-long internship, in which an intern is rotated across various specialties. Besides standard clinical care, one also gets a thorough experience of ward management, staff management, and thorough counselling skills.
The degree awarded is "Bachelor of Medicine and Bachelor of Surgery". The minimum requirements for the MBBS course are 50% marks in physics, chemistry, biology and English in a student's secondary school examinations and student need to pass National Eligibility cum Entrance Test examination for the admission in Ukraine Universities.
=== United Kingdom ===
==== England, Wales, and Northern Ireland ====
While first degrees in medicine meet the expectations of the descriptor for higher education qualification at "level 7 (the UK master's degree)", these degrees usually retain, for historical reasons, "Bachelor of Medicine, Bachelor of Surgery" and are abbreviated to MBChB or MBBS.
Varied abbreviations are used for these degrees in these areas:
MB ChB is used at the universities of Aston, Anglia Ruskin, Birmingham, Bristol, Buckingham, Lancaster, Leeds, Leicester, Liverpool, Keele, Manchester, Sheffield, Sunderland (in partnership with Keele) and Warwick.
MB BCh is used by the Welsh universities, Cardiff University and Swansea University.
MB, BCh, BAO is used at the Queen's University, Belfast
MB BS is used at all medical schools currently or previously part of the University of London (aka The United Hospitals) (Imperial College School of Medicine, UCL Medical School, King's College London School of Medicine, Barts and The London School of Medicine and St George's, University of London). Other medical schools that also award an "MB BS" are Norwich Medical School, Hull York Medical School, Newcastle University, University of Central Lancashire and Ulster University (which is currently partnered with St George's)
BM BCh is awarded by the University of Oxford.
BM BS is used at the University of Nottingham, University of Exeter, University of Plymouth, University of Southampton, University of Surrey, Kent and Medway Medical School and Brighton and Sussex Medical School (formerly at Peninsula College of Medicine and Dentistry)
BM was previously awarded at the University of Southampton. However, beginning in 2013 students have been awarded BMBS. Although no degree in surgery was formally awarded by Southampton, this degree was equivalent to the MB ChB; students may go on to a career in surgery the same as any other graduates in medicine and surgery.
MB BChir is awarded by the University of Cambridge.
At the universities of Oxford and Cambridge, the preclinical course leads to an additional Bachelor of Arts (BA), degree (upgradable after three or four years to Master of Arts), after which most students used to go elsewhere (but usually to one of the London teaching hospitals) to complete clinical training. They could then take the degrees of their new university: They used to have the options of returning to their old university to take the clinical examinations or taking one of the old non-university qualifying examinations. All students at Oxford and Cambridge now remain in place to take their clinical training.
==== Scotland ====
All medical schools in Scotland (Aberdeen, Dundee, Edinburgh and Glasgow) award MB ChB.
The University of St Andrews School of Medicine awarded MB ChB until the early 1970s, but since the incorporation of its clinical medical school into the University of Dundee, St Andrews now only awards a pre-clinical BSc or BSc (Hons), and students go to a Partner Medical School (Aberdeen, Dundee, Edinburgh, Glasgow, or Manchester), where they are awarded an MB ChB after a further three years' study. There is also a programme for Canadian Citizens and residents whereby they complete 3 years at St. Andrews, then 3 years at Edinburgh and are assisted with applying for residency back in Canada.
Since 2018, a joint initiative coordinated by both the Universities of St Andrews and Dundee, the Scottish Graduate Entry Medicine (ScotGEM) programme, has based its first and second year students at St Andrews, and its third and fourth year students at Dundee. This is Scotland's first graduate entry medical degree programme. The intention is that the students of the inaugural cohort, due to graduate in July 2022, will be conferred a joint MB ChB by both universities – the first to graduate with this professional degree directly from St Andrews in over fifty years.
The Scottish Triple Qualification of LRCPE, LRCSE, LRCPSG (earlier LRCPE, LRCSE, LRFPSG) is an old non-university qualifying examination in medicine and surgery awarded jointly by the Royal College of Physicians of Edinburgh, Royal College of Surgeons of Edinburgh and Royal College of Physicians and Surgeons of Glasgow, previously through a Conjoint Board and from 1994 through the United Examining Board. The UEB was dissolved in 2007. These qualifications are still registrable with the GMC, but permission to award them was withdrawn by the Privy Council of the UK in 1999.
==== Historical Primary Medical Qualifications ====
The Conjoint diplomas LRCP MRCS LMSSA were non-university qualifying examinations in medicine and surgery awarded jointly by the Royal College of Physicians of London, Royal College of Surgeons of England and Society of Apothecaries through the United Examining Board from 1994 until 1999, when the General Medical Council withdrew permission. Before 1994, the English Conjoint diploma of LRCP, MRCS was awarded for 110 years, and the LMSSA was a distinct and sometimes less-esteemed qualification. These diplomas slowly became less popular among British medical students, but as recently as 1938 only a half of them qualified with university degrees. The diplomas came to be taken mostly by those who had already qualified in medicine overseas or who failed their medical school finals.
=== United States ===
International medical graduates with an MBBS from foreign countries are generally exempt from having to attend medical school in the United States, but must still undergo US residency and pass the United States Medical Licensing Examination (USMLE), which is given in three exams. The MBBS is not offered at medical schools in the United States as the majority of medical school programs are graduate entry and by tradition offer the MD degree as a primary medical qualification.
There are a number of institutions in the United States that offer a combined 6-year BS-MD joint degree, notably Northeast Ohio Medical University whereby graduating high school seniors complete an accelerated bachelor's degree in two years followed by an MD at the traditional four-year pace. Although the BS-MD pathway is a hybrid undergraduate/graduate program, the result is a primary medical qualification equivalent to an MBBS degree and graduates of these schools go on to enter their intern year at roughly the same age as their UK counterparts. Most American schools offering a BS-MD program do so in 7 years, such as the Indiana University School of Medicine, or in 8 years, such as the Baylor College of Medicine. The Association of American Medical Colleges maintains a list of such schools.
Primarily US-educated MDs and Doctors of Osteopathic Medicine (DOs) go through four years of undergraduate education and apply to professional medical graduate schools with a competitive Medical College Admission Test score and GPA. They then go through two more years of didactic medical science study, and take the pass-fail USMLE Step 1 exam. DO students take a similar exam known as COMLEX Level 1. Following a pass, they then undergo experiential learning of medicine by taking part in patient care in clinics and hospitals under the close supervision of board-certified physicians. After this year, they take the Step 2 Clinical Knowledge exam and formerly took the Step 2 Clinical Skills exam as well. DO students take the COMLEX Level 2-Cognitive Evaulation exam and previously took the COMLEX Level 2-Performance Evaluation exam. COMLEX 2-PE and Step 2 CS were discontinued in 2021 during the COVID-19 pandemic. They then go through one more year of experiential learning, often with elective rotations tailored to particular interests of study or future specialization. They also apply for the National Resident Matching Program in this year. Following their fourth and final year, they graduate from medical school and are awarded their MD or DO degree. If selected for a residency, they continue for a minimum of three to eight years in their specialty where they are officially licensed to practise after completion. New resident physicians, or interns, in the first year of residency, known as intern year or internship, often take the USMLE Step 3 exam or COMLEX Level 3 exam during that year.
Undergraduate students applying to medical school also have the option to apply to an MD/PhD Medical Scientist Training Program at various academic institutions, which entails 7–8 years of primary medical education that is combined with a doctoral thesis. MD/PhD students are required to take all USMLE exams and postgraduate residency training if they wish to practise medicine. A few schools, such as Ohio University's Heritage College of Osteopathic Medicine or the Michigan State University College of Osteopathic Medicine, offer DO/PhD programs.
Most MBBS physicians visiting or practising in the United States use the designation of MD for various personal and professional reasons, but laws may change to require full disclosure when presenting as a clinical practitioner for litigious reasons. The MD title is distinctly used in the US for physicians who earned their medical degree in the US who practise evidence-based medicine. They separate themselves from DOs who go through a different type of education and training that focuses on the patient as a whole and an array of treatments inclusive of medicine and surgery as well.
=== Vietnam ===
There are many medical schools in Vietnam, such as Hanoi Medical University, Vietnam University of Traditional Medicine, and Hue University of Medicine and Pharmacy. Most of them require six years to receive a Doctor of Medicine degree.
=== West Indies ===
All constituent countries of the University of the West Indies (UWI) confer MB BS, due to the historical affiliation of UWI to the University of London. The degree is a 5-year programme. The three physical campuses are Mona in Jamaica, Saint Augustine in Trinidad and Tobago, and Cave Hill in Barbados, with each campus having a Medical Faculty.
The University of Guyana (UG) also confers "MB BS" to their medical school graduates. There are other medical schools in the West Indies, but these follow the North-American system leading to MD.
=== Zambia ===
All schools in Zambia award the MBChB degree.
=== Zimbabwe ===
The University of Zimbabwe College of Health Sciences (UZ-CHS) awards the MBChB degree. Midlands State University (MSU) also offers the MBChB degree. The National University of Science and Technology (NUST) awards the MBBS.
== Classification ==
Medical degrees differ from other undergraduate degrees in that they are professional qualifications that lead holders to enter a particular career upon receipt. This is not the case with most other undergraduate degrees, so whilst the Bachelor of Medicine and Bachelor of Surgery are undergraduate or graduate degrees (depending on the institution), they are perhaps more accurately conceptualised as a so-called first professional degree. Other professions whose qualifications follow a similar pattern include:
Dentistry
Education
Engineering
Environmental Health
Medical Laboratory Science
Occupational Therapy
Optometry
Pharmacy
Physical Therapy
Clinical Psychology
Law
Veterinary Medicine
Osteopathy
Physician Assistant
Nursing
OT Technician
Bachelor of Medicine, Bachelor of Surgery are usually awarded as professional degrees, not as honours degrees, and as such the graduate is not classified as for honours degrees in other subjects. However, at many institutions (for example the University of Aberdeen, University of Birmingham, University of Sheffield, University of Liverpool, University of Leicester, Hull York Medical School, and University of Manchester in England, Queen's University Belfast in Northern Ireland, Cardiff University in Wales and the University of Dundee in Scotland), it is possible for the degrees to be awarded with Honours (i.e. MB ChB (Hons.)) or with Commendation, if the board of examiners recognises exceptional performance throughout the degree course. Very few of these are awarded.
More often, it is possible to study one subject for an extra year for an intercalated honours degree. This is usually a Bachelor of Science (BSc), Bachelor of Medical Science (BMedSci), Bachelor of Medical Biology (BMedBiol) or similar: at Oxford and Cambridge in England and Dublin in Ireland Bachelor of Arts degrees are awarded. At a few universities most medical students obtain an ordinary degree in science as well: when the University of Edinburgh had a six-year course, the third year was followed by the award of an ordinary BSc(MedSci). In Australia, The University of Melbourne in Australia offers an Arts Degree (BA) to a medical student on the completion of two extra years of undergraduate study, and Monash University offers a law degree (LLB); if the optional law degree is undertaken, on completion of their degree the student may choose to do a one-year internship at a hospital and become a doctor, or spend one year doing articles to practise thereafter as a lawyer. At the University of Nottingham and the University of Southampton, both in England, all medical students on the five-year course obtain a Bachelor of Medical Sciences (BMedSci) degree without an extra intercalated year. At the University of Cambridge, Imperial College London and University College London, certain medical students are able to extend their intercalated year to an extra three years, thus temporarily exiting the MBBS course to complete a PhD. Upon completion of the PhD, the student is required to sit the remaining 2 years of the medicine course to receive his/her MBBS degree. The University of the West Indies, Mona in Kingston, Jamaica automatically awards a Bachelor of Medical Sciences (BMedSci) degree to all students who have successfully completed three years of their MBBS programme.
== Progression ==
Medical graduates are eligible to sit postgraduate examinations, including examinations for membership and fellowship of professional institutions. Among the latter are the Membership of the Royal College of Surgeons, postgraduate master's degrees (such as a Master of Surgery or Master of Medicine), and a postgraduate doctorate in medicine (such as Doctor of Medicine or Doctor of Science, if earned in Ireland, the UK or Commonwealth nations, and board certification examinations).
== See also ==
Bachelor of Ayurveda, Medicine and Surgery
Bachelor of Unani Medicine and Surgery
Bachelor's degree
Doctor of Medicine
Doctor of Osteopathic Medicine
Homologation
List of medical schools
Master of Medicine
Master of Surgery
Medical education
Medical school
Pre-medical
== References == | Wikipedia/Bachelor_of_Medicine,_Bachelor_of_Surgery |
Myelography is a type of radiographic examination that uses a contrast medium (e.g. iodised oil) to detect pathology of the spinal cord, including the location of a spinal cord injury, cysts, and tumors. Historically the procedure involved the injection of a radiocontrast agent into the cervical or lumbar spine, followed by several X-ray projections. Today, myelography has largely been replaced by the use of MRI scans, although the technique is still sometimes used under certain circumstances – though now usually in conjunction with CT rather than X-ray projections.
== Types ==
=== Cervical myelography ===
This procedure is used to look for the level of where spinal cord disease occurs or compression of the spinal cord at the neck region for those who are unable or unwilling to undergone MRI scan of the spine.
=== Lumbar myelography ===
This procedure is to look for the level of spinal cord disease such as lumbar nerve root compression, cauda equina syndrome, conus medullaris lesions, and spinal stenosis. This is done for those who are unwilling or unable to do MRI scan of the spine. Lumbar puncture is done before injected contrast into the thecal sac. However, it is dangerous to do lumbar puncture in those who have raised intracranial pressure (ICP). For those who had recently done lumbar puncture in one week time, there may be some cerebrospinal fluid (CSF) accumulates in the subdural space. Thus needle maybe mistakenly inserted into subdural space rather than the targeted subarachnoid space.
AP, lateral, and oblique radiographic views of the lumbar spine are taken. The oblique view is used to examine the exiting nerve roots from cauda equina.
=== Thoracic myelography ===
To image the thoracic spine, lumbar puncture is done and contrast medium is injected into the puncture site. The subject lie down on one side, then head of the table is lowered, with subject's head supported by bolster or pad to prevent the contrast from flowing up into the neck.
=== CT myelography ===
Contrast media is injected into the thecal sac. The subject is then rotated longitudinally a few times to ensure even coating of the contrast around spinal cord and reduce the possibility of layering of the contrast media just before CT scan.
=== Myelography in children ===
General anesthesia is required for all children before 6 years old, and most of the children before 12 years old. For those children with spinal cord diseases, lumbar puncture may damage the spinal cord due to possibility of tethered spinal cord syndrome where the spinal cord is located below than the usual spinal termination level. Therefore, lumbar puncture should be done at the lowest position as possible for such cases. However, spinal cord injury is rare. There is also a possibility of herniation of cerebellar tonsils when C1/C2 puncture is done laterally.
== Procedure ==
Water-soluble non-ionic iodinated contrast agent is used nowadays and cause very little complication, unlike oil-based dye that was used previously which can cause arachnoiditis. However, history of allergy to iodine is contraindicated for the use of iodinated contrast.
A CT scan is typically performed after radiographic contrast media (dye) has been placed with fluoroscopic guidance into a sac-like lining (the first- and hardest and outermost- layer of the spinal meninges, the spinal dura mater) surrounding the spinal cord and nerves. The material is typically water-soluble, which has largely replaced nonsoluble oil-based fluids, while CT has largely replaced the conventional X-ray projections used for image acquisition in the past.
The process usually involves lying face down on a table, with the lower extremities secured tightly with straps to the table. After the skin area has been numbed, the dye is injected into the thecal sac, then the table is slowly rotated in a circular motion, first down at the head end for approximately 4 to 6 minutes, then rotated up at the head end for the same duration. Several more minutes lying flat and the process is complete. This movement ensures the contrast has sufficiently worked its way through the spinal cord, followed by X-rays or a CT scan.
Post-procedure care centers around ensuring that infection (especially skin or subcutaneous infections, myelitis or meningitis or encephalitis, or sepsis) does not set in and that the "plug" at the site of the spinal tap does not become dislodged. Patients are usually instructed to avoid strenuous activity and heavy lifting, for example. Some patients are given instructions to keep their heads elevated at least 30 degrees for a specified number of hours. Complications from the surgery can cause a loss of cerebrospinal fluid (CSF), which could cause severe headaches. This can be corrected by returning to the medical facility and having them perform a blood patch. In this procedure, a small amount of blood is taken from the arm and injected into the exact spinal tap location to stop the leaking of CSF.
== Decline in use due to MRI ==
Nowadays, MRI has all but replaced myelography. MRI is preferable because injection of contrast medium into the spinal canal is infrequently needed for better images. However, a CT myelogram may be useful for patients who cannot undergo MRI (e.g., those with pacemakers or cochlear implants). CT is preferred when MRI images are limited by metallic artifact from titanium disc replacement implants, screws, and other metals reactive with MRI device components.
== Contrast agent ==
Prior to the late 1970s, iofendylate (trade names: Pantopaque, Myodil) was the radiocontrast agent typically employed in the procedure. It was an iodinated oil-based substance that the physician performing the spinal tap usually attempted to remove at the end of the procedure. This step was both difficult and painful and complete removal could not always be achieved. The process of removing the contrast agent necessitated removing some of the patient's CSF along with it and the resulting deficiency of CSF gave rise to severe headache if the patient was raised from the prone position, requiring bed rest in the laying position. Moreover, iofendylate's persistence in the body might sometimes lead to arachnoiditis, a potentially painful and debilitating lifelong disorder of the spine. This led to extensive litigation around the world since the substance was administered to millions of myelography patients over the course of more than three decades. After water-soluble agents (such as metrizamide) became available it was no longer necessary to remove the contrast agent as it would eventually be absorbed into the body although the water-soluble agent sometimes gave rise to severe headaches if it got into the head, requiring bed rest in the upright position.
== Complications ==
Headache occurs in about 25% of the cases after the procedure and the incidence is more frequent in females. 5% of those who undergone the procedure may experience nausea and vomiting. There is also a risk of contrast medium being injected into the subdural space when part of the bevel of the needle is in the subarachnoid space and another part is in the subdural space. The contrast medium would flow freely in the subdural space, mimicking the flow as if it was in the subarachnoid space. If there is doubt that the needle is in the subdural space, AP and lateral views of the radiograph should be taken and the subject is to be rebook for another date for the same procedure.
== References ==
Bontranger, Kenneth L. & Lampignano, John P. (2005). Radiographic Positioning and Related Anatomy, St. Louis: Elsevier Mosby. ISBN 0-323-02507-2.
== External links ==
U of Maryland | Wikipedia/Myelography |
Moyamoya disease is a disease in which certain arteries in the brain are constricted. Blood flow is blocked by constriction and blood clots (thrombosis). A collateral circulation develops around the blocked vessels to compensate for the blockage, but the collateral vessels are small, weak, and prone to bleeding, aneurysm, and thrombosis. On a conventional angiography, these collateral vessels have the appearance of a "puff of smoke", described as moyamoya (もやもや) in Japanese.
When moyamoya is diagnosed by itself, with no underlying correlational conditions, it is diagnosed as moyamoya disease. This is also the case when the arterial constriction and collateral circulation are bilateral. Moyamoya syndrome is unilateral arterial constriction, or occurs when one of the several specified conditions is also present. This may also be considered as moyamoya being secondary to the primary condition. Mainly, occlusion of the distal internal carotid artery occurs. On angiography, a "puff of smoke" appearance is seen, and the treatment of choice is surgical bypass.
== Presentation ==
Patients usually present with TIA, ischemic/hemorrhagic stroke, or seizure. The age distribution is bimodal being either young adolescence or mid-forties.
== Cause ==
About 10% of cases of moyamoya disease are familial, and some cases result from specific genetic mutations. Susceptibility to moyamoya disease-2 (MYMY2; 607151) is caused by variation in the RNF213 gene (613768) on the long arm of chromosome 17 (17q25). Moyamoya disease-5 (MYMY5; 614042) is caused by mutation in the ACTA2 gene (102620) on the long arm of chromosome 10 (10q23.3); and moyamoya disease-6 with achalasia (MYMY6; 615750) is caused by mutation in the GUCY1A3 gene (139396) on the long arm of chromosome 4 (4q32). Loci for the disorder have been mapped to the short arm of chromosome 3 (MYMY1) and the long arm of chromosome 8 (8q23) (MYMY3; 608796). See also MYMY4 (300845), an X-linked recessive syndromic disorder characterized by moyamoya disease, short stature, hypergonadotropic hypogonadism, and facial dysmorphism, and linked to q25.3, on chromosome 17.
In the United States moyamoya has an incidence rate of 0.086 per 100,000. In Japan the overall incidence is higher (0.35 per 100,000). In North America, women in the third or fourth decade of life are most often affected, but the condition may also occur during infancy or childhood. These women frequently experience transient ischaemic attacks (TIA), cerebral hemorrhage, or may not experience any symptoms at all. They have a higher risk of recurrent stroke and may be experiencing a distinct underlying pathophysiology compared to patients from Japan.
Moyamoya disease can be either congenital or acquired. Patients with Down syndrome, sickle cell anemia, neurofibromatosis type 1, congenital heart disease, fibromuscular dysplasia, activated protein C resistance, or head trauma can develop moyamoya malformations. It is more common in women than in men, although about a third of those affected are male.
== Pathophysiology ==
The disease moyamoya, which is a Japanese mimetic word, gets its characteristic name due to the appearance of smoke on relevant angiographs resultant from the tangle of tiny vessels in response to stenosis. This makes the blood leak out of the arteries, causing pressure to the brain and subsequent headaches. Over the last six decades since the disease was first described, pathogenesis of moyamoya disease remained elusive, although the gene ring finger protein 213 (RNF213) has been implicated. In September 2021, a south Indian researcher has proposed a pathbreaking theory on moyamoya pathogenesis. Coined the "Mechano-biological theory", the disease has a multifactorial pathogenesis. The authors provide a tangible explanation of the occurrence of moyamoya phenomenon in the idiopathic and syndromic variants of the disease. In short, the authors report that moyamoya disease likely occurs due to a number of factors (e.g., differences in vascular anatomy) that ultimately contribute to broad cerebral blood vessel occlusion and consequent shifts in vessel connections to try to provide blood for the compromised brain.
Once it begins, the vascular occlusion tends to continue despite any known medical management. In some people this leads to transient ischemic attacks or repeated strokes with severe functional impairment or even death. In others, the blockage may not cause any symptoms.
The disease causes constrictions primarily in the internal carotid artery, and often extends to the middle and anterior cerebral arteries, branches of the internal carotid artery inside the skull. When the internal carotid artery becomes completely blocked, the fine collateral circulation that it supplies is obliterated. Patients often survive on the collateral circulation from the back (posterior) of the circle of Willis, arising from the basilar artery.
The arterial constrictions in moyamoya disease are unlike the constrictions in atherosclerosis. In atherosclerosis, the walls of arteries are damaged, leading to the deposition of fat and immune cells, and ultimately the accumulation of immune cells laden with fat. In moyamoya, the inner layer of the carotid artery proliferates within the arterial lumen. The artery also fills with blood clots, which may cause strokes.
Moyamoya disease tends to affect adults in the third to fourth decade of life. In children it tends to cause strokes or seizures. In adults it tends to cause strokes or bleeding. The clinical features are strokes, recurrent transient ischemic attacks (TIAs), sensorimotor paralysis (numbness and paralysis of the extremities), convulsions and/or migraine-like headaches. Moreover, following a stroke, secondary bleeding may occur. Such bleeding, called hemorrhagic strokes, may also stem from rupture of the weak neovascular vessel walls.
== Diagnosis ==
Cerebral angiography is the gold standard of diagnosing moyamoya disease and its progression. According to Suzuki's system, it can be classified into six stages:
Stage 1 Narrowing of carotid fork
Stage 2 Initiation of the moyamoya and dilatation of intracranial main arteries
Stage 3 Intensification of the moyamoya and defects of the anterior cerebral artery and middle cerebral artery
Stage 4 Minimization of the moyamoya and defects of the posterior cerebral artery
Stage 5 Reduction of the moyamoya and development of external carotid artery collaterals
Stage 6 Disappearance of the moyamoya and circulation only via external carotid artery and vertebral artery
Magnetic resonance angiography (MRA) is also useful in diagnosing the disease with good correlation with Suzuki's grading system.
Proliferation of smooth muscle cells in the walls of the moyamoya-affected arteries has been found to be representative of the disease. A study of six autopsies of six patients who died from moyamoya disease lead to the finding that there is evidence that supports the theory that there is a thickening, or proliferation, of the innermost layer of the vessels affected by moyamoya. These vessels are the ACA (anterior cerebral artery), MCA (middle cerebral artery), and ICA (internal carotid artery). The occlusion of the ICA results in concomitant diminution of the "puff-of-smoke" collaterals, as they are supplied by the ICA.
Often nuclear medicine studies such as SPECT (single photon emission computerized tomography) are used to demonstrate the decreased blood and oxygen supply to areas of the brain involved with moyamoya disease. Conventional cerebral angiography provides the conclusive diagnosis of moyamoya disease in most cases and should be performed before any surgical considerations.
Darren B. Orbach explains how the disease progresses as well as the role angiography plays in detecting the progression of moyamoya in a short video. In 2019, author and artist Sarah Lippett published a graphic novel about her decade-long struggle to get a diagnosis and treatment for moyamoya disease, called A Puff of Smoke (published with Jonathan Cape). The book was praised in the newspaper The Guardian as a "wonderfully drawn memoir of a serious childhood illness." It was one of the paper's "graphic novels of the year" in 2019 and The Observer newspaper's graphic novel of the month in November 2019.
=== Associated biomarkers ===
Smith (2015) conducted a study that looked into specific biological markers that correlate to moyamoya disease. Some of the categories of these biomarkers include phenotypes - conditions commonly related to moyamoya, radiographical markers for the diagnosis of moyamoya, and proteins as well as cellular changes that occur in cases of moyamoya.
Similar to moyamoya disease, there are conditions that are closely associated with moyamoya disease. Some of the more common medical conditions that are closely associated with moyamoya disease include trisomy 21 (Down Syndrome), sickle cell disease, and neurofibromatosis type 1. There is also evidence that identifies hyperthyroidism and congenital dwarfing syndromes as two of the more loosely associated syndromes that correlate with the possibility of being diagnosed with moyamoya disease later in life.
There is also research that has shown that certain radiographic biomarkers that lead to the diagnosis of moyamoya disease have been identified. The specific radiographic markers are now considered an acceptable key component to moyamoya disease and have been added to the International Classification of Diseases (ICD). These biomarkers of moyamoya are "stenosis of the distal ICA's up to and including the bifurcation, along with segments of the proximal ACA and MCA...dilated basal collateral vessels must be present" Some other common findings that have not been added to the classification index of those with moyamoya disease which are found using radiography involve very distinct changes in the vessels of the brain. These changes include newly formed vessels made to compensate for another change noted, ischemia and cerebrovascular reserve, both found on MRI. Functional changes include evidence of ischemia in vessels of the brain (ICA, ACA, MCA, specifically). It is important to also note that the radiographic biomarkers, in order to be classified as moyamoya disease, all findings must be bilateral. If this is not the case and the findings are unilateral, it is diagnosed as moyamoya syndrome. This recently changed in 2021 as the Research Committee of Moyamoya Disease (RCMD) has "removed limitations of the previous definition that required bilateral involvement of the intracranial carotid artery. Now, proximal middle cerebral artery or anterior cerebral artery involvement suffices, and unilateral disease is acceptable to make the diagnosis, given the increasing evidence of progression to bilateral involvement in unilateral MMD."
There are also several protein biomarkers that have been linked to the moyamoya disease diagnosis. Although the sample size of the studies performed are small due to the rarity of the disease, the findings are indicative of a correlation between the disease and several specific protein biomarkers. Other studies have confirmed the correlation of moyamoya and adhesion molecule 1 (ICAM-1) being increased as compared to normal vascular function counterparts. Furthermore, it has been concluded that the localization of inflammatory cells suggests that the inflammation stimulus itself may be responsible for the proliferation and occlusion in the ICA, ACA, and MCA found in those with moyamoya disease.
== Treatment ==
Antiplatelet drugs (including aspirin) are usually given to prevent clots, but surgery is usually recommended. Because moyamoya tends to affect only the internal carotid artery and nearby sections of the adjacent anterior and middle cerebral arteries, surgeons can direct other arteries, such as the external carotid artery or the superficial temporal artery to replace its circulation. The arteries are either sewn directly into the brain circulation, or placed on the surface of the brain to reestablish new circulation after a few weeks.
Many operations have been developed for the condition, but currently the most favored are the in-direct procedures EDAS, EMS, and multiple burr holes and the direct procedure STA-MCA. Combined revascularisation procedure, which includes both the direct superficial temporal artery (STA) to middle cerebral artery (MCA) bypass (also known as ECIC bypass) performed with a combination of in-direct procedures is considered the treatment of choice. Although its efficacy, particularly for hemorrhagic disease, remains uncertain, the procedure is thought to reduce the hemodynamic burden on the engorged collateral blood vessels. Multiple burr holes have been used in frontal and parietal lobes with good neovascularisation achieved.
In-direct Procedures
The EDAS (encephaloduroarteriosynangiosis) procedure is a synangiosis procedure that requires dissection of a scalp artery over a course of several centimeters and then making a small temporary opening in the skull directly beneath the artery. The artery is then sutured to a branch of the middle cerebral artery on the surface of the brain and the bone is replaced.
In the EMS (encephalomyosynangiosis) procedure, the temporalis muscle, which is located in the temple region of the forehead, is dissected and through an opening in the skull placed onto the surface of the brain.
In the multiple burr holes procedure, multiple small holes (burr holes) are placed in the skull to allow for growth of new vessels into the brain from the scalp.
Direct Procedures
In the STA-MCA procedure, the scalp artery (superficial temporal artery or STA) is directly sutured to an artery on the surface of the brain (middle cerebral artery or MCA). This procedure is also commonly referred to as an EC-IC (External Carotid-Internal Carotid) bypass.
All of these operations have in common the concept of a blood and oxygen "starved" brain reaching out to grasp and develop new and more efficient means of bringing blood to the brain and bypassing the areas of blockage. The modified direct anastomosis and encephalo-myo-arterio-synangiosis play a role in this improvement by increasing cerebral blood flow (CBF) after the operation. A significant correlation is found between the postoperative effect and the stages of preoperative angiograms. It is crucial for surgery that the anesthesiologist have experience in managing children being treated for moyamoya, as the type of anesthesia they require is very different from the standard anesthetic children get for almost any other type of neurosurgical procedure.
== Prognosis ==
The natural history of this disorder is not well known. The long term outlook for patients with treated moyamoya seems to be good when direct bypass is used. Although symptoms may seem to improve almost immediately after the in-direct EDAS, EMS, and multiple burr holes surgeries, it will take probably 6 to 12 months before new vessels can develop to give a sufficient blood supply. With the direct STA-MCA surgery, increased blood supply is immediate.
Once a major stroke or bleeding takes place, even with treatment, the patient may be left with permanent loss of function so it is very important to treat this condition promptly.
== Research ==
In June 2008, a case report established that both moyamoya disease and arteriovenous fistulas (AVFs) of the lining of the brain, the dura, are associated with dural angiogenesis. These factors may represent a mechanism for ischemia contributing to the formation of dural AVFs. At least one case of simultaneous unilateral moyamoya syndrome and ipsilateral dural arteriovenous fistula has been reported at the Barrow Neurological Institute. In this case a 44-year-old man presented with headache, tinnitus, and an intraventricular hemorrhage, as seen on computed tomographic scans. Cerebral angiography showed a right moyamoya pattern and an ipsilateral dural AVF fed by branches of the external carotid artery and draining into the transverse sinus. This extremely rare coincidental presentation may have deeper pathogenic implications.
The research into the pathogenesis of moyamoya disease has found a breakthrough with the proposal of a "Mechano-biological theory" of pathogenesis of this disease. A research group in southern India have proposed this unifying theory based on computational fluid dynamics studies and longitudinal data. This proposal unifies the pathogenesis of moyamoya disease and moyamoya syndromes described in literature under a single mechanism.
== References ==
== External links ==
moyamoya.eu—International website for information about diagnostics and treatment of moyamoya patients
Orphanet's disease page on moyamoya disease
Moyamoya Disease Portal—Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum (SCTIMST) | Wikipedia/Moyamoya_disease |
Endoscopic endonasal surgery is a minimally invasive technique used mainly in neurosurgery and otolaryngology. A neurosurgeon or an otolaryngologist, using an endoscope that is entered through the nose, fixes or removes brain defects or tumors in the anterior skull base. Normally an otolaryngologist performs the initial stage of surgery through the nasal cavity and sphenoid bone; a neurosurgeon performs the rest of the surgery involving drilling into any cavities containing a neural organ such as the pituitary gland. The use of endoscope was first introduced in Transsphenoidal Pituitary Surgery by R Jankowsky, J Auque, C Simon et al. in 1992 G (Laryngoscope. 1992 Feb;102(2):198-202).
== Introduction ==
=== History of endoscopic endonasal surgery ===
Antonin Jean Desomeaux, a urologist from Paris, was the first person to use the term, endoscope.
However, the precursor to the modern endoscope was invented in the 1800s when a physician in Frankfurt, Germany by the name of Philipp Bozzini, developed a tool to see the inner workings of the body. Bozzini called his invention a Light Conductor, or Lichtleiter in German, and later wrote about his experiments on live patients with this device that consisted of an eyepiece and a container for a candle. Following Bozzini's success, The University of Vienna starting using the device to test its practicality in other forms of medicine. After Bozzini's device received negative results from live human trials, it had to be discontinued. However, Maximilian Nitze and Joseph Leiter used the invention of the light bulb by Thomas Edison to make a more refined device similar to modern day endoscopes. This iteration was used for urological procedures, and eventually otolaryngologists began to use Nitze and Leiter's device for eustachian tube manipulation and removal of foreign bodies. The endoscope made its way to the US when Walter Messerklinger began teaching David Kennedy at Johns Hopkins Hospital.
The transsphenoidal and intracranial approaches to pituitary tumors began in the 1800s but with little success. Gerard Guiot popularized the transphenoidal approach which later became part of the neurosurgical curriculum, however he himself discontinued the use of this technique because of inadequate sight. In the late 1970s, the endoscopic endonasal approach was used by neurosurgeons to augment microsurgery which allowed them to view objects out of their line of sight. Another surgeon, Axel Perneczky, is considered to be a pioneer of the use of an endoscope in neurosurgery. Perneczky said that endoscopy, "improved appreciation of micro-anatomy not apparent with the microscope."
The surgery was pioneered in Algeria by Bouyoucef Kheireddine and Faiza Lalam.
=== Endoscopic instrumentation ===
The endoscope consists of a glass fiber bundle for cold light illumination, a mechanical housing, and an optics component with four different views: 0 degree for straight forward, 30 degrees for forward plane, 90 degrees for lateral view, and 120 degrees for retrospective view. For endoscopic endonasal surgery, rigid rod-lens endoscopes are used for better quality of vision, since these endoscopes are smaller than the normal endoscope used colonoscopies. The endoscope has an eyepiece for the surgeon, but it is rarely used because it requires the surgeon to be in a fixed position. Instead, a video camera broadcasts the image to a monitor that shows the surgical field.
== Areas of interest for surgical planning ==
Several specialties need to be involved to determine the complete surgical plan. These include: an Endocrinologist, a Neuroradiologist, an Ophthalmologist, a Neurosurgeon, and an Otolaryngologist.
=== Endocrinology ===
An endocrinologist is only involved in preparation for an endoscopic endonasal surgery, if the tumor is located on the pituitary gland. The tumor is first treated pharmacologically in two ways: controlling the levels of hormones that the pituitary gland secretes and reducing the size of the tumor. If this approach does not work, the patient is referred to surgery. The main types of pituitary adenomas are:
PRL-secreting or prolactinomas: These are the most common pituitary tumors. They are associated with infertility, gonad, and sexual dysfunction because they increase the secretion of prolactin or PRL. One drug that endocrinologist use is bromocriptine (BRC), which normalizes PRL levels and has been shown to lead to tumor shrinkage. Other drugs to treat prolactinomas include quinagolide (CV) or cabergoline (CAB) acting as dopamine (D2) antagonists. Endoscopic endonasal surgery is normally performed as a last resort when the tumor is resistant to the drugs, shows no tumor shrinkage, or the PRL levels cannot be normalized.
GH-secreting: A very rare condition that is a result of the increase in the secretion of growth hormone. There are currently less than 400,000 cases worldwide and approximately 30,000 new cases every year. Despite the rarity of this condition, these tumors constitute 16% of the pituitary tumors that are removed. The tumor normally results in acral enlargement, arthropathy, hyperhidrosis, changes in facial features, soft tissue swelling, headaches, visual changes, or hypopituitarism. Since pharmacological therapy has had little effect on these tumors, a trans-sphenoidal surgery to remove part of the pituitary gland is the first treatment option.
TSH-secreting: Another rare condition only resulting in 1% of pituitary surgeries is a result of the increase in the secretion of the thyroid-stimulating hormone. This tumor leads to hyperthyroidism, resulting in headaches and visual disturbances. Although surgery is the first step of treatment, it does not usually cure the patient. After surgery, patients are treated by somatostatin analogues, a type of hormone replacement therapy, because TSH related tumors increase the expression of somatostatin receptors.
ACTH-secreting: This tumor is a result of the increase in the secretion of adrenocorticotropic hormone (ACTH) and leads to Cushing's syndrome. Pharmacology has little effect and therefore surgery is the best option. Removal of the tumor results in an 80%-90% cure rate.
=== Neuroradiology ===
A neuroradiologist takes images of the defect so that the surgeon is prepared on what to expect before surgery. This includes identifying the lesion or tumor, controlling the effects of the medical therapy, defining the spatial situation of the lesions, and verifying the removal of the lesions. The lesions associated with endoscopic endonasal surgery include:
Pituitary microadenomas
Pituitary macroadenomas
Rathke's cleft cysts
Pituitary inflammatory disease
Pituitary metastasis
Empty Sella
Craniopharyngiomas
Meningiomas
Chiasmatic and Hypothalamic gliomas
Germinomas
Tuber Cinereum Hamartomas
Arachnoid cysts
Neurinomas of the trigeminal nerve
=== Ophthalmology ===
Some suprasellar tumors invade the chiasmatic cistern, causing impaired vision. In these cases, an ophthalmologist maintains optic health by administering pre-surgical treatment, advising proper surgical techniques so that the optic nerve is not in danger, and managing post-surgery eye care. Common problems include:
Visual field defects
Reduced visual activity
Visually evoked potential (VEP) abnormalities
Color blindness
Eye motility impairment
== Surgical approaches to the anterior skull base ==
=== Transnasal approach ===
The transnasal approach is used when the surgeon needs to access the roof of the nasal cavity, the clivus, or the odontoid. This approach is used to remove chordomas, chondrosarcoma, inflammatory lesions of the clivus, or metastasis in the cervical spine region. The anterior septum or posterior septum is removed so that the surgeon can use both sides of the nose. One side can be used for a microscope and the other side for a surgical instrument, or both sides can be used for surgical instruments.
=== Transsphenoidal approach ===
This approach is the most common and useful technique of endoscopic endonasal surgery and was first described in 1910 concurrently by Harvey Cushing and Oskar Hirsch. This procedure allows the surgeon to access the sellar space, or sella turcica. The sella is a cradle where the pituitary gland sits. Under normal circumstances, a surgeon would use this approach on a patient with a pituitary adenoma. The surgeon starts with the transnasal approach prior to using the transsphenoidal approach. This allows access to the sphenoid ostium and sphenoid sinus. The sphenoid ostium is located on the anterosuperior surface of the sphenoid sinus. The anterior wall of the sphenoid sinus and the sphenoid rostrum is then removed to allow the surgeon a panoramic view of the surgical area. This procedure also requires the removal of the posterior septum to allow the use of both nostrils for tools during surgery. There are several triangles of blood vessels traversing this region, which are just very delicate areas of blood vessels that can be deadly if injured. A surgeon uses stereotactic imaging and a micro Doppler to visualize the surgical field.
The invention of the angled endoscope is used to go beyond the sella to the suprasellar (above the sellar) region. This is done with the addition of four approaches. First the transtuberculum and transplanum approaches are used to reach the suprasellar cistern. The lateral approach is then used to reach the medial cavernous sinus and petrous apex. Lastly, the inferior approach is used to reach the superior clivus. Endoscopic endonasal transclival approaches are often described according to which segment of the clivus is involved in the approach, with the clivus typically divided into three regions. Depending on which segment of the clivus is involved in the surgical approach, different neurovascular structures are placed at risk. The upper third lies inferior to the dorsum sellae and posterior clinoid processes and superior to the petrous apex, the middle third lies at the level of the petrous segments of the internal carotid artery (ICA), and the inferior third extends from the jugular tubercle to the foramen magnum. It is important that the Perneczky triangle is treated carefully. This triangle has optic nerves, cerebral arteries, the third cranial nerve, and the pituitary stalk. Damage to any of these could provide a devastating post-surgical outcome.
=== Transpterygoidal approach ===
The transpterygoidal approach enters through the posterior edge of the maxillary sinus ostium and posterior wall of the maxillary sinus. This involves penetrating three separate sinus cavities: the ethmoid sinus, the sphenoidal sinus, and the maxillary sinus. Surgeons use this method to reach the cavernous sinus, lateral sphenoid sinus, infra temporal fossa, pterygoid fossa, and the petrous apex. Surgery includes a uninectomy (removal of the osteomeatal complex), a medial maxillectomy (removal of maxilla), an ethmoidectomy (removal of ethmoid cells and/or ethmoid bone), a sphenoidectomy (removal of part of sphenoid), and removal of the maxillary sinus and the palatine bone. The posterior septum is also removed at the beginning to allow use of both nostrils.
=== Transethmoidal approach ===
This approach makes a surgical corridor from the frontal sinus to the sphenoid sinus. This is done by the complete removal of the ethmoid bone, which allows a surgeon to expose the roof of the ethmoid, and the medial orbital wall. This procedure is often successful in the removal of small encephaloceles of the ethmoid osteomas of the ethmoid sinus wall or small olfactory groove meningiomas. However, with larger tumors or lesions, one of the other approaches listed above is required.
== Different approaches to specific regions ==
=== Approach to sellar region ===
For removal of a small tumor, it is accessed through one nostril. However, for larger tumors, access through both nostrils is required and the posterior nasal septum must be removed. Then the surgeon slides the endoscope into the nasal choana until the sphenoid ostium is found. Then the mucosa around the ostium is cauterized for microadenomas and removed completely for macroadenomas. Then the endoscope enters the ostium and meets the sphenoid rostrum where the mucosa is retracted from this structure and is removed from the sphenoid sinus to open the surgical pathway. At this point, imaging and Doppler devices are used to define the important structures. Then the floor of the sella turcica is opened with a high speed drill being careful to not pierce the dura mater. Once the dura is visible, it is cut with microscissors for precision. If the tumor is small, the tumor can be removed by an en bloc procedure, which consists of cutting the tumor into many sections for removal. If the tumor is larger, the center of the tumor is removed first, then the back, then the sides, then top of the tumor to make sure that the arachnoid membrane does not expand into the surgical view. This will happen if the top part of the tumor is taken out too early. After tumor removal, CSF leaks are tested for with fluorescent dye, and if there are no leaks, the patient is closed.
=== Approach to suprasellar region ===
This technique is the same as to the sellar region. However the tuberculum sellae is drilled into instead of the sella. Then an opening is made that extends halfway down the sella to expose the dura, and the intercavernous sinuses is exposed. When the optic chiasm, optic nerve, and pituitary gland are visible, the pituitary gland and optic chasm are pushed apart to see the pituitary stalk. An ethmoidectomy is performed, the dura is then cut, and the tumor is removed. These types of tumors are separated into two types:
Prechiasmal Lesions: This tumor is closest to the dura. The tumor is decompressed by the surgeon. After decompression, the tumor is removed taking care to not disrupt any optic nerve or major arteries.
Postchiasmal Lesions: This time the pituitary stalk is in the front because the tumor is pushing it towards the area the dura was opened. Removal then starts on both sides of the stalk to preserve the connection between the pituitary and the hypothalamus and above pituitary gland to protect the stalk. The tumor is carefully removed and the patient is closed up.
=== Skull base reconstruction ===
When there is a tumor, injury, or some type of defect at the skull base whether the surgeon used an endoscopic or open surgical method, the problem still arises of providing separation of the cranial cavity and cavity between the sinuses and nose to prevent cerebrospinal fluid leakage through the opening referred to as a defect.
For this procedure, there are two ways to start: with a free graft repair or with a vascularized flap repair. The free grafts use secondary material like cadaver flaps or titanium mesh to repair the skull base defects, which is very successful (95% without CSF leaks) with small CSF fistulas or small defects. The local or regional vascularized flaps are pieces of tissue relatively close to the surgery site that have been mostly freed up but are still attached to the original tissue. These flaps are then stretched or maneuvered onto the desired location. When technology advanced and larger defects could be fixed endoscopically, more and more failures and leaks started to occur with the free graft technique. The larger defects are associated with a wider dural removal and an exposure to high flow CSF, which could be the reason for failure among the free graft.
== Pituitary gland surgery ==
This surgery is turned from a very serious surgery into a minimally invasive one through the nose with the use of the endoscope. For instance craniopharyngiomas (CRAs) are starting to be removed via this method. Dr. Paolo Cappabianca described the perfect CRA for this surgery to be a median lesion with a solid parasellar component (beside the sellar) or encasement of the main neuromuscular structures that are localized in the subchiasmatic (below the optic chiasm) and retrochiasmatic (behind the optic chiasm) regions. He also says that when these conditions are met, endoscopic endonasal surgery is a valid surgical option. For a case study on large adenomas, the doctors showed that out of 50 patients, 19 had complete tumor removal, 9 had near complete removal, and 22 had partial removal. The partial removal came from the tumors extending into more dangerous areas. They concluded that endoscopic endonasal surgery was a valid option for surgery if the patients used pharmacological therapy after surgery. Another study showed that with endoscopic endonasal surgery 90% of microadenomas could be removed, and that 2/3 of normal macroadenomas could be removed if they did not go into the cavernous sinus, which means fragile blood vessel triangles would have to be dealt with so only 1/3 of those patients recovered. Endoscopic endonasal approach has been shown even among young patients to be superior to traditional microscopic transsphenoidal surgery.
=== 3-D approach vs 2-D approach ===
The newer 3-D technique is gaining ground as the ideal way to do surgery because it gives the surgeon a better understanding of the spatial configuration of what they are seeing on a computer screen. Dr. Nelson Oyesiku at Emory University helped develop the 3-D technique. In an article he helped write, he and the other authors compared the effects of the 2-D technique vs the 3-D technique on patient outcome. It showed that the 3-D endoscopy gave the surgeon more depth of field and stereoscopic vision and that the new technique did not show any significant changes in patient outcomes during or after surgery.
== Endoscopic techniques vs open techniques ==
In a case study from 2013, they compared the open vs endoscopic techniques for 162 other studies that contained 5,701 patients. They only looked at four tumor types: the olfactory groove meningiomas (OGM), tuberculum sellae meningiomas (TSM), craniopharyngiomas (CRA), and clival chordomas (CHO). They looked at gross total resection and cerebrospinal fluid (CSF) leaks, neurological death, post-operative visual function, post operative diabetes insipidus, and post-operative obesity. The study showed that there was a greater chance of CSF leaks with endoscopic endonasal surgery. The visual function improved more with endoscopic surgery for TSM, CRA, and CHO patients. Diabetes insipidus occurred more in open procedure patients. The endoscopic patients showed a higher recurrence rate. In another case study on CRAs, they showed similar results with the CSF leaks being more of a problem in endoscopic patients. Open procedure patients showed a higher rate of post operative seizures as well. Both of these studies still suggest that despite the CSF leaks, that the endoscopic technique is still an appropriate and suitable surgical option. Otologic surgery, which is traditionally performed via an open approach using a microscope, may also be performed endoscopically, and is called Endoscopic Ear Surgery or EES.
== References == | Wikipedia/Endoscopic_endonasal_surgery |
Reproductive surgery is surgery in the field of reproductive medicine. It can be used for contraception, e.g. in vasectomy, wherein the vasa deferentia of a male are severed, but is also used plentifully in assisted reproductive technology. Reproductive surgery is generally divided into three categories: surgery for infertility, in vitro fertilization, and fertility preservation.
A reproductive surgeon is an obstetrician-gynecologist or urologist who specializes in reproductive surgery.
Reproductive surgeries will be referred to based on biological sex, and terms such male and female will be used to denote to men and women respectively.
== Uses ==
Reproductive surgery aims to address concerns spanning from male and female fertility to gender-affirming care. Uses for reproductive surgery may encompass different abnormalities, dysfunctions, and areas of focus that are unable to be treated solely through medication or nonsurgical treatment. Screening measures may be completed to determine the necessity of surgery. For example, intrauterine pathology may be assessed by utilizing techniques such as hysteroscopy to identify complications for reproductive surgical interventions.
Assisted reproductive technology (ART) supports enhancement of fertility success through processes such as in vitro fertilization (IVF). Screening and reproductive surgery also have a role in identifying and addressing abnormalities, such as notable cysts, prior to initiating IVF. Surgical sperm retrieval is an alternative means of semen collection, where other means are not possible in circumstances like posthumous sperm retrieval or male infertility.
These surgical techniques may also be utilized as a form of permanent contraception referred to as sterilization. A vasectomy or tubal ligation would be examples of this procedure for male and female individuals respectively. Reproductive surgeons can potentially perform a reverse vasectomy to restore male reproductive function following the vasectomy. Individuals may choose to reverse the procedure due to pain experience after the surgery.
People might find themselves wanting to preserve their fertility. Biological material such as sperm or oocyte are capable of being surgically collected and preserved cryogenically. Fertility preservation also provides individuals who are receiving gender-affirming surgeries the option of preserving gametes if having biological children is desired following the procedures and hormonal therapy.
Reproductive surgery is also considered for complications such as endometriosis, polycystic ovary syndrome, ectopic pregnancy, and vas deferens obstruction.
== Trends ==
=== History ===
Albeit an increase in overall use of assisted reproductive technology (ART), surgeries on the fallopian tubes and ovaries have decreased, leading to a rise in insecurity in the field of reproductive surgery. Reproductive surgery in women has largely been complementary to other ART methods such as medication, except for in tubal infertility, where surgery remains the main treatment. Although reproductive surgery has been most relevant for severe symptoms, there has been a strong interest in greater analysis surrounding this topic of research.
Reproductive surgery first began with fertility sparing surgeries, such as uterine myomectomy, and was transitioned later into the addition of surgeries for infertility and the advancement of success rates for fertility. Hysterectomies and myomectomies date back to ancient times, where fascination grew around fertility sparing surgeries, specifically for young women who were able to conceive but were considered to have suspected ailments. However, the lack of knowledge of medicine eventually led to mortality, thereby causing myomectomies to become more uncommon. Overtime, various advancements and extensive research allowed for the discovery of minimally invasive myomectomies, which became popular among women who were capable of bearing children.
Laparoscopy continues to be a common procedure approach as it is minimally invasive and is thought to be associated with a decrease in hospital stay and surgical complications. The development of newer technology and surgical techniques allowed for the increase in success rates for various other surgeries, such as endometriosis and adenomyosis surgeries or adnexal surgeries.
=== The future of reproductive surgery ===
With respect to the future of reproductive surgeries, greater advancements of surgical techniques and equipment are growing in popularity to increase the potential of fertility success rates. For example, vaginal natural orifice transluminal endoscopic surgery (vNOTES) is a new innovative approach that has been used for ovarian torsion, tubal ectopic pregnancy, and ovarian cystectomies. This surgical approach is minimally invasive and has emerged in an effort to reduce pain, risks, and potential for scarring. Another technique that has emerged is radiofrequency ablation (RFA) which has been used for uterine fibroids. It works to necrotize fibroids through the use of laparoscopic and transcervical procedures with two devices, Acessa (Hologic) and Sonata (Gynesonics). However, these two medical devices come with the caveat that fertility may not be preserved in those with uterine leiomyoma. Although not ideal for people who are able to and wanting to bear children, RFA still poses as an alternative successful technique to reducing the volume of fibroids.
A new common interest in alliance with reproductive surgery is the use of regenerative medicine. Although it has not been studied in its entirety, the use of stem cells to restore damaged endometrium has shown promising improvements. Regenerative medicine has been used for premature ovarian failure and will continue to be studied for in vitro fertilization (IVF). With the use of various stem cells, researchers hope to mitigate and treat any future signs of infertility with the use of two specific stem cells, induced pluripotent stem cells (iPSCs) and mesenchymal stem cells (MSC).
== Risks/complications ==
The risks and complications of reproductive surgery depend on patient specific characteristics and the degree of the surgery itself; however, some common complications of general reproductive surgery are hemorrhage, visceral damage, infection, and blot clotting.
In vasectomies, infection and hematomas are the most frequently reported complications of surgery, with the incidence rate of infection being 3-4% and the incidence rate of hematoma ranging around 0-29%. An important note to consider is the fact that the surgical technique of the vasectomy did have an impact on the incident rates of these complications. No-scalpel vasectomy (NSV) is widely recognized due to its low incident rate of complications. Another common complication of vasectomy is post-vasectomy pain syndrome (PVPS). PVPS involves chronic pain that may be persistent or intermittent in one or both of the testicles, and lasting longer than three months after the procedure. While the pathophysiology of PVPS is unknown, various causes include damage to structures of the testis, buildup of pressure from epididymal congestion, and compression of nerves in the testis. The pain in PVPS can manifest in various forms, such as pain and tenderness in the scrotum, pressure or pain after ejaculation, pain with sex, etc. Incidence rates of PVPS are around 1-14%.
In hysterectomies, complications of the procedure include infection, gastrointestinal injury, and venous thromboembolic injury. Similar to vasectomies, one of the most common complications is infection, with the incidence rate being 10.5% for abdominal hysterectomy, 13% for vaginal hysterectomy, and 9% for laparoscopic hysterectomy.
Today, one of the most effective forms of ART is in vitro fertilization (IVF). While it is very effective in those experiencing infertility, there are numerous risks of IVF, such as multiple births, premature delivery, and ovarian hyper-stimulation syndrome. Ovarian hyper-stimulation syndrome is a condition that involves enlargement of the ovaries as the result of the injected fertility drugs causing increased capacity of the blood vessels to allow molecules to go in and out. It can lead to abdominal pain, soreness, and nausea for those experiencing it. The symptoms and severity of ovarian hyper-stimulation syndrome can be classified amongst various grades. Grade 1 involves mild discomfort and abdominal distention, and as the grades increase, severity and symptoms also increase. Grade 4 and grade 5 encompass severe ovarian hyper-stimulation syndrome and involve changes in blood volume and viscosity due to the condition. Those who have a history of heightened response to gonadotropins, history of previous ovarial hyper-stimulation, and/or have a history of polycystic ovary syndrome (PCOS) are at increased risk of developing this complication.
== Contraindications ==
There are no existing medical guidelines that outline the absolute contraindications to reproductive surgery. However, there are relative contraindications recommended in the current literature. There are several circumstances under which having reproductive surgery is contraindicated. This is because surgery itself may cause extensive tissue damage to the person, the success of the procedure is limited (i.e. the condition is invasive or metastatic), or the surgery's potential risk outweighs the potential benefits. However, each person's situation is different and the possibility of reproductive surgery should be consulted with a healthcare professional.
Uterine atony after fetal extraction, and pre-existing maternal bleeding disorders have been reported as accepted contraindications for cesarean myomectomies in women. Contraindications to reproductive surgery used for tubal surgery and infertility include women ages 43 and older, tubal disease that surgery cannot treat (i.e., surgery cannot be safely performed without hurting the person or the patient has multiple medical conditions that reduces the chance of success), bipolar disease, and abnormal semen analysis.
Many studies examining surgery for endometriosis excluded women who previously received medical or surgical treatment for endometriosis. Women with a pre-operative diagnosis of a deep endometriosis of their bowel or bladder were also excluded from surgery.
For male reproductive surgery for the treatment of varicocele by percutaneous embolization, current literature considers adolescents, allergies to contrast, men with a bilateral grade 3 varicocele, and men with primary infertility as relative contraindications to surgery.
== References == | Wikipedia/Reproductive_surgery |
Medicine is the science and practice of caring for patients, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness. Contemporary medicine applies biomedical sciences, biomedical research, genetics, and medical technology to diagnose, treat, and prevent injury and disease, typically through pharmaceuticals or surgery, but also through therapies as diverse as psychotherapy, external splints and traction, medical devices, biologics, and ionizing radiation, amongst others.
Medicine has been practiced since prehistoric times, and for most of this time it was an art (an area of creativity and skill), frequently having connections to the religious and philosophical beliefs of local culture. For example, a medicine man would apply herbs and say prayers for healing, or an ancient philosopher and physician would apply bloodletting according to the theories of humorism. In recent centuries, since the advent of modern science, most medicine has become a combination of art and science (both basic and applied, under the umbrella of medical science). For example, while stitching technique for sutures is an art learned through practice, knowledge of what happens at the cellular and molecular level in the tissues being stitched arises through science.
Prescientific forms of medicine, now known as traditional medicine or folk medicine, remain commonly used in the absence of scientific medicine and are thus called alternative medicine. Alternative treatments outside of scientific medicine with ethical, safety and efficacy concerns are termed quackery.
== Etymology ==
Medicine (UK: , US: ) is the science and practice of the diagnosis, prognosis, treatment, and prevention of disease. The word "medicine" is derived from Latin medicus, meaning "a physician". The word "physic" itself, from which "physician" derives, was the old word for what is now called a medicine, and also the field of medicine.
== Clinical practice ==
Medical availability and clinical practice vary across the world due to regional differences in culture and technology. Modern scientific medicine is highly developed in the Western world, while in developing countries such as parts of Africa or Asia, the population may rely more heavily on traditional medicine with limited evidence and efficacy and no required formal training for practitioners.
In the developed world, evidence-based medicine is not universally used in clinical practice; for example, a 2007 survey of literature reviews found that about 49% of the interventions lacked sufficient evidence to support either benefit or harm.
In modern clinical practice, physicians and physician assistants personally assess patients to diagnose, prognose, treat, and prevent disease using clinical judgment. The doctor-patient relationship typically begins with an interaction with an examination of the patient's medical history and medical record, followed by a medical interview and a physical examination. Basic diagnostic medical devices (e.g., stethoscope, tongue depressor) are typically used. After examining for signs and interviewing for symptoms, the doctor may order medical tests (e.g., blood tests), take a biopsy, or prescribe pharmaceutical drugs or other therapies. Differential diagnosis methods help to rule out conditions based on the information provided. During the encounter, properly informing the patient of all relevant facts is an important part of the relationship and the development of trust. The medical encounter is then documented in the medical record, which is a legal document in many jurisdictions. Follow-ups may be shorter but follow the same general procedure, and specialists follow a similar process. The diagnosis and treatment may take only a few minutes or a few weeks, depending on the complexity of the issue.
The components of the medical interview and encounter are:
Chief complaint (CC): the reason for the current medical visit. These are the symptoms. They are in the patient's own words and are recorded along with the duration of each one. Also called chief concern or presenting complaint.
Current activity: occupation, hobbies, what the patient actually does.
Family history (FH): listing of diseases in the family that may impact the patient. A family tree is sometimes used.
History of present illness (HPI): the chronological order of events of symptoms and further clarification of each symptom. Distinguishable from history of previous illness, often called past medical history (PMH). Medical history comprises HPI and PMH.
Medications (Rx): what drugs the patient takes including prescribed, over-the-counter, and home remedies, as well as alternative and herbal medicines or remedies. Allergies are also recorded.
Past medical history (PMH/PMHx): concurrent medical problems, past hospitalizations and operations, injuries, past infectious diseases or vaccinations, history of known allergies.
Review of systems (ROS) or systems inquiry: a set of additional questions to ask, which may be missed on HPI: a general enquiry (have you noticed any weight loss, change in sleep quality, fevers, lumps and bumps? etc.), followed by questions on the body's main organ systems (heart, lungs, digestive tract, urinary tract, etc.).
Social history (SH): birthplace, residences, marital history, social and economic status, habits (including diet, medications, tobacco, alcohol).
The physical examination is the examination of the patient for medical signs of disease that are objective and observable, in contrast to symptoms that are volunteered by the patient and are not necessarily objectively observable. The healthcare provider uses sight, hearing, touch, and sometimes smell (e.g., in infection, uremia, diabetic ketoacidosis). Four actions are the basis of physical examination: inspection, palpation (feel), percussion (tap to determine resonance characteristics), and auscultation (listen), generally in that order, although auscultation occurs prior to percussion and palpation for abdominal assessments.
The clinical examination involves the study of:
Abdomen and rectum
Cardiovascular (heart and blood vessels)
General appearance of the patient and specific indicators of disease (nutritional status, presence of jaundice, pallor or clubbing)
Genitalia (and pregnancy if the patient is or could be pregnant)
Head, eye, ear, nose, and throat (HEENT)
Musculoskeletal (including spine and extremities)
Neurological (consciousness, awareness, brain, vision, cranial nerves, spinal cord and peripheral nerves)
Psychiatric (orientation, mental state, mood, evidence of abnormal perception or thought).
Respiratory (large airways and lungs)
Skin
Vital signs including height, weight, body temperature, blood pressure, pulse, respiration rate, and hemoglobin oxygen saturation
It is to likely focus on areas of interest highlighted in the medical history and may not include everything listed above.
The treatment plan may include ordering additional medical laboratory tests and medical imaging studies, starting therapy, referral to a specialist, or watchful observation. A follow-up may be advised. Depending upon the health insurance plan and the managed care system, various forms of "utilization review", such as prior authorization of tests, may place barriers on accessing expensive services.
The medical decision-making (MDM) process includes the analysis and synthesis of all the above data to come up with a list of possible diagnoses (the differential diagnoses), along with an idea of what needs to be done to obtain a definitive diagnosis that would explain the patient's problem.
On subsequent visits, the process may be repeated in an abbreviated manner to obtain any new history, symptoms, physical findings, lab or imaging results, or specialist consultations.
== Institutions ==
Contemporary medicine is, in general, conducted within health care systems. Legal, credentialing, and financing frameworks are established by individual governments, augmented on occasion by international organizations, such as churches. The characteristics of any given health care system have a significant impact on the way medical care is provided.
From ancient times, Christian emphasis on practical charity gave rise to the development of systematic nursing and hospitals, and the Catholic Church today remains the largest non-government provider of medical services in the world. Advanced industrial countries (with the exception of the United States) and many developing countries provide medical services through a system of universal health care that aims to guarantee care for all through a single-payer health care system or compulsory private or cooperative health insurance. This is intended to ensure that the entire population has access to medical care on the basis of need rather than ability to pay. Delivery may be via private medical practices, state-owned hospitals and clinics, or charities, most commonly a combination of all three.
Most tribal societies provide no guarantee of healthcare for the population as a whole. In such societies, healthcare is available to those who can afford to pay for it, have self-insured it (either directly or as part of an employment contract), or may be covered by care financed directly by the government or tribe.
Transparency of information is another factor defining a delivery system. Access to information on conditions, treatments, quality, and pricing greatly affects the choice of patients/consumers and, therefore, the incentives of medical professionals. While the US healthcare system has come under fire for its lack of openness, new legislation may encourage greater openness. There is a perceived tension between the need for transparency on the one hand and such issues as patient confidentiality and the possible exploitation of information for commercial gain on the other.
The health professionals who provide care in medicine comprise multiple professions, such as medics, nurses, physiotherapists, and psychologists. These professions will have their own ethical standards, professional education, and bodies. The medical profession has been conceptualized from a sociological perspective.
=== Delivery ===
Provision of medical care is classified into primary, secondary, and tertiary care categories.
Primary care medical services are provided by physicians, physician assistants, nurse practitioners, or other health professionals who have first contact with a patient seeking medical treatment or care. These occur in physician offices, clinics, nursing homes, schools, home visits, and other places close to patients. About 90% of medical visits can be treated by the primary care provider. These include treatment of acute and chronic illnesses, preventive care and health education for all ages and both sexes.
Secondary care medical services are provided by medical specialists in their offices or clinics or at local community hospitals for a patient referred by a primary care provider who first diagnosed or treated the patient. Referrals are made for those patients who required the expertise or procedures performed by specialists. These include both ambulatory care and inpatient services, emergency departments, intensive care medicine, surgery services, physical therapy, labor and delivery, endoscopy units, diagnostic laboratory and medical imaging services, hospice centers, etc. Some primary care providers may also take care of hospitalized patients and deliver babies in a secondary care setting.
Tertiary care medical services are provided by specialist hospitals or regional centers equipped with diagnostic and treatment facilities not generally available at local hospitals. These include trauma centers, burn treatment centers, advanced neonatology unit services, organ transplants, high-risk pregnancy, radiation oncology, etc.
Modern medical care also depends on information – still delivered in many health care settings on paper records, but increasingly nowadays by electronic means.
In low-income countries, modern healthcare is often too expensive for the average person. International healthcare policy researchers have advocated that "user fees" be removed in these areas to ensure access, although even after removal, significant costs and barriers remain.
Separation of prescribing and dispensing is a practice in medicine and pharmacy in which the physician who provides a medical prescription is independent from the pharmacist who provides the prescription drug. In the Western world there are centuries of tradition for separating pharmacists from physicians. In Asian countries, it is traditional for physicians to also provide drugs.
== Branches ==
Working together as an interdisciplinary team, many highly trained health professionals besides medical practitioners are involved in the delivery of modern health care. Examples include: nurses, emergency medical technicians and paramedics, laboratory scientists, pharmacists, podiatrists, physiotherapists, respiratory therapists, speech therapists, occupational therapists, radiographers, dietitians, and bioengineers, medical physicists, surgeons, surgeon's assistant, surgical technologist.
The scope and sciences underpinning human medicine overlap many other fields. A patient admitted to the hospital is usually under the care of a specific team based on their main presenting problem, e.g., the cardiology team, who then may interact with other specialties, e.g., surgical, radiology, to help diagnose or treat the main problem or any subsequent complications/developments.
Physicians have many specializations and subspecializations into certain branches of medicine, which are listed below. There are variations from country to country regarding which specialties certain subspecialties are in.
The main branches of medicine are:
Basic sciences of medicine; this is what every physician is educated in, and some return to in biomedical research.
Interdisciplinary fields, where different medical specialties are mixed to function in certain occasions.
Medical specialties
=== Basic sciences ===
Anatomy is the study of the physical structure of organisms. In contrast to macroscopic or gross anatomy, cytology and histology are concerned with microscopic structures.
Biochemistry is the study of the chemistry taking place in living organisms, especially the structure and function of their chemical components.
Biomechanics is the study of the structure and function of biological systems by means of the methods of Mechanics.
Biophysics is an interdisciplinary science that uses the methods of physics and physical chemistry to study biological systems.
Biostatistics is the application of statistics to biological fields in the broadest sense. A knowledge of biostatistics is essential in the planning, evaluation, and interpretation of medical research. It is also fundamental to epidemiology and evidence-based medicine.
Cytology is the microscopic study of individual cells.
Embryology is the study of the early development of organisms.
Endocrinology is the study of hormones and their effect throughout the body of animals.
Epidemiology is the study of the demographics of disease processes, and includes, but is not limited to, the study of epidemics.
Genetics is the study of genes, and their role in biological inheritance.
Gynecology is the study of female reproductive system.
Histology is the study of the structures of biological tissues by light microscopy, electron microscopy and immunohistochemistry.
Immunology is the study of the immune system, which includes the innate and adaptive immune system in humans, for example.
Lifestyle medicine is the study of the chronic conditions, and how to prevent, treat and reverse them.
Medical physics is the study of the applications of physics principles in medicine.
Microbiology is the study of microorganisms, including protozoa, bacteria, fungi, and viruses.
Molecular biology is the study of molecular underpinnings of the process of replication, transcription and translation of the genetic material.
Neuroscience includes those disciplines of science that are related to the study of the nervous system. A main focus of neuroscience is the biology and physiology of the human brain and spinal cord. Some related clinical specialties include neurology, neurosurgery and psychiatry.
Nutrition science (theoretical focus) and dietetics (practical focus) is the study of the relationship of food and drink to health and disease, especially in determining an optimal diet. Medical nutrition therapy is done by dietitians and is prescribed for diabetes, cardiovascular diseases, weight and eating disorders, allergies, malnutrition, and neoplastic diseases.
Pathology as a science is the study of disease – the causes, course, progression and resolution thereof.
Pharmacology is the study of drugs and their actions.
Photobiology is the study of the interactions between non-ionizing radiation and living organisms.
Physiology is the study of the normal functioning of the body and the underlying regulatory mechanisms.
Radiobiology is the study of the interactions between ionizing radiation and living organisms.
Toxicology is the study of hazardous effects of drugs and poisons.
=== Specialties ===
In the broadest meaning of "medicine", there are many different specialties. In the UK, most specialities have their own body or college, which has its own entrance examination. These are collectively known as the Royal Colleges, although not all currently use the term "Royal". The development of a speciality is often driven by new technology (such as the development of effective anaesthetics) or ways of working (such as emergency departments); the new specialty leads to the formation of a unifying body of doctors and the prestige of administering their own examination.
Within medical circles, specialities usually fit into one of two broad categories: "Medicine" and "Surgery". "Medicine" refers to the practice of non-operative medicine, and most of its subspecialties require preliminary training in Internal Medicine. In the UK, this was traditionally evidenced by passing the examination for the Membership of the Royal College of Physicians (MRCP) or the equivalent college in Scotland or Ireland. "Surgery" refers to the practice of operative medicine, and most subspecialties in this area require preliminary training in General Surgery, which in the UK leads to membership of the Royal College of Surgeons of England (MRCS). At present, some specialties of medicine do not fit easily into either of these categories, such as radiology, pathology, or anesthesia. Most of these have branched from one or other of the two camps above; for example anaesthesia developed first as a faculty of the Royal College of Surgeons (for which MRCS/FRCS would have been required) before becoming the Royal College of Anaesthetists and membership of the college is attained by sitting for the examination of the Fellowship of the Royal College of Anesthetists (FRCA).
==== Surgical specialty ====
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate or treat a pathological condition such as disease or injury, to help improve bodily function or appearance or to repair unwanted ruptured areas (for example, a perforated ear drum). Surgeons must also manage pre-operative, post-operative, and potential surgical candidates on the hospital wards. In some centers, anesthesiology is part of the division of surgery (for historical and logistical reasons), although it is not a surgical discipline. Other medical specialties may employ surgical procedures, such as ophthalmology and dermatology, but are not considered surgical sub-specialties per se.
Surgical training in the U.S. requires a minimum of five years of residency after medical school. Sub-specialties of surgery often require seven or more years. In addition, fellowships can last an additional one to three years. Because post-residency fellowships can be competitive, many trainees devote two additional years to research. Thus in some cases surgical training will not finish until more than a decade after medical school. Furthermore, surgical training can be very difficult and time-consuming.
Surgical subspecialties include those a physician may specialize in after undergoing general surgery residency training as well as several surgical fields with separate residency training. Surgical subspecialties that one may pursue following general surgery residency training:
Bariatric surgery
Cardiovascular surgery – may also be pursued through a separate cardiovascular surgery residency track
Colorectal surgery
Endocrine surgery
General surgery
Hand surgery
Hepatico-Pancreatico-Biliary Surgery
Minimally invasive surgery
Pediatric surgery
Plastic surgery – may also be pursued through a separate plastic surgery residency track
Surgical critical care
Surgical oncology
Transplant surgery
Trauma surgery
Vascular surgery – may also be pursued through a separate vascular surgery residency track
Other surgical specialties within medicine with their own individual residency training:
Dermatology
Neurosurgery
Ophthalmology
Oral and maxillofacial surgery
Orthopedic surgery
Otorhinolaryngology
Podiatric surgery – do not undergo medical school training, but rather separate training in podiatry school
Urology
==== Internal medicine specialty ====
Internal medicine is the medical specialty dealing with the prevention, diagnosis, and treatment of adult diseases. According to some sources, an emphasis on internal structures is implied. In North America, specialists in internal medicine are commonly called "internists". Elsewhere, especially in Commonwealth nations, such specialists are often called physicians. These terms, internist or physician (in the narrow sense, common outside North America), generally exclude practitioners of gynecology and obstetrics, pathology, psychiatry, and especially surgery and its subspecialities.
Because their patients are often seriously ill or require complex investigations, internists do much of their work in hospitals. Formerly, many internists were not subspecialized; such general physicians would see any complex nonsurgical problem; this style of practice has become much less common. In modern urban practice, most internists are subspecialists: that is, they generally limit their medical practice to problems of one organ system or to one particular area of medical knowledge. For example, gastroenterologists and nephrologists specialize respectively in diseases of the gut and the kidneys.
In the Commonwealth of Nations and some other countries, specialist pediatricians and geriatricians are also described as specialist physicians (or internists) who have subspecialized by age of patient rather than by organ system. Elsewhere, especially in North America, general pediatrics is often a form of primary care.
There are many subspecialities (or subdisciplines) of internal medicine:
Training in internal medicine (as opposed to surgical training), varies considerably across the world: see the articles on medical education for more details. In North America, it requires at least three years of residency training after medical school, which can then be followed by a one- to three-year fellowship in the subspecialties listed above. In general, resident work hours in medicine are less than those in surgery, averaging about 60 hours per week in the US. This difference does not apply in the UK where all doctors are now required by law to work less than 48 hours per week on average.
==== Diagnostic specialties ====
Clinical laboratory sciences are the clinical diagnostic services that apply laboratory techniques to diagnosis and management of patients. In the United States, these services are supervised by a pathologist. The personnel that work in these medical laboratory departments are technically trained staff who do not hold medical degrees, but who usually hold an undergraduate medical technology degree, who actually perform the tests, assays, and procedures needed for providing the specific services. Subspecialties include transfusion medicine, cellular pathology, clinical chemistry, hematology, clinical microbiology and clinical immunology.
Clinical neurophysiology is concerned with testing the physiology or function of the central and peripheral aspects of the nervous system. These kinds of tests can be divided into recordings of: (1) spontaneous or continuously running electrical activity, or (2) stimulus evoked responses. Subspecialties include electroencephalography, electromyography, evoked potential, nerve conduction study and polysomnography. Sometimes these tests are performed by techs without a medical degree, but the interpretation of these tests is done by a medical professional.
Diagnostic radiology is concerned with imaging of the body, e.g. by x-rays, x-ray computed tomography, ultrasonography, and nuclear magnetic resonance tomography. Interventional radiologists can access areas in the body under imaging for an intervention or diagnostic sampling.
Nuclear medicine is concerned with studying human organ systems by administering radiolabelled substances (radiopharmaceuticals) to the body, which can then be imaged outside the body by a gamma camera or a PET scanner. Each radiopharmaceutical consists of two parts: a tracer that is specific for the function under study (e.g., neurotransmitter pathway, metabolic pathway, blood flow, or other), and a radionuclide (usually either a gamma-emitter or a positron emitter). There is a degree of overlap between nuclear medicine and radiology, as evidenced by the emergence of combined devices such as the PET/CT scanner.
Pathology as a medical specialty is the branch of medicine that deals with the study of diseases and the morphologic, physiologic changes produced by them. As a diagnostic specialty, pathology can be considered the basis of modern scientific medical knowledge and plays a large role in evidence-based medicine. Many modern molecular tests such as flow cytometry, polymerase chain reaction (PCR), immunohistochemistry, cytogenetics, gene rearrangements studies and fluorescent in situ hybridization (FISH) fall within the territory of pathology.
==== Other major specialties ====
The following are some major medical specialties that do not directly fit into any of the above-mentioned groups:
Anesthesiology (also known as anaesthetics): concerned with the perioperative management of the surgical patient. The anesthesiologist's role during surgery is to prevent derangement in the vital organs' (i.e. brain, heart, kidneys) functions and postoperative pain. Outside of the operating room, the anesthesiology physician also serves the same function in the labor and delivery ward, and some are specialized in critical medicine.
Emergency medicine is concerned with the diagnosis and treatment of acute or life-threatening conditions, including trauma, surgical, medical, pediatric, and psychiatric emergencies.
Family medicine, family practice, general practice or primary care is, in many countries, the first port-of-call for patients with non-emergency medical problems. Family physicians often provide services across a broad range of settings including office based practices, emergency department coverage, inpatient care, and nursing home care.
Medical genetics is concerned with the diagnosis and management of hereditary disorders.
Neurology is concerned with diseases of the nervous system. In the UK, neurology is a subspecialty of general medicine.
Obstetrics and gynecology (often abbreviated as OB/GYN (American English) or Obs & Gynae (British English)) are concerned respectively with childbirth and the female reproductive and associated organs. Reproductive medicine and fertility medicine are generally practiced by gynecological specialists.
Pediatrics (AE) or paediatrics (BE) is devoted to the care of infants, children, and adolescents. Like internal medicine, there are many pediatric subspecialties for specific age ranges, organ systems, disease classes, and sites of care delivery.
Pharmaceutical medicine is the medical scientific discipline concerned with the discovery, development, evaluation, registration, monitoring and medical aspects of marketing of medicines for the benefit of patients and public health.
Physical medicine and rehabilitation (or physiatry) is concerned with functional improvement after injury, illness, or congenital disorders.
Podiatric medicine is the study of, diagnosis, and medical and surgical treatment of disorders of the foot, ankle, lower limb, hip and lower back.
Preventive medicine is the branch of medicine concerned with preventing disease.
Community health or public health is an aspect of health services concerned with threats to the overall health of a community based on population health analysis.
Psychiatry is the branch of medicine concerned with the bio-psycho-social study of the etiology, diagnosis, treatment and prevention of cognitive, perceptual, emotional and behavioral disorders. Related fields include psychotherapy and clinical psychology.
=== Interdisciplinary fields ===
Some interdisciplinary sub-specialties of medicine include:
Addiction medicine deals with the treatment of addiction.
Aerospace medicine deals with medical problems related to flying and space travel.
Biomedical Engineering is a field dealing with the application of engineering principles to medical practice.
Clinical pharmacology is concerned with how systems of therapeutics interact with patients.
Conservation medicine studies the relationship between human and non-human animal health, and environmental conditions. Also known as ecological medicine, environmental medicine, or medical geology.
Disaster medicine deals with medical aspects of emergency preparedness, disaster mitigation and management.
Diving medicine (or hyperbaric medicine) is the prevention and treatment of diving-related problems.
Evolutionary medicine is a perspective on medicine derived through applying evolutionary theory.
Forensic medicine deals with medical questions in legal context, such as determination of the time and cause of death, type of weapon used to inflict trauma, reconstruction of the facial features using remains of deceased (skull) thus aiding identification.
Gender-based medicine studies the biological and physiological differences between the human sexes and how that affects differences in disease.
Health informatics is a relatively recent field that deal with the application of computers and information technology to medicine.
Hospice and Palliative Medicine is a relatively modern branch of clinical medicine that deals with pain and symptom relief and emotional support in patients with terminal illnesses including cancer and heart failure.
Hospital medicine is the general medical care of hospitalized patients. Physicians whose primary professional focus is hospital medicine are called hospitalists in the United States and Canada. The term Most Responsible Physician (MRP) or attending physician is also used interchangeably to describe this role.
Laser medicine involves the use of lasers in the diagnostics or treatment of various conditions.
Many other health science fields, e.g. dietetics
Medical ethics deals with ethical and moral principles that apply values and judgments to the practice of medicine.
Medical humanities includes the humanities (literature, philosophy, ethics, history and religion), social science (anthropology, cultural studies, psychology, sociology), and the arts (literature, theater, film, and visual arts) and their application to medical education and practice.
Nosokinetics is the science/subject of measuring and modelling the process of care in health and social care systems.
Nosology is the classification of diseases for various purposes.
Occupational medicine is the provision of health advice to organizations and individuals to ensure that the highest standards of health and safety at work can be achieved and maintained.
Pain management (also called pain medicine, or algiatry) is the medical discipline concerned with the relief of pain.
Pharmacogenomics is a form of individualized medicine.
Podiatric medicine is the study of, diagnosis, and medical treatment of disorders of the foot, ankle, lower limb, hip and lower back.
Sexual medicine is concerned with diagnosing, assessing and treating all disorders related to sexuality.
Sports medicine deals with the treatment and prevention and rehabilitation of sports/exercise injuries such as muscle spasms, muscle tears, injuries to ligaments (ligament tears or ruptures) and their repair in athletes, amateur and professional.
Therapeutics is the field, more commonly referenced in earlier periods of history, of the various remedies that can be used to treat disease and promote health.
Travel medicine or emporiatrics deals with health problems of international travelers or travelers across highly different environments.
Tropical medicine deals with the prevention and treatment of tropical diseases. It is studied separately in temperate climates where those diseases are quite unfamiliar to medical practitioners and their local clinical needs.
Urgent care focuses on delivery of unscheduled, walk-in care outside of the hospital emergency department for injuries and illnesses that are not severe enough to require care in an emergency department. In some jurisdictions this function is combined with the emergency department.
Veterinary medicine; veterinarians apply similar techniques as physicians to the care of non-human animals.
Wilderness medicine entails the practice of medicine in the wild, where conventional medical facilities may not be available.
== Education and legal controls ==
Medical education and training varies around the world. It typically involves entry level education at a university medical school, followed by a period of supervised practice or internship, or residency. This can be followed by postgraduate vocational training. A variety of teaching methods have been employed in medical education, still itself a focus of active research. In Canada and the United States of America, a Doctor of Medicine degree, often abbreviated M.D., or a Doctor of Osteopathic Medicine degree, often abbreviated as D.O. and unique to the United States, must be completed in and delivered from a recognized university.
Since knowledge, techniques, and medical technology continue to evolve at a rapid rate, many regulatory authorities require continuing medical education. Medical practitioners upgrade their knowledge in various ways, including medical journals, seminars, conferences, and online programs. A database of objectives covering medical knowledge, as suggested by national societies across the United States, can be searched at http://data.medobjectives.marian.edu/ Archived 4 October 2018 at the Wayback Machine.
In most countries, it is a legal requirement for a medical doctor to be licensed or registered. In general, this entails a medical degree from a university and accreditation by a medical board or an equivalent national organization, which may ask the applicant to pass exams. This restricts the considerable legal authority of the medical profession to physicians that are trained and qualified by national standards. It is also intended as an assurance to patients and as a safeguard against charlatans that practice inadequate medicine for personal gain. While the laws generally require medical doctors to be trained in "evidence based", Western, or Hippocratic Medicine, they are not intended to discourage different paradigms of health.
In the European Union, the profession of doctor of medicine is regulated. A profession is said to be regulated when access and exercise is subject to the possession of a specific professional qualification. The regulated professions database contains a list of regulated professions for doctor of medicine in the EU member states, EEA countries and Switzerland. This list is covered by the Directive 2005/36/EC.
Doctors who are negligent or intentionally harmful in their care of patients can face charges of medical malpractice and be subject to civil, criminal, or professional sanctions.
== Medical ethics ==
Medical ethics is a system of moral principles that apply values and judgments to the practice of medicine. As a scholarly discipline, medical ethics encompasses its practical application in clinical settings as well as work on its history, philosophy, theology, and sociology. Six of the values that commonly apply to medical ethics discussions are:
autonomy – the patient has the right to refuse or choose their treatment. (Latin: Voluntas aegroti suprema lex.)
beneficence – a practitioner should act in the best interest of the patient. (Latin: Salus aegroti suprema lex.)
justice – concerns the distribution of scarce health resources, and the decision of who gets what treatment (fairness and equality).
non-maleficence – "first, do no harm" (Latin: primum non-nocere).
respect for persons – the patient (and the person treating the patient) have the right to be treated with dignity.
truthfulness and honesty – the concept of informed consent has increased in importance since the historical events of the Doctors' Trial of the Nuremberg trials, Tuskegee syphilis experiment, and others.
Values such as these do not give answers as to how to handle a particular situation, but provide a useful framework for understanding conflicts. When moral values are in conflict, the result may be an ethical dilemma or crisis. Sometimes, no good solution to a dilemma in medical ethics exists, and occasionally, the values of the medical community (i.e., the hospital and its staff) conflict with the values of the individual patient, family, or larger non-medical community. Conflicts can also arise between health care providers, or among family members. For example, some argue that the principles of autonomy and beneficence clash when patients refuse blood transfusions, considering them life-saving; and truth-telling was not emphasized to a large extent before the HIV era.
== History ==
=== Ancient world ===
Prehistoric medicine incorporated plants (herbalism), animal parts, and minerals. In many cases these materials were used ritually as magical substances by priests, shamans, or medicine men. Well-known spiritual systems include animism (the notion of inanimate objects having spirits), spiritualism (an appeal to gods or communion with ancestor spirits); shamanism (the vesting of an individual with mystic powers); and divination (magically obtaining the truth). The field of medical anthropology examines the ways in which culture and society are organized around or impacted by issues of health, health care and related issues.
The earliest known medical texts in the world were found in the ancient Syrian city of Ebla and date back to 2500 BCE. Other early records on medicine have been discovered from ancient Egyptian medicine, Babylonian Medicine, Ayurvedic medicine (in the Indian subcontinent), classical Chinese medicine (Alternative medicine) predecessor to the modern traditional Chinese medicine), and ancient Greek medicine and Roman medicine.
In Egypt, Imhotep (3rd millennium BCE) is the first physician in history known by name. The oldest Egyptian medical text is the Kahun Gynaecological Papyrus from around 2000 BCE, which describes gynaecological diseases. The Edwin Smith Papyrus dating back to 1600 BCE is an early work on surgery, while the Ebers Papyrus dating back to 1500 BCE is akin to a textbook on medicine.
In China, archaeological evidence of medicine in Chinese dates back to the Bronze Age Shang dynasty, based on seeds for herbalism and tools presumed to have been used for surgery. The Huangdi Neijing, the progenitor of Chinese medicine, is a medical text written beginning in the 2nd century BCE and compiled in the 3rd century.
In India, the surgeon Sushruta described numerous surgical operations, including the earliest forms of plastic surgery.Earliest records of dedicated hospitals come from Mihintale in Sri Lanka where evidence of dedicated medicinal treatment facilities for patients are found.
In Greece, the ancient Greek physician Hippocrates, the "father of modern medicine", laid the foundation for a rational approach to medicine. Hippocrates introduced the Hippocratic Oath for physicians, which is still relevant and in use today, and was the first to categorize illnesses as acute, chronic, endemic and epidemic, and use terms such as, "exacerbation, relapse, resolution, crisis, paroxysm, peak, and convalescence". The Greek physician Galen was also one of the greatest surgeons of the ancient world and performed many audacious operations, including brain and eye surgeries. After the fall of the Western Roman Empire and the onset of the Early Middle Ages, the Greek tradition of medicine went into decline in Western Europe, although it continued uninterrupted in the Eastern Roman (Byzantine) Empire.
Most of our knowledge of ancient Hebrew medicine during the 1st millennium BC comes from the Torah, i.e. the Five Books of Moses, which contain various health related laws and rituals. The Hebrew contribution to the development of modern medicine started in the Byzantine Era, with the physician Asaph the Jew.
=== Middle Ages ===
The concept of hospital as institution to offer medical care and possibility of a cure for the patients due to the ideals of Christian charity, rather than just merely a place to die, appeared in the Byzantine Empire.
Although the concept of uroscopy was known to Galen, he did not see the importance of using it to localize the disease. It was under the Byzantines with physicians such of Theophilus Protospatharius that they realized the potential in uroscopy to determine disease in a time when no microscope or stethoscope existed. That practice eventually spread to the rest of Europe.
After 750 CE, the Muslim world had the works of Hippocrates, Galen and Sushruta translated into Arabic, and Islamic physicians engaged in some significant medical research. Notable Islamic medical pioneers include the Persian polymath, Avicenna, who, along with Imhotep and Hippocrates, has also been called the "father of medicine". He wrote The Canon of Medicine which became a standard medical text at many medieval European universities, considered one of the most famous books in the history of medicine. Others include Abulcasis, Avenzoar, Ibn al-Nafis, and Averroes. Persian physician Rhazes was one of the first to question the Greek theory of humorism, which nevertheless remained influential in both medieval Western and medieval Islamic medicine. Some volumes of Rhazes's work Al-Mansuri, namely "On Surgery" and "A General Book on Therapy", became part of the medical curriculum in European universities. Additionally, he has been described as a doctor's doctor, the father of pediatrics, and a pioneer of ophthalmology. For example, he was the first to recognize the reaction of the eye's pupil to light. The Persian Bimaristan hospitals were an early example of public hospitals.
In Europe, Charlemagne decreed that a hospital should be attached to each cathedral and monastery and the historian Geoffrey Blainey likened the activities of the Catholic Church in health care during the Middle Ages to an early version of a welfare state: "It conducted hospitals for the old and orphanages for the young; hospices for the sick of all ages; places for the lepers; and hostels or inns where pilgrims could buy a cheap bed and meal". It supplied food to the population during famine and distributed food to the poor. This welfare system the church funded through collecting taxes on a large scale and possessing large farmlands and estates. The Benedictine order was noted for setting up hospitals and infirmaries in their monasteries, growing medical herbs and becoming the chief medical care givers of their districts, as at the great Abbey of Cluny. The Church also established a network of cathedral schools and universities where medicine was studied. The Schola Medica Salernitana in Salerno, looking to the learning of Greek and Arab physicians, grew to be the finest medical school in medieval Europe.
However, the fourteenth and fifteenth century Black Death devastated both the Middle East and Europe, and it has even been argued that Western Europe was generally more effective in recovering from the pandemic than the Middle East. In the early modern period, important early figures in medicine and anatomy emerged in Europe, including Gabriele Falloppio and William Harvey.
The major shift in medical thinking was the gradual rejection, especially during the Black Death in the 14th and 15th centuries, of what may be called the "traditional authority" approach to science and medicine. This was the notion that because some prominent person in the past said something must be so, then that was the way it was, and anything one observed to the contrary was an anomaly (which was paralleled by a similar shift in European society in general – see Copernicus's rejection of Ptolemy's theories on astronomy). Physicians like Vesalius improved upon or disproved some of the theories from the past. The main tomes used both by medicine students and expert physicians were Materia Medica and Pharmacopoeia.
Andreas Vesalius was the author of De humani corporis fabrica, an important book on human anatomy. Bacteria and microorganisms were first observed with a microscope by Antonie van Leeuwenhoek in 1676, initiating the scientific field microbiology. Independently from Ibn al-Nafis, Michael Servetus rediscovered the pulmonary circulation, but this discovery did not reach the public because it was written down for the first time in the "Manuscript of Paris" in 1546, and later published in the theological work for which he paid with his life in 1553. Later this was described by Renaldus Columbus and Andrea Cesalpino. Herman Boerhaave is sometimes referred to as a "father of physiology" due to his exemplary teaching in Leiden and textbook 'Institutiones medicae' (1708). Pierre Fauchard has been called "the father of modern dentistry".
=== Modern ===
Veterinary medicine was, for the first time, truly separated from human medicine in 1761, when the French veterinarian Claude Bourgelat founded the world's first veterinary school in Lyon, France. Before this, medical doctors treated both humans and other animals.
Modern scientific biomedical research (where results are testable and reproducible) began to replace early Western traditions based on herbalism, the Greek "four humours" and other such pre-modern notions. The modern era really began with Edward Jenner's discovery of the smallpox vaccine at the end of the 18th century (inspired by the method of variolation originated in ancient China), Robert Koch's discoveries around 1880 of the transmission of disease by bacteria, and then the discovery of antibiotics around 1900.
The post-18th century modernity period brought more groundbreaking researchers from Europe. From Germany and Austria, doctors Rudolf Virchow, Wilhelm Conrad Röntgen, Karl Landsteiner and Otto Loewi made notable contributions. In the United Kingdom, Alexander Fleming, Joseph Lister, Francis Crick and Florence Nightingale are considered important. Spanish doctor Santiago Ramón y Cajal is considered the father of modern neuroscience.
From New Zealand and Australia came Maurice Wilkins, Howard Florey, and Frank Macfarlane Burnet.
Others that did significant work include William Williams Keen, William Coley, James D. Watson (United States); Salvador Luria (Italy); Alexandre Yersin (Switzerland); Kitasato Shibasaburō (Japan); Jean-Martin Charcot, Claude Bernard, Paul Broca (France); Adolfo Lutz (Brazil); Nikolai Korotkov (Russia); Sir William Osler (Canada); and Harvey Cushing (United States).
As science and technology developed, medicine became more reliant upon medications. Throughout history and in Europe right until the late 18th century, not only plant products were used as medicine, but also animal (including human) body parts and fluids. Pharmacology developed in part from herbalism and some drugs are still derived from plants (atropine, ephedrine, warfarin, aspirin, digoxin, vinca alkaloids, taxol, hyoscine, etc.). Vaccines were discovered by Edward Jenner and Louis Pasteur.
The first antibiotic was arsphenamine (Salvarsan) discovered by Paul Ehrlich in 1908 after he observed that bacteria took up toxic dyes that human cells did not. The first major class of antibiotics was the sulfa drugs, derived by German chemists originally from azo dyes.
Pharmacology has become increasingly sophisticated; modern biotechnology allows drugs targeted towards specific physiological processes to be developed, sometimes designed for compatibility with the body to reduce side-effects. Genomics and knowledge of human genetics and human evolution is having increasingly significant influence on medicine, as the causative genes of most monogenic genetic disorders have now been identified, and the development of techniques in molecular biology, evolution, and genetics are influencing medical technology, practice and decision-making.
Evidence-based medicine is a contemporary movement to establish the most effective algorithms of practice (ways of doing things) through the use of systematic reviews and meta-analysis. The movement is facilitated by modern global information science, which allows as much of the available evidence as possible to be collected and analyzed according to standard protocols that are then disseminated to healthcare providers. The Cochrane Collaboration leads this movement. A 2001 review of 160 Cochrane systematic reviews revealed that, according to two readers, 21.3% of the reviews concluded insufficient evidence, 20% concluded evidence of no effect, and 22.5% concluded positive effect.
== Quality, efficiency, and access ==
Evidence-based medicine, prevention of medical error (and other "iatrogenesis"), and avoidance of unnecessary health care are a priority in modern medical systems. These topics generate significant political and public policy attention, particularly in the United States where healthcare is regarded as excessively costly but population health metrics lag similar nations.
Globally, many developing countries lack access to care and access to medicines. As of 2015, most wealthy developed countries provide health care to all citizens, with a few exceptions such as the United States where lack of health insurance coverage may limit access.
== See also ==
== Notes ==
== References == | Wikipedia/Clinical_practice |
General surgery is a surgical specialty that focuses on alimentary canal and abdominal contents including the esophagus, stomach, small intestine, large intestine, liver, pancreas, gallbladder, appendix and bile ducts, and often the thyroid gland. General surgeons also deal with diseases involving the skin, breast, soft tissue, trauma, peripheral artery disease and hernias and perform endoscopic as such as gastroscopy, colonoscopy and laparoscopic procedures.
== Scope ==
General surgeons may sub-specialise into one or more of the following disciplines:
=== Trauma surgery ===
In many parts of the world including North America, Australia and the United Kingdom, the overall responsibility for trauma care falls under the auspices of general surgery. Some general surgeons obtain advanced training in this field (most commonly surgical critical care) and specialty certification surgical critical care. General surgeons must be able to deal initially with almost any surgical emergency. Often, they are the first port of call to critically ill or gravely injured patients, and must perform a variety of procedures to stabilize such patients, such as thoracostomy, cricothyroidotomy, compartment fasciotomies and emergency laparotomy or thoracotomy to stanch bleeding. They are also called upon to staff surgical intensive care units or trauma intensive care units.
All general surgeons are trained in emergency surgery. Bleeding, infections, bowel obstructions and organ perforations are the main problems they deal with. Cholecystectomy, the surgical removal of the gallbladder, is one of the most common surgical procedures done worldwide. This is most often done electively, but the gallbladder can become acutely inflamed and require an emergency operation. Infections and rupture of the appendix and small bowel obstructions are other common emergencies.
=== Laparoscopic surgery ===
This is a relatively new specialty dealing with minimal access techniques using cameras and small instruments inserted through 3- to 15-mm incisions. Robotic surgery is now evolving from this concept (see below). Gallbladders, appendices, and colons can all be removed with this technique. Hernias are also able to be repaired laparoscopically. Bariatric surgery can be performed laparoscopically and there are benefits of doing so to reduce wound complications in obese patients. General surgeons that are trained today are expected to be proficient in laparoscopic procedures.
=== Colorectal surgery ===
General surgeons treat a wide variety of major and minor colon and rectal diseases including inflammatory bowel diseases (such as ulcerative colitis or Crohn's disease), diverticulitis, colon and rectal cancer, gastrointestinal bleeding and hemorrhoids.
=== Upper Gastrointestinal Surgery ===
General surgeons can specialise in Upper Gastro-intestinal (or foregut) surgery, which includes the surgical treatment of diseases of the stomach and oesophagus, liver, pancreas and gallbladder. In the UK, Upper GI surgeons can subspecialise further as benign surgeons, dealing with hiatus hernias and gallbladder diseases, bariatric surgeons, providing surgical care for weight management and metabolic diseases, or oesophago-gastric surgeons, dealing with complex problems related to the upper gastrointestinal tract (the foregut), including cancer. Surgical care of complex liver and pancreatic problems (including liver cancer and pancreatic cancer) is undertaken by Hepatobiliary and Pancreatic Surgery sub-specialists.
=== Breast surgery ===
General surgeons perform a majority of all non-cosmetic breast surgery from lumpectomy to mastectomy, especially pertaining to the evaluation, diagnosis and treatment of breast cancer.
=== Vascular surgery ===
General surgeons can perform vascular surgery if they receive special training and certification in vascular surgery. Otherwise, these procedures are typically performed by vascular surgery specialists. However, general surgeons are capable of treating minor vascular disorders.
=== Endocrine surgery ===
General surgeons are trained to remove all or part of the thyroid and parathyroid glands in the neck and the adrenal glands just above each kidney in the abdomen. In many communities, they are the only surgeon trained to do this. In communities that have a number of subspecialists, other subspecialty surgeons may assume responsibility for these procedures.
=== Transplant surgery ===
Responsible for all aspects of pre-operative, operative, and post-operative care of abdominal organ transplant patients. Transplanted organs include liver, kidney, pancreas, and more rarely small bowel.
=== Surgical oncology ===
Surgical oncologist refers to a general surgical oncologist (a specialty of a general surgeon), but thoracic surgical oncologists, gynecologist and so forth can all be considered surgeons who specialize in treating cancer patients. The importance of training surgeons who sub-specialize in cancer surgery lies in evidence, supported by a number of clinical trials, that outcomes in surgical cancer care are positively associated to surgeon volume (i.e., the more cancer cases a surgeon treats, the more proficient he or she becomes, and his or her patients experience improved survival rates as a result). This is another controversial point, but it is generally accepted, even as common sense, that a surgeon who performs a given operation more often, will achieve superior results when compared with a surgeon who rarely performs the same procedure. This is particularly true of complex cancer resections such as pancreaticoduodenectomy for pancreatic cancer, and gastrectomy with extended (D2) lymphadenectomy for gastric cancer. Surgical oncology is generally a 2-year fellowship following completion of a general surgery residency (5–7 years).
=== Cardiothoracic surgery ===
Most cardiothoracic surgeons in the U.S. (D.O. or M.D.) first complete a general surgery residency (typically 5–7 years), followed by a cardiothoracic surgery fellowship (typically 2–3 years). However, new programmes are currently offering cardiothoracic surgery as a residency (6–8 years).
=== Pediatric surgery ===
Pediatric surgery is a subspecialty of general surgery. Pediatric surgeons do surgery on patients under age 18. Pediatric surgery is 5–7 years of residency and a 2–3 year fellowship.
== Trends ==
In the 2000s, minimally invasive surgery became more prevalent. Considerable enthusiasm has been built around robot-assisted surgery (also known as robotic surgery), despite a lack of data suggesting it has significant benefits that justify its cost.
== Training ==
In Canada, Australia, New Zealand, and the United States general surgery is a five to seven year residency and follows completion of medical school, either MD, MBBS, MBChB, or DO degrees. In Australia and New Zealand, a residency leads to eligibility for Fellowship of the Royal Australasian College of Surgeons. In Canada, residency leads to eligibility for certification by and Fellowship of the Royal College of Physicians and Surgeons of Canada, while in the United States, completion of a residency in general surgery leads to eligibility for board certification by the American Board of Surgery or the American Osteopathic Board of Surgery which is also required upon completion of training for a general surgeon to have operating privileges at most hospitals in the United States.
In the United Kingdom, surgical trainees may apply to enter training after five years of medical school and two years of the Foundation Programme. During the two year core surgical training programme ("phase 1"), doctors are required to sit the Membership of the Royal College of Surgeons (MRCS) examination. On award of the MRCS by one of the four surgical colleges, surgeons may hold the title 'Mister' or 'Miss/Ms./Mrs' rather than doctor. This tradition dates back hundreds of years in the United Kingdom from when only physicians attended medical school and surgeons did not, but were rather associated with barbers in the Barber Surgeon's Guild. The tradition is also present in many Commonwealth countries including New Zealand and some states of Australia. After completion of phase 1 training, trainees may apply for a nationally awarded Higher Surgical Training (HST) programme, which lasts six years and is now divided into two further phases (phases 2 and 3). Trainees are expected to declare a sub-specialty before the end of phase 2, and training during phase 3 focuses on that sub-specialty. Before the end of HST, the examination for Fellowship of the Royal College of Surgeons (FRCS) must be taken in general surgery plus the subspeciality. Upon completion of training, the surgeon will be eligible for entry on the GMC Specialist Register. They may then apply to work both in the NHS and independent sector as a consultant surgeon, although many trainees complete further fellowships. The implementation of the European Working Time Directive limited UK surgical residents to an average 48-hour working week.
== See also ==
Abdominal surgery
Physician
Reconstructive surgery
Surgeon
Surgery
Traumatology
== References ==
== External links ==
American College of Surgeons
Association of Surgeons of Great Britain and Ireland
General Surgeons Australia
Canadian Association of General Surgeons
International Society of Surgery | Wikipedia/General_surgery |
Infectious diseases (ID), also known as infectiology, is a medical specialty dealing with the diagnosis and treatment of infections. An infectious diseases specialist's practice consists of managing nosocomial (healthcare-acquired) infections or community-acquired infections. An ID specialist investigates and determines the cause of a disease (bacteria, virus, parasite, fungus or prions). Once the cause is known, an ID specialist can then run various tests to determine the best drug to treat the disease. While infectious diseases have always been around, the infectious disease specialty did not exist until the late 1900s after scientists and physicians in the 19th century paved the way with research on the sources of infectious disease and the development of vaccines.
== Scope ==
Infectious diseases specialists typically serve as consultants to other physicians in cases of complex infections, and often manage patients with HIV/AIDS and other forms of immunodeficiency. Although many common infections are treated by physicians without formal expertise in infectious diseases, specialists may be consulted for cases where an infection is difficult to diagnose or manage. They may also be asked to help determine the cause of a fever of unknown origin.
Specialists in infectious diseases can practice both in hospitals (inpatient) and clinics (outpatient). In hospitals, specialists in infectious diseases help ensure the timely diagnosis and treatment of acute infections by recommending the appropriate diagnostic tests to identify the source of the infection and by recommending appropriate management such as prescribing antibiotics to treat bacterial infections. For certain types of infections, involvement of specialists in infectious diseases may improve patient outcomes. In clinics, specialists in infectious diseases can provide long-term care to patients with chronic infections such as HIV/AIDS.
== History ==
Infectious diseases are historically associated with hygiene and epidemiology due to periodic outbreaks ravaging countries, especially in the cities before the advent of sanitation, but also with travel medicine and tropical medicine, as many diseases acquired in tropical and subtropical areas are infectious in nature.
Western innovations for treating infectious diseases originated in Ancient Greece, and before infectious disease was even conceptualized, a Greek Physician named Hippocrates formed the Hippocratic Corpus. Included in this collection of 70 documents was a text that contained illness-causing infectious diseases. This text, called the Epidemiai volumes, played a key role in forming the western approach to infectious disease. A physician during the Roman empire, Galen of Pergamon, also made great impacts on the western perception of infectious disease with his multiple treatises. These treatises gave insight into the Antonine Plague which we now recognize as smallpox based on the description in Galen's treatises.
Between the 16th and 18th centuries, medical professionals were educating more people, learning more from their research, and gaining access to information from other professionals in the field due to the use of printers like Gutenberg and the mass production of medical books. These books, now in the hands of many, included observations of infectious diseases. Such as syphilis, malaria, and smallpox. In the late 18th century we start to see vaccinations forming and the first vaccination for smallpox was established. Although there were records of individual infectious diseases spread out over medical documents, a combined perception of infectious disease as an area of medicine did not exist at that time.
During the 19th century, modern medicine began to develop and the sources of infectious diseases became more clear. Robert Koch, a German physician who studied pathogens, discovered three major pathogens that were the cause of Anthrax, Tuberculosis, and Cholera. Louis Pasteur was a pioneer in the creation of vaccines for infectious diseases, one being a vaccine for Anthrax. He also developed the germ theory of infectious diseases which influenced Joseph Lister to practice methods during surgery that reduce the growth of pathogens that cause infectious disease. Although infectious disease started to become a more collective concept in the 19th-century it was not considered a medical specialty until the 1970s due to a number of newly discovered diseases and vaccines.
== Investigations ==
When diagnosing, a medical professional must first determine if a patient has an infectious disease or another condition not caused by infection but exhibits similar symptoms. Once the illness is confirmed to be caused by an infection, Infectious diseases specialists employ a variety of diagnostic tests to help identify the pathogen that is causing an infection. Common tests include staining, culture tests, serological tests, susceptibility tests, genotyping, nucleic acid-base test, and polymerase chain reaction. Seeing as samples of bodily fluid or tissue are used in these tests, a specialist will have to distinguish between the non-disease-causing bacteria and disease-causing bacteria inhabiting the body to effectively identify and treat the infection.
Staining is a method of testing that uses a special dye to change the color of pathogens and a microscope to view them. The change in color helps doctors distinguish the pathogen from its surrounding and identify what it is. This method is only successful with large and plentiful pathogens present. Therefore, this method is unsuccessful with viruses because they can not be viewed under a microscope due to their small size. Staining has more of an effect on bacteria where a violet colored stain is used, this is called gram staining. If the bacteria appears blue it is considered gram positive and if it appears red it is gram negative.
Culture tests are done when there is not enough of the pathogen to be seen through other tests. ID specialists will grow the pathogen in the lab until they have enough to work with. Although cultures work on some pathogens, such as the bacteria that causes strep throat, it is ineffective on many others, such as syphilis. A test to identify the pathogen, such as staining, would take place after culture tests.
Susceptibility tests are done by ID specialists to discover which antimicrobial drug would be most effective at killing the pathogen. Cultures can also be used as a form of susceptibility testing by adding the drug to the cultured pathogens and observing whether or not it kills the pathogen and how much of the drug is needed to kill it.
Nucleic acid-base tests are used to detect genetic material. For pathogens that can't be cultured, ID specialists can identify them by looking for specific DNA or RNA. Polymerase chain reaction (PCR), a type of nucleic acid-base test, is similar to culture tests in that genes from the pathogen are duplicated. This method is mainly used when a specific pathogen is suspected.
== Treatments ==
Infectious diseases specialists employ a variety of antimicrobial agents to help treat infections. The type of antimicrobial depends on the organism that is causing the infection. Antibiotics are used to treat bacterial infections; antiviral agents treat viral infections; and antifungal agents treat fungal infections.
== Training ==
=== United States ===
In the United States, infectious diseases is a subspecialty of internal medicine and pediatrics. In order to "sit" for the infectious diseases' board certification test (administered by the American Board of Internal Medicine, or the American Board of Pediatrics), physicians must have completed their residency (in internal medicine, or pediatrics), then undergo additional fellowship training (for at least two, or three years, respectively). The exam has been given as a subspecialty of internal medicine since 1972 and as a subspecialty of pediatrics since 1994.
== References ==
== External links ==
IDSA - Infectious Diseases Society of America | Wikipedia/Infectious_diseases_(medical_specialty) |
Pneumoencephalography (sometimes abbreviated PEG; also referred to as an "air study") was a common medical procedure in which most of the cerebrospinal fluid (CSF) was drained from around the brain by means of a lumbar puncture and replaced with air, oxygen, or helium to allow the structure of the brain to show up more clearly on an X-ray image. It was derived from ventriculography, an earlier and more primitive method in which the air is injected through holes drilled in the skull.
The procedure was introduced in 1919 by the American neurosurgeon Walter Dandy and was performed extensively until the late 1970s, when it was replaced by more-sophisticated and less-invasive modern neuroimaging techniques.
== Procedure ==
Though pneumoencephalography was the single most important way of localizing brain lesions of its time, it was nevertheless extremely painful and generally not well tolerated by conscious patients. Pneumoencephalography was associated with a wide range of side effects, including headaches and severe vomiting, often lasting well past the procedure. During the study, the patient's entire body would be rotated into different positions in order to allow air to displace the CSF in different areas of the ventricular system and around the brain. The patient would be strapped into an open-backed chair, which allowed the spinal needle to be inserted, and they would need to be secured well, for they would be turned upside down at times during the procedure and then somersaulted into a face-down position in a specific order to follow the air to different areas in the ventricles. This further added to the patient's already heightened level of discomfort (if not anesthetized). A related procedure is pneumomyelography, in which gas is used similarly to investigate the spinal canal.
== Limitations ==
Pneumoencephalography makes use of plain X-ray images. These are very poor at resolving soft tissues, such as the brain. Moreover, all the structures captured in the image are superimposed on top of each other, which makes it difficult to pick out individual items of interest (unlike modern scanners, which are able to produce fine virtual slices of the body, including of soft tissues). Therefore, pneumoencephalography did not usually image abnormalities directly; rather, their secondary effects. The overall structure of the brain contains crevices and cavities that are filled by the CSF. Both the brain and the CSF produce similar signals on an X-ray image. However, draining the CSF allows for greater contrast between the brain matter and the (now drained) crevices in and around it, which then show up as dark shadows on the X-ray image. The aim of pneumoencephalography is to outline these shadow-forming air-filled structures so that their shape and anatomical location can be examined. Following the procedure, an experienced radiologist reviews the X-ray films to see if the shape or location of these structures have been distorted or shifted by the presence of certain kinds of lesions. This also means that in order to show up on the images, lesions have to either be located right on the edge of the structures or if located elsewhere in the brain, be large enough to push on surrounding healthy tissues to an extent necessary to cause a distortion in the shape of the more distant air-filled cavities (and hence more-distant tumors detected this way tended to be fairly large).
Despite its overall usefulness, there were major portions of the brain and other structures of the head that pneumoencephalography was unable to image. This was partially compensated by increased use of angiography as a complementary diagnostic tool, often in an attempt to infer the condition of non-neurovascular pathology from its secondary vascular characteristics. This additional testing was not without risk, though, particularly due to the rudimentary catheterization techniques and deleterious radiocontrast agents of the day. Another drawback of pneumoencephalography was that the risk and discomfort it carried meant that repeat studies were generally avoided, thus making it difficult to assess disease progression over time.
== Current use ==
Modern imaging techniques such as MRI and CT have rendered pneumoencephalography obsolete. Widespread clinical use of diagnostic tools using these newer technologies began in the mid-to-late 1970s. These revolutionized the field of neuroimaging by not only being able to non-invasively examine all parts of the brain and its surrounding tissues, but also by doing so in much greater detail than previously available with plain X-rays, therefore making it possible to directly visualize and precisely localize soft-tissue abnormalities inside the skull. This led to significantly improved patient outcomes while reducing discomfort. Today, pneumoencephalography is limited to the research field and is used under rare circumstances.
== See also ==
Mass effect
History of neuroimaging
Neuroimaging
== References ==
== External links ==
Neuroradiology in the pre CT era – Presentation about historical neuroradiology techniques from the Yale Medical School. Pneumoencephalography discussion begins approximately 21 minutes into the presentation. | Wikipedia/Pneumoencephalography |
Trauma surgery is a surgical specialty that utilizes both operative and non-operative management to treat traumatic injuries, typically in an acute setting. Trauma surgeons generally complete residency training in general surgery and often fellowship training in trauma or surgical critical care. The trauma surgeon is responsible for initially resuscitating and stabilizing and later evaluating and managing the patient. The attending trauma surgeon also leads the trauma team, which typically includes nurses and support staff, as well as resident physicians in teaching hospitals.
== Training ==
Most United States trauma surgeons practice in larger centers and complete a 1- to 2-year trauma-surgery fellowship, which often includes a surgical critical-care fellowship. They may therefore sit for the American Board of Surgery (ABS) certifying examination in surgical critical care.
National surgical boards usually supervise European training programs; they also certify for subspecialization in trauma surgery. An official European trauma surgical examination exists.
Training for trauma surgeons is sometimes difficult to obtain. In the US, the Advanced Trauma Operative Management (ATOM) course and the Advanced Surgical Skills for Exposure in Trauma (ASSET) provide operative trauma training to surgeons and surgeons in training. The Advanced Trauma Life Support course (ATLS) is what most US practitioners who take care of trauma patients are required to take (emergency medicine, surgery, and trauma attending physicians, physician extenders, as well as trainees).
== Responsibilities ==
The broad scope of their surgical critical care training enables trauma surgeons to address most injuries to the neck, chest, abdomen, and extremities. In large parts of Europe, trauma surgeons treat most of the musculoskeletal trauma, whereas injuries to the central nervous system are generally treated by neurosurgeons. In the US and Britain, skeletal injuries are treated by trauma orthopedic surgeons. Facial injuries are often treated by maxillofacial surgeons. Significant variation occurs across hospitals in the degree to which other specialists, such as cardiothoracic surgeons, plastic surgeons, vascular surgeons, and interventional radiologists are involved in treating trauma patients.
Trauma surgeons must be familiar with a large variety of general surgical, thoracic, and vascular procedures and must be able to make complex decisions, often with little time and incomplete information. Proficiency in all aspects of intensive care medicine/critical care is required. Hours are irregular with a considerable amount of night, weekend, and holiday work.
Most patients presenting to trauma centers have multiple injuries involving different organ systems, so the care of such patients often requires a significant number of diagnostic studies and operative procedures. The trauma surgeon is responsible for prioritizing such procedures and for designing the overall treatment plan. This process starts as soon as the patient arrives in the emergency department and continues to the operating room, intensive care unit, and hospital floor. In most settings, patients are evaluated according to a set of predetermined protocols (triage) designed to detect and treat life-threatening conditions as soon as possible. After such conditions have been addressed (or ruled out), nonlife-threatening injuries are addressed.
== Acute care surgery ==
Over the last few decades, a large number of advances in trauma and critical care have led to an increasing frequency of non-operative care for injuries to the neck, chest, and abdomen. Most injuries requiring operative treatment are musculoskeletal. For this reason, part of US trauma surgeons devote at least some of their practice to general surgery. In most American university hospitals and medical centers, a significant portion of the emergency general surgery calls are taken by trauma surgeons. The field combining trauma surgery and emergency general surgery is often called acute care surgery.
== History ==
Dr. George E. Goodfellow is credited as the United States' first civilian trauma surgeon. He opened a medical practice in the silver boom town of Tombstone, Arizona Territory, in November 1880, where he practiced for the next 11 years.
On July 2, 1881, U.S. President Garfield was shot in the abdomen by Charles J. Guiteau. Two days later, a miner was shot outside Tombstone. On July 13, 1881, Goodfellow performed the first recorded laparotomy to treat the miner's gunshot wound. The man had a perforated small intestine, large intestine, and bowel. Goodfellow sutured six holes in the man's organs. Similarly, President Garfield was thought later to have a bullet possibly lodged near his liver, but it could not be found.: M-9 Sixteen doctors attended to Garfield and most probed the wound with their fingers or dirty instruments. Unlike the President, the miner survived.
Goodfellow treated a number of notorious outlaw cowboys in Tombstone, Arizona, during the 1880s, including Curly Bill Brocius. During the gunfight at the O.K. Corral on October 26, 1881, Deputy U.S. Marshal Virgil Earp and his brother Assistant Deputy U.S. Marshal Morgan Earp were both seriously wounded. Goodfellow treated both men's injuries.: 27 Goodfellow treated Virgil Earp again two months later on December 28, 1881, after he was ambushed, removing 3 inches (76 mm) of bone from his humerus and attended to Morgan Earp on March 18, 1882, when he was shot while playing a round of billiards at the Campbell and Hatch Billiard Parlor. Morgan died of his wounds.: 38
Goodfellow once traveled to Bisbee, 30 miles (48 km) from Tombstone, to treat an abdominal gunshot wound. He operated on the patient stretched out on a billiard table. Goodfellow removed a .45-caliber bullet, washed out the cavity with hot water, folded the intestines back into position, stitched the wound closed with silk thread, and ordered the patient to take it to a hard bed for recovery. He wrote about the operation: "I was entirely alone having no skilled assistant of any sort, therefore was compelled to depend for aid upon willing friends who were present—these consisting mostly of hard-handed miners just from their work on account of the fight. The anesthetic was administered by a barber, lamps held, hot water brought, and other assistance rendered by others."
Goodfellow pioneered the use of sterile techniques in treating gunshot wounds, washing the patient's wound and his hands with lye soap or whisky. He became America's leading authority on gunshot wounds and was widely recognized for his skill as a surgeon.
By the late 1950s, mandatory laparotomy had become the standard of care for managing patients with abdominal penetrating trauma. A laparotomy is still the standard procedure for treating abdominal gunshot wounds today.
== In the United Kingdom ==
In the United Kingdom, trauma surgery is now generally considered a subspeciality of general surgery. However, at the Royal London Hospital, which is Britain's busiest major trauma centre and the busiest trauma unit in Europe, their trauma surgeons come from backgrounds in vascular surgery.
Courses in the UK for aspiring trauma surgeons include the advanced trauma life support and Definitive Surgical Trauma Skills courses, both provided by the Royal College of Surgeons.
== See also ==
Transmediastinal gunshot wound
Eastern Association for the Surgery of Trauma, is a major association of trauma surgeons in the US.
== References ==
== External links ==
Anaesthesia Trauma and Critical Care (ATACC)
trauma.org Archived 2019-08-24 at the Wayback Machine a website dedicated to trauma
National Foundation for Trauma Care
| Wikipedia/Trauma_surgery |
Cardiothoracic surgery is the field of medicine involved in surgical treatment of organs inside the thoracic cavity — generally treatment of conditions of the heart (heart disease), lungs (lung disease), and other pleural or mediastinal structures.
In most countries, cardiothoracic surgery is further subspecialized into cardiac surgery (involving the heart and the great vessels) and thoracic surgery (involving the lungs, esophagus, thymus, etc.); the exceptions are the United States, Australia, New Zealand, the United Kingdom, India and some European Union countries such as Portugal.
== Training ==
A cardiac surgery residency typically comprises anywhere from four to six years (or longer) of training to become a fully qualified surgeon. Cardiac surgery training may be combined with thoracic surgery and/or vascular surgery and called cardiovascular (CV) / cardiothoracic (CT) / cardiovascular thoracic (CVT) surgery. Cardiac surgeons may enter a cardiac surgery residency directly from medical school, or first complete a general surgery residency followed by a fellowship. Cardiac surgeons may further sub-specialize cardiac surgery by doing a fellowship in a variety of topics including pediatric cardiac surgery, cardiac transplantation, adult-acquired heart disease, weak heart issues, and many more problems in the heart.
=== Australia and New Zealand ===
The highly competitive Surgical Education and Training (SET) program in Cardiothoracic Surgery is six years in duration, usually commencing several years after completing medical school. Training is administered and supervised via a bi-national (Australia and New Zealand) training program. Multiple examinations take place throughout the course of training, culminating in a final fellowship exam in the final year of training. Upon completion of training, surgeons are awarded a Fellowship of the Royal Australasian College of Surgeons (FRACS), denoting that they are qualified specialists. Trainees having completed a training program in General Surgery and have obtained their FRACS will have the option to complete fellowship training in Cardiothoracic Surgery of four years in duration, subject to college approval. It takes around eight to ten years minimum of post-graduate (post-medical school) training to qualify as a cardiothoracic surgeon. Competition for training places and for public (teaching) hospital places is very high currently, leading to concerns regarding workforce planning in Australia.
=== Canada ===
Historically, cardiac surgeons in Canada completed general surgery followed by a fellowship in CV / CT / CVT. During the 1990s, the Canadian cardiac surgery training programs changed to six-year "direct-entry" programs following medical school. The direct-entry format provides residents with experience related to cardiac surgery they would not receive in a general surgery program (e.g. echocardiography, coronary care unit, cardiac catheterization etc.). Residents in this program will also spend time training in thoracic and vascular surgery. Typically, this is followed by a fellowship in either Adult Cardiac Surgery, Heart Failure/Transplant, Minimally Invasive Cardiac Surgery, Aortic Surgery, Thoracic Surgery, Pediatric Cardiac Surgery or Cardiac ICU. Contemporary Canadian candidates completing general surgery and wishing to pursue cardiac surgery often complete a cardiothoracic surgery fellowship in the United States. The Royal College of Physicians and Surgeons of Canada also provides a three-year cardiac surgery fellowship for qualified general surgeons that is offered at several training sites including the University of Alberta, the University of British Columbia and the University of Toronto.
Thoracic surgery is its own separate 2–3 year fellowship of general or cardiac surgery in Canada.
Cardiac surgery programs in Canada:
University of Alberta – 1 position
University of British Columbia – 1 position
University of Calgary – 1 position
Dalhousie University – 1 position every other year
Université Laval – 1 position every three years
University of Manitoba – 1 position
McGill University – 1 position every three years
McMaster University – 1 position every other year
Université de Montréal – 1 position every three years
University of Ottawa – 1 position
University of Toronto – 1 position
Western University – 1 position
=== United States ===
Cardiac surgery training in the United States is combined with general thoracic surgery and called cardiothoracic surgery or thoracic surgery. A cardiothoracic surgeon in the U.S. is a physician who first completes a general surgery residency (typically 5–7 years), followed by a cardiothoracic surgery fellowship (typically 2–3 years). The cardiothoracic surgery fellowship typically spans two or three years, but certification is based on the number of surgeries performed as the operating surgeon, not the time spent in the program, in addition to passing rigorous board certification tests. Two other pathways to shorten the duration of training have been developed: (1) a combined general-thoracic surgery residency consisting of four years of general surgery training and three years of cardiothoracic training at the same institution and (2) an integrated six-year cardiothoracic residency (in place of the general surgery residency plus cardiothoracic residency), which have each been established at many programs (over 20). Applicants match into the integrated six-year (I-6) programs directly out of medical school, and the application process has been extremely competitive for these positions as there were approximately 160 applicants for 10 spots in the U.S. in 2010. As of May 2013, there are 20 approved programs, which include the following:
Integrated six-year Cardiothoracic Surgery programs in the United States:
Medical College of Wisconsin
Stanford University – two positions
University of North Carolina at Chapel Hill
University of Virginia
Columbia University – two positions
University of Pennsylvania
University of Pittsburgh – two positions
University of Washington
Northwestern University
Mount Sinai Hospital, New York
University of Maryland
University of California, Los Angeles UCLA – two resident positions, one Transplant Fellowship; one Congenital resident position
University of Texas Health Science Center at San Antonio
Medical University of South Carolina
University of Southern California – two positions
University of Rochester
University of California, Davis
Indiana University
University of Kentucky
Emory University
University of Michigan
Yale University
The American Board of Thoracic Surgery offers a special pathway certificate in congenital cardiac surgery which typically requires an additional year of fellowship. This formal certificate is unique because congenital cardiac surgeons in other countries do not have formal evaluation and recognition of pediatric training by a licensing body.
== Cardiac surgery ==
The earliest operations on the pericardium (the sac that surrounds the heart) took place in the 19th century and were performed by Francisco Romero (1801) Dominique Jean Larrey, Henry Dalton, and Daniel Hale Williams. The first surgery on the heart itself was performed by Norwegian surgeon Axel Cappelen on 4 September 1895 at Rikshospitalet in Kristiania, now Oslo. He ligated a bleeding coronary artery in a 24-year-old man who had been stabbed in the left axilla and was in deep shock upon arrival. Access was through a left thoracotomy. The patient awoke and seemed fine for 24 hours, but became ill with increasing temperature and he ultimately died from what the post mortem proved to be mediastinitis on the third postoperative day. The first successful surgery of the heart, performed without any complications, was by Ludwig Rehn of Frankfurt, Germany, who repaired a stab wound to the right ventricle on September 7, 1896.
Surgery in great vessels (aortic coarctation repair, Blalock-Taussig shunt creation, closure of patent ductus arteriosus) became common after the turn of the century and falls in the domain of cardiac surgery, but technically cannot be considered heart surgery. One of the more commonly known cardiac surgery procedures is the coronary artery bypass graft (CABG), also known as "bypass surgery."
=== Early approaches to heart malformations ===
In 1925 operations on the heart valves were unknown. Henry Souttar operated successfully on a young woman with mitral stenosis. He made an opening in the appendage of the left atrium and inserted a finger into this chamber in order to palpate and explore the damaged mitral valve. The patient survived for several years but Souttar's physician colleagues at that time decided the procedure was not justified and he could not continue.
Cardiac surgery changed significantly after World War II. In 1948 four surgeons carried out successful operations for mitral stenosis resulting from rheumatic fever. Horace Smithy (1914–1948) revived an operation due to Dr Dwight Harken of the Peter Bent Brigham Hospital using a punch to remove a portion of the mitral valve. Charles Bailey (1910–1993) at the Hahnemann Hospital, Philadelphia, Dwight Harken in Boston and Russell Brock at Guy's Hospital all adopted Souttar's method. All these men started work independently of each other, within a few months. This time Souttar's technique was widely adopted although there were modifications.
In 1947 Thomas Holmes Sellors (1902–1987) of the Middlesex Hospital operated on a Fallot's Tetralogy patient with pulmonary stenosis and successfully divided the stenosed pulmonary valve. In 1948, Russell Brock, probably unaware of Sellor's work, used a specially designed dilator in three cases of pulmonary stenosis. Later in 1948 he designed a punch to resect the infundibular muscle stenosis which is often associated with Fallot's Tetralogy. Many thousands of these "blind" operations were performed until the introduction of heart bypass made direct surgery on valves possible.
=== Open heart surgery ===
Open heart surgery is a procedure in which the patient's heart is opened and surgery is performed on the internal structures of the heart. It was discovered by Wilfred G. Bigelow of the University of Toronto that the repair of intracardiac pathologies was better done with a bloodless and motionless environment, which means that the heart should be stopped and drained of blood. The first successful intracardiac correction of a congenital heart defect using hypothermia was performed by C. Walton Lillehei and F. John Lewis at the University of Minnesota on September 2, 1952. The following year, Soviet surgeon Aleksandr Aleksandrovich Vishnevskiy conducted the first cardiac surgery under local anesthesia.
Surgeons realized the limitations of hypothermia – complex intracardiac repairs take more time and the patient needs blood flow to the body, particularly to the brain. The patient needs the function of the heart and lungs provided by an artificial method, hence the term cardiopulmonary bypass. John Heysham Gibbon at Jefferson Medical School in Philadelphia reported in 1953 the first successful use of extracorporeal circulation by means of an oxygenator, but he abandoned the method, disappointed by subsequent failures. In 1954 Lillehei realized a successful series of operations with the controlled cross-circulation technique in which the patient's mother or father was used as a 'heart-lung machine'. John W. Kirklin at the Mayo Clinic in Rochester, Minnesota started using a Gibbon type pump-oxygenator in a series of successful operations, and was soon followed by surgeons in various parts of the world.
Nazih Zuhdi performed the first total intentional hemodilution open heart surgery on Terry Gene Nix, age 7, on February 25, 1960, at Mercy Hospital, Oklahoma City, OK. The operation was a success; however, Nix died three years later in 1963. In March, 1961, Zuhdi, Carey, and Greer, performed open heart surgery on a child, age 3+1⁄2, using the total intentional hemodilution machine. In 1985 Zuhdi performed Oklahoma's first successful heart transplant on Nancy Rogers at Baptist Hospital. The transplant was successful, but Rogers, who had cancer, died from an infection 54 days after surgery.
=== Modern beating-heart surgery ===
Since the 1990s, surgeons have begun to perform "off-pump bypass surgery" – coronary artery bypass surgery without the aforementioned cardiopulmonary bypass. In these operations, the heart is beating during surgery, but is stabilized to provide an almost still work area in which to connect the conduit vessel that bypasses the blockage; in the U.S., most conduit vessels are harvested endoscopically, using a technique known as endoscopic vessel harvesting (EVH).
Some researchers believe that the off-pump approach results in fewer post-operative complications, such as postperfusion syndrome, and better overall results. Study results are controversial as of 2007, the surgeon's preference and hospital results still play a major role.
=== Minimally invasive surgery ===
A new form of heart surgery that has grown in popularity is robot-assisted heart surgery. This is where a machine is used to perform surgery while being controlled by the heart surgeon. The main advantage to this is the size of the incision made in the patient. Instead of an incision being at least big enough for the surgeon to put his hands inside, it does not have to be bigger than "pencil-sized" holes for the robot's much smaller "hands" to enter a surgical patient's body.
In September 2024, the first successful fully robotic heart transplant took place at King Faisal Specialist Hospital and Research Centre in Riyadh, led by surgeon Feras Khaliel, head of the hospital's cardiac surgery and director of its Robotics and Minimally Invasive Surgery Program. In December 2024, the first robotic surgery for a combined robotic aortic valve replacement (AVR) and coronary artery bypass grafting (CABG) was successfully performed through one small incision at West Virginia University, led by surgeon Vinay Badhwar, who is the executive chair of the WVU Heart and Vascular Institute and a vice president of the Society of Thoracic Surgeons.
=== Pediatric cardiovascular surgery ===
Pediatric cardiovascular surgery is surgery of the heart of children. The first operations to repair cardio-vascular defects in children were performed by Clarence Crafoord in Sweden when he repaired coarctation of the aorta in a 12-year-old boy. The first attempts to palliate congenital heart disease were performed by Alfred Blalock with the assistance of William Longmire, Denton Cooley, and Blalock's experienced technician, Vivien Thomas in 1944 at Johns Hopkins Hospital. Techniques for repair of congenital heart defects without the use of a bypass machine were developed in the late 1940s and early 1950s. Among them was an open repair of an atrial septal defect using hypothermia, inflow occlusion and direct vision in a 5-year-old child performed in 1952 by Lewis and Lillihei. Lillihei used cross-circulation between a boy and his father to maintain perfusion while performing a direct repair of a ventricular septal defect in a 4-year-old child in 1954. He continued to use cross-circulation and performed the first corrections of tetralogy of Fallot and presented those results in 1955 at the American Surgical Association. In the long-run, pediatric cardiovascular surgery would rely on the cardiopulmonary bypass machine developed by Gibbon and Lillehei as noted above.
=== Risks of cardiac surgery ===
The development of cardiac surgery and cardiopulmonary bypass techniques has reduced the mortality rates of these surgeries to relatively low ranks. For instance, repairs of congenital heart defects are currently estimated to have 4–6% mortality rates. A major concern with cardiac surgery is the incidence of neurological damage. Stroke occurs in 5% of all people undergoing cardiac surgery, and is higher in patients at risk for stroke. A more subtle constellation of neurocognitive deficits attributed to cardiopulmonary bypass is known as postperfusion syndrome, sometimes called "pumphead". The symptoms of postperfusion syndrome were initially felt to be permanent, but were shown to be transient with no permanent neurological impairment.
To assess the performance of surgical units and individual surgeons, a popular risk model has been created called the EuroSCORE. This takes a number of health factors from a patient and using precalculated logistic regression coefficients attempts to give a percentage chance of survival to discharge. Within the UK this EuroSCORE was used to give a breakdown of all the centres for cardiothoracic surgery and to give some indication of whether the units and their individual surgeons performed within an acceptable range. The results are available on the CQC website. The precise methodology used has however not been published to date nor has the raw data on which the results are based.
Infection represents the primary non-cardiac complication from cardiothoracic surgery. Infections include mediastinitis, infectious myo- or pericarditis, endocarditis, cardiac device infection, pneumonia, empyema, and bloodstream infections. Clostridioides difficile colitis can develop when prophylactic or post-operative antibiotics are used.
Post-operative patients of cardiothoracic surgery are at risk of nausea, vomiting, dysphagia, and aspiration pneumonia.
== Thoracic surgery ==
A pleurectomy is a surgical procedure in which part of the pleura is removed. It is sometimes used in the treatment of pneumothorax and mesothelioma. In case of pneumothorax, only the apical and the diaphragmatic portions of the parietal pleura are removed.
=== Lung volume reduction surgery ===
Lung volume reduction surgery, or LVRS, can improve the quality of life for certain patients with COPD of emphysematous type, when other treatment options are not enough. Parts of the lung that are particularly damaged by emphysema are removed, allowing the remaining, relatively good lung to expand and work more efficiently. The beneficial effects are correlated with the achieved reduction in residual volume. Conventional LVRS involves resection of the most severely affected areas of emphysematous, non-bullous lung (aim is for 20–30%). This is a surgical option involving a mini-thoracotomy for patients in end stage COPD due to underlying emphysema, and can improve lung elastic recoil as well as diaphragmatic function.
The National Emphysema Treatment Trial (NETT) was a large multicentre study (N = 1218) comparing LVRS with non-surgical treatment. Results suggested that there was no overall survival advantage in the LVRS group, except for mainly upper-lobe emphysema + poor exercise capacity, and significant improvements were seen in exercise capacity in the LVRS group. Later studies have shown a wider scope of treatment with better outcomes.
Possible complications of LVRS include prolonged air leak (mean duration post surgery until all chest tubes removed is 10.9 ± 8.0 days.
In people who have a predominantly upper lobe emphysema, lung volume reduction surgery could result in better health status and lung function, though it also increases the risk of early mortality and adverse events.
LVRS is used widely in Europe, though its application in the United States is mostly experimental.
A less invasive treatment is available as a bronchoscopic lung volume reduction procedure.
=== Lung cancer surgery ===
Not all lung cancers are suitable for surgery. The stage, location and cell type are important limiting factors. In addition, people who are very ill with a poor performance status or who have inadequate pulmonary reserve would be unlikely to survive. Even with careful selection, the overall operative death rate is about 4.4%.
In non-small cell lung cancer staging, stages IA, IB, IIA, and IIB are suitable for surgical resection.
Pulmonary reserve is measured by spirometry. If there is no evidence of undue shortness of breath or diffuse parenchymal lung disease, and the FEV1 exceeds 2 litres or 80% of predicted, the person is fit for pneumonectomy. If the FEV1 exceeds 1.5 litres, the patient is fit for lobectomy.
There is weak evidence to indicate that participation in exercise programs before lung cancer surgery may reduce the risk of complications after surgery.
==== Complications ====
A prolonged air leak (PAL) can occur in 8–25% of people following lung cancer surgery. This complication delays chest tube removal and is associated with an increased length of hospital stay following a lung resection (lung cancer surgery). The use of surgical sealants may reduce the incidence of prolonged air leaks, however, this intervention alone has not been shown to results in a decreased length of hospital stay following lung cancer surgery.
There is no strong evidence to support using non-invasive positive pressure ventilation following lung cancer surgery to reduce pulmonary complications.
==== Types ====
Lobectomy (removal of a lobe of the lung)
Sublobar resection (removal of part of lobe of the lung)
Segmentectomy (removal of an anatomic division of a particular lobe of the lung)
Pneumonectomy (removal of an entire lung)
Wedge resection
Sleeve/bronchoplastic resection (removal of an associated tubular section of the associated main bronchial passage during lobectomy with subsequent reconstruction of the bronchial passage)
VATS lobectomy (minimally invasive approach to lobectomy that may allow for diminished pain, quicker return to full activity, and diminished hospital costs)
esophagectomy (removal of the esophagus)
== See also ==
Annals of Thoracic Surgery
European Journal of Cardio-Thoracic Surgery
Journal of Thoracic and Cardiovascular Surgery
== References ==
== External links ==
The Cardiothoracic Surgery Network
The Society of Thoracic Surgeons
American Association for Thoracic Surgery
International Society for Minimally Invasive Cardiothoracic Surgery | Wikipedia/Cardiothoracic_surgery |
Endocrine surgery is a surgical sub-speciality focusing on surgery of the endocrine glands, including the thyroid gland, the parathyroid glands, the adrenal glands, glands of the endocrine pancreas, and some neuroendocrine glands.
== Types ==
=== Thyroid surgery ===
Surgery of the thyroid gland constitutes the bulk of endocrine surgical procedures worldwide. This may be done for a variety of conditions, help ranging from benign multinodular goiter to thyroid cancer. In the United Kingdom it was developed as a separate specialty from general surgery by Richard Welbourne and John Lynn, surgeons at what was then the 'Royal Postgraduate Medical School' and is now the Hammersmith Hospital and contains the Department of Thyroid and Endocrine Surgery staffed by consultant surgeons Professor Fausto Palazzo, Professor Neil Tolley and Miss Aimee Di Marco.
Operations involve removal of the thyroid gland (thyroidectomy) either as a part of the gland (lobectomy or hemithyroidectomy), or the whole gland (total thyroidectomy). Incomplete resections (sub-total or near total thyroidectomy) are also infrequently performed, but are disfavored by most surgeons.
=== Parathyroid surgery ===
Removal of the parathyroid gland(s) is referred to as parathyroidectomy and is most commonly performed for primary hyperparathyroidism. Parathyroidectomy is also performed to treat tertiary hyperparathyroidism arising from chronic kidney failure.
=== Adrenal surgery ===
Adrenalectomy, the surgical removal of the adrenal gland, is performed to treat conditions including Conn syndrome, pheochromocytoma, and adreno-cortical cancer.
=== Pancreatic surgery ===
Diseases of the endocrine pancreas occur very infrequently; these include insulinomas, gastrinomas etc. Surgery for these conditions range from simple tumor enucleation to more larger resections.
== Development ==
Endocrine surgery is generally well developed. Endocrine surgery has developed as a sub-specialty surgical category because of the technical nature of these operations and the associated risks of operating in the neck. In Surgery: Basic Science and Clinical Evidence, the book the efficacy prior research:
Surgeons and physicians have advanced endocrine surgery by careful description of unusual patients and families with endocrine syndromes...Surgeons have also improved techniques for preparation for surgery and methods...
In the 1970s, a specialty training program at Hammersmith Hospital was the primary location for early work in training a large number of surgeons. It is well established that complications are much less common if performed by surgeons who do at least 100 thyroid operations per year. In the United Kingdom most thyroid surgery is performed by surgeons doing less than 20 thyroid operations per year. Permanent damage to both voice box nerves is an extreme rarity and needs in most cases a permanent tracheostomy. Data on the outcomes of all surgeons performing endocrine surgery in the UK is publicly available via the 'British Association of Endocrine and Thyroid Surgeons' website.
== Technique ==
=== Thyroid surgery ===
Some surgical teams leave wound drains in place after surgery to the thyroid gland. There is no strong evidence that wound drains improve outcomes following surgery and there is low-quality evidence that wound drains increase the length of time a person stays in the hospital following thyroid surgery.
== References == | Wikipedia/Endocrine_surgery |
Ancient Roman surgical practices developed from Greek techniques. Roman surgeons and doctors usually learned through apprenticeships or studying. Ancient Roman doctors such as Galen and Celsus described Roman surgical techniques in their medical literature, such as De Medicina. These methods encompassed modern oral surgery, cosmetic surgery, sutures, ligatures, amputations, tonsillectomies, mastectomies, cataract surgeries, lithotomies, hernia repair, gynecology, neurosurgery, and others. Surgery was a rare practice, as it was dangerous and often had fatal results. To perform these procedures, they used tools such as specula, catheters, enemas, bone levers, osteotomes, phlebotomes, probes, curettes, bone drills, bone forceps, cupping vessels, knives, scalpels, scissors, and spathas.
== History ==
Roman medical practices, including surgery, were borrowed from the Greeks, with many Roman surgeons coming from Greece. In the 2nd century CE, Galen, a Greek physician advanced Roman surgical knowledge by combining Greek and Roman medical knowledge.
Aulus Cornelius Celsus was a Roman encyclopedist notable for his work De Medicina. The text describes operations such as tonsillectomies and cataract surgery. Alongside these surgeons and doctors, Soranus of Ephesus introduced technology such as the birthing chair.
Surgeons were attracted to ancient Rome due to the potential for success and wealth. Doctors learned through private courses from other doctors, their relatives, in the city of Alexandria, or through self-teaching.
Charlatans and malpractice were common in ancient Rome, as any individual, regardless of their training or qualifications could practice medicine. This resulted in the general public becoming distrustful of doctors. Higher-quality surgeons often served the upper classes.
According to Celsus the perfect surgeon would be a younger man with strong and steady hands, sharp eyes, a strong spirit, and a strong sense of empathy and compassion. Surgery was rare in ancient Rome, it was rare for a patient to recover, and the procedure was dangerous. Most surgical procedures were limited to skin lacerations or amputations.
== Tools ==
=== Cupping vessels ===
Cupping vessels were round suction cups usually made of bronze or horns. They were made of different materials and had different designs and purposes. Bronze vessels were also used. They usually contained burning lint and were closed at one end and open at the other. Horn cups had small foramens at the ends and cavities closed off with wax. Cups had holes that were placed over injured areas and sweat glands. Following this, the tool would be used to draw out pus and "vicious humor." Cupping vessels were also used to aid bloodletting. First, heat was applied to the area to warm it up. Then, the skin was cut with a scalpel, following this, the cup would be fastened to the area to draw blood. Larger cupping devices were used for larger parts of the body, such as the back. Smaller cups were used for smaller parts of the body, such as the arms or the neck.
=== Chisels and raspatories ===
Raspatories, also called rugines, were made of a blade fixed to a shaft at a right angle. They were used to treat bone fractures. In this procedure, the wound was filled with black ointment, then a linen rag filled with oil, and finally, it was used to scrape the bones. They would make incisions into and remove the skin to hold it or the bones in place. These tools were made of steel and covered in spiral decorations. Chisels were used during surgeries on teeth or bones. One kind of chisel, known as the lenticular, was used in neurosurgery. It was made of a rounded smooth knob, which was inserted into the open cranium or meninges. Hammers and blocks would be used alongside the chisels. To amputate a limb, it was placed on a block, then a chisel would be used to cut it off. Lithorites were kinds of chisels designed to remove calculus from the bladder. They would be struck through the calculus, eventually breaking it.
=== Drills and levers ===
In ancient Rome, there were two kinds of surgical drills. One type was driven by a leather cord, the other type used a guard and a collar. This was designed to stop the instrument from penetrating too deeply into the bone. It was thought that this would minimize the risk of damage to the brain and meninges. Drills would also be frequently dipped in water to reduce heat, which was supposed to limit the danger of the surgery. The primary purpose of a drill was to remove large diseased portions of skulls. For example, drills were used to remove weapons lodged into the skull. Small drills were used to perforate the nasal bone. Which would create a "passage for the fluid or matter to the nose," thus treating the fistula. Drills were shaped like wine corkscrews. Bone levers were ancient steel tools shaped like rods with flattened and curved tips resembling stone cutters. They were used to level fractures, extract teeth, and realign broken bones.
=== Saws and trephines ===
Saws were primarily used to cut through bone. In one procedure for treating gangrene, a band was used to retract the skin to prevent the saw from tearing through the flesh. Then the saw could amputate the infected limb. Trephines were in the form of a circular saw. Doctors believed it needed to be frequently removed from the skull and placed in cold water during an operation. This was designed to alleviate the "heat" in the "bone." Trephines were used to saw the bone to the meninges thus treating injuries to young people's heads.
=== Forceps ===
Bone forceps were used to extract injured bones from the body. They were common tools, despite the Roman preference for using fingers instead of tools to fix bone injuries. Bone forceps were primarily used for instances in which pieces of bone were too small for fingers to remove. They would also cut off broken parts of the skull, or even drill through to the brain. Another kind of forceps, called Epilation forceps was primarily used to remove hair. Polypus forceps were used to remove polyps or tumors from the nose.
Tumor vulsellums, also known as Myzons, were toothed forceps that were used to remove tumors. In one procedure, they were used to "seize" the clitoris and cut off the tumor. To amputate the uvula, they used a tool known as uvula forceps to crush it and prevent bleeding. Following this, the vulsellum was used to twist it until a torsion was created. Then the uvula was cut off. Forceps could also be used to apply corrosive substances to the uvula to destroy it. These tools were made of two crossing branches which were fixed to the middle of the tool with a rivet.
Pharyngeal forceps were made of fishbones and they were used to remove entities from the pharynx. Varix extractors were a type of forceps used to extract varicose veins, which is a medical condition characterized by abnormally large veins. This procedure would be conducted by mapping out the locations of the afflicted veins, then the skin would be held and divided. Following this the extractor would hold and cut the skin, allowing for the veins to be removed. Tooth and stump forceps were used to extract teeth. This operation, and hence these tools were rarely employed due to how dangerous the operation was.
=== Probes and curettes ===
Probes and curettes were used to mix and apply medication to the skin or to lift tissue. When pushed into the fistula they were used to measure their dimensions. Roman probes had parts known as the nucleus. The nucleus was used primarily to apply medication. Sodium hydroxide was applied to the nucleus, which would then be used to burn out the eyelid. Wax was warmed on the nucleus of the probe, and then it was used to apply pomade to the face.
One type of probe consisted of a rod rounded off at one end. Another type was slender with enlarged ends. It was used to burn tissue and for organ transplantation. The largest probes were known as spathomeles. These tools were very common, with almost every ancient Roman medical writer mentioning them. Cyathiscomeles were types of spathomeles with large nuclei and a plain or fluted shaft overlaid with silver. Screw probes were designed to wrap around wool. Rasping probes were used to curette granular lids. Another kind of probe, called styli or styloid probes was used to puncture bladders. Grooved directors were instruments used to make incisions into the skin. These tools were usually made out of boxwood. Eyed probes were made from a rod of tin, and they were used to treat fistula. Bifurcated probes and retractors were used to extract weapons buried in the flesh.
Ear probes, also known as ear specilla, were made of a narrow scoop and an enlargement at each end. These tools had no nucleus or tip. They could also be used as curettes. Their primary purposes was cutting the interior of the chalazion and applying medications or liquids. The sharp end of the ear probe was used to treat fistula. A large ball of wood would be saturated with water and wrapped around the probe. Once squeezed, the liquid would drip onto the ear canal, which was thought to extract entities from the canal. A larger version of the ear probe, possibly with a slight enlargement at the ends, was used for treating wounds. This would be done through an incision behind the ear, following this the ear scoop was used to remove the objects. A common symptom of this procedure was dullness of hearing, often preceded by persistent headaches. Scabs and ulcers were other common side effects. To treat this, they were typically fomented with warm water, or verdigris drenched in honey, leek juice, and niter in mead. Following this, water was used to wash the ears. This tool could also be used as a curette.
=== Scalpels ===
Scalpels were tools made of a steel blade and a bronze handle. The bronze handle could be round, square, horizontal, or trapezoidal. Some scalpels had handles made of copper alloys with grips, dissectors, and an iron blade. This design was used to maximize efficiency. A slot was placed at one of the ends to connect to the steel blade. On the other end of the handle was connected to a leaf-shaped spatula. This spatula functioned as a blunt tool for dissection. A groove or a long and narrow indentation was located near the end of the handle. Alternatively, a cylindrical roll perforated with a hole could be used instead. Threads, wires, rolls, and perforations were used to attach the blade to the handle. Handles would have been decorated with moldings or inlay. The blade was made detachable to allow for cleaning and the usage of several blades. There were a variety of kinds of blades. One was straight, sharp, and pointed. Another was curved with sharp or blunt points. Blades were secured to the handles using simply sockets or key-hole shaped sockets using an alloy known as solder. The scalpel had great flexibility and performed a wide variety of functions, such as tearing away muscle and tissue during amputation, severing the umbilical cord, removing nasal polyps, mastectomies, making incisions, cutting through bone, and hernia repair.
=== Specula ===
The rectal speculum also called the catopter was a dual-bladed surgical instrument in ancient Rome. Feminine specula were used to dilate vaginas. These specula were sized according to the age of the patient, and it was ensured that it was not larger than the urethra. To open the vagina, an assistant would turn a screw, expanding the blades, and therefore the vagina. Rectal specula were used to examine the bowels and its damaged parts. In the Republic these tools were made of copper and tin, by the Empire these tools began to be made of silver, as this material was less brittle. Specula also had rounded mirrors with handles. The surgeon, or another person, usually a slave would hold these mirrors.
=== Spoon of Diocles ===
The Spoon of Diocles also called the Dioclean kyathiskos was an ancient medical tool allegedly designed by Diocles of Carystus for removing arrowheads. It was a long bronze or iron tool with two hooks ending a curved scoop with a hole and a perforation. This tool would be pushed under and then between the arrow and the flesh. The head of the arrow would be caught in the hole, and the scoops would cover the barbs. Thus, when the arrow was dragged out the flesh would not be pierced. This instrument may have not existed. It is only mentioned by Celsus, who was a Roman physician, and no other writers.
=== Catheters ===
Catheters were also inserted into the bladder to treat urinary tract infections, ureteral stones, prostate cancer, bladder stones, sexually transmitted infections, painful urination, and difficulty urinating. The size and shape of the catheters depended on the gender and size of the individual. Bladders were drained through the urethra using an S-shaped catheter. Another procedure involved injecting a piece of thread with wool wrapped around it into the pipe of the tool. Then it was dipped in oil and used to make an incision into the perineum.
=== Strigils ===
This tool was used for scraping off dirt, perspiration, and oil to cleanse the body. The strigil was most commonly used by male athletes, although in other cultures such as the Etruscans it was used by a wider variety of people. They could also be used as burial goods and these tools are commonly depicted on works of art. It generally consisted of a curved metal blade, and a metal handle. Other materials that could be used included bronze, iron, and reeds.
=== Knives and needles ===
Another kind of knife, known as the polypus knife, was sharply pointed and shaped like a myrtle leaf. The knife was used to cut around tumors. To make an incision between the anus and the testicles a knife known as the lithotomy knife was used. The uvula knife was designed to perform operations on the throat and the uvula. There is little information on its shape and characteristics. Tonsil knives were used to remove the tonsil from mouths. To treat pterygium it was raised with a sharp hook, then a needle with a flaxen thread and horsehair was passed under it. The horsehair was used to saw off the pterygium and a scalpel was used to sever the base of it. Alternatively, the pterygium knife was a kind of knife used to cure pterygium. It was used to separate the adhesion to the sclerotic. This tool was narrow and sharply pointed.
=== Hooks ===
Obstetrical hooks may have existed in ancient Rome. These hooks were smooth and had short points, which were inserted into the ears, eyes, mouths, and forehead to extract children. Sharp hooks were used to hold open incisions, removing tissue, fixing and retracting wounds, raising blood vessels, removing tonsils, transfixing the pterygium, and for dissection. Blunt hooks were used to stretch adhesions near the eye and to pierce lips. Traction hooks were used to remove the fetus during especially tough labor. These hooks were smooth and round, with a short point. Once the head presented itself, the hook was inserted into the area and then used to extract the child. This procedure needed to execute carefully and gently. If it was not then there was an increased risk of death. It was common practice to use two hooks at once in these procedures. Another kind of hook, known as a decapitator, was used to decapitate the fetus during an abortion.
=== Other tools ===
In ancient Rome saws could be used to amputate limbs for surgical purposes. Osteotomes were used to cut away at bone and remove membranes. Thigh tourniquets would stop bleeding and prevent the venom from spreading. Another common tool was bronze or iron cross-bladed scissors. During surgeries spatulas could also be used. Although they were primarily used to produce and apply medicine. Ancient Roman surgical tools called phlebotomes were used in operations known as phlebotomies. This tool is one of the most commonly mentioned tools in Ancient Roman medical literature. Despite this, there are no detailed descriptions of the phlebotome. This likely stems from the commonality of the instrument. Due to its popularity, doctors and writers assumed all readers would already be familiar with its appearance and usage. Hemispathions were used to divide the fistula. Syringes in ancient Rome had a variety of uses. Nasal syringes were made of two bronze or horn pipes that were used to inject liquids into the nostrils. Ear syringes were also common tools. They were used to remove unhealthy substances from the ears, and clean the ears, the bladder, the vagina, and the foreskin. Cannulae were used to heal ascites and empyema. This was done by using the bronze cannulae to make an incision into the abdomen and the peritoneum. Cauteries were common ancient surgical tools with a variety of types. Cautery knives were used to remove cancers such as malignant polyps as well as hydroceles. Cauteries could also remove eschars in the spleen, and hernias. It was also used to treat hemorrhoids, diseases of the liver, and trichiasis. The lithotomy scoop was a long and slender semicircular tool used to extract calculi. Enemas were usually made of long silver tubes with perforations attached to a pig's bladder. This bladder was filled with horse milk and closed with a cord. To treat dysentery, enemas were injected into the body's orifices, such as vaginas, bladders, or uteruses. In this operation, cannulae were inserted into the body. These cannulae had circles of small holes to prevent ascariasis, a disease caused by a parasitic roundworm.
== Techniques ==
=== Abortion ===
There were surgical procedures for abortion in ancient Rome, but they were rarely used, and most abortions were conducted using herbs or other drugs. When surgery was used, it involved the use of surgical instruments to penetrate the mother. Usually this procedure ended in the death of both the fetus and the mother. Soranus of Ephesus wrote that purging, carrying heavy weights, and the injection of olive oil into the vagina or uterus, were all procedures used to carry out abortions.
=== Amputations and dissections ===
Amputations were used to treat gangrene. Ancient Roman surgeons utilized tools known as "blunt dissectors" to expose "vessels." Blunt dissectors were also involved in another procedure designed to treat headaches and ophthalmia. This operation began by shaving the patient's hair off. Then, a warm headband or fomentation was placed around their neck. Following this, ink was used to map the "vessels." The surgeon would then proceed to use their fingers to stretch the skin, and then an assistant would make an incision. To finish the procedure, hooks and dissectors were used to expose the "vessels." Blunt dissectors were usually leaf-shaped, and possibly with hexagonal handles. Another kind of dissector was curved dissectors. They were used to dissect lips that had been incised with a hook. One of these dissectors, which was stored in the National Archaeological Museum in France, was made of an ornamented handle with a small hook at one end. On the other was a leaf-shaped dissector.
=== Bloodletting ===
Bloodletting or a phlebotomy was a common practice in ancient Rome. It was common for surgeons to use a tool known as the phlebotome or the katias to make an incision into another point, which would cause the wound to bleed at another point. Another process involved putting a burning piece of cloth into the patient's mouth to draw out blood. Alternatively, leeches could be used. Ear scoops would be pressed on the proximal end of the vein. This would obstruct the blood flow, which would allow the phlebotome to be used to discharge blood.
=== Caesarean section ===
During a Roman Caesarean section the doctors would make an incision into the abdomen and uterus of the mother. Following this, the baby was removed. This practice could also be conducted on dead mothers to remove the babies from their corpses. It was rare for doctors to perform this operation, as it bore a high mortality rate. According to Roman religion the god Asclepius was born by a Caesarian section. Roman historians Suetonius and Pliny the Elder also record Julius Caesar as being born through a Caesarian section. The veracity of these claims is debated.
=== Cataract surgery ===
Cataract surgery is a surgery in which cataracts are removed. This kind of surgery has been practiced since 29 CE in Ancient Rome. According to Celsus' description of cataract surgery, surgeons would use their right hand to perform on the left eye, and vice versa. During the procedure a needle was inserted between the pupil and the temple until it "meets resistance." Then, the surgeon would rotate the needle until the cataract had been pushed beneath the pupil. Following the cataract surgery, the patient would be treated with "soothing Medicants" and wool soaked in the white of the egg. The patient would also exclusively drink water and abstain from solid food until they no longer had an inflammation, which was a side effect of the surgery.
=== Cosmetic surgery ===
Modern cosmetic surgery has origins in the ancient Greco-Roman world. Roman surgeons were capable of repairing damaged ears, noses, and lips. Celsus discussed rhinoplasty techniques in his De Medicina. Ancient rhinoplasty involved the grafting of a new nose onto the old one. Burns were treated using vinegar, ashes, cork, bran, or honey. To treat both, skin grafting was used. Galen, alongside Celsus, described the use of cheek reconstruction to heal facial injuries.
=== Hernia treatment ===
Hernia repair was done using trusses and bandages. Roman surgeons would conduct an operation designed to treat hernia. Usually, it was only used to treat small hernias belonging to young patients. It consisted of an incision into the scrotum. A tool known as the crow bill or the corvus was used to open the scrotum and cure the hernia. Another process involved using two blocks of wood to clamp the hemiscrotum, causing the sac to be inflamed, thus reducing its size. It also could be treated by removing the testicles and ligating the scrotum. Ligatures could also be used during these operations to avoid bleeding. The ancient Romans had treatments for umbilical hernia, a medical condition in which the abdominal wall behind the navel is damaged. Before this procedure, the patient was laid on their back to cause the hernia to fall back into the abdomen. Afterwards the navel was placed between two rods with their ends tied together, then a needle was placed inside of the protrusion.
=== Lithotomy ===
The ancient Romans practiced lithotomy, a surgical procedure to remove calculi. Usually, they were only conducted on individuals younger than 14. This was because the more developed prostate of older people enhanced the difficulty of the operation. One way this procedure could be practiced is by cutting through the bladder until the surgeon reached the perineum. An assistant held the patient in a lithotomy position, exposing their perineum. Two fingers were placed into the patient's rectum and against the perineum. Another procedure involved the usage of a scoop at the end of a probe to remove objects such as stones or beans and kidney stones.
=== Neurosurgery ===
Ancient Roman doctors were capable of performing neurosurgery on depressed skull fractures. Celsus believed that this surgery should be conducted with as little bone removed as possible. Galen disagreed, he wrote that doctors should elevate the bones and the bone fragments using forceps. During this operation a hole was drilled into the skull. Roman doctors believed this would cure headaches and relieve pressure. Flat chisels were used to cut away at overlying edges, and trepans were used to carve holes into interlocking bones.
=== Sutures, ligatures, and contractions ===
Celsus describes the ligature technique for treating hemorrhoids. He also mentions that after the surgery patients suffered from urinary retention, which is the inability to fully empty the bladder. Galen believed that surgeons should choose to amputate, instead of sawing into healthy bones. He also wrote that to stop bleeding, pressure should be used instead of ligatures. Surgical techniques like tracheal intubation and tracheotomy date back to Ancient Rome. The ancient Roman writer Aulus Gellius described a technique that functioned similarly to bariatric surgery. Which is conducted to reduce the weight of obese individuals. In this technique the surgeon would forcefully contract the stomach, thus limiting the passage of food. Catgut sutures were used by the ancient Romans as early as the 2nd century CE. They also used sutures with metallic hooks. Celsus discusses other kinds of suturing techniques in his medical literature. He wrote that the wounds were to be stitched up. Roman doctors used linen, wool, silk, hair, and clips to seal wounds.
=== Tonsillectomies and mastectomies ===
The ancient Romans practiced tonsillectomies. Roman surgeons would use their fingers or a blunt hook to separate the tissue by the tonsils. Vinger mouthwash was used to induce hematopoiesis, or the stable production of blood cells. Following the surgery, the tonsils were cut out. It was common for patients to profusely bleed following the procedure. Roman surgeons usually would also remove the vulva. To treat breast cancer, the Romans had an operation similar to a mastectomy. It would remove the pectoral muscles of the sufferer. Galen wrote that doctors should cut through healthy tissue around the infected tissue, ensuring that all cancerous material was removed. This operation could also be used as a punishment. For example, Agatha of Sicily was a Christian saint who had her breasts cut off.
=== Tooth extraction ===
It is unclear which Roman profession or professions would have performed dentistry. There may have been medical specialists trained to perform dental procedures, it is also possible that dentistry was practiced as a subset of other professions, such as barbery. Tooth extraction is an oral surgical procedure conducted to remove teeth. In ancient Rome, it may have been practiced by specialists who were not associated with any other medical professionals in ancient Rome. This practice required teeth to be extracted softly to avert the danger involved. This danger also resulted in the practice becoming rare. Ancient literature describes another process dedicated to extracting teeth. In this process, the tooth would be grabbed and rocked until it could be removed with hands. Another practice involved cutting the gum and bone surrounding a tooth and then extracting it. Celsus recommended that physicians should also extract the bone near the teeth and that they should refuse to extract children's teeth unless they were preventing adult teeth from growing.
=== Other techniques ===
The ancient surgeon Dioscorides used Mandragora offcinarum as a painkiller during surgery. Other substances were used, such as opium, henbane, wine, belladonna, and alcohol. Anal fistula were treated by passing probes through the anus, then once it was drawn out, a linen thread was placed into it. Following this the ends of the linen were tied to grip the skin by the fistula. To treat stab wounds in which the intestines fell out of the body, the surgeon would first examine the injuries to the intestines and their color. The large intestine was sutured, and if either intestine was pallid, black, or livid the patient was laid on their back with their hips raised. If the wound was too narrow to allow for an easy replacement of the intestines, the surgeon would cut it until it was "sufficiently wide." If the intestines were too dry, they were coated in water. Following this, an assistant would use their hands or hooks to separate the margins of the wound. Then the skin would be stitched with two rows of stitches. Projectiles were removed by enlarging the wound area with a scalpel, then using a forceps to drag the projectile out. To treat abscesses a scalpel or a spathion was used to make linear incisions. Afterwards, all the skin covering the pus was cut off. Following the surgery, the area was disinfected with honey. Another procedure involved using tongue depressors or spathomeles to depress the tongues of adult patients. Following this, the abscess was opened with a probe or a needle knife.
== References ==
=== Bibliography ===
Milne, John (1907). Surgical Instruments in Greek and Roman times. Oxford: At the Clarendon Press. ISBN 978-859-100-771-4. {{cite book}}: ISBN / Date incompatibility (help)
Celsus, Aulus. De Medicina.
== External links ==
Surgical Instruments from Ancient Rome | Wikipedia/Surgery_in_Ancient_Rome |
Drug-resistant epilepsy (DRE), also known as refractory epilepsy, intractable epilepsy, or pharmacoresistant epilepsy, refers to a state in which an individual with a diagnosis of epilepsy is unresponsive to multiple first-line therapies. Based on the 2010 guidelines from the International League against Epilepsy (ILAE), DRE is officially diagnosed following a lack of therapeutic relief in the form of continued seizure burden after trialing at least two antiepileptic drugs (AEDs) at the appropriate dosage and duration. The probability that the next medication will achieve seizure freedom drops with every failed AED. For example, after two failed AEDs, the probability that the third will achieve seizure freedom is around 4%. Drug-resistant epilepsy is commonly diagnosed after several years of uncontrolled seizures; however, in most cases, it is evident much earlier. Approximately 30% of people with epilepsy have a drug-resistant form. Achieving seizure control in DRE patients is critical, as uncontrolled seizures can lead to irreversible damage to the brain, cognitive impairment, and increased risk for sudden unexpected death in epilepsy. Indirect consequences of DRE include seizure-related injuries and/or accidents, impairment in daily life, adverse medication effects, increased co-morbidities (especially psychological), and increased economic burden, etc.
Some clinical factors that are thought to be predictive of DRE include the female sex, focal epilepsy, developmental delay, status epilepticus, earlier age of onset of epilepsy, neurological deficits, having an abnormal EEG and/or imaging findings, genetic predisposition, association with the ABCB1 gene, and inborn errors of metabolism. Especially among pediatric populations, there is a growing association between DRE and genetic conditions or developmental disorders such as Lennox–Gastaut syndrome or Dravet syndrome.
There are numerous theories regarding the mechanism of action behind DRE, many of which have been studied in human and/or animal models. However, the exact pathogenesis of this condition still remains unclear.
Transporter Hypothesis: Changes to transporters in the blood-brain barrier lead to decreased effectiveness of AEDs through decreased drug concentration. These changes could be in the form of increased efflux transporters or fewer transporters overall.
Pharmacokinetic Hypothesis: Changes to transporters (increased efflux) peripherally in places like the intestines influence efficacy of AEDs and ability to ultimately reach target sites in the brain.
Target Hypothesis: Changes to target protein sites of AEDs influence their effectiveness.
Intrinsic Severity Hypothesis: Refers to the severity of epilepsy and impact increased seizure burden can have on drug efficacy.
Gene Variant Hypothesis: AEDs may not be as effective due to inherent genetic variability, whether in transporters, target sites, and/or the specific kind of epilepsy.
Neural Network Hypothesis: Increased seizure burden may impact the structure of the brain through neural connections, which worsens clinical symptoms and reduces drug efficacy.
== Diagnostic evaluation ==
The first step is for physicians to refer their DRE patients to an epilepsy specialist in a comprehensive epilepsy center where further diagnostic work-up can be performed.
=== Prolonged EEG/Continuous video EEG/Epilepsy Monitoring Unit monitoring ===
One of the first steps in management of drug-resistant epilepsy is confirming the diagnosis by EEG. Typically patients are admitted to hospital for prolonged EEG monitoring with video technology used to capture clinical events as they occur. Typically patients are taken off their anti-seizure medications in order to characterize the evolution of seizure symptoms and their relation with changes in electrical activity of brain. This is done while simultaneously minimizing the adverse consequences of seizures. Additional maneuvers to provoke seizures are also frequently performed, like sleep deprivation, photic stimulation, and hyperventilation. This study can take anywhere from 1–14 days. The length of the study depends on factors like baseline seizure frequency, the number and type of seizure medications the patient is taking prior to the study, institutional protocols, etc. The goal is to record 3-4 typical seizures, though in some cases more or fewer seizures may need to be recorded. After this evaluation, some patients may be determined to have non-epileptic causes of their symptoms, e.g., syncope, psychogenic nonepileptic seizures, cardiac arrhythmia, etc.
For patients who are confirmed to have epilepsy, this testing helps further elucidate the type of epilepsy (generalized vs focal), type of seizures (atonic, absence, GTC, etc.), and can be used for pre-surgical evaluation or to guide further management. Changes on EEG in relation to clinical seizure symptoms are used to determine the likely area of the brain responsible (symptomatic zone) and by extrapolation the area where seizure activity likely starts (seizure onset zone). In some specific cases, prolonged EEG may be done as an outpatient or ambulatory study where the patient goes home with an EEG set-up. This type of monitoring is usually limited to 2–3 days and patients are not taken off their AEDs.
=== Neuroimaging ===
MRI of brain is the most common first-line neuroimaging modality to be used in evaluation of a structural cause of epilepsy. A 3 Tesla MRI is generally recommended, as opposed to scanning on lower magnet strengths. MRI for evaluation of epilepsy often include T1 and T2 images that are optimized to appreciate gray-white matter differentiation and oblique coronal images along the axis of hippocampus. Identification of common lesions associated with epilepsy, like focal cortical dysplasia, mesial temporal sclerosis, microencephalocele, and heterotopia, require thorough review of images by trained clinicians, as the changes can be very subtle and easily missed if not specifically evaluated for. Oftentimes, repeat MRI is required to elucidate an etiology to epilepsy, and typically an epilepsy imaging protocol is followed to identify these subtle changes. There is ongoing quantitative analysis of standard MRI images to identify subtle lesions and use of stronger magnetic fields, like 7 Tesla MRI, for better delineation of anatomical details. Additionally, not all structural abnormalities seen on MRI correlate with epilepsy and may represent incidental findings.
Positron emission tomography scan (PET) using the 18F-FDG radiotracer can also be used in evaluation of DRE. Its use in epilepsy evaluation is based on the premise that areas of the brain responsible for seizure onset also have persistent metabolic dysfunction and do not use glucose at the same rate as neurotypical areas of the brain. Specifically, during seizure activity (ictal) one would expect a hypermetabolic state with increased radiotracer uptake on PET scan, while in between events (interictal) one would expect a hypometabolic state with lower radiotracer uptake on PET scan. Oftentimes findings on PET scan are often correlated with other diagnostic workup that has already/concurrently been obtained to further localize an epileptogenic area of the brain, particularly in the case of focal epilepsy. Other ligands like 11C-flumazenil, 11C-alpha-methyl-L-tryptophan, 11C-methionine, have also been used, mostly on research basis to help identify areas of seizure onset.
Single-Photon Emission Computerized Tomography (SPECT scan) is another radiotracer based imaging technique that uses an oxygen radio-isotope to assess blood flow in the brain. This imaging is performed during inpatient video EEG monitoring in which the tracer is injected into the patient's bloodstream as soon as a seizure starts. Areas of the brain associated with seizure onset will have increased blood flow, hence increased uptake of the tracer if injected at an appropriate time. Imaging is performed after seizure activity is over to assess areas showing a significant increase in blood flow at seizure onset. A major limitation with this technique is the logistics required when injecting the radiotracer and quality of the images produced.
Magnetoencephalography (MEG): A newer non-invasive imaging technique that measures the magnetic field associated with neuronal firing in the brain. While each individual neuron's magnetic field is undetectable, when neurons are firing concurrently, such as during a seizure, the magnetic field generated is detected via MEG. This data provides real-time brain mapping and has proven to be extremely effective in pre-surgical planning and localization of epilepsy. MEG is particularly useful in detecting more superficial abnormalities and is more sensitive than other imaging modalities.
=== Neuropsychological testing ===
Neuropsychological testing involves a series of tests aimed at assessing higher-order mental functions like memory, executive function, language, overall IQ, etc. in order to establish baseline cognitive function. If there is poor performance in measures of specific cognitive domains like verbal memory, naming, or visual-spatial orientation, it may point to areas of the brain that are dysfunctional and likely related to seizure onset. This testing could also indicate poor performance on most measures and suggest more widespread dysfunction in the brain. Besides helping assess the likely area of seizure onset, this testing can be informative post surgical intervention and/or epilepsy therapy.
=== Language lateralization ===
If epilepsy surgery is being considered, testing is often performed to determine the hemisphere of the brain involved in language and memory function. This helps inform about potential risks to language and memory with surgery. There are two main tests available for this objective: the Wada test and fMRI.
The Wada test has been one of the most commonly used tests around the world since the 1960s. This is an invasive testing technique that requires neurointerventionalists, neuropsychologists, neurophysiologists, EEG technologists, and anesthesiologists. When conducting the Wada test, a catheter is threaded from wrist or groin into the carotid artery and finally the middle cerebral artery. An injection of sodium amytal is given to temporarily anesthetize 2/3rd of the cerebral hemisphere on one side. Neuropsychological testing is then done to assess language and memory function of the other hemisphere. Once the patient is fully recovered from the injection on the first side, the catheter is withdrawn and threaded up the contralateral middle cerebral artery with neuropsychological testing repeated. This testing informs the "reserve" for memory and language function in each hemisphere and the potential for impairment with resective surgery on a given side. In some cases additional testing with selective injection of the posterior cerebral artery (that supplies the mesial temporal region including hippoampus) can be done.
The Wada test is increasingly being replaced by the noninvasive fMRI imaging technique. Functional MRI (fMRI) measures the change in blood flow and oxygenation in different parts of the brain in response to an activity. Different tasks or paradigms are presented to a patient while they are in an MRI scanner. These tasks are designed to activate areas involved in different language functions and post processing of the images helps identify areas that are activated during different language tasks.
== Pharmacotherapy ==
While the term drug-resistant epilepsy implies ineffectiveness of pharmacologic therapy, recent advances in the pharmaceutical industry have introduced new drugs that have proven to be effective in the management of DRE patients. Given the novel nature of these drugs, many of the sources utilized are primary/case studies.
=== Cenobamate ===
Approved by the FDA in 2019 for treatment of epilepsy in adults, cenobamate is primarily used to treat patients with focal onset seizures. The mechanism of action of this drug is unclear, but is likely related to the inactivation of Na Channels and action as a GABA modulator. The dosing range for this drug is anywhere from 100-400 mg with a half-life of 55 hours. There have been at least three separate clinical trials involving cenobamate with results showing a reduction in seizure burden by at least 50% in the experimental groups, especially at higher doses of the drug. Of note, cenobamate can interact with other medications, especially other AEDs, and as such requires medication titration.
=== Fenfluramine ===
This drug was used at high doses as an obesity drug that was later recalled given adverse cardiac effects. Fenfluramine is now approved at lower doses as of 2020 for treatment of seizures in patients 2 years and older with Lennox-Gastaut and Dravet syndrome. Fenfluramine is an amphetamine derivative that acts as a serotonin agonist and on GABA and NMDA receptors. The dosing range is anywhere from 0.2-0.7 mg/kg/day, with higher dosing being the most effective for seizure burden. Among Dravet and LGS patients, it has been shown to be helpful with most seizure types, including atonic, GTC, and tonic. This medication has also been reported to be helpful in behavioral and cognitive symptoms associated with intractable epilepsy. At higher doses there are reports of patients showing improvement in daily executive functioning and emotional regulation. No adverse cardiac events have been reported with the use of fenfluramine for epilepsy treatment, with the main side effects being diarrhea, weight loss, and fatigue.
=== Cannabidiol ===
Cannabidiol has recently been emerging as an effective treatment for epilepsy without the psychoactive effects of the Cannabis Sativa plant it is derived from. It gained approval in 2019 for treatment of DRE associated with Dravet, LGS, and more recently seizures associated with tuberous sclerosis in patients over the age of 2 years old. The mechanism of action of cannabidiol is unclear but hypothesized to be related to Ca channels, adenosine signaling, and overall modulation of neuronal hyperexcitability. Cannabidiol is often used concurrently with another AED, especially clobazam, although there is evidence of the efficacy of cannabidiol when used on its own. Some studies suggest the efficacy of cannabidiol for all forms of DRE regardless of the underlying etiology. Similar to fenfluramine, there has been evidence of improvements in cognition, emotional regulation, and communication in addition to seizure control for patients taking cannabidiol.
=== Perampanel ===
First gained approval in the US in 2012 for the treatment of drug-resistant focal epilepsy in patients 12 years and older. It is an antagonist at AMPA receptors with a dosing range from 4-12 mg/day. It is primarily used as an adjunctive treatment option and at higher doses is associated with adverse symptoms like dizziness, ataxias, and withdrawal symptoms. Perampanel has also been studied in the context of sleep and has been shown to help with sleep maintenance and reduction of daytime sleepiness.
== Diets ==
For over 100 years it has been known that a diet with a high fat content and a low carbohydrate content can reduce seizures. Radically curbing carbohydrate intake imitates starvation and forces the body to draw energy from ketone bodies that form when fat is metabolized instead of drawing its energy from sugar. This state is called ketosis and it changes several biochemical processes in the brain in a way that inhibits epileptic activity. On this basis there are several diets that are often recommended to children under 12 years old, but are also effective in adults for DRE management.
=== Ketogenic diet ===
The ketogenic diet is the diet that is most commonly recommended by doctors for patients with epilepsy. In this diet the ratio of fat to carbohydrates and proteins is 4:1. That means that the fat content of the consumed food must be around 80%, the protein content must be around 15%, and the carbohydrate content must be around 5%. For comparison, the average western diet consists of a carbohydrate content of over 50%. After one year on the ketogenic diet, the success rate (seizure reduction over 50%) is between 30 and 50% and the dropout rate is around 45%. Although the ketogenic diet can be very effective, some families report that it's not compatible with daily life given its restrictive nature. It can be especially difficult for adolescents to follow as their autonomy increases. For this reason a fat ratio of 3:1 instead of 4:1 can be recommended to make meals more palatable. Side effects of the ketogenic diet include constipation, fatigue, weight loss, and kidney stones (typically after long-term adherence).
=== MCT-Ketogenic diet ===
In the 1960s, it was discovered that when medium-chain triglycerides (MCT) are metabolized, more ketone bodies are produced than from metabolizing any other fat. This discovery sparked the introduction of the MCT-ketogenic diet, a modification of the ketogenic diet. In the MCT-ketogenic diet, MCT oil is added to ketogenic meals, which allows the carbohydrate content to be increased. The efficacy of the MCT ketogenic diet does not differ significantly from the classic ketogenic diet; however, not all patients, especially pediatric populations, can tolerate the large amounts of MCT oil required. This diet can also be costly.
=== Modified Atkins ===
A modified Atkins diet was coined after the popular Atkins diet with the goal of reducing seizures through ketosis. In this diet, the fat content is slightly lower than in the ketogenic diet at around 60%; the protein content is around 30% and the carbohydrate content is around 10%. Several studies show that the modified Atkins diet is just as effective as the ketogenic diet. Some physicians recommend the modified Atkins diet because they assume that patients will adhere to it on the long-term because it is more compatible with daily life and the meals are more enjoyable.
=== Low Glycemic Index (LGI) ===
The aim of the LGI diet is to keep blood glucose levels at a stable state. Rapid fluctuations in glucose levels both high and low is thought to be a trigger for seizures in some patients with epilepsy. This diet permits 40-60 gram of carbohydrates daily but with the goal of a glycemic index of <50. This diet has been studied among pediatric populations as an effective form of management for DRE.
== Surgery ==
In epilepsy surgery, a distinction can be made between resective and disconnective procedures. In a resective procedure, the area of the brain that causes the seizures is removed. In a disconnective procedure, the neural connections in the brain that allow the seizures to spread are disconnected. In most cases, epilepsy surgery is only an option when the area of the brain that causes the seizures – the so-called epileptic focus – can be clearly identified and is not responsible for critical functions such as language. Several imaging techniques such as magnetic resonance tomography and functional techniques like electrocorticography are used to demarcate the epileptic focus clearly. Recording fMRI and EEG simultaneously is a noninvasive method of detecting cerebral hemodynamic changes related to interictal epileptic discharges (IEDs) on scalp EEG. This has been shown through different studies to help diagnose different types of epilepsy.
=== Lobe resection ===
Temporal lobe epilepsy (TLE), in which the epileptic focus is in the temporal lobe, is one of the most common types of epilepsy in adolescents and adults. Hence temporal lobe resection, during which the whole temporal lobe or just a part of the temporal lobe (for example, the hippocampus or the amygdala) is removed, is the most common epilepsy surgery procedure. Between 40 and 60% of patients who undergo temporal lobe resection are continuously seizure-free. The surgery itself is very safe, with a mortality of 0%. The risk for neurologic complications from a temporal lobe resection is around 3 to 7%.
=== Lesionectomy ===
If the source of seizures is a lesion – for example, scar tissue from a brain injury, a tumor, or malformed blood vessels – this lesion can be removed surgically in a lesionectomy.
=== Corpus callosotomy ===
Corpus callosotomy is a palliative procedure for especially severe cases of epilepsy. The corpus callosum is a large bundle of nerve fibers that connects both brain halves with each other. To prevent the spreading of seizures from one brain hemisphere (brain half) to the other, the corpus callosum can be split. This procedure is mostly carried out on patients with so-called drop attacks that come with a very high risk of injury and in which the epileptic focus is not clearly delimitable. It is very rare that a corpus callosotomy causes seizure freedom; however, in half of the patients, the dangerous drop attacks are less severe. After a corpus callosotomy there is the risk that language is temporarily or permanently impaired. The younger a patient is at the time of the corpus callosotomy, the better the prognosis.
=== Functional hemispherectomy ===
This procedure is a modern adaptation of the radical hemispherectomy in which one brain hemisphere is removed to prevent the spread of seizures from one brain hemisphere to the other. In the functional version, only a part of the hemisphere is removed but the connections to the other brain hemisphere are cut through. This procedure is only performed on a small group of patients under the age of 13 who have severe damage or malformation of one hemisphere, patients with Sturge Weber syndrome, or patients with Rasmussen's encephalitis. Surgical intervention is considered a viable option for infants with drug-resistant epilepsy, particularly when anti-seizure medications fail to achieve seizure control. For this population, surgery can lead to favorable outcomes in a substantial number of cases. The functional hemispherectomy can achieve long-term seizure freedom in over 80% of patients, though often at the price of hemiplegia and hemianopsy. The death rate is around 1 to 2%, and 5% of patients develop a hydrocephalus that needs to be treated with a shunt.
=== Multiple subpial transection ===
Multiple subpial transection (MST) is a palliative procedure that is considered when an epileptic focus can be identified but cannot be removed because it is in a functionally relevant brain region – a so-called eloquent region. In an MST, nerve fibers are disconnected so that seizures cannot spread from the epileptic focus into the rest of the brain. Between 60 and 70% of patients experienced a seizure reduction of over 95% after an MST, and the risk for neurologic deficits is around 19%.
=== Vagus nerve stimulation ===
Vagus nerve stimulation (VNS) involves implanting a pacemaker-like generator below the skin in the chest area that intermittently sends electrical impulses to the left vagus nerve in the neck. The impulses are mediated to the brain by the vagus nerve and thereby help to inhibit electrical disturbances that cause seizures. The antiepileptic effect of vagus nerve stimulation increases over several months: after two years, around half of VNS patients experience a reduction of their seizures by at least 50%, and after 10 years, the average seizure reduction is around 75%. Furthermore, in most patients mood (VNS has a significant antidepressant effect and is approved for depression in some countries), alertness and quality of life are increased significantly within the first year of vagus nerve stimulation. VNS patients can induce an extra stimulation themselves with a VNS magnet when they notice that a seizure is approaching, and it has been shown that the majority of seizures can be interrupted with this type of on-demand stimulation.
The procedure to implant a vagus nerve stimulator is very safe: no case of death related to VNS implantation surgery has ever occurred. Infection of the tissue pocket in which the generator is located that requires antibiotic treatment occurs in around 3% of patients. The most common side effect is hoarseness or change in voice. Headaches and shortness of breath are less common. In most cases, side effects only occur during activity of the stimulation (mostly every 3 to 5 minutes) and reduce over time. In most cases, VNS does not replace antiepileptic medication; however, in many cases, the dose can be reduced over time so that patients experience fewer side effects. The battery of the VNS generator can, depending on the model and the settings, last between 3 and 10 years.
=== VNS with cardiac-based seizure detection ===
In 82% of epilepsy patients, the heart rate increases quickly and suddenly upon a seizure. This is known as ictal tachycardia. Ictal tachycardia is so characteristic that it can be distinguished from the slow gradual increase of heart rate that occurs during physical activity. This way, in the majority of epilepsy patients, seizures can be detected in the ECG. In addition to classical VNS, some new VNS generators continuously monitor heart rate and identify fast and sudden heart rate increases associated with seizures with intelligent software. Then an automatic additional stimulation can be triggered to interrupt, prevent or alleviate the seizure. This new generator type was shown to detect and treat at least four out of five seizures and 60% of seizures were shown to be interrupted with this heart-rate triggered stimulation. The earlier in the course of the seizure the stimulation occurred, the quicker the seizure ended; generally, seizures were shown to be reduced by around 35% by stimulation.
=== Other ===
Deep brain stimulation of the anterior nuclei of the thalamus is approved for DRE in some countries in Europe, but has been and continues to only be used in a very few patients. After 5 years of DBS, a seizure reduction of 69% and a 50%-responder rate of 68% was reported in a randomized-double blinded trial. The rate of serious device related events was 34% in this study.
Responsive neurostimulation (RNS) is approved for DRE in the US and involves stimulation directly to 1 or 2 seizure foci when abnormal electrocorticographic activity is detected by the device's software. After 2 years of RNS, a seizure reduction of 53% was reported in a randomized-double blinded trial, as well as a rate of serious device-related events of 2.5%.
Transcutaneous vagus nerve stimulation (tVNS) is approved for DRE in some European countries and involves externally stimulating the auricular branch of the vagus nerve in the ear. tVNS failed to demonstrate efficacy in a first randomized-double blinded trial: responder rates did not differ between active and control groups, potentially indicating a placebo effect behind the 34% seizure reduction seen in the patients who completed the full follow-up period.
== References == | Wikipedia/Drug-resistant_epilepsy |
A clinical prediction rule or clinical probability assessment specifies how to use medical signs, symptoms, and other findings to estimate the probability of a specific disease or clinical outcome.
Physicians have difficulty in estimated risks of diseases; frequently erring towards overestimation, perhaps due to cognitive biases such as base rate fallacy in which the risk of an adverse outcome is exaggerated.
== Methods ==
In a prediction rule study, investigators identify a consecutive group of patients who are suspected of having a specific disease or outcome. The investigators then obtain a standard set of clinical observations on each patient and a test or clinical follow-up to define the true state of the patient. They then use statistical methods to identify the best clinical predictors of the patient's true state. The probability of disease will depend on the patient's key clinical predictors. Published methodological standards specify good practices for developing a clinical prediction rule.
A survey of methods concluded "the majority of prediction studies in high impact journals do not follow current methodological recommendations, limiting their reliability and applicability", confirming earlier findings from the diabetic literature. The TRIPOD statement is now widely used to improve the quality of reporting of clinical prediction rules, with an extension to provide guidance for clinical prediction rules developed using artificial intelligence methods
== Effect on health outcomes ==
Few prediction rules have had the consequences of their usage by physicians quantified.
When studied, the impact of providing the information alone (for example, providing the calculated probability of disease) has been negative.
However, when the prediction rule is implemented as part of a critical pathway, so that a hospital or clinic has procedures and policies established for how to manage patients identified as high or low risk of disease, the prediction rule has more impact on clinical outcomes.
The more intensively the prediction rule is implemented the more benefit will occur.
== Examples of prediction rules ==
Apache II
CHADS2 for risk of stroke with atrial fibrillation
CURB-65
Model for End-Stage Liver Disease
Ranson criteria
Centor criteria
Pneumonia severity index
Wells score (disambiguation)
Orthopaedics
Abbreviated Injury Scale
Harris Hip Score
Injury Severity Score
Kocher criteria
Mirel's Score
NACA score
Ottawa ankle rules
Ottawa knee rules
Pittsburgh knee rules
Revised Trauma Score
== References ==
== External links ==
Clinical Prediction Website
Clinical prediction rules online calculators | Wikipedia/Clinical_prediction_rule |
A mental disorder, also referred to as a mental illness, a mental health condition, or a psychiatric disability, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. A mental disorder is also characterized by a clinically significant disturbance in an individual's cognition, emotional regulation, or behavior, often in a social context. Such disturbances may occur as single episodes, may be persistent, or may be relapsing–remitting. There are many different types of mental disorders, with signs and symptoms that vary widely between specific disorders. A mental disorder is one aspect of mental health.
The causes of mental disorders are often unclear. Theories incorporate findings from a range of fields. Disorders may be associated with particular regions or functions of the brain. Disorders are usually diagnosed or assessed by a mental health professional, such as a clinical psychologist, psychiatrist, psychiatric nurse, or clinical social worker, using various methods such as psychometric tests, but often relying on observation and questioning. Cultural and religious beliefs, as well as social norms, should be taken into account when making a diagnosis.
Services for mental disorders are usually based in psychiatric hospitals, outpatient clinics, or in the community, Treatments are provided by mental health professionals. Common treatment options are psychotherapy or psychiatric medication, while lifestyle changes, social interventions, peer support, and self-help are also options. In a minority of cases, there may be involuntary detention or treatment. Prevention programs have been shown to reduce depression.
In 2019, common mental disorders around the globe include: depression, which affects about 264 million people; dementia, which affects about 50 million; bipolar disorder, which affects about 45 million; and schizophrenia and other psychoses, which affect about 20 million people. Neurodevelopmental disorders include attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), and intellectual disability, of which onset occurs early in the developmental period. Stigma and discrimination can add to the suffering and disability associated with mental disorders, leading to various social movements attempting to increase understanding and challenge social exclusion.
== Definition ==
The definition and classification of mental disorders are key issues for researchers as well as service providers and those who may be diagnosed. For a mental state to be classified as a disorder, it generally needs to cause dysfunction. Most international clinical documents use the term mental "disorder", while "illness" is also common. It has been noted that using the term "mental" (i.e., of the mind) is not necessarily meant to imply separateness from the brain or body.
According to the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), published in 1994, a mental disorder is a psychological syndrome or pattern that is associated with distress (e.g., via a painful symptom), disability (impairment in one or more important areas of functioning), increased risk of death, or causes a significant loss of autonomy; however, it excludes normal responses such as the grief from loss of a loved one and also excludes deviant behavior for political, religious, or societal reasons not arising from a dysfunction in the individual.
DSM-IV predicates the definition with caveats, stating that, as in the case with many medical terms, mental disorder "lacks a consistent operational definition that covers all situations", noting that different levels of abstraction can be used for medical definitions, including pathology, symptomology, deviance from a normal range, or etiology, and that the same is true for mental disorders, so that sometimes one type of definition is appropriate and sometimes another, depending on the situation.
In 2013, the American Psychiatric Association (APA) redefined mental disorders in the DSM-5 as "a syndrome characterized by clinically significant disturbance in an individual's cognition, emotion regulation, or behavior that reflects a dysfunction in the psychological, biological, or developmental processes underlying mental functioning." The final draft of ICD-11 contains a very similar definition.
The terms "mental breakdown" or "nervous breakdown" may be used by the general population to mean a mental disorder. The terms "nervous breakdown" and "mental breakdown" have not been formally defined through a medical diagnostic system such as the DSM-5 or ICD-10 and are nearly absent from scientific literature regarding mental illness. Although "nervous breakdown" is not rigorously defined, surveys of laypersons suggest that the term refers to a specific acute time-limited reactive disorder involving symptoms such as anxiety or depression, usually precipitated by external stressors. Many health experts today refer to a nervous breakdown as a mental health crisis.
=== Nervous illness ===
In addition to the concept of mental disorder, some people have argued for a return to the old-fashioned concept of nervous illness. In How Everyone Became Depressed: The Rise and Fall of the Nervous Breakdown (2013), Edward Shorter, a professor of psychiatry and the history of medicine, says:
About half of them are depressed. Or at least that is the diagnosis that they got when they were put on antidepressants. ... They go to work but they are unhappy and uncomfortable; they are somewhat anxious; they are tired; they have various physical pains—and they tend to obsess about the whole business. There is a term for what they have, and it is a good old-fashioned term that has gone out of use. They have nerves or a nervous illness. It is an illness not just of mind or brain, but a disorder of the entire body. ... We have a package here of five symptoms—mild depression, some anxiety, fatigue, somatic pains, and obsessive thinking. ... We have had nervous illness for centuries. When you are too nervous to function ... it is a nervous breakdown. But that term has vanished from medicine, although not from the way we speak.... The nervous patients of yesteryear are the depressives of today. That is the bad news.... There is a deeper illness that drives depression and the symptoms of mood. We can call this deeper illness something else, or invent a neologism, but we need to get the discussion off depression and onto this deeper disorder in the brain and body. That is the point.
In eliminating the nervous breakdown, psychiatry has come close to having its own nervous breakdown.
"Nervous breakdown" is a pseudo-medical term to describe a wealth of stress-related feelings and they are often made worse by the belief that there is a real phenomenon called "nervous breakdown".
Nerves stand at the core of common mental illness, no matter how much we try to forget them.
== Classifications ==
There are currently two widely established systems that classify mental disorders:
ICD-11 Chapter 06: Mental, behavioural or neurodevelopmental disorders, part of the International Classification of Diseases produced by the WHO (in effect since 1 January 2022).
Diagnostic and Statistical Manual of Mental Disorders (DSM-5) produced by the APA since 1952.
Both of these list categories of disorder and provide standardized criteria for diagnosis. They have deliberately converged their codes in recent revisions so that the manuals are often broadly comparable, although significant differences remain. Other classification schemes may be used in non-western cultures, for example, the Chinese Classification of Mental Disorders, and other manuals may be used by those of alternative theoretical persuasions, such as the Psychodynamic Diagnostic Manual. In general, mental disorders are classified separately from neurological disorders, learning disabilities or intellectual disability.
Unlike the DSM and ICD, some approaches are not based on identifying distinct categories of disorder using dichotomous symptom profiles intended to separate the abnormal from the normal. There is significant scientific debate about the relative merits of categorical versus such non-categorical (or hybrid) schemes, also known as continuum or dimensional models. A spectrum approach may incorporate elements of both.
In the scientific and academic literature on the definition or classification of mental disorder, one extreme argues that it is entirely a matter of value judgements (including of what is normal) while another proposes that it is or could be entirely objective and scientific (including by reference to statistical norms). Common hybrid views argue that the concept of mental disorder is objective even if only a "fuzzy prototype" that can never be precisely defined, or conversely that the concept always involves a mixture of scientific facts and subjective value judgments. Although the diagnostic categories are referred to as 'disorders', they are presented as medical diseases, but are not validated in the same way as most medical diagnoses. Some neurologists argue that classification will only be reliable and valid when based on neurobiological features rather than clinical interview, while others suggest that the differing ideological and practical perspectives need to be better integrated.
The DSM and ICD approach remains under attack both because of the implied causality model and because some researchers believe it better to aim at underlying brain differences which can precede symptoms by many years.
=== Dimensional models ===
The high degree of comorbidity between disorders in categorical models such as the DSM and ICD have led some to propose dimensional models. Studying comorbidity between disorders have demonstrated two latent (unobserved) factors or dimensions in the structure of mental disorders that are thought to possibly reflect etiological processes. These two dimensions reflect a distinction between internalizing disorders, such as mood or anxiety symptoms, and externalizing disorders such as behavioral or substance use symptoms. A single general factor of psychopathology, similar to the g factor for intelligence, has been empirically supported. The p factor model supports the internalizing-externalizing distinction, but also supports the formation of a third dimension of thought disorders such as schizophrenia. Biological evidence also supports the validity of the internalizing-externalizing structure of mental disorders, with twin and adoption studies supporting heritable factors for externalizing and internalizing disorders. A leading dimensional model is the Hierarchical Taxonomy of Psychopathology.
== Disorders ==
There are many different categories of mental disorder, and many different facets of human behavior and personality that can become disordered.
=== Anxiety disorders ===
An anxiety disorder is anxiety or fear that interferes with normal functioning may be classified as an anxiety disorder. Commonly recognized categories include specific phobias, generalized anxiety disorder, social anxiety disorder, panic disorder, agoraphobia, obsessive–compulsive disorder and post-traumatic stress disorder.
=== Mood disorders ===
Other affective (emotion/mood) processes can also become disordered. Mood disorder involving unusually intense and sustained sadness, melancholia, or despair is known as major depression (also known as unipolar or clinical depression). Milder, but still prolonged depression, can be diagnosed as dysthymia. Bipolar disorder (also known as manic depression) involves abnormally "high" or pressured mood states, known as mania or hypomania, alternating with normal or depressed moods. The extent to which unipolar and bipolar mood phenomena represent distinct categories of disorder, or mix and merge along a dimension or spectrum of mood, is subject to some scientific debate.
=== Psychotic disorders ===
Patterns of belief, language use and perception of reality can become dysregulated (e.g., delusions, thought disorder, hallucinations). Psychotic disorders in this domain include schizophrenia, and delusional disorder. Schizoaffective disorder is a category used for individuals showing aspects of both schizophrenia and affective disorders. Schizotypy is a category used for individuals showing some of the characteristics associated with schizophrenia, but without meeting cutoff criteria.
=== Personality disorders ===
Personality—the fundamental characteristics of a person that influence thoughts and behaviors across situations and time—may be considered disordered if judged to be abnormally rigid and maladaptive. Although treated separately by some, the commonly used categorical schemes include them as mental disorders, albeit on a separate axis II in the case of the DSM-IV. A number of different personality disorders are listed, including those sometimes classed as eccentric, such as paranoid, schizoid and schizotypal personality disorders; types that have described as dramatic or emotional, such as antisocial, borderline, histrionic or narcissistic personality disorders; and those sometimes classed as fear-related, such as anxious-avoidant, dependent, or obsessive–compulsive personality disorders. Personality disorders, in general, are defined as emerging in childhood, or at least by adolescence or early adulthood. The ICD also has a category for enduring personality change after a catastrophic experience or psychiatric illness. If an inability to sufficiently adjust to life circumstances begins within three months of a particular event or situation, and ends within six months after the stressor stops or is eliminated, it may instead be classed as an adjustment disorder. There is an emerging consensus that personality disorders, similar to personality traits in general, incorporate a mixture of acute dysfunctional behaviors that may resolve in short periods, and maladaptive temperamental traits that are more enduring. Furthermore, there are also non-categorical schemes that rate all individuals via a profile of different dimensions of personality without a symptom-based cutoff from normal personality variation, for example through schemes based on dimensional models.
=== Neurodevelopmental disorders ===
Neurodevelopmental disorders is a group of mental disorder that affect the central nervous system, such as the brain and spinal cord. These disorders can appear in early childhood. They can even persist into adulthood. A few of the common ones are attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), intellectual disabilities, motor disorders, and communication disorders among others. Some causes can contribute to these disorders like genetic factors (genetics, family medical history), environmental factors (excessive stress, exposure to neurotoxins, pollution, viral infections, and bacterial infections), physical factors (traumatic brain injury, illness), and prenatal factors (birth defects, exposure to drugs during pregnancy, low birth weight). Neurodevelopmental disorders can be managed with behavioral therapy, applied behavior analysis (ABA), educational interventions, specific medications, and other such treatments.
Approximately 8 in 10 people with autism suffer from a mental health problem in their lifetime, in comparison to 1 in 4 of the general population that suffers from a mental health problem in their lifetimes.
=== Eating disorders ===
An eating disorder is a serious mental health condition that involves an unhealthy relationship with food and body image. They can cause severe physical and psychological problems. Eating disorders involve disproportionate concern in matters of food and weight. Categories of disorder in this area include anorexia nervosa, bulimia nervosa, exercise bulimia or binge eating disorder.
=== Sleep disorders ===
Sleep disorders are associated with disruption to normal sleep patterns. A common sleep disorder is insomnia, which is described as difficulty falling and/or staying asleep. Other sleep disorders include narcolepsy, sleep apnea, REM sleep behavior disorder, chronic sleep deprivation, and restless leg syndrome.
Narcolepsy is a condition of extreme tendencies to fall asleep whenever and wherever. People with narcolepsy feel refreshed after their random sleep, but eventually get sleepy again. Narcolepsy diagnosis requires an overnight stay at a sleep center for analysis, during which doctors ask for a detailed sleep history and sleep records. Doctors also use actigraphs and polysomnography. Doctors will do a multiple sleep latency test, which measures how long it takes a person to fall asleep.
Sleep apnea, when breathing repeatedly stops and starts during sleep, can be a serious sleep disorder. Three types of sleep apnea include obstructive sleep apnea, central sleep apnea, and complex sleep apnea. Sleep apnea can be diagnosed at home or with polysomnography at a sleep center. An ear, nose, and throat doctor may further help with the sleeping habits.
=== Sexuality related ===
Sexual disorders include dyspareunia and various kinds of paraphilia (sexual arousal to objects, situations, or individuals that are considered abnormal or harmful to the person or others). Sexual dysfunction is common among psychiatric patients, yet the specific impact of psychopathology independent of factors like psychotropic substances or somatic symptom disorders, remains unclear.
A systematic review explored the prevalence of sexual dysfunction in psychiatric patients free from psychotropic medications and somatic diseases. The review included 24 studies with 1,199 participants and identified high rates of sexual dysfunction across various psychiatric disorders. Reported prevalence ranged from 45%-93% for depressive disorders, 33%-75% for anxiety disorders, 25%-81% for obsessive–compulsive disorder (OCD), and 25% for schizophrenia. Sexual desire was frequently impaired in depressive disorders, PTSD, and schizophrenia, while OCD and anxiety disorders were associated with difficulties during the orgasm phase.
The findings emphasize the importance of addressing sexual health in psychiatric care through psychoeducation, sexual history assessments, and targeted interventions. This highlights the significant impact of psychopathology on sexual functioning.
=== Other ===
Impulse control disorders: People who are abnormally unable to resist certain urges or impulses that could be harmful to themselves or others, may be classified as having an impulse control disorder, and disorders such as kleptomania (stealing) or pyromania (fire-setting). Various behavioral addictions, such as gambling addiction, may be classed as a disorder. Obsessive–compulsive disorder can sometimes involve an inability to resist certain acts but is classed separately as being primarily an anxiety disorder.
Substance use disorders: This disorder refers to the use of drugs (legal or illegal, including alcohol) that persists despite significant problems or harm related to its use. Substance dependence and substance abuse fall under this umbrella category in the DSM. Substance use disorder may be due to a pattern of compulsive and repetitive use of a drug that results in tolerance to its effects and withdrawal symptoms when use is reduced or stopped.
Dissociative disorders: People with severe disturbances of their self-identity, memory, and general awareness of themselves and their surroundings may be classified as having these types of disorders, including depersonalization derealization disorder or dissociative identity disorder (which was previously referred to as multiple personality disorder or "split personality").
Cognitive disorders: These affect cognitive abilities, including learning and memory. This category includes delirium and mild and major neurocognitive disorder (previously termed dementia).
Somatoform disorders may be diagnosed when there are problems that appear to originate in the body that are thought to be manifestations of a mental disorder. This includes somatization disorder and conversion disorder. There are also disorders of how a person perceives their body, such as body dysmorphic disorder. Neurasthenia is an old diagnosis involving somatic complaints as well as fatigue and low spirits/depression, which is officially recognized by the ICD-10 but no longer by the DSM-IV.
Factitious disorders are diagnosed where symptoms are thought to be reported for personal gain. Symptoms are often deliberately produced or feigned, and may relate to either symptoms in the individual or in someone close to them, particularly people they care for.
There are attempts to introduce a category of relational disorder, where the diagnosis is of a relationship rather than on any one individual in that relationship. The relationship may be between children and their parents, between couples, or others. There already exists, under the category of psychosis, a diagnosis of shared psychotic disorder where two or more individuals share a particular delusion because of their close relationship with each other.
There are a number of uncommon psychiatric syndromes, which are often named after the person who first described them, such as Capgras syndrome, De Clerambault syndrome, Othello syndrome, Ganser syndrome, Cotard delusion, and Ekbom syndrome, and additional disorders such as the Couvade syndrome and Geschwind syndrome.
== Signs and symptoms ==
=== Course ===
The onset of psychiatric disorders usually occurs from childhood to early adulthood. Impulse-control disorders and a few anxiety disorders tend to appear in childhood. Some other anxiety disorders, substance disorders, and mood disorders emerge later in the mid-teens. Symptoms of schizophrenia typically manifest from late adolescence to early twenties.
The likely course and outcome of mental disorders vary and are dependent on numerous factors related to the disorder itself, the individual as a whole, and the social environment. Some disorders may last a brief period of time, while others may be long-term in nature.
All disorders can have a varied course. Long-term international studies of schizophrenia have found that over a half of individuals recover in terms of symptoms, and around a fifth to a third in terms of symptoms and functioning, with many requiring no medication. While some have serious difficulties and support needs for many years, "late" recovery is still plausible. The World Health Organization (WHO) concluded that the long-term studies' findings converged with others in "relieving patients, carers and clinicians of the chronicity paradigm which dominated thinking throughout much of the 20th century."
A follow-up study by Tohen and coworkers revealed that around half of people initially diagnosed with bipolar disorder achieve symptomatic recovery (no longer meeting criteria for the diagnosis) within six weeks, and nearly all achieve it within two years, with nearly half regaining their prior occupational and residential status in that period. Less than half go on to experience a new episode of mania or major depression within the next two years.
=== Disability ===
Some disorders may be very limited in their functional effects, while others may involve substantial disability and support needs. In this context, the terms psychiatric disability and psychological disability are sometimes used instead of mental disorder. The degree of ability or disability may vary over time and across different life domains. Furthermore, psychiatric disability has been linked to institutionalization, discrimination and social exclusion as well as to the inherent effects of disorders. Alternatively, functioning may be affected by the stress of having to hide a condition in work or school, etc., by adverse effects of medications or other substances, or by mismatches between illness-related variations and demands for regularity.
It is also the case that, while often being characterized in purely negative terms, some mental traits or states labeled as psychiatric disabilities can also involve above-average creativity, non-conformity, goal-striving, meticulousness, or empathy. In addition, the public perception of the level of disability associated with mental disorders can change.
Nevertheless, internationally, people report equal or greater disability from commonly occurring mental conditions than from commonly occurring physical conditions, particularly in their social roles and personal relationships. The proportion with access to professional help for mental disorders is far lower, however, even among those assessed as having a severe psychiatric disability. Disability in this context may or may not involve such things as:
Basic activities of daily living. Including looking after the self (health care, grooming, dressing, shopping, cooking etc.) or looking after accommodation (chores, DIY tasks, etc.)
Interpersonal relationships. Including communication skills, ability to form relationships and sustain them, ability to leave the home or mix in crowds or particular settings
Occupational functioning. Ability to acquire an employment and hold it, cognitive and social skills required for the job, dealing with workplace culture, or studying as a student.
In terms of total disability-adjusted life years (DALYs), which is an estimate of how many years of life are lost due to premature death or to being in a state of poor health and disability, psychiatric disabilities rank amongst the most disabling conditions. Unipolar (also known as Major) depressive disorder is the third leading cause of disability worldwide, of any condition mental or physical, accounting for 65.5 million years lost. The first systematic description of global disability arising in youth, in 2011, found that among 10- to 24-year-olds nearly half of all disability (current and as estimated to continue) was due to psychiatric disabilities, including substance use disorders and conditions involving self-harm. Second to this were accidental injuries (mainly traffic collisions) accounting for 12 percent of disability, followed by communicable diseases at 10 percent. The psychiatric disabilities associated with most disabilities in high-income countries were unipolar major depression (20%) and alcohol use disorder (11%). In the eastern Mediterranean region, it was unipolar major depression (12%) and schizophrenia (7%), and in Africa it was unipolar major depression (7%) and bipolar disorder (5%).
Suicide, which is often attributed to some underlying mental disorder, is a leading cause of death among teenagers and adults under 35. There are an estimated 10 to 20 million non-fatal attempted suicides every year worldwide.
== Risk factors ==
The predominant view as of 2018 is that genetic, psychological, and environmental factors all contribute to the development or progression of mental disorders. Different risk factors may be present at different ages, with risk occurring as early as during prenatal period.
=== Genetics ===
A number of psychiatric disorders are linked to a family history (including depression, narcissistic personality disorder and anxiety). Twin studies have also revealed a very high heritability for many mental disorders (especially autism and schizophrenia). Although researchers have been looking for decades for clear linkages between genetics and mental disorders, that work has not yielded specific genetic biomarkers yet that might lead to better diagnosis and better treatments.
Statistical research looking at eleven disorders found widespread assortative mating between people with mental illness. That means that individuals with one of these disorders were two to three times more likely than the general population to have a partner with a mental disorder. Sometimes people seemed to have preferred partners with the same mental illness. Thus, people with schizophrenia or ADHD are seven times more likely to have affected partners with the same disorder. This is even more pronounced for people with Autism spectrum disorders who are 10 times more likely to have a spouse with the same disorder.
=== Environment ===
During the prenatal stage, factors like unwanted pregnancy, lack of adaptation to pregnancy or substance use during pregnancy increases the risk of developing a mental disorder. Maternal stress and birth complications including prematurity and infections have also been implicated in increasing susceptibility for mental illness. Infants neglected or not provided optimal nutrition have a higher risk of developing cognitive impairment.
Social influences have also been found to be important, including abuse, neglect, bullying, social stress, traumatic events, and other negative or overwhelming life experiences. Aspects of the wider community have also been implicated, including employment problems, socioeconomic inequality, lack of social cohesion, problems linked to migration, and features of particular societies and cultures. The specific risks and pathways to particular disorders are less clear, however.
Nutrition also plays a role in mental disorders.
In schizophrenia and psychosis, risk factors include migration and discrimination, childhood trauma, bereavement or separation in families, recreational use of drugs, and urbanicity.
In anxiety, risk factors may include parenting factors including parental rejection, lack of parental warmth, high hostility, harsh discipline, high maternal negative affect, anxious childrearing, modelling of dysfunctional and drug-abusing behavior, and child abuse (emotional, physical and sexual). Adults with imbalance work to life are at higher risk for developing anxiety.
For bipolar disorder, stress (such as childhood adversity) is not a specific cause, but does place genetically and biologically vulnerable individuals at risk for a more severe course of illness.
=== Drug use ===
Mental disorders are associated with drug use including: cannabis, alcohol and caffeine, use of which appears to promote anxiety. For psychosis and schizophrenia, usage of a number of drugs has been associated with development of the disorder, including cannabis, cocaine, and amphetamines. There has been debate regarding the relationship between usage of cannabis and bipolar disorder. Cannabis has also been associated with depression. Adolescents are at increased risk for tobacco, alcohol and drug use; Peer pressure is the main reason why adolescents start using substances. At this age, the use of substances could be detrimental to the development of the brain and place them at higher risk of developing a mental disorder.
=== Chronic disease ===
People living with chronic conditions like HIV and diabetes are at higher risk of developing a mental disorder. People living with diabetes experience significant stress from the biological impact of the disease, which places them at risk for developing anxiety and depression. Diabetic patients also have to deal with emotional stress trying to manage the disease. Conditions like heart disease, stroke, respiratory conditions, cancer, and arthritis increase the risk of developing a mental disorder when compared to the general population.
=== Personality traits ===
Risk factors for mental illness include a propensity for high neuroticism or "emotional instability". In anxiety, risk factors may include temperament and attitudes (e.g. pessimism). Key personality traits, including Neuroticism, Extraversion, Agreeableness, Conscientiousness, and Openness, significantly influence various dimensions of mental health, as measured by the General Health Questionnaire(GHQ-12). The GHQ-12 assesses mental health across three dimensions: GHQ-12A (social dysfunction & anhedonia), GHQ-12B (depression & anxiety), and GHQ-12C (loss of confidence). Neuroticism was found to be strongly linked to all three dimensions, indicating greater vulnerability to mental health issues, while Extraversion was negatively associated with social dysfunction and depression, suggesting better mental health outcomes.Agreeableness and Conscientiousness were both negatively related to social dysfunction and loss of confidence, highlighting their protective roles. Openness showed a negative relationship with depression and anxiety.
These findings support several models of personality's impact on mental health, including the predisposition/vulnerability, complication/scar, and pathoplasty/exacerbation models. This underscores the importance of considering personality traits in mental health assessments and interventions, as they help identify individuals at higher risk for mental health challenges and guide targeted psychological care.
=== Causal models ===
Mental disorders can arise from multiple sources, and in many cases there is no single accepted or consistent cause currently established. An eclectic or pluralistic mix of models may be used to explain particular disorders. The primary paradigm of contemporary mainstream Western psychiatry is said to be the biopsychosocial model which incorporates biological, psychological and social factors, although this may not always be applied in practice.
Biological psychiatry follows a biomedical model where many mental disorders are conceptualized as disorders of brain circuits likely caused by developmental processes shaped by a complex interplay of genetics and experience. A common assumption is that disorders may have resulted from genetic and developmental vulnerabilities, exposed by stress in life (for example in a diathesis–stress model), although there are various views on what causes differences between individuals. Some types of mental disorders may be viewed as primarily neurodevelopmental disorders.
Evolutionary psychology may be used as an overall explanatory theory, while attachment theory is another kind of evolutionary-psychological approach sometimes applied in the context of mental disorders. Psychoanalytic theories have continued to evolve alongside and cognitive-behavioral and systemic-family approaches. A distinction is sometimes made between a "medical model" or a "social model" of psychiatric disability.
== Diagnosis ==
Psychiatrists seek to provide a medical diagnosis of individuals by an assessment of symptoms, signs and impairment associated with particular types of mental disorder. Other mental health professionals, such as clinical psychologists, may or may not apply the same diagnostic categories to their clinical formulation of a client's difficulties and circumstances. The majority of mental health problems are, at least initially, assessed and treated by family physicians (in the UK general practitioners) during consultations, who may refer a patient on for more specialist diagnosis in acute or chronic cases.
Routine diagnostic practice in mental health services typically involves an interview known as a mental status examination, where evaluations are made of appearance and behavior, self-reported symptoms, mental health history, and current life circumstances. The views of other professionals, relatives, or other third parties may be taken into account. A physical examination to check for ill health or the effects of medications or other drugs may be conducted. Psychological testing is sometimes used via paper-and-pen or computerized questionnaires, which may include algorithms based on ticking off standardized diagnostic criteria, and in rare specialist cases neuroimaging tests may be requested, but such methods are more commonly found in research studies than routine clinical practice.
Time and budgetary constraints often limit practicing psychiatrists from conducting more thorough diagnostic evaluations. It has been found that most clinicians evaluate patients using an unstructured, open-ended approach, with limited training in evidence-based assessment methods, and that inaccurate diagnosis may be common in routine practice. In addition, comorbidity is very common in psychiatric diagnosis, where the same person meets the criteria for more than one disorder. On the other hand, a person may have several different difficulties only some of which meet the criteria for being diagnosed. There may be specific problems with accurate diagnosis in developing countries.
More structured approaches are being increasingly used to measure levels of mental illness.
HoNOS is the most widely used measure in English mental health services, being used by at least 61 trusts. In HoNOS a score of 0–4 is given for each of 12 factors, based on functional living capacity. Research has been supportive of HoNOS, although some questions have been asked about whether it provides adequate coverage of the range and complexity of mental illness problems, and whether the fact that often only 3 of the 12 scales vary over time gives enough subtlety to accurately measure outcomes of treatment.
=== Criticism ===
Since the 1980s, Paula Caplan has been concerned about the subjectivity of psychiatric diagnosis, and people being arbitrarily "slapped with a psychiatric label." Caplan says because psychiatric diagnosis is unregulated, doctors are not required to spend much time interviewing patients or to seek a second opinion. The Diagnostic and Statistical Manual of Mental Disorders can lead a psychiatrist to focus on narrow checklists of symptoms, with little consideration of what is actually causing the person's problems. So, according to Caplan, getting a psychiatric diagnosis and label often stands in the way of recovery.
In 2013, psychiatrist Allen Frances wrote a paper entitled "The New Crisis of Confidence in Psychiatric Diagnosis", which said that "psychiatric diagnosis... still relies exclusively on fallible subjective judgments rather than objective biological tests." Frances was also concerned about "unpredictable overdiagnosis". For many years, marginalized psychiatrists (such as Peter Breggin, Thomas Szasz) and outside critics (such as Stuart A. Kirk) have "been accusing psychiatry of engaging in the systematic medicalization of normality." More recently these concerns have come from insiders who have worked for and promoted the American Psychiatric Association (e.g., Robert Spitzer, Allen Frances). A 2002 editorial in the British Medical Journal warned of inappropriate medicalization leading to disease mongering, where the boundaries of the definition of illnesses are expanded to include personal problems as medical problems or risks of diseases are emphasized to broaden the market for medications.
Gary Greenberg, a psychoanalyst, in his book "the Book of Woe", argues that mental illness is really about suffering and how the DSM creates diagnostic labels to categorize people's suffering. Indeed, the psychiatrist Thomas Szasz, in his book "the Medicalization of Everyday Life", also argues that what is psychiatric illness, is not always biological in nature (i.e. social problems, poverty, etc.), and may even be a part of the human condition.
=== Potential routine use of MRI/fMRI in diagnosis ===
in 2018 the American Psychological Association commissioned a review to reach a consensus on whether modern clinical MRI/fMRI will be able to be used in the diagnosis of mental health disorders. The criteria presented by the APA stated that the biomarkers used in diagnosis should:
"have a sensitivity of at least 80% for detecting a particular psychiatric disorder"
should "have a specificity of at least 80% for distinguishing this disorder from other psychiatric or medical disorders"
"should be reliable, reproducible, and ideally be noninvasive, simple to perform, and inexpensive"
proposed biomarkers should be verified by 2 independent studies each by a different investigator and different population samples and published in a peer-reviewed journal.
The review concluded that although neuroimaging diagnosis may technically be feasible, very large studies are needed to evaluate specific biomarkers which were not available.
== Prevention ==
The 2004 WHO report "Prevention of Mental Disorders" stated that "Prevention of these disorders is obviously one of the most effective ways to reduce the [disease] burden."
The 2011 European Psychiatric Association (EPA) guidance on prevention of mental disorders states "There is considerable evidence that various psychiatric conditions can be prevented through the implementation of effective evidence-based interventions."
A 2011 UK Department of Health report on the economic case for mental health promotion and mental illness prevention found that "many interventions are outstandingly good value for money, low in cost and often become self-financing over time, saving public expenditure".
In 2016, the National Institute of Mental Health re-affirmed prevention as a research priority area.
Parenting may affect the child's mental health, and evidence suggests that helping parents to be more effective with their children can address mental health needs.
Universal prevention (aimed at a population that has no increased risk for developing a mental disorder, such as school programs or mass media campaigns) need very high numbers of people to show effect (sometimes known as the "power" problem). Approaches to overcome this are (1) focus on high-incidence groups (e.g. by targeting groups with high risk factors), (2) use multiple interventions to achieve greater, and thus more statistically valid, effects, (3) use cumulative meta-analyses of many trials, and (4) run very large trials.
== Management ==
Treatment and support for mental disorders are provided in psychiatric hospitals, clinics or a range of community mental health services. In some countries services are increasingly based on a recovery approach, intended to support individual's personal journey to gain the kind of life they want.
There is a range of different types of treatment and what is most suitable depends on the disorder and the individual. Many things have been found to help at least some people, and a placebo effect may play a role in any intervention or medication. In a minority of cases, individuals may be treated against their will, which can cause particular difficulties depending on how it is carried out and perceived. Compulsory treatment while in the community versus non-compulsory treatment does not appear to make much of a difference except by maybe decreasing victimization.
=== Lifestyle ===
Lifestyle strategies, including dietary changes, exercise and quitting smoking may be of benefit.
Dietary patterns can influence the risk and management of mental disorders. Observational studies have shown that nutrient-dense, whole-food diets - such as the Mediterranean diet, which is rich in fruits, vegetables, whole grains, legumes, nuts, fish, and healthy fats like olive oil - are associated with a lower risk of depression and anxiety. In contrast, Western diets high in ultra-processed foods, refined sugars, and saturated fats are linked to a greater incidence of mental health disorders, potentially due to their impact on neuroinflammation, oxidative stress, gut microbiota, and neuroplasticity.
=== Therapy ===
There is also a wide range of psychotherapists (including family therapy), counselors, and public health professionals. In addition, there are peer support roles where personal experience of similar issues is the primary source of expertise.
A major option for many mental disorders is psychotherapy. There are several main types. Cognitive behavioral therapy (CBT) is widely used and is based on modifying the patterns of thought and behavior associated with a particular disorder. Other psychotherapies include dialectic behavioral therapy (DBT) and interpersonal psychotherapy (IPT). Psychoanalysis, addressing underlying psychic conflicts and defenses, has been a dominant school of psychotherapy and is still in use. Systemic therapy or family therapy is sometimes used, addressing a network of significant others as well as an individual.
Some psychotherapies are based on a humanistic approach. There are many specific therapies used for particular disorders, which may be offshoots or hybrids of the above types. Mental health professionals often employ an eclectic or integrative approach. Much may depend on the therapeutic relationship, and there may be problems with trust, confidentiality and engagement.
=== Medication ===
A major option for many mental disorders is psychiatric medication and there are several main groups. Antidepressants are used for the treatment of clinical depression, as well as often for anxiety and a range of other disorders. Anxiolytics (including sedatives) are used for anxiety disorders and related problems such as insomnia. Mood stabilizers are used primarily in bipolar disorder. Antipsychotics are used for psychotic disorders, notably for positive symptoms in schizophrenia, and also increasingly for a range of other disorders. Stimulants are commonly used, notably for ADHD.
=== Other ===
Electroconvulsive therapy (ECT) is sometimes used in severe cases when other interventions for severe intractable depression have failed. ECT is usually indicated for treatment resistant depression, severe vegetative symptoms, psychotic depression, intense suicidal ideation, depression during pregnancy, and catatonia. Psychosurgery is considered experimental but is advocated by some neurologists in certain rare cases.
Counseling (professional) and co-counseling (between peers) may be used. Psychoeducation programs may provide people with the information to understand and manage their problems. Creative therapies are sometimes used, including music therapy, art therapy or drama therapy. Lifestyle adjustments and supportive measures are often used, including peer support, self-help groups for mental health and supported housing or supported employment (including social firms). Some advocate dietary supplements.
Reasonable accommodations (adjustments and supports) might be put in place to help an individual cope and succeed in environments despite potential disability related to mental health problems. This could include an emotional support animal or specifically trained psychiatric service dog. As of 2019 cannabis is specifically not recommended as a treatment.
== Epidemiology ==
Mental disorders are common. Worldwide, more than one in three people in most countries report sufficient criteria for at least one at some point in their life. In the United States, 46% qualify for a mental illness at some point. An ongoing survey indicates that anxiety disorders are the most common in all but one country, followed by mood disorders in all but two countries, while substance disorders and impulse-control disorders were consistently less prevalent. Rates varied by region.
A review of anxiety disorder surveys in different countries found average lifetime prevalence estimates of 16.6%, with women having higher rates on average. A review of mood disorder surveys in different countries found lifetime rates of 6.7% for major depressive disorder (higher in some studies, and in women) and 0.8% for Bipolar I disorder.
In the United States the frequency of disorder is: anxiety disorder (28.8%), mood disorder (20.8%), impulse-control disorder (24.8%) or substance use disorder (14.6%).
A 2004 cross-Europe study found that approximately one in four people reported meeting criteria at some point in their life for at least one of the DSM-IV disorders assessed, which included mood disorders (13.9%), anxiety disorders (13.6%), or alcohol disorder (5.2%). Approximately one in ten met the criteria within a 12-month period. Women and younger people of either gender showed more cases of the disorder. A 2005 review of surveys in 16 European countries found that 27% of adult Europeans are affected by at least one mental disorder in a 12-month period.
An international review of studies on the prevalence of schizophrenia found an average (median) figure of 0.4% for lifetime prevalence; it was consistently lower in poorer countries.
Studies of the prevalence of personality disorders (PDs) have been fewer and smaller-scale, but one broad Norwegian survey found a five-year prevalence of almost 1 in 7 (13.4%). Rates for specific disorders ranged from 0.8% to 2.8%, differing across countries, and by gender, educational level and other factors. A US survey that incidentally screened for personality disorder found a rate of 14.79%.
Approximately 7% of a preschool pediatric sample were given a psychiatric diagnosis in one clinical study, and approximately 10% of 1- and 2-year-olds receiving developmental screening have been assessed as having significant emotional/behavioral problems based on parent and pediatrician reports.
While rates of psychological disorders are often the same for men and women, women tend to have a higher rate of depression. Each year 73 million women are affected by major depression, and suicide is ranked 7th as the cause of death for women between the ages of 20–59. Depressive disorders account for close to 41.9% of the psychiatric disabilities among women compared to 29.3% among men.
== History ==
=== Ancient civilizations ===
Ancient civilizations described and treated a number of mental disorders. Mental illnesses were well known in ancient Mesopotamia, where diseases and mental disorders were believed to be caused by specific deities. Because hands symbolized control over a person, mental illnesses were known as "hands" of certain deities. One psychological illness was known as Qāt Ištar, meaning "Hand of Ishtar". Others were known as "Hand of Shamash", "Hand of the Ghost", and "Hand of the God". Descriptions of these illnesses, however, are so vague that it is usually impossible to determine which illnesses they correspond to in modern terminology. Mesopotamian doctors kept detailed record of their patients' hallucinations and assigned spiritual meanings to them. The royal family of Elam was notorious for its members often being insane. The Greeks coined terms for melancholy, hysteria and phobia and developed the humorism theory. Mental disorders were described, and treatments developed, in Persia, Arabia and in the medieval Islamic world.
=== Europe ===
==== Middle Ages ====
Conceptions of madness in the Middle Ages in Christian Europe were a mixture of the divine, diabolical, magical and humoral, and transcendental. In the early modern period, some people with mental disorders may have been victims of the witch-hunts. While not every witch and sorcerer accused were mentally ill, all mentally ill were considered to be witches or sorcerers. Many terms for mental disorders that found their way into everyday use first became popular in the 16th and 17th centuries.
==== Eighteenth century ====
By the end of the 17th century and into the Enlightenment, madness was increasingly seen as an organic physical phenomenon with no connection to the soul or moral responsibility. Asylum care was often harsh and treated people like wild animals, but towards the end of the 18th century a moral treatment movement gradually developed. Clear descriptions of some syndromes may be rare before the 19th century.
==== Nineteenth century ====
Industrialization and population growth led to a massive expansion of the number and size of insane asylums in every Western country in the 19th century. Numerous different classification schemes and diagnostic terms were developed by different authorities, and the term psychiatry was coined (1808), though medical superintendents were still known as alienists.
==== Twentieth century ====
The turn of the 20th century saw the development of psychoanalysis, which would later come to the fore, along with Kraepelin's classification scheme. Asylum "inmates" were increasingly referred to as "patients", and asylums were renamed as hospitals.
=== Europe and the United States ===
Early in the 20th century in the United States, a mental hygiene movement developed, aiming to prevent mental disorders. Clinical psychology and social work developed as professions. World War I saw a massive increase of conditions that came to be termed "shell shock".
World War II saw the development in the U.S. of a new psychiatric manual for categorizing mental disorders, which along with existing systems for collecting census and hospital statistics led to the first Diagnostic and Statistical Manual of Mental Disorders. The International Classification of Diseases (ICD) also developed a section on mental disorders. The term stress, having emerged from endocrinology work in the 1930s, was increasingly applied to mental disorders.
Electroconvulsive therapy, insulin shock therapy, lobotomies and the neuroleptic chlorpromazine came to be used by mid-century. In the 1960s there were many challenges to the concept of mental illness itself. These challenges came from psychiatrists like Thomas Szasz who argued that mental illness was a myth used to disguise moral conflicts; from sociologists such as Erving Goffman who said that mental illness was merely another example of how society labels and controls non-conformists; from behavioral psychologists who challenged psychiatry's fundamental reliance on unobservable phenomena; and from gay rights activists who criticised the APA's listing of homosexuality as a mental disorder. A study published in Science by Rosenhan received much publicity and was viewed as an attack on the efficacy of psychiatric diagnosis.
Deinstitutionalization gradually occurred in the West, with isolated psychiatric hospitals being closed down in favor of community mental health services. A consumer/survivor movement gained momentum. Other kinds of psychiatric medication gradually came into use, such as "psychic energizers" (later antidepressants) and lithium. Benzodiazepines gained widespread use in the 1970s for anxiety and depression, until dependency problems curtailed their popularity.
Advances in neuroscience, genetics, and psychology led to new research agendas. Cognitive behavioral therapy and other psychotherapies developed. The DSM and then ICD adopted new criteria-based classifications, and the number of "official" diagnoses saw a large expansion. Through the 1990s, new SSRI-type antidepressants became some of the most widely prescribed drugs in the world, as later did antipsychotics. Also during the 1990s, a recovery approach developed.
=== Africa and Nigeria ===
Most Africans view mental disturbances as external spiritual attack on the person. Those who have a mental illness are thought to be under a spell or bewitched. Often than usual, People view a mentally ill person as possessed of an evil spirit and is seen as more of sociological perspective than a psychological order.
The WHO estimated that fewer than 10% of mentally ill Nigerians have access to a psychiatrist or health worker, because there is a low ratio of mental-health specialists available in a country of 200 million people. WHO estimates that the number of mentally ill Nigerians ranges from 40 million to 60 million. Disorders such as depression, anxiety, schizophrenia, personality disorder, old age-related disorder, and substance-abuse disorder are common in Nigeria, as in other countries in Africa.
Nigeria is still nowhere near being equipped to solve prevailing mental health challenges. With little scientific research carried out, coupled with insufficient mental-health hospitals in the country, traditional healers provide specialized psychotherapy care to those that require their services and pharmacotherapy
=== China ===
The history of mental illness management in China dates back to the Tang Dynasty (618-907 AD), when the Bei Tian Fang, a charity facility run by monks, provided care for homeless widows, orphans, and individuals with mental illness. This early approach laid the foundation for structured mental health care. The first Western-style psychiatric hospital was established in 1898 by American missionary John Kerr in what is now the Guangzhou Brain Hospital. However, psychiatric hospital development was slow over the next 50 years, with only a handful of facilities emerging in major cities. By mid-20th century, China had approximately 100 psychiatrists and 1,000 psychiatric beds.
Following the establishment of the People's Republic of China in 1949, psychiatric hospitals were introduced in every province, primarily aimed at maintaining social stability. The first National Mental Health Meeting in 1958 initiated community mental health programs in key regions like Beijing, Shanghai, Hunan, Sichuan, and Jiangsu. These programs focused on professional training, early intervention, and relapse prevention. However, during the Cultural Revolution (1966-1976), most community mental health initiatives ceased, although localized rehabilitation centers and community care networks persisted in places like Shanghai and Beijing.
== Society and culture ==
Different societies or cultures, even different individuals in a subculture, can disagree as to what constitutes optimal versus pathological biological and psychological functioning. Research has demonstrated that cultures vary in the relative importance placed on, for example, happiness, autonomy, or social relationships for pleasure. Likewise, the fact that a behavior pattern is valued, accepted, encouraged, or even statistically normative in a culture does not necessarily mean that it is conducive to optimal psychological functioning.
People in all cultures find some behaviors bizarre or even incomprehensible. But just what they feel is bizarre or incomprehensible is ambiguous and subjective. These differences in determination can become highly contentious. The process by which conditions and difficulties come to be defined and treated as medical conditions and problems, and thus come under the authority of doctors and other health professionals, is known as medicalization or pathologization.
=== Mental illness in the Latin American community ===
There is a perception in Latin American communities, especially among older people, that discussing problems with mental health can create embarrassment and shame for the family. This results in fewer people seeking treatment.
Latin Americans from the US are slightly more likely to have a mental health disorder than first-generation Latin American immigrants, although differences between ethnic groups were found to disappear after adjustment for place of birth.
From 2015 to 2018, rates of serious mental illness in young adult Latin Americans increased by 60%, from 4% to 6.4%. The prevalence of major depressive episodes in young and adult Latin Americans increased from 8.4% to 11.3%. More than a third of Latin Americans reported more than one bad mental health day in the last three months. The rate of suicide among Latin Americans was about half the rate of non-Latin American white Americans in 2018, and this was the second-leading cause of death among Latin Americans ages 15 to 34. However, Latin American suicide rates rose steadily after 2020 in relation to the COVID-19 pandemic, even as the national rate declined.
Family relations are an integral part of the Latin American community. Some research has shown that Latin Americans are more likely rely on family bonds, or familismo, as a source of therapy while struggling with mental health issues. Because Latin Americans have a high rate of religiosity, and because there is less stigma associated with religion than with psychiatric services, religion may play a more important therapeutic role for the mentally ill in Latin American communities. However, research has also suggested that religion may also play a role in stigmatizing mental illness in Latin American communities, which can discourage community members from seeking professional help.
=== Religion ===
Religious, spiritual, or transpersonal experiences and beliefs meet many criteria of delusional or psychotic disorders. A belief or experience can sometimes be shown to produce distress or disability—the ordinary standard for judging mental disorders. There is a link between religion and schizophrenia, a complex mental disorder characterized by a difficulty in recognizing reality, regulating emotional responses, and thinking in a clear and logical manner. Those with schizophrenia commonly report some type of religious delusion, and religion itself may be a trigger for schizophrenia.
=== Movements ===
Controversy has often surrounded psychiatry, and the term anti-psychiatry was coined by the psychiatrist David Cooper in 1967. The anti-psychiatry message is that psychiatric treatments are ultimately more damaging than helpful to patients, and psychiatry's history involves what may now be seen as dangerous treatments. Electroconvulsive therapy was one of these, which was used widely between the 1930s and 1960s. Lobotomy was another practice that was ultimately seen as too invasive and brutal. Diazepam and other sedatives were sometimes over-prescribed, which led to an epidemic of dependence. There was also concern about the large increase in prescribing psychiatric drugs for children. Some charismatic psychiatrists came to personify the movement against psychiatry. The most influential of these was R.D. Laing who wrote a series of best-selling books, including The Divided Self. Thomas Szasz wrote The Myth of Mental Illness. Some ex-patient groups have become militantly anti-psychiatric, often referring to themselves as survivors. Giorgio Antonucci has questioned the basis of psychiatry through his work on the dismantling of two psychiatric hospitals (in the city of Imola), carried out from 1973 to 1996.
The consumer/survivor movement (also known as user/survivor movement) is made up of individuals (and organizations representing them) who are clients of mental health services or who consider themselves survivors of psychiatric interventions. Activists campaign for improved mental health services and for more involvement and empowerment within mental health services, policies and wider society. Patient advocacy organizations have expanded with increasing deinstitutionalization in developed countries, working to challenge the stereotypes, stigma and exclusion associated with psychiatric conditions. There is also a carers rights movement of people who help and support people with mental health conditions, who may be relatives, and who often work in difficult and time-consuming circumstances with little acknowledgement and without pay. An anti-psychiatry movement fundamentally challenges mainstream psychiatric theory and practice, including in some cases asserting that psychiatric concepts and diagnoses of 'mental illness' are neither real nor useful.
Alternatively, a movement for global mental health has emerged, defined as 'the area of study, research and practice that places a priority on improving mental health and achieving equity in mental health for all people worldwide'.
=== Cultural bias ===
Diagnostic guidelines of the 2000s, namely the DSM and to some extent the ICD, have been criticized as having a fundamentally Euro-American outlook. Opponents argue that even when diagnostic criteria are used across different cultures, it does not mean that the underlying constructs have validity within those cultures, as even reliable application can prove only consistency, not legitimacy. Advocating a more culturally sensitive approach, critics such as Carl Bell and Marcello Maviglia contend that the cultural and ethnic diversity of individuals is often discounted by researchers and service providers.
Cross-cultural psychiatrist Arthur Kleinman contends that the Western bias is ironically illustrated in the introduction of cultural factors to the DSM-IV. Disorders or concepts from non-Western or non-mainstream cultures are described as "culture-bound", whereas standard psychiatric diagnoses are given no cultural qualification whatsoever, revealing to Kleinman an underlying assumption that Western cultural phenomena are universal. Kleinman's negative view towards the culture-bound syndrome is largely shared by other cross-cultural critics. Common responses included both disappointment over the large number of documented non-Western mental disorders still left out and frustration that even those included are often misinterpreted or misrepresented.
Many mainstream psychiatrists are dissatisfied with the new culture-bound diagnoses, although for partly different reasons. Robert Spitzer, a lead architect of the DSM-III, has argued that adding cultural formulations was an attempt to appease cultural critics, and has stated that they lack any scientific rationale or support. Spitzer also posits that the new culture-bound diagnoses are rarely used, maintaining that the standard diagnoses apply regardless of the culture involved. In general, mainstream psychiatric opinion remains that if a diagnostic category is valid, cross-cultural factors are either irrelevant or are significant only to specific symptom presentations.
Clinical conceptions of mental illness also overlap with personal and cultural values in the domain of morality, so much so that it is sometimes argued that separating the two is impossible without fundamentally redefining the essence of being a particular person in a society. In clinical psychiatry, persistent distress and disability indicate an internal disorder requiring treatment; but in another context, that same distress and disability can be seen as an indicator of emotional struggle and the need to address social and structural problems. This dichotomy has led some academics and clinicians to advocate a postmodernist conceptualization of mental distress and well-being.
Such approaches, along with cross-cultural and "heretical" psychologies centered on alternative cultural and ethnic and race-based identities and experiences, stand in contrast to the mainstream psychiatric community's alleged avoidance of any explicit involvement with either morality or culture. In many countries there are attempts to challenge perceived prejudice against minority groups, including alleged institutional racism within psychiatric services. There are also ongoing attempts to improve professional cross cultural sensitivity.
=== Laws and policies ===
Three-quarters of countries around the world have mental health legislation. Compulsory admission to mental health facilities (also known as involuntary commitment) is a controversial topic. It can impinge on personal liberty and the right to choose, and carry the risk of abuse for political, social, and other reasons; yet it can potentially prevent harm to self and others, and assist some people in attaining their right to healthcare when they may be unable to decide in their own interests. Because of this it is a concern of medical ethics.
All human rights oriented mental health laws require proof of the presence of a mental disorder as defined by internationally accepted standards, but the type and severity of disorder that counts can vary in different jurisdictions. The two most often used grounds for involuntary admission are said to be serious likelihood of immediate or imminent danger to self or others, and the need for treatment. Applications for someone to be involuntarily admitted usually come from a mental health practitioner, a family member, a close relative, or a guardian. Human-rights-oriented laws usually stipulate that independent medical practitioners or other accredited mental health practitioners must examine the patient separately and that there should be regular, time-bound review by an independent review body. The individual should also have personal access to independent advocacy.
For involuntary treatment to be administered (by force if necessary), it should be shown that an individual lacks the mental capacity for informed consent (i.e. to understand treatment information and its implications, and therefore be able to make an informed choice to either accept or refuse). Legal challenges in some areas have resulted in supreme court decisions that a person does not have to agree with a psychiatrist's characterization of the issues as constituting an "illness", nor agree with a psychiatrist's conviction in medication, but only recognize the issues and the information about treatment options.
Proxy consent (also known as surrogate or substituted decision-making) may be transferred to a personal representative, a family member, or a legally appointed guardian. Moreover, patients may be able to make, when they are considered well, an advance directive stipulating how they wish to be treated should they be deemed to lack mental capacity in the future. The right to supported decision-making, where a person is helped to understand and choose treatment options before they can be declared to lack capacity, may also be included in the legislation. There should at the very least be shared decision-making as far as possible. Involuntary treatment laws are increasingly extended to those living in the community, for example outpatient commitment laws (known by different names) are used in New Zealand, Australia, the United Kingdom, and most of the United States.
The World Health Organization reports that in many instances national mental health legislation takes away the rights of persons with mental disorders rather than protecting rights, and is often outdated. In 1991, the United Nations adopted the Principles for the Protection of Persons with Mental Illness and the Improvement of Mental Health Care, which established minimum human rights standards of practice in the mental health field. In 2006, the UN formally agreed the Convention on the Rights of Persons with Disabilities to protect and enhance the rights and opportunities of disabled people, including those with psychiatric disabilities.
The term insanity, sometimes used colloquially as a synonym for mental illness, is often used technically as a legal term.
=== Perception and discrimination ===
==== Stigma ====
The social stigma associated with mental disorders is a widespread problem. The US Surgeon General stated in 1999 that: "Powerful and pervasive, stigma prevents people from acknowledging their own mental health problems, much less disclosing them to others." Additionally, researcher Wulf Rössler in 2016, in his article, "The Stigma of Mental Disorders" stated:
For millennia, society did not treat persons suffering from depression, autism, schizophrenia and other mental illnesses much better than slaves or criminals: they were imprisoned, tortured or killed.
In the United States, racial and ethnic minorities are more likely to experience mental health disorders often due to low socioeconomic status, and discrimination. In Taiwan, people with mental disorders often face misconceptions from the general public. These misconceptions include the belief that mental health issues stem from excessive worry, having too much free time, a lack of progress or ambition, not taking life seriously, neglecting real-life responsibilities, mental weakness, unwillingness to be resilient, perfectionism, or a lack of courage.
Employment discrimination is reported to play a significant part in the high rate of unemployment among those with a diagnosis of mental illness. An Australian study found that having a psychiatric disability is a bigger barrier to employment than a physical disability. The mentally ill are stigmatized in Chinese society and can not legally marry.
Efforts are being undertaken worldwide to eliminate the stigma of mental illness, although the methods and outcomes used have sometimes been criticized.
==== Media and general public ====
Media coverage of mental illness comprises predominantly negative and pejorative depictions, for example, of incompetence, violence or criminality, with far less coverage of positive issues such as accomplishments or human rights issues. Such negative depictions, including in children's cartoons, are thought to contribute to stigma and negative attitudes in the public and in those with mental health problems themselves, although more sensitive or serious cinematic portrayals have increased in prevalence.
In the United States, the Carter Center has created fellowships for journalists in South Africa, the U.S., and Romania, to enable reporters to research and write stories on mental health topics. Former US First Lady Rosalynn Carter began the fellowships not only to train reporters in how to sensitively and accurately discuss mental health and mental illness, but also to increase the number of stories on these topics in the news media. There is also a World Mental Health Day, which in the United States and Canada falls within a Mental Illness Awareness Week.
The general public have been found to hold a strong stereotype of dangerousness and desire for social distance from individuals described as mentally ill. A US national survey found that a higher percentage of people rate individuals described as displaying the characteristics of a mental disorder as "likely to do something violent to others", compared to the percentage of people who are rating individuals described as being troubled. In the article, "Discrimination Against People with a Mental Health Diagnosis: Qualitative Analysis of Reported Experiences", an individual who has a mental disorder, revealed that, "If people don't know me and don't know about the problems, they'll talk to me quite happily. Once they've seen the problems or someone's told them about me, they tend to be a bit more wary." In addition, in the article, "Stigma and its Impact on Help-Seeking for Mental Disorders: What Do We Know?" by George Schomerus and Matthias Angermeyer, it is affirmed that "Family doctors and psychiatrists have more pessimistic views about the outcomes for mental illnesses than the general public (Jorm et al., 1999), and mental health professionals hold more negative stereotypes about mentally ill patients, but, reassuringly, they are less accepting of restrictions towards them."
Recent depictions in media have included leading characters successfully living with and managing a mental illness, including in bipolar disorder in Homeland (2011) and post-traumatic stress disorder in Iron Man 3 (2013).
=== Crime ===
The insanity defense may be used in a legal trial as an legal excuse for crime.
Despite public or media opinion, national studies have indicated that severe mental illness does not independently predict future violent behavior, on average, and is not a leading cause of violence in society. There is a statistical association with various factors that do relate to violence (in anyone), such as substance use and various personal, social, and economic factors. A 2015 review found that in the United States, about 4% of violence is attributable to people diagnosed with mental illness, and a 2014 study found that 7.5% of crimes committed by mentally ill people were directly related to the symptoms of their mental illness. The majority of people with serious mental illness are never violent.
In fact, findings consistently indicate that it is many times more likely that people diagnosed with a serious mental illness living in the community will be the victims rather than the perpetrators of violence. In a study of individuals diagnosed with "severe mental illness" living in a US inner-city area, a quarter were found to have been victims of at least one violent crime over the course of a year, a proportion eleven times higher than the inner-city average, and higher in every category of crime including violent assaults and theft. People with a diagnosis may find it more difficult to secure prosecutions, however, due in part to prejudice and being seen as less credible.
However, there are some specific diagnoses, such as childhood conduct disorder or adult antisocial personality disorder or psychopathy, which are defined by, or are inherently associated with, conduct problems and violence. There are conflicting findings about the extent to which certain specific symptoms, notably some kinds of psychosis (hallucinations or delusions) that can occur in disorders such as schizophrenia, delusional disorder or mood disorder, are linked to an increased risk of serious violence on average. The mediating factors of violent acts, however, are most consistently found to be mainly socio-demographic and socio-economic factors such as being young, male, of lower socioeconomic status and, in particular, substance use (including alcohol use) to which some people may be particularly vulnerable.
High-profile cases have led to fears that serious crimes, such as homicide, have increased due to deinstitutionalization, but the evidence does not support this conclusion. Violence that does occur in relation to mental disorder (against the mentally ill or by the mentally ill) typically occurs in the context of complex social interactions, often in a family setting rather than between strangers. It is also an issue in health care settings and the wider community.
== Mental health ==
The recognition and understanding of mental health conditions have changed over time and across cultures and there are still variations in definition, assessment, and classification, although standard guideline criteria are widely used. In many cases, there appears to be a continuum between mental health and mental illness, making diagnosis complex.: 39 According to the World Health Organization, over a third of people in most countries report problems at some time in their life which meet the criteria for diagnosis of one or more of the common types of mental disorder. Corey M Keyes has created a two continua model of mental illness and health which holds that both are related, but distinct dimensions: one continuum indicates the presence or absence of mental health, the other the presence or absence of mental illness. For example, people with optimal mental health can also have a mental illness, and people who have no mental illness can also have poor mental health.
== Other animals ==
Psychopathology in non-human primates has been studied since the mid-20th century. Over 20 behavioral patterns in captive chimpanzees have been documented as (statistically) abnormal for frequency, severity or oddness—some of which have also been observed in the wild. Captive great apes show gross behavioral abnormalities such as stereotypy of movements, self-mutilation, disturbed emotional reactions (mainly fear or aggression) towards companions, lack of species-typical communications, and generalized learned helplessness. In some cases such behaviors are hypothesized to be equivalent to symptoms associated with psychiatric disorders in humans such as depression, anxiety disorders, eating disorders and post-traumatic stress disorder. Concepts of antisocial, borderline and schizoid personality disorders have also been applied to non-human great apes.
The risk of anthropomorphism is often raised concerning such comparisons, and assessment of non-human animals cannot incorporate evidence from linguistic communication. However, available evidence may range from nonverbal behaviors—including physiological responses and homologous facial displays and acoustic utterances—to neurochemical studies. It is pointed out that human psychiatric classification is often based on statistical description and judgment of behaviors (especially when speech or language is impaired) and that the use of verbal self-report is itself problematic and unreliable.
Psychopathology has generally been traced, at least in captivity, to adverse rearing conditions such as early separation of infants from mothers; early sensory deprivation; and extended periods of social isolation. Studies have also indicated individual variation in temperament, such as sociability or impulsiveness. Particular causes of problems in captivity have included integration of strangers into existing groups and a lack of individual space, in which context some pathological behaviors have also been seen as coping mechanisms. Remedial interventions have included careful individually tailored re-socialization programs, behavior therapy, environment enrichment, and on rare occasions psychiatric drugs. Socialization has been found to work 90% of the time in disturbed chimpanzees, although restoration of functional sexuality and caregiving is often not achieved.
Laboratory researchers sometimes try to develop animal models of human mental disorders, including by inducing or treating symptoms in animals through genetic, neurological, chemical or behavioral manipulation, but this has been criticized on empirical grounds and opposed on animal rights grounds.
== See also ==
50 Signs of Mental Illness
List of mental disorders
Mental disorders and LGBTQ
Mental illness portrayed in media
Mental disorders in film
Mental illness in fiction
Neurotherapy
Parity of esteem
Psychological evaluation
Youth mental health crisis
== References ==
== Further reading ==
== External links ==
Defining Mental Disorder: Jerome Wakefield and His Critics
National Institute of Mental Health Archived 29 May 2009 at the Wayback Machine
International Committee of Women Leaders on Mental Health Archived 30 October 2008 at the Wayback Machine | Wikipedia/Psychiatric_diseases |
Colorectal surgery is a field in medicine dealing with disorders of the rectum, anus, and colon. The field is also known as proctology, but this term is now used infrequently within medicine and is most often employed to identify practices relating to the anus and rectum in particular. The word proctology is derived from the Greek words πρωκτός proktos, meaning "anus" or "hindparts", and -λογία -logia, meaning "science" or "study".
Physicians specializing in this field of medicine are called colorectal surgeons or proctologists. In the United States, to become colorectal surgeons, surgical doctors have to complete a general surgery residency as well as a colorectal surgery fellowship, upon which they are eligible to be certified in their field of expertise by the American Board of Colon and Rectal Surgery or the American Osteopathic Board of Proctology. In other countries, certification to practice proctology is given to surgeons at the end of a 2–3 year subspecialty residency by the country's board of surgery.
== Scope of the specialty ==
Colorectal surgical disorders include:
varicosities or swelling, and inflammation of veins in the rectum and anus (hemorrhoids)
unnatural cracks or tears in the anus (anal fissures)
abnormal connections or passageways between the rectum or other anorectal area to the skin surface (fistulas)
severe constipation conditions
fecal incontinence
protrusion of the walls of the rectum through the anus (rectal prolapse)
birth defects such as the imperforate anus
treatment of severe colic disorders, such as Crohn's disease
cancer of the colon and rectum (colorectal cancer)
repositioning of the rectal area if fallen out
anal cancer
any injuries to the anus
removal of objects inserted into anus
performing colonoscopies
performing hemorrhoidectomies
== Surgical treatment and diagnostic procedures ==
Surgical forms of treatment for these conditions include: colectomy, ileo/colostomy, polypectomy, strictureplasty, hemorrhoidectomy (in severe cases of hemorrhoids), minimally invasive surgery, anoplasty, and more depending on the condition the patient has. Diagnostic procedures, such as a colonoscopy, are very important in colorectal surgery, as they can tell the physician what type of diagnosis should be given and what procedure should be done to correct the condition. Other diagnostic procedures used by colorectal surgeons include: proctoscopy, defecating proctography, sigmoidoscopy. In recent times, the laparoscopic method of surgery has seen a surge of popularity, due to its lower risks, decreased recovery time, and smaller, more precise incisions achieved by using laparoscopic instruments.
== Mechanical bowel preparation ==
Mechanical bowel preparation (MBP) is a procedure lacking evidence in literature, wherein fecal matter is expelled from the bowel lumen prior to surgery, most commonly by using sodium phosphate.
== See also ==
Proctalgia fugax
== References == | Wikipedia/Colorectal_surgery |
Pediatric surgery is a subspecialty of surgery involving the surgery of fetuses, infants, children, adolescents, and young adults.
== History ==
Pediatric surgery arose in the middle of the 1879 century as the surgical care of birth defects required novel techniques and methods, and became more commonly based at children's hospitals. One of the sites of this innovation was the Children's Hospital of Philadelphia. Beginning in the 1940s under the surgical leadership of C. Everett Koop, newer techniques for endotracheal anesthesia of infants allowed surgical repair of previously untreatable birth defects. By the late 1970s, the infant death rate from several major congenital malformation syndromes had been reduced to near zero.
== Specialties ==
Subspecialties of pediatric surgery itself include: neonatal surgery and fetal surgery.
Other areas of surgery also have pediatric specialties of their own that require further training during the residencies and in a fellowship: pediatric cardiothoracic (surgery on the child's heart and/or lungs, including heart and/or lung transplantation), pediatric nephrological surgery (surgery on the child's kidneys and ureters, including renal, or kidney, transplantation), pediatric neurosurgery (surgery on the child's brain, central nervous system, spinal cord, and peripheral nerves), pediatric urological surgery (surgery on the child's urinary bladder and other structures below the kidney necessary for ejaculation), pediatric emergency surgery, surgery involving fetuses or embryos (overlapping with obstetric/gynecological surgery, neonatology, and maternal-fetal medicine), surgery involving adolescents or young adults, pediatric hepatological (liver) and gastrointestinal (stomach and intestines) surgery (including liver and intestinal transplantation in children), pediatric orthopedic surgery (muscle and bone surgery in children), pediatric plastic and reconstructive surgery (such as for burns, or for congenital defects like cleft palate not involving the major organs), and pediatric oncological (childhood cancer) surgery.
== Conditions ==
Common pediatric diseases that may require pediatric surgery include:
Congenital malformations: lymphangioma, cleft lip and palate, esophageal atresia and tracheoesophageal fistula, hypertrophic pyloric stenosis, intestinal atresia, necrotizing enterocolitis, meconium plugs, Hirschsprung's disease, Anorectal Malformations, Undescended Testes (Cryptorchidism), intestinal malrotation, Biliary Atresia, Pelviureteric Junction Obstruction
Abdominal wall defects: Omphalocele, Gastroschisis, Hernias
Chest wall deformities: Pectus Excavatum
Childhood tumors: like Neuroblastoma, Wilms' tumor, Rhabdomyosarcoma, ATRT, Liver tumors, Teratomas, kidney tumors:
Separation of conjoined twins
Disorders of Sexual Development
== See Related Syndromes ==
VACTERL Association
Apert Syndrome
CHARGE Syndrome
Currarino Syndrome
Pierre Robin Sequence
Prune Belly Syndrome
== See also ==
William E. Ladd; known as the father of pediatric surgery.
Lewis Spitz; Emeritus Nuffield Professor of Paediatric Surgery. Spitz was awarded Denis Browne Gold Medal, Rehbein Medal and the American Ladd Medal.
Robert Edward Gross; president of the American Association for Thoracic Surgery, a member of the National Academy of Sciences and a fellow of the American Academy of Arts and Sciences. He was also awarded the Denis Browne Gold Medal and the American Ladd Medal for his contributions in Pediatric Surgery research.
Morio Kasai; best known for the procedure that came to bear his name. He received the William E. Ladd Medal from the American Academy of Pediatrics, the Denis Browne Gold Medal from the British Association of Paediatric Surgeons and the Asahi Prize from the national newspaper known as the Asahi Shimbun.
== Associations of Pediatric Surgery ==
European Paediatric Surgeons’ Association: EUPSA
World Federation of Associations of Pediatric Surgeons: WOFAPS
American Pediatric Surgical Association: APSA
British Association of Paediatric Surgeons: BAPS
Deutsche Gesellschaft für Kinderchirurgie: German Association of Paediatric Surgeons (DKH)
Pan-African Paediatric Surgical Association: PAPSA
== References == | Wikipedia/Pediatric_surgery |
Cerebral angiography is a form of angiography which provides images of blood vessels in and around the brain, thereby allowing detection of abnormalities such as arteriovenous malformations and aneurysms.
It was pioneered in 1927 by the Portuguese neurologist Egas Moniz at the University of Lisbon, who also helped develop thorotrast for use in the procedure.
Typically a catheter is inserted into a large artery (such as the femoral artery) and threaded through the circulatory system to the carotid artery, where a contrast agent is injected. A series of radiographs are taken as the contrast agent spreads through the brain's arterial system, then a second series as it reaches the venous system.
For some applications, cerebral angiography may yield better images than less invasive methods such as computed tomography angiography and magnetic resonance angiography.
In addition, cerebral angiography allows certain treatments to be performed immediately, based on its findings. In recent decades, cerebral angiography has so assumed a therapeutic connotation thanks to the elaboration of endovascular therapeutic techniques. Embolization (a minimally invasive surgical technique) over time has played an increasingly significant role in the multimodal treatment of cerebral MAVs, facilitating subsequent microsurgical or radiosurgical treatment. Another type of treatment possible by angiography (if the images reveal an aneurysm) is the introduction of metal coils through the catheter already in place and maneuvered to the site of aneurysm; over time these coils encourage formation of connective tissue at the site, strengthening the vessel walls.
In some jurisdictions, cerebral angiography is required to confirm brain death.
Prior to the advent of modern neuroimaging techniques such as MRI and CT in the mid-1970s, cerebral angiographies were frequently employed as a tool to infer the existence and location of certain kinds of lesions and hematomas by looking for secondary vascular displacement caused by the mass effect related to these medical conditions. This use of angiography as an indirect assessment tool is nowadays obsolete as modern non-invasive diagnostic methods are available to image many kinds of primary intracranial abnormalities directly. It is still widely used however for evaluating various types of vascular pathologies within the skull.
== Uses ==
Cerebral angiography is used for diagnosis but may be followed by treatment procedures in the same setting. Cerebral angiography is used to image various intracranial (within the head) or extracranial (outside the head) diseases.
Intracranial diseases are: non-traumatic subarachnoid haemorrhage, non-traumatic intracerebral haemorrhage, intracranial aneurysm, stroke, cerebral vasospasm, cerebral arteriovenous malformation (for Spetzler-Martin grading and plan for intervention), dural arteriovenous fistula, embolisation of brain tumours such as meningioma, cavernous sinus haemangioma, for Wada test, and to obtain haemodynamics of cerebral blood flow such as cross flow, circulation time, and collateral flow.
Extracranial diseases are: Subclavian steal syndrome, rupture of the carotid artery, carotid artery stenosis, cervical spine trauma, epistaxis (nose bleeding) and plan for embolisation of juvenile nasopharyngeal angiofibroma before operation.
Although computed tomography angiography (CTA) and Magnetic resonance angiography (MRA) has been used widely in evaluation of intracranial disease, cerebral angiography provides higher resolution on the conditions of blood vessel lumens and vasculature. Cerebral angiography is also the standard of detecting intracranial aneurysm and evaluating the feasibility of endovascular coiling. Performing a cerebral angiogram by gaining access through the femoral artery or radial artery is feasible in order to treat cerebral aneurysms with a number of devices
Certain conditions such as contrast allergy, renal insufficiency, and coagulation disorders are contraindicated in this procedure.
== Technique ==
Before the procedure, focused history and neurological examination is performed, available imaging, and blood parameters are reviewed. When reviewing imaging, arch anatomy and variants are evaluated to select suitable catheters to assess the vessels. Complete blood count is reviewed to ensure adequate amount of haemoglobin in subject's body, and to rule out the presence of sepsis. Serum creatinine is assessed to rule out renal dysfunction. Meanwhile, prothrombin time is assessed to rule out coagulopathy. Informed consent regarding the risks of the procedure is taken. Anticoagulants are withheld if possible. Fasting is required 6 hours before the procedure and insulin requirement is reduced by half for those diabetics who are fasting. Bilateral groins (for femoral artery access) and left arm/forearm (for brachial artery/radial artery access) are prepared. Neurological status of the patient before sedation or anesthesia is recorded.
Sedation drug such as intravenous midazolam and painkiller such as fentanyl can be used if the subject is restless or painful. The subject is then lie down on supine position with arm at the sides. Uncooperative subjects may have their forehead tapped to reduce motion. The subject is advised to stay as still as possible especially when fluoroscopy images are taken. The subject is also advised to avoid swallowing when images of neck are taken. These measures are taken to reduce motion artifact in the images.
Right common femoral artery (RFA) is the preferred site of access. If RFA access is not optimal, then brachial artery access is chosen. Either a micropuncture system or an 18G access needle can be used with or without ultrasound guidance. There are four types of catheters that can be used: angled vertebral catheter for usual cases, Judkins right coronary catheter (Terumo) for tourtous vessels, Simmons's catheter and Mani's head hunter catheter (Terumo) for extremely tortous vessels. A 5Fr sheath is also placed within and flushed with heparinised saline to prevent clotting around the sheath. In terms of guidewire, Terumo hydrophilic Glidewire 0.035 inches can be used.
To prevent embolism (either due to blood clot or air embolism, "double flush" and "wet connect" techniques are used. In "double flush" technique, a saline syringe is used to aspirate blood from the catheter. Then, a second heparinised saline syringe is used to flush the catheter. "Wet connect" is the technique that connects syringe to a sheath without air bubbles within.
Digital subtraction angiography is the main technique of imaging the cerebral blood vessels. Catheter should be advanced over the guidewire. Rotating the catheter during advancement is also helpful. Roadmap (superimposing previous image on live fluoroscopic image) is used to advance catheters or guidewires before any vessel bifurcation can help to prevent vessel dissection. After the catheter is in position, guidewire is removed slowly with heparinised saline dripping into the catheter at the same time to prevent air embolism. Prior to contrast injection, backflow of the catheter should be established to ensure there is no wedging, dissection, or intracatheter clotting. During the catheterisation of vertebral artery, extra care should be taken to prevent vessel dissection or vasospasm. Delayed or incomplete contrast washout may indicate vasospasm or dissection.
=== Radiographic views ===
Cervical arch angiogram is taken if there is any suspicion of aortic arch narrowing, or any anatomical variants such as bovine arch (brachiocephalic trunk shares a common origin with left common carotid artery). If such abnormality is present, it results it difficulty in cannulation of the main branches of the aortic arch. The catheter of choice to cannulate this area is pigtail catheter with multiple side holes. Contrast injection rate of 20 to 25ml/sec is given with total volume of 40 to 50 ml of contrast. The frame rate of fluoroscopy is 4 to 6 frames per second. The image is taken in with the x-ray tube in left anterior oblique position.
To image the vessels of the neck such as common carotid, internal and external carotid arteries, AP, lateral, and 45 degrees bilateral oblique positions are taken. Contrast injection rate is 3 to 4 ml/sec with total volume of 7 to 9 ml. The frame rate of fluoroscopy is 3 to 4 frames/sec.
To image the anterior cerebral circulation such as internal and external carotid arteries and its branches, AP, Towne's and lateral views are taken. The petrous part of the temporal bone should be superimposed at the mid or lower orbits when taking the AP/Towne's view. Contrast injection rate is 6 to 7 ml/sec with total volume of contrast at 10 ml. The frame rate of fluoroscopy is 2 to 4 frames/sec. Neck extension can help to navigate into tortous cerival part of the internal carotid artery.
At the level of carotid bifurcation, AP and oblique images are taken. At the cavernous (C4) and ophthalmic segments (C6) of the internal carotid artery, Caldwell and lateral views are taken. At the supraclinoid segment (C5-clinoid, C6-ophthalmic, and C7-bifurcation to posterior communicating artery (PCOM) segments), AP view is used to access the terminal branches such as anterior cerebral artery (ACA), middle cerebral artery (MCA) while oblique view (25 to 35 degrees) is used to access the ACA, anterior communicating artery (ACOM), and MCA bifurcations. Lateral view is useful to visualise the PCOM while submentovertical view is useful to project ACOM above the nasal cavity, thus making it easier to access the anatomy of ACOM. Transorbital oblique view is useful to access the MCA anatomy.
The anatomy of external carotid artery is access via AP and lateral views.
To image the posterior circulation, such as vertebral and basilar arteries, AP, Towne's view, lateral projections near the back of the head and upper part of the neck is taken. In this case, petrous bone should be projected at the bottom or below the orbits to visualise the basilar artery and its branches in AP/Towne's view. The rate of injection is 3 to 5 ml/sec, for a total of 8ml. The fluoroscope will be catching images at a rate of 2 to 4 frames per second. Posterior cerebral artery (PCA) can be seen in AP view. The left vertebral artery is easier to cannulate than the right vertebral because of the straightforward anatomy of the left vertebral artery.
Any activation of primary collateral system (ACOM and PCOM arteries) or secondary collateral system (pial-pial and leptomeningeal-dural) in case of occlusion of internal carotid artery should also be documented. Leptomeningeal collaterals or pial collaterals are the small arterial connections that join the terminal branches of ACAs, MCAs, and PCAs on the surface of the brain.
=== Post-procedural care ===
Manual compression or percutaneous closure device can be used to stop the bleeding from common femoral artery. Groin haematoma should be monitored during intensive care unit (ICU) monitoring. The puncture should be immobilised (to prevent movement) for 24 hours post puncture. Neurological examination should be performed and new neurological deficit should be documented. Significant neurological changes should be evaluated with MRI scan or a repeat cerebral angiography to rule out acute stroke or vessel dissection. Painkiller should be administered if there is any puncture site pain.
== Complications ==
The most common complication is groin haematoma which occurs in 4% of those affected. Neurologic complications such as transient ischemic attack in 2.5% of the cases. There is also the risk of stroke with permanent neurological defect in 0.1% of the cases and may lead to death in 0.06%. Rarely, 0.3 to 1% of the cases experience cortical blindness from 3 minutes to 12 hours after the procedure. It is a condition where those affected experienced loss of vision with normal pupillary light reflex, and normal extraocular muscles movement. The condition can sometimes be accompanied by headaches, mental state changes, and memory losses.
Some risk factors of complications are if the subject is having subarachnoid haemorrhage, atherosclerotic cerebrovascular disease, frequent transient ischemic attacks, age more than 55 years, and poorly controlled diabetes. Besides, longer procedures, increased in number of catheter exchanges, and the use of larger size of catheters also increases the risk of complications.
== History ==
In 1896, E. Haschek and O.T. Lindenthal in Vienna, Austria, reported angiography of blood vessels by taking a series of X-rays after injecting a mixture of petroleum, quicklime, and mercuric sulfide into the hand of a cadaver.
Cerebral angiography was first described by Egas Moniz, a Portuguese physician and politician, in 1927. He performed this procedure on six patients. Two developed Horner's syndrome due to leaking of contrast material around the carotid artery, one developed temporary aphasia, and another died due to thromboembolism to the anterior circulation of the brain.
Prior to the 1970s the typical technique involved a needle puncture directly into the carotid artery, as depicted in the 1973 horror film The Exorcist, which was replaced by the current method of threading a catheter from a distant artery due to common complications caused by trauma to the artery at the puncture site in the neck (particularly hematomas of the neck, with possible compromission of the airway).
== References ==
== External links ==
Cerebral Angiography | Wikipedia/Cerebral_angiography |
World Neurosurgery is a monthly peer-reviewed medical journal that was established in 1973 as Surgical Neurology before obtaining its current name in 2010. It is published by Elsevier and is the official journal of the World Federation of Neurosurgical Societies. The editor-in-chief is Edward C. Benzel (Department of Neurosurgery, Cleveland Clinic).
== Editors-in-chief ==
Editors-in-chief have included:
Paul Bucy (Wake Forest University School of Medicine) and Robert J. White (Case Western Reserve University), 1973-1985
Eben Alexander Jr (Bowman Gray School of Medicine), 1986-1993
James I. Ausman (University of Illinois at Chicago and University of California, Los Angeles), 1994-2009
Michael L.J. Apuzzo (Keck School of Medicine of USC), 2010–2015
Edward C. Benzel (Department of Neurosurgery, Cleveland Clinic, January, 2015–present
== Abstracting and indexing ==
The journal is abstracted and indexed in:
According to the Journal Citation Reports, the journal has a 2020 impact factor of 2.104.
== References == | Wikipedia/World_Neurosurgery |
Microneurography is a neurophysiological method employed to visualize and record the traffic of nerve impulses that are conducted in peripheral nerves of waking human subjects. It can also be used in animal recordings. The method has been successfully employed to reveal functional properties of a number of neural systems, e.g. sensory systems related to touch, pain, and muscle sense as well as sympathetic activity controlling the constriction state of blood vessels. To study nerve impulses of an identified nerve, a fine tungsten needle microelectrode is inserted into the nerve and connected to a high input impedance differential amplifier. The exact position of the electrode tip within the nerve is then adjusted in minute steps until the electrode discriminates nerve impulses of interest. A unique feature and a significant strength of the microneurography method is that subjects are fully awake and able to cooperate in tests requiring mental attention, while impulses in a representative nerve fibre or set of nerve fibres are recorded, e.g. when cutaneous sense organs are stimulated or subjects perform voluntary precision movements.
== History ==
Before the microneurography technique was developed in the late 1960s, impulses in peripheral nerves had been recorded in animal experiments alone using a technique that involved dissection and splitting the nerve. This approach is not tolerable for general use in humans although it has been pursued in one single study. Actually, the concern of nerve damage was a major obstacle for the development of microneurography because the approach of inserting a needle electrode in a human nerve was generally regarded as potentially dangerous and involving substantial risk of permanent nerve damage. The two Swedish scientists who developed the microneuropgraphy technique (Hagbarth and Vallbo) handled the medical-ethical concern by performing a large series of experiments on their own nerves during a period of about 2 years while carefully checking for nerve damage. Working at the Department of Clinical Neurophysiology, Academic Hospital, Uppsala, they collected data resulting in the first papers representing three areas to become major fields of microneurography, i.e. afference from intra-muscular sense organs during voluntary contractions, response of cutaneous sense organs related to touch stimuli, and efferent sympathetic activity controlling the constriction of human blood vessels. The microneurography approach of Hagbarth and Vallbo based on epoxy resin coated tungsten microelectrodes is now generally accepted whereas an alternative attempt using glass coated platina-iridium electrodes had obviously limited success as it yielded a single short note alone.
== Structure of nerves ==
Nerve fibers (axons) of various kinds are more or less randomly mixed in most nerves. This is true for fibers of different functions as well as fibers of different sizes. Basically fiber diameter is closely related to function, e.g. the cutaneous pain system is dependent on small nerve fibers whereas discriminative touch is dependent on large fibers. With regard to fiber diameter there are two main categories: myelinated A-fibers are large and conduct impulses at high or moderate speed (5–75 m/s) while unmyelinated C-fibers are small and conduct impulses at low speed (around 1 m/s). In microneurography recordings, A- and C-fiber impulses differ in shape and polarity of the main upstroke of the action potential. Because fibers are mixed in most nerves, it is usually essential to record from an individual nerve fiber at a time to explore the properties of a functional system, although multi-unit recording has been very rewarding in studies of sympathetic efferent activity. An individual nerve consists of a number of fascicles, i.e. bundles of nerve fibers enclosed within a connective tissue sheath containing the different nerve fibers. Therefore, the tip of the microelectrode needs to be not only intraneural but also intrafascicular for a recording to be possible.
== Methods ==
Microneurography is based on tungsten needle microelectrodes which are inserted through the skin and into a nerve. Anaesthetics are not required because the procedure induces only minimal discomfort. The tungsten microelectrodes have a shaft diameter of 100-200 μm, a tip diameter of 1-5 μm, and they are insulated to the tip with an epoxy resin. Electrode impedance varies between 0.3 and 5 MΩ at 1 kHz as measured initially. However, the impedance tends to decrease during experiment and is usually below 1 MΩ while impulses are recorded. Nerve discharges are determined by voltage differences between the intra-neural electrode and a reference needle electrode in the vicinity. The 2 electrodes are connected to a differential amplifier with a high input impedance and an appropriate band-pass filtering, often 500 to 5000 Hz. Signals are monitored on a computer screen and stored on a hard disc for off-line analysis. Any peripheral nerve that can be reached may be a target for microneurography recordings, typically in the arm or leg, although recording from facial nerves and the vagus nerve have also been achieved.
In order to locate deep nerves, electrical stimulation through a needle electrode or ultrasonic monitoring is often used. This is rarely needed when recording from cutaneous superficial nerves, such as the superficial peroneal or superficial radial nerves, that can easily be located visually and by palpation.
When electrical localization is needed, weak electrical shocks are delivered either through the recording electrode or through a separate stimulation needle while adjusting the electrode tip until a neural response is observed, either a muscle twitch or a cutaneous sensation reported by the subject. In ultrasonic monitoring, a linear, high frequency ultrasound probe is used.
The microelectrode is then inserted 1–2 cm from the probe, ideally in a 90° angle to the ultrasonic beam. This generates the best wave reflection and image. Ultrasonic approach accurately locates the depth of the nerve and identifies surrounding anatomical structures of interest, such as blood vessels and bony structures, which may affect the placement of a microelectrode. A particular advantage is that the ultrasonic approach visualizes the electrode and the nerve at the same time, thereby facilitating electrode manipulation to reach the nerve. Once the electrode tip is in the nerve, small adjustments are required, first, to penetrate the sheath of an individual fascicle and, second, to take the tip close to the nerve fibers of the kind you are interested to explore, be it multi-unit sympathetic activity or single unit activity of either a myelinated afferent or a small unmyelinated fibres.
=== The marking technique ===
Recording of single afferent impulses from C-fibers was greatly improved by the development of the so-called 'marking technique'. This technique is based on a unique property of many kinds of C-fibres, i.e. a decrease of conduction velocity in the wake of preceding impulses.
By combining repetitive electrical stimulation and physical stimulation, e.g. mechanical or thermal stimuli, units responding to the physical stimulation will display sudden slowing of their conduction velocity which can be easily visualized in raster plots of latency. This allows identification and characterization of nerve fiber responsiveness to natural stimulation. The marking technique is very efficient as it allows simultaneous recordings of several fibers. However, it generates only semi-quantitative information about unitary activity, whereas recordings of impulse trains allow more comprehensive description of functional properties of sense organs.
=== Micro-stimulation ===
The microneurography electrode may be used not only for recording of nerve impulses but for stimulation of individual fibers as well. An interesting application is to combine successive recording and stimulation of the same afferent. Once the functional properties of an afferent have been defined, e.g. with regard to sensitivity, receptive field structure, and adaptation, the electrode may be reconnected to a stimulator to give trains of electrical pulses of controlled strength, rate, and duration. It has been found that the percept elicited from a single tactile afferent in the glabrous skin of the hand, may be remarkably detailed and closely matching the properties of the afferent, indicating a high degree of specificity. Although this approach to bridge the gap between biophysical events in a single afferent and mental phenomena within the mind is simple and straight forward in principle it is demanding in practice for a number of reasons. Micro-stimulation has also been used to characterize individual motor units with regard to contraction properties.
== Functional systems explored ==
Microneurography recordings have elucidated the organization as well as normal and pathological function of a fair number of neural systems in human. Recently, the technique has also been used in clinical situations for diagnostic purposes to clarify the condition of the individual patient. Three main groups of neural systems have been explored, i.e. proprioception, cutaneous sensibility, and sympathetic efferent activity.
== Proprioception and motor control ==
Information from a variety of sense organs provides information about joint positions and movements. The most elaborate proprioceptive sense organ is the muscle spindle. It is unique because its functional state is continually controlled from the brain through the fusimotor system. Recordings from muscle spindle afferents indicate that the fusimotor system remains largely passive when the parent muscle is relaxed whereas is it regularly activated in voluntary contractions and more so the stronger the contraction. Thus microneurography suggests a parallelism between the two motor systems, i.e. the skeletomotor system controlling the ordinary muscle fibers and the fusimotor system. This seems to hold at least for weak contractions and small movements which have been explored so far. In contrast, more independent fusimotor activity has been reported in animal experiments, mainly cat hind limb, where larger movements are allowed. Thanks to fusimotor activation, the afferent signal from muscle spindles remains efficient in monitoring large changes of muscle length without turning silent during muscle shortening. On the other hand, very small intramuscular events are monitored as well, thanks to the extreme sensitivity of the sense organ.
An example is the small pulsatile component of the muscle contraction which is due to a periodic fluctuation at 8–10 Hz of the motor command. These small variations are insentient but readily monitored by the population of spindle afferents. They are akin to the tremor we may experience when emotionally excited. The functional significance of the insentient spindle response to faint intramuscular events remains to be assessed. However, it seems likely that detailed information on large as well as small mechanical events in the muscles is essential for neural systems in the brain to produce appropriate commands for dexterous movements.
Microneurography has demonstrated that our brains make use of detailed proprioceptive information not only by deep sense organs but by cutaneous mechanoreceptors as well. Any joint movement causing the slightest skin stretch is accurately monitored by cutaneous Ruffini endings in the skin area surrounding the joint.
== Cutaneous sensibility ==
Cutaneous sensibility includes a number of functions. Microneurography has been particularly used to investigate discriminative and affective touch mechanisms, as well as pain mechanisms, although afferents related to pruritus and temperature have been studied to some extent as well. A separate set of studies concern motor effects from cutaneous tactile afferents in the glabrous skin.
=== Discriminative touch ===
Two different tactile systems have been identified. A system for discriminative touch has been intensely studied since long whereas a system for affective touch was understood and explored more recently. Discriminative touch is based on large myelinated afferents from skin as well as afferents from deeper structures. This system allows us to extract detailed information on spatial and temporal features of any skin deformation as well as properties of physical objects such as size, shape, and surface structure. The glabrous skin of the human hand has a paramount role in discriminative touch. Thus the tactile organization of this skin area has therefore been extensively explored.
Altogether there are about 17,000 tactile afferents in the glabrous skin area of one hand. They are of four distinct types. Two kinds of afferents have small receptive fields suited for high spatial resolution (Merkel and Meissner). They are particularly numerous in the pulp of the finger, a region often engaged in exploration of object properties. Pacini units are extremely sensitive to fast movements whereas spatial resolution is poor. Ruffini units are characterized by high sensitivity to skin stretch and forces acting on the nails. Micro-stimulation has shown that input from one single Meissner, Merkel, or Pacini unit may produce a distinct and differential percept in the mind of the subject indicating an absolute specificity within the tactile system. It has even been demonstrated that a single impulse in a Meissner afferent may produce a percept.
In contrast, no percept is reported when a single Ruffini afferent is stimulated which might indicate that spatial summation is required. Consistent with the perceptive findings, neural responses in the somatosensory cortex have been recorded on micro-stimulation of single afferents connected to Meissner, Merkel, Pacini endings but not with single Ruffini afferents. On the basis of collateral studies in man and monkey a very tight match has been claimed between magnitude estimation of sensation of skin deformation, on the one hand, and response of Merkel afferents in the monkey, on the other. In man, deviations from such a linear relation was found in combined psychophysical and microneurography recordings.
In the hairy skin Meissner units are lacking altogether. Instead there are hair follicle and field afferents which have large receptive fields while Merkel, Pacini, and Ruffini are present. Cutaneous Ruffini units in the hairy skin are important for position sense and kinesthesia as pointed out in another section. A caveat is justified with regard to end organ morphology. The four kinds of units considered above were physiologically identified in man (FA/RA and SA units, i.e. fast and slowly adapting type I and type II, ) whereas end organ morphology has been inferred on the basis of animal studies. Particularly, it seems likely that SAII afferents may be connected to other morphological structures than the classical Ruffini ending.
=== Affective touch ===
Light touch is coded not only in large myelinated afferents but in small unmyelinated afferents as well. Tactile C-afferents (CT) were described long ago in non-human species but did not attract much interest until it was shown that they are numerous in human hairy skin. In contrast, they are lacking altogether in glabrous skin. A number of findings from both normal subjects and from unique patients lacking large tactile afferents indicate that CT afferents are essential for the pleasurable aspect of friendly touch.
Particularly, CT afferents respond vigorously to slow caressing movements, and, importantly, the size of the afferent response matches the sense of pleasure reported by the subject. fMRI studies of brain activity indicate that CT activate the insular cortex but not the primary or secondary somatosensory cortex consistent with the hypothesis that CT may play a role in emotional, behavioral, and hormonal responses to pleasant skin-to-skin contact between individuals.
=== Tactile afferents in motor control ===
It has been shown that tactile afferents from the glabrous skin of the hand exert profound effects on hand and finger muscles in the subconscious control of grip force whenever we lift and manipulate objects.
The friction between skin and object surface is extracted as soon as your fingers close around the object and contraction force of the muscles gripping the object is adjusted accordingly. Moreover, any tendency to slipping is monitored by tactile afferents and gives rise to swift reflexes resulting in subconscious adjustments of motor output. Many forms of dexterous handling of objects include successive phases of different motor activity. It has been shown that tactile sense organs in the glabrous skin are involved in timely linking the separated phases to a purposeful motor act.
=== Pain related afferents ===
Afferents responding to noxious stimuli are known as nociceptors. There are 2 main groups, unmyelinated C afferents and small myelinated Aδ fibers. Most studies are focused on C nociceptors.
The nociceptive C-fibers constitute a very large proportion of somatic afferent nerve fibers. There are two main groups: mechano-sensitive and mechano-insensitive C nociceptors. Mechano-sensitive C nociceptors, also known as polymodal C nociceptors are activated by several kinds of stimuli, i.e. mechanical, thermal, and chemical. The mechano-insensitive C nociceptors, also known as silent nociceptors, differ from polymodal afferents in other respects as well, e.g. they do not respond to heat or they have very high heat thresholds, receptive fields on the skin are larger, conduction velocity is slower, and activity-dependent slowing of conduction velocity of the axon is more pronounced. The mechano-insensitive nociceptors may be sensitized particularly by inflammatory mediators to render them mechano-responsive, a process that may account for the tenderness we experience following a physical injury. Moreover, electrical activation of C-mechano-insensitive fibers demonstrates that they have a role in neurogenic vasodilation which has not been found with polymodal nociceptors. It is suspected that the inflammatory mediators bind to protein receptors on mechano-insensitive nociceptors, but sensitization may also be caused by changes in gene expression that affect expression of transduction proteins. In either case, the sensitization of mechano-insensitive nociceptors has been observed to result in hyperalgesia, chronic pain. About ten percent of the afferents classified as mechano-insensitive nociceptors seem to constitute a group of “itch specific” units because they respond to pruritogen substances including histamine with an activity that corresponds to the sensation of itch.
=== Temperature sensibility ===
Thermoreceptors can be separated into two groups for warmth and cold detection. A subset of unmyelinated fibers are responsible for warmth detection. They are mechano-insensitive, low in number, and innervate small receptive fields. Aδ fibers are responsible for cold detection. However, there seems to be a subset of C-fibers that may function as cold-receptors along with A-fibers. Remarkably, these C-cold fibers seem to produce a sensation of unpleasant heat when there is no input from A-fibers. Altogether thermoreceptive afferents have not been studied as much as other systems.
== Autonomic efferent activity ==
Microneurography exploration of sympathetic efferent system is unique from technical point of view as multiunit recordings have been very prosperous whereas single unit recording is essential with most other systems. Soon after microneurography was launched it was demonstrated that sympathetic activity is much different in muscle and skin nerves.
Instantaneous sympathetic activity in muscle nerves (MSA / MSNA) is heavily controlled by baroreflex mechanisms, resulting in a characteristic cardiac rhythmicity as well as a close and inverse relation to the small variations of blood pressure that normally occur continuously in phase with respiration. In contrast, the sympathetic activity in skin nerves (SSA/SSNA) lacks a tight relation to cardiac and respiratory events. On the other hand, sympathetic activity in skin nerves is dependent on a number of other mechanisms because changes are easily evoked e.g. by arousal, emotions, and ambient temperature changes, which stimuli are not effective with efferents in muscle nerves. These and other findings demonstrate that sympathetic efferent activity is highly differentiated, as individual effectors are governed by their own control systems and specific reflexes. The amount of muscular sympathetic activity, measured as number of bursts per 100 heart beats, varies considerably between subjects but, on the other hand, it is highly reproducible over time within the individual subject. However, there is some increase with age. Counter-intuitively, there seems to be only a weak and barely significant correlation between sympathetic efferent activity and hypertension as found in group studies.
In 1998, microneurography recordings were performed for the first time on a spaceflight aboard the Space Shuttle Columbia with the purpose to explore the effect of microgravity on the human sympathetic nerve system. Two astronauts measured MSNA from peroneal nerves of their fellow astronauts. The findings support earlier observations that weightlessness results in a decrease of MSNA activity through a baroreflex mechanism.
== Strengths and limitations ==
The microneurography technique allows the recording of impulse activity of individual nerve fibers with absolute resolution in attending human subjects. Hence the subject is able to cooperate in various kinds of tests while the exact and complete information carried by the individual nerve fiber is monitored and offered for analysis of correlations between neural activity and physical or mental events. On the other hand, the particular physical conditions involving a microelectrode freely floating in the tissue preclude brisk and large movements because the exact electrode position is easily jeopardized. The experiment can be time-consuming when targeting deeply located nerves because the search procedure can be particularly demanding. However, accessing superficial subcutaneous nerves such as the superficial peroneal nerve on the dorsum of the foot is very rapid. This has permitted that the technique that was initially felt to be unsuited as a diagnostic test can now be applied for clinical purposes. Microneurography strength is in its unique power for exploration of normal neural mechanisms as well as pathophysiological conditions of various neurological disorders. Microneurography records intact axons in vivo and is minimally invasive. There have been no reports of persistent nerve damage. As a result, repeated recordings with the same subject are possible and longitudinal observations can be made. The technique has recently been used in clinical trials of new anti-neuropathic pain agents. During the recording, it is important to create an atmosphere of psychological confidence and to observe carefully the subject´s reactions so that the procedure can be adjusted accordingly. The technique requires training and skill and it is highly recommended to take up the method in an experienced laboratory where the method is regularly used.
== See also ==
Electroneuronography
== References ==
== Further reading ==
Katayama, K.; Iwamoto, E.; Ishida, K.; Koike, T.; Saito, M. (2012). "Inspiratory muscle fatigue increases sympathetic vasomotor outflow and blood pressure during submaximal exercise". AJP: Regulatory, Integrative and Comparative Physiology. 302 (10): R1167-75. doi:10.1152/ajpregu.00006.2012. PMID 22461178. S2CID 18567092.
Straznicky, N. E.; Eikelis, N.; Nestel, P. J.; Dixon, J. B.; Dawood, T.; Grima, M. T.; Sari, C. I.; Schlaich, M. P.; et al. (2011). "Baseline Sympathetic Nervous System Activity Predicts Dietary Weight Loss in Obese Metabolic Syndrome Subjects". Journal of Clinical Endocrinology & Metabolism. 97 (2): 605–13. doi:10.1210/jc.2011-2320. PMID 22090279.
Horwich, Tamara B.; Middlekauff, Holly R.; MacLellan, W. Robb; Fonarow, Gregg C. (2011). "Statins Do Not Significantly Affect Muscle Sympathetic Nerve Activity in Humans with Nonischemic Heart Failure: A Double-Blind Placebo-Controlled Trial". Journal of Cardiac Failure. 17 (11): 879–86. doi:10.1016/j.cardfail.2011.07.008. PMC 3206298. PMID 22041323.
Martinez, D. G.; Nicolau, J. C.; Lage, R. L.; Toschi-Dias, E.; De Matos, L. D. N. J.; Alves, M. J. N. N.; Trombetta, I. C.; Dias Da Silva, V. J.; et al. (2011). "Effects of Long-Term Exercise Training on Autonomic Control in Myocardial Infarction Patients". Hypertension. 58 (6): 1049–56. doi:10.1161/HYPERTENSIONAHA.111.176644. PMID 22025377.
Grassi, G.; Seravalle, G.; Ghiadoni, L.; Tripepi, G.; Bruno, R. M.; Mancia, G.; Zoccali, C. (2011). "Sympathetic Nerve Traffic and Asymmetric Dimethylarginine in Chronic Kidney Disease". Clinical Journal of the American Society of Nephrology. 6 (11): 2620–7. doi:10.2215/CJN.06970711. PMC 3359568. PMID 21940841.
Parati, G.; Esler, M. (2012). "The human sympathetic nervous system: Its relevance in hypertension and heart failure". European Heart Journal. 33 (9): 1058–66. doi:10.1093/eurheartj/ehs041. PMID 22507981. | Wikipedia/Microneurography |
Stereotactic surgery is a minimally invasive form of surgical intervention that makes use of a three-dimensional coordinate system to locate small targets inside the body and to perform on them some action such as ablation, biopsy, lesion, injection, stimulation, implantation, radiosurgery (SRS), etc.
In theory, any organ system inside the body can be subjected to stereotactic surgery. However, difficulties in setting up a reliable frame of reference (such as bone landmarks, which bear a constant spatial relation to soft tissues) mean that its applications have been, traditionally and until recently, limited to brain surgery. Besides the brain, biopsy and surgery of the breast are done routinely to locate, sample (biopsy), and remove tissue. Plain X-ray images (radiographic mammography), computed tomography, and magnetic resonance imaging can be used to guide the procedure.
Another accepted form of "stereotactic" is "stereotaxic". The word roots are stereo-, a prefix derived from the Greek word στερεός (stereos, "solid"), and -taxis (a suffix of Neo-Latin and ISV, derived from Greek taxis, "arrangement", "order", from tassein, "to arrange").
== Uses ==
The surgery is used to treat various brain cancers, benign, and functional disorders of the brain. This is sometimes combined with whole brain radiotherapy, and a 2021 systematic review found this combination led to the greatest improvement of survival for those with single brain metastasis.
Amongst the malignant brain disorders are: brain metastasis and glioblastoma. The benign brain disorders are: meningioma, cerebral arteriovenous malformation, vestibular schwannoma, and pituitary adenoma. Functional disorders are: trigeminal neuralgia, Parkinson's disease, and epilepsy.
== Procedure ==
Stereotactic surgery works on the basis of three main components:
A stereotactic planning system, including atlas, multimodality image matching tools, coordinates calculator, etc.
A stereotactic device or apparatus
A stereotactic localization and placement procedure
Modern stereotactic planning systems are computer based. The stereotactic atlas is a series of cross sections of anatomical structure (for example, a human brain), depicted in reference to a two-coordinate frame. Thus, each brain structure can be easily assigned a range of three coordinate numbers, which will be used for positioning the stereotactic device. In most atlases, the three dimensions are: latero-lateral (x), dorso-ventral (y) and rostro-caudal (z).
The stereotactic apparatus uses a set of three coordinates (x, y and z) in an orthogonal frame of reference (cartesian coordinates), or, alternatively, a cylindrical coordinates system, also with three coordinates: angle, depth and antero-posterior (or axial) location. The mechanical device has head-holding clamps and bars which puts the head in a fixed position in reference to the coordinate system (the so-called zero or origin). In small laboratory animals, these are usually bone landmarks which are known to bear a constant spatial relation to soft tissue. For example, brain atlases often use the external auditory meatus, the inferior orbital ridges, the median point of the maxilla between the incisive teeth. or the bregma (confluence of sutures of frontal and parietal bones), as such landmarks. In humans, the reference points, as described above, are intracerebral structures which are clearly discernible in a radiograph or tomograph. In newborn human babies, the "soft spot" where the coronal and sagittal sutures meet (known as the fontanelle) becomes the bregma when this gap closes.
Guide bars in the x, y and z directions (or alternatively, in the polar coordinate holder), fitted with high precision vernier scales allow the neurosurgeon to position the point of a probe (an electrode, a cannula, etc.) inside the brain, at the calculated coordinates for the desired structure, through a small trephined hole in the skull.
Currently, a number of manufacturers produce stereotactic devices fitted for neurosurgery in humans, for both brain and spine procedures, as well as for animal experimentation.
=== Types frame systems ===
Simple orthogonal system: The probe is directed perpendicular to a square base unit fixed to the skull. These provide three degrees of freedom by means of a carriage that moved orthogonally along the base plate or along a bar attached parallel to the base plate of the instrument. Attached to the carriage was a second track that extended across the head frame perpendicularly.
Burr hole mounted system: This provides a limited range of possible intracranial target points with a fixed entry point. They provided two angular degrees of freedom and a depth adjustment. The surgeon could place the burr hole over nonessential brain tissue and utilize the instrument to direct the probe to the target point from the fixed entry point at the burr hole.
Arc-quadrant systems: Probes are directed perpendicular to the tangent of an arc (which rotates about the vertical axis) and a quadrant (which rotates about the horizontal axis). The probe, directed to a depth equal to the radius of the sphere defined by the arc-quadrant, will always arrive at the center or focal point of that sphere.
Arc-phantom systems: An aiming bow attaches to the head ring, which is fixed to the patient's skull, and can be transferred to a similar ring that contains a simulated target. In this system, the phantom target is moved on the simulator to 3D coordinates. After adjusting the probe holder on the aiming bow so that the probe touches the desired target on the phantom, the transferable aiming bow is moved from the phantom base ring to the base ring on the patient. The probe is then lowered to the determined depth in order to reach the target point deep in the patient's brain.
== Treatment ==
=== Stereotactic radiosurgery ===
Stereotactic radiosurgery utilizes externally generated ionizing radiation to inactivate or eradicate defined targets in the head or spine without the need to make an incision. This concept requires steep dose gradients to reduce injury to adjacent normal tissue while maintaining treatment efficacy in the target. As a consequence of this definition, the overall treatment accuracy should match the treatment planning margins of 1–2 mm or better. To use this paradigm optimally and treat patients with the highest possible accuracy and precision, all errors, from image acquisition over treatment planning to mechanical aspects of the delivery of treatment and intra-fraction motion concerns, must be systematically optimized. To assure quality of patient care the procedure involves a multidisciplinary team consisting of a radiation oncologist, medical physicist, and radiation therapist. Dedicated, commercially available stereotactic radiosurgery programs are provided by the irrespective Gamma Knife, CyberKnife, and Novalis Radiosurgery devices.
Stereotactic radiosurgery provides an efficient, safe, and minimal invasive treatment alternative for patients diagnosed with malignant, benign and functional indications in the brain and spine, including but not limited to both primary and secondary tumors. Stereotactic radiosurgery is a well-described management option for most metastases, meningiomas, schwannomas, pituitary adenomas, arteriovenous malformations, and trigeminal neuralgia, among others.
Irrespective of the similarities between the concepts of stereotactic radiosurgery and fractionated radiotherapy and although both treatment modalities are reported to have identical outcomes for certain indications, the intent of both approaches is fundamentally different. The aim of stereotactic radiosurgery is to destroy target tissue while preserving adjacent normal tissue, where fractionated radiotherapy relies on a different sensitivity of the target and the surrounding normal tissue to the total accumulated radiation dose. Historically, the field of fractionated radiotherapy evolved from the original concept of stereotactic radiosurgery following discovery of the principles of radiobiology: repair, reassortment, repopulation, and reoxygenation. Today, both treatment techniques are complementary as tumors that may be resistant to fractionated radiotherapy may respond well to radiosurgery and tumors that are too large or too close to critical organs for safe radiosurgery may be suitable candidates for fractionated radiotherapy.
A second, more recent evolution extrapolates the original concept of stereotactic radiosurgery to extra-cranial targets, most notably in the lung, liver, pancreas, and prostate. This treatment approach, entitled stereotactic body radiotherapy or SBRT, is challenged by various types of motion. On top of patient immobilization challenges and the associated patient motion, extra-cranial lesions move with respect to the patient's position due to respiration, bladder and rectum filling. Like stereotactic radiosurgery, the intent of stereotactic body radiotherapy is to eradicate a defined extra-cranial target. However, target motion requires larger treatment margins around the target to compensate for the positioning uncertainty. This in turn implies more normal tissue exposed to high doses, which could result in negative treatment side effects. As a consequence, stereotactic body radiotherapy is mostly delivered in a limited number of fractions, thereby blending the concept of stereotactic radiosurgery with the therapeutic benefits of fractionated radiotherapy. To monitor and correct target motion for accurate and precise patient positioning prior and during treatment, advanced image-guided technologies are commercially available and included in the radiosurgery programs offered by the CyberKnife and Novalis communities.
=== Parkinson's disease ===
Functional neurosurgery comprises treatment of several disorders such as Parkinson's disease, hyperkinesia, disorder of muscle tone, intractable pain, convulsive disorders and psychological phenomena. Treatment for these phenomena was believed to be located in the superficial parts of the CNS and PNS. Most of the interventions made for treatment consisted of cortical extirpation.
To alleviate extra pyramidal disorders, pioneer Russell Meyers dissected or transected the head of the caudate nucleus in 1939, and part of the putamen and globus pallidus.
Attempts to abolish intractable pain were made with success by transection of the spinothalamic tract at spinal medullary level and further proximally, even at mesencephalic levels.
In 1939-1941 Putnam and Oliver tried to improve Parkinsonism and hyperkinesias by trying a series of modifications of the lateral and antero-lateral cordotomies. Additionally, other scientists like Schurman, Walker, and Guiot made significant contributions to functional neurosurgery. In 1953, Cooper discovered by chance that ligation of the anterior chorioidal artery resulted in improvement of Parkinson's disease. Similarly, when Grood was performing an operation in a patient with Parkinson's, he accidentally lesioned the thalamus. This caused the patient's tremors to stop. From then on, thalamic lesions became the target point with more satisfactory results.
More recent clinical applications can be seen in surgeries used to treat Parkinson's disease, such as Pallidotomy or Thalamotomy (lesioning procedures), or Deep Brain Stimulation (DBS). During DBS, an electrode is placed into the thalamus, the pallidum of the subthalmamic nucleus, parts of brain that are involved in motor control, and are affected by Parkinson's disease. The electrode is connected to a small battery operated stimulator that is placed under the collarbone, where a wire runs beneath the skin to connect it to the electrode in the brain. The stimulator produces electrical impulses that affect the nerve cells around the electrode and should help alleviate tremors or symptoms that are associated with the affected area.
In Thalamotomy, a needle electrode is placed into the thalamus, and the patient must cooperate with tasks assigned to find the affected area- after this area of the thalamus is located, a small high frequency current is applied to the electrode and this destroys a small part of the thalamus. Approximately 90% of patients experience instantaneous tremor relief.
In Pallidotomy, an almost identical procedure to thalamotomy, a small part of the pallidum is destroyed and 80% of patients see improvement in rigidity and hypokinesia and a tremor relief or improvement comes weeks after the procedure.
== History ==
The stereotactic method was first published in 1908 by two British scientists, Victor Horsley, a physician and neurosurgeon, and Robert H. Clarke, a physiologist, and was built by Swift & Son; the two scientists stopped collaborating after the 1908 publication. The Horsley–Clarke apparatus used a Cartesian (three-orthogonal axis) system. That device is in the Science Museum, London; a copy was brought to the US by Ernest Sachs and is in the Department of Neurosurgery at UCLA. Clarke used the original to do research that led to publications of primate and cat brain atlases. There is no evidence it was ever used in a human surgery.: 12 The first stereotactic device designed for the human brain appears to have been an adaptation of the Horseley–Clarke frame built at Aubrey T. Mussen's behest by a London workshop in 1918, but it received little attention and does not appear to have been used on people. It was a frame made of brass.: 12
The first stereotactic device used in humans was used by Martin Kirschner, for a method to treat trigeminal neuralgia by inserting an electrode into the trigeminal nerve and ablating it. He published this in 1933.: 13 : 420
In 1947 and 1949, two neurosurgeons working at Temple University in Philadelphia, Ernest A. Spiegel (who had fled Austria when the Nazis took over) and Henry T. Wycis, published their work on a device similar to the Horsley–Clarke apparatus in using a cartesian system; it was attached to the patient's head with a plaster cast instead of screws. Their device was the first to be used for brain surgery; they used it for psychosurgery. They also created the first atlas of the human brain, and used intracranial reference points, generated by using medical images acquired with contrast agents.: 13 : 72
The work of Spiegel and Wycis sparked enormous interest and research.: 13 In Paris, Jean Talairach collaborated with Marcel David, Henri Hacaen, and Julian de Ajuriaguerra on a stereotactic device, publishing their first work in 1949 and eventually developing the Talairach coordinates.: 13 : 93 In Japan, Hirotaro Narabayashi was doing similar work.
In 1949, Lars Leksell published a device that used polar coordinates instead of cartesian, and two years later he published work where he used his device to target a beam of radiation into a brain.: 13 : 91 Leksell's radiosurgery system is also used by the Gamma Knife device, and by other neurosurgeons, using linear accelerators, proton beam therapy and neutron capture therapy. Lars Leksell went on to commercialize his inventions by founding Elekta in 1972.
In 1979, Russell A. Brown proposed a device, now known as the N-localizer, that enables guidance of stereotactic surgery using tomographic images that are obtained via medical imaging technologies such as X-ray computed tomography (CT), magnetic resonance imaging (MRI), or positron emission tomography (PET). The N-localizer comprises a diagonal rod that spans two vertical rods to form an N-shape that allows tomographic images to be mapped to physical space. This device became almost universally adopted by the 1980s and is included in the Brown-Roberts-Wells (BRW), Kelly-Goerss, Leksell, Cosman-Roberts-Wells (CRW), Micromar-ETM03B, FiMe-BlueFrame, Macom, and Adeor-Zeppelin stereotactic frames and in the Gamma Knife radiosurgery system. An alternative to the N-localizer is the Sturm-Pastyr localizer that is included in the Riechert-Mundinger and Zamorano-Dujovny stereotactic frames.
Other localization methods also exist that do not make use of tomographic images produced by CT, MRI, or PET, but instead conventional radiographs.
The stereotactic method has continued to evolve, and at present employs an elaborate mixture of image-guided surgery that uses computed tomography, magnetic resonance imaging and stereotactic localization.
== History in Latin America ==
In 1970, in the city of Buenos Aires, Argentina, Aparatos Especiales company, produced the first Stereotactic System in Latin America. Antonio Martos Calvo, together with Jorge Candia and Jorge Olivetti through the request of neurosurgeon Jorge Schvarc (1942-2019), developed an equipment based on the principle of Hitchcock Stereotactic System. The patient was seated in an adapted chair with two telescopic arms attached at it base, which fixed the stereotactic frame preventing the patient’s movement.
A double radiopaque ruler attached to the side of the frame made it possible to obtain the antero-posterior and latero-lateral X-ray images without the need of moving the radiopaque ruler. The thermal coagulation lesion was performed using tungsten monopole electrodes of 1,5mm of diameter (without temperature control) with a 3mm active tip, utilizing an electrical bipolar coagulator. The lesion size was previously determined by testing the electrode in egg albumin. Coagulation size was the result of the electrical coagulator power regulation and the application time of the radiofrequency. The first surgery performed with this system was a Trigeminal Nucleotractothomy. Jorge Schvarcz performed more than 700 functional surgeries until 1994 when, due to health problems he stopped exercising his profession. But the equipment developed kept improving on a neurosurgery history.
This was the beginning of the developing of technology to produce stereotactic devices in Latin America. This was the beginning of the first stereotactic manufacturer of Latin America – The Brazilian Micromar.
== Research ==
Stereotactic surgery is sometimes used to aid in several different types of animal research studies. Specifically, it is used to target specific sites of the brain and directly introduce pharmacological agents to the brain which otherwise may not be able to cross the blood–brain barrier. In rodents, the main applications of stereotactic surgery are to introduce fluids directly to the brain or to implant cannulae and microdialysis probes. Site specific central microinjections are used when rodents do not need to be awake and behaving or when the substance to be injected has a long duration of action. For protocols in which rodents’ behaviors must be assessed soon after injection, stereotactic surgery can be used to implant a cannula through which the animal can be injected after recovery from the surgery. These protocols take longer than site-specific central injections in anesthetized mice because they require the construction of cannulae, wire plugs, and injection needles, but induce less stress in the animals because they allow for a recovery period for the healing of trauma induced to the brain before injection. Surgery can also be used for microdialysis protocols to implant and tether the dialysis probe and guide cannula.
== See also ==
== References ==
== Further reading ==
Armando Alaminos Bouza, "Imaging, Stereotactic Space and Targeting in Functional Neurosurgery", Functional Neurosurgery, First Edition, Publisher: Alaúde Editorial LTDA, Editor: Arthur Cukiert, pp. 67–79, (2014), ISBN 978-85-7881-248-5
Philip L. Gildenberg, "Stereotactic Surgery: Present and Past", Stereotactic Neurosurgery (Editor: M. Peter Heilbrun). Baltimore: Williams and Wilkins (1988)
Patrick J. Kelly, "Introduction and Historical Aspects", Tumor Stereotaxis, Philadelphia: W. B. Saunders Company (1991)
Robert Levy, A Short History of Stereotactic Surgery Archived 2017-05-13 at the Wayback Machine, Cyber Museum of Neurosurgery.
William Regine; Lawrence Chin (2008). Principles of Stereotactic Surgery. Berlin: Springer. ISBN 978-0-387-71069-3.
Steel, G. Gordon (2002). Basic clinical radiobiology (3rd ed.). London: Hodder Arnold. ISBN 978-0340807835.
Tasker RR, Organ LW, Hawrylyshyn P (1976). "Sensory organization of the human thalamus". Applied Neurophysiology. 39 (3–4): 139–53. doi:10.1159/000102487. PMID 801856.
Tasker RR, Hawrylyshyn P, Rowe IH, Organ LW (1977). "Computerized Graphic Display of Results of Subcortical Stimulation During Stereotactic Surgery". Advances in Stereotactic and Functional Neurosurgery 2. Acta Neurochirurgica Supplementum. Vol. 24. pp. 85–98. doi:10.1007/978-3-7091-8482-0_14. ISBN 978-3-211-81422-2. PMID 335811.
van Manen, Jaap (1967). Stereotactic Methods and their Applications in Disorders of the Motor System. Springfield, IL: Royal Van Gorcum.
Zapata, A.; Chefer, V.I.; Shippenberg, T.S. (2009). "Microdialysis in Rodents". Current Protocols in Neuroscience. 47: 7.2.1–7.2.29. doi:10.1002/0471142301.ns0702s47. PMC 2945307. PMID 19340813. | Wikipedia/Stereotactic_radiosurgery |
Polysomnography (PSG) is a multi-parameter type of sleep study and a diagnostic tool in sleep medicine. The test result is called a polysomnogram, also abbreviated PSG. The name is derived from Greek and Latin roots: the Greek πολύς (polus for "many, much", indicating many channels), the Latin somnus ("sleep"), and the Greek γράφειν (graphein, "to write").
Type I polysomnography is a sleep study performed overnight with the patient continuously monitored by a credentialed technologist. It records the physiological changes that occur during sleep, usually at night, though some labs can accommodate shift workers and people with circadian rhythm sleep disorders who sleep at other times. The PSG monitors many body functions, including brain activity (EEG), eye movements (EOG), muscle activity or skeletal muscle activation (EMG), and heart rhythm (ECG). After the identification of the sleep disorder sleep apnea in the 1970s, breathing functions, respiratory airflow, and respiratory effort indicators were added along with peripheral pulse oximetry. Polysomnography no longer includes NPT monitoring for erectile dysfunction, as it is reported that all male patients will experience erections during phasic REM sleep, regardless of dream content.
Limited channel polysomnography, or unattended home sleep tests, are called Type II–IV channel polysomnography. Polysomnography should only be performed by technicians and technologists who are specifically accredited in sleep medicine. However, at times nurses and respiratory therapists perform polysomnography without specific knowledge and training in the field.
Polysomnography data can be directly related to sleep onset latency (SOL), REM-sleep onset latency, number of awakenings during the sleep period, total sleep duration, percentages and durations of every sleep stage, and number of arousals. It may also record other information crucial for diagnostics that are not directly linked with sleep, such as movements, respiration, and cardiovascular parameters. In any case, through polysomnographic evaluation, other information (such as body temperature or esophageal pH) can be obtained according to the patient's or the study's needs.
Video-EEG polysomnography, which combines polysomnography with video recording, has been described as more effective than polysomnography alone for the evaluation of sleep troubles such as parasomnias, because it allows easier correlation of EEG and polysomnography with bodily motion.
== Medical uses ==
Polysomnography is used to diagnose or rule out many types of sleep disorders, including narcolepsy, idiopathic hypersomnia, periodic limb movement disorder (PLMD), REM behavior disorder, parasomnias, and sleep apnea. Although it is not directly useful in diagnosing circadian rhythm sleep disorders, it may be used to rule out other sleep disorders.
The use of polysomnography as a screening test for persons with excessive daytime sleepiness as their sole presenting complaint is controversial.
== Mechanism ==
A polysomnogram will typically record a minimum of 12 channels, requiring a minimum of 22 wire attachments to the patient. These channels vary in every lab and may be adapted to meet the doctor's requests. A minimum of three channels are used for the EEG, one or two measure airflow, one or two are for chin muscle tone, one or more for leg movements, two for eye movements (EOG), one or two for heart rate and rhythm, one for oxygen saturation, and one each for the belts, which measure chest wall movement and upper abdominal wall movement. The movement of the belts is typically measured with piezoelectric sensors or respiratory inductance plethysmography. This movement is equated to effort and produces a low-frequency sinusoidal waveform as the patient inhales and exhales.
Wires for each channel of recorded data lead from the patient and converge into a central box, which in turn is connected to a computer system for recording, storing and displaying the data. During sleep, the computer monitor can display multiple channels continuously. In addition, most labs have a small video camera in the room so the technician can observe the patient visually from an adjacent room.
The electroencephalogram (EEG) will generally use six "exploring" electrodes and two "reference" electrodes, unless a seizure disorder is suspected, in which case more electrodes will be applied to document the appearance of seizure activity. The exploring electrodes are usually attached to the scalp near the frontal, central (top) and occipital (back) portions of the brain via a paste that will conduct electrical signals originating from the neurons of the cortex. These electrodes will provide a readout of the brain activity that can be "scored" into different stages of sleep (N1, N2, and N3 – which combined are referred to as NREM sleep – and Stage R, which is rapid eye movement sleep, or REM, and wakefulness). The EEG electrodes are placed according to the International 10-20 system.
The electrooculogram (EOG) uses two electrodes, one that is placed 1 cm above the outer canthus of the right eye and one that is placed 1 cm below the outer canthus of the left eye. These electrodes pick up the activity of the eyes in virtue of the electropotential difference between the cornea and the retina (the cornea is positively charged relative to the retina). This helps to determine when REM sleep occurs, of which rapid eye movements are characteristic, and also essentially aids in determining when sleep occurs.
The electromyogram (EMG) typically uses four electrodes to measure muscle tension in the body as well as to monitor for an excessive amount of leg movements during sleep (which may be indicative of periodic limb movement disorder, PLMD). Two leads are placed on the chin with one above the jawline and one below. This, like the EOG, helps determine when sleep occurs as well as REM sleep. Sleep generally includes relaxation and so a marked decrease in muscle tension occurs. A further decrease in skeletal muscle tension occurs in REM sleep. A person becomes partially paralyzed to make acting out of dreams impossible, although people that do not have this paralysis can develop REM behavior disorder. Finally, two more leads are placed on the anterior tibialis of each leg to measure leg movements.
Though a typical electrocardiogram (ECG or EKG) would use ten electrodes, only two or three are used for a polysomnogram. They can either be placed under the collarbone on each side of the chest or one under the collarbone and the other six inches above the waist on either side of the body. These electrodes measure the electrical activity of the heart as it contracts and expands, recording such features as the "P" wave, "QRS" complex, and "T" wave. These can be analyzed for any abnormalities that might be indicative of an underlying heart pathology.
Nasal and oral airflow can be measured using pressure transducers, and/or a thermocouple, fitted in or near the nostrils; the pressure transducer is considered the more sensitive. This allows the clinician/researcher to measure the rate of respiration and identify interruptions in breathing. Respiratory effort is also measured in concert with nasal/oral airflow by the use of belts. These belts expand and contract upon breathing effort. However, this method of respiration may also produce false negatives. Some patients will open and close their mouth while obstructive apneas occur. This forces air in and out of the mouth while no air enters the airway and lungs. Thus, the pressure transducer and thermocouple will detect this diminished airflow and the respiratory event may be falsely identified as a hypopnea, or a period of reduced airflow, instead of an obstructive apnea.
Pulse oximetry determines changes in blood oxygen levels that often occur with sleep apnea and other respiratory problems. The pulse oximeter fits over a fingertip or an earlobe.
Snoring may be recorded with a sound probe over the neck, though more commonly the sleep technician will just note snoring as "mild", "moderate" or "loud" or give a numerical estimate on a scale of 1 to 10. Also, snoring indicates airflow and can be used during hypopneas to determine whether the hypopnea may be an obstructive apnea.
== Procedure ==
For the standard test, the patient comes to a sleep lab in the early evening and over the next 1–2 hours is introduced to the setting and "wired up" so that multiple channels of data can be recorded when they fall asleep. The sleep lab may be in a hospital, a free-standing medical office, or a hotel. A sleep technician should always be in attendance and is responsible for attaching the electrodes to the patient and monitoring the patient during the study.
During the study, the technician observes sleep activity by looking at the video monitor and the computer screen that displays all the data second by second. In most labs, the test is completed and the patient is discharged home by 7 a.m. unless a Multiple Sleep Latency Test (MSLT) is to be done during the day to test for excessive daytime sleepiness.
Most recently, health care providers may prescribe home studies to enhance patient comfort and reduce expense. The patient is given instructions after a screening tool is used, uses the equipment at home and returns it the next day. Most screening tools consist of an airflow measuring device (thermistor) and a blood oxygen monitoring device (pulse oximeter). The patient would sleep with the screening device for one to several days, then return the device to the health care provider. The provider would retrieve data from the device and could make assumptions based on the information given. For example, series of drastic blood oxygen desaturations during night periods may indicate some form of respiratory event (apnea). The equipment monitors, at a minimum, oxygen saturation. More sophisticated home study devices have most of the monitoring capability of their counterparts run by sleep lab technicians, and can be complex and time-consuming to set up for self-monitoring.
== Interpretation ==
After the test is completed, a "scorer" analyzes the data by reviewing the study in 30-second "epochs".
The score consists of the following information:
Onset of sleep from time the lights were turned off: this is called "sleep onset latency" and normally is less than 20 minutes. (Note that determining "sleep" and "waking" is based solely on the EEG. Patients sometimes feel they were awake when the EEG shows they were sleeping. This may be because of sleep state misperception, drug effects on brain waves, or individual differences in brain waves.)
Sleep efficiency: the number of minutes of sleep divided by the number of minutes in bed. Normal is approximately 85 to 90% or higher.
Sleep stages: these are based on 3 sources of data coming from 7 channels: EEG (usually 4 channels), EOG (2), and chin EMG (1). From this information, each 30-second epoch is scored as "awake" or one of 4 sleep stages: 1, 2, 3, and REM, or Rapid Eye Movement, sleep. Stages 1–3 are together called non-REM sleep. Non-REM sleep is distinguished from REM sleep, which is altogether different. Within non-REM sleep, stage 3 is called "slow wave" sleep because of the relatively wide brain waves compared to other stages; another name for stage 3 is "deep sleep". By contrast, stages 1 and 2 are "light sleep". The figures show stage 3 sleep and REM sleep; each figure is a 30-second epoch from an overnight PSG.
(The percentage of each sleep stage varies by age, with decreasing amounts of REM and deep sleep in older people. The majority of sleep at all ages except infancy is stage 2. REM normally occupies about 20-25% of sleep time. Many factors besides age can affect both the amount and percentage of each sleep stage, including drugs [particularly anti-depressants and pain medication], alcohol taken before bedtime, and sleep deprivation.)
Any breathing irregularities, mainly apneas and hypopneas. Apnea is a complete or near complete cessation of airflow for at least 10 seconds followed by an arousal and/or 3% oxygen desaturation; hypopnea is a 30% or greater decrease in airflow for at least 10 seconds followed by an arousal and/or 4% oxygen desaturation. (The national insurance program Medicare in the US requires a 4% desaturation in order to include the event in the report.)
"Arousals" are sudden shifts in brain wave activity. They may be caused by numerous factors, including breathing abnormalities, leg movements, environmental noises, etc. An abnormal number of arousals indicates "interrupted sleep" and may explain a person's daytime symptoms of fatigue and/or sleepiness.
Cardiac rhythm abnormalities.
Leg movements.
Body position during sleep.
Oxygen saturation during sleep.
Once scored, the test recording and the scoring data are sent to the sleep medicine physician for interpretation. Ideally, interpretation is done in conjunction with the medical history, a complete list of drugs the patient is taking, and any other relevant information that might impact the study such as napping done before the test.
After interpreting the data, the sleep physician writes a report that is sent to the referring provider, usually with specific recommendations based on the test results.
== Examples of summary reports ==
The below example report describes a patient's situation and the results of some tests, and mentions CPAP as a treatment for obstructive sleep apnea. CPAP is continuous positive airway pressure and is delivered via a mask to the patient's nose or the patient's nose and mouth. (Some masks cover one, some both.) CPAP is typically prescribed after the diagnosis of OSA is made from a sleep study (i.e., after a PSG test). To determine the correct amount of pressure and the right mask type and size, and also to make sure the patient can tolerate this therapy, a "CPAP titration study" is recommended. This is the same as a PSG but with the addition of the mask applied so the technician can increase the airway pressure inside the mask as needed until all, or most, of the patient's airway obstructions are eliminated.
Mr. J----, age 41, 5'8" tall, 265 lbs., came to the sleep lab to rule out obstructive sleep apnea. He complains of some snoring and daytime sleepiness. His score on the Epworth Sleepiness Scale is elevated at 15 (out of possible 24 points), affirming excessive daytime sleepiness (normal is <10/24).
This single-night diagnostic sleep study shows evidence for obstructive sleep apnea (OSA). For the full night his apnea+hypopnea index was elevated at 18.1 events/hr. (normal <5 events/hr; this is "moderate" OSA). While sleeping supine, his AHI was twice that, at 37.1 events/hr. He also had some oxygen desaturation; for 11% of sleep time his SaO2 was between 80% and 90%.
Results of this study indicate Mr. J---- would benefit from CPAP. To this end, I recommend that he return to the lab for a CPAP titration study.
This report recommends that Mr. J---- return for a CPAP titration study, which means a return to the lab for a second all-night PSG (this one with the mask applied). Often, however, when a patient manifests OSA in the first 2 or 3 hours of the initial PSG, the technician will interrupt the study and apply the mask right then and there; the patient is awakened and fitted for a mask. The rest of the sleep study is then a "CPAP titration." When both the diagnostic PSG and a CPAP titration are done the same night, the entire study is called "split night".
The split-night study has these advantages:
The patient only has to come to the lab once, so it is less disruptive than is coming two different nights;
It is "half as expensive" to whoever is paying for the study.
The split-night study has these disadvantages:
There is less time to make a diagnosis of OSA (Medicare in the US requires a minimum of 2 hours of diagnosis time before the mask can be applied); and
There is less time to assure an adequate CPAP titration. If the titration begins with only a few hours of sleep left, the remaining time may not assure a proper CPAP titration, and the patient may still have to return to the lab.
Because of costs, more and more studies for "sleep apnea" are attempted as split-night studies when there is early evidence for OSA. (Note that both types of study, with and without a CPAP mask, are still polysomnograms.) When the CPAP mask is worn, however, the flow-measurement lead in the patient's nose is removed. Instead, the CPAP machine relays all flow-measurement data to the computer. The below is an example report that might be produced from a split night study:
Mr. B____, age 38, 6 ft. tall, 348 lbs., came to the Hospital Sleep Lab to diagnose or rule out obstructive sleep apnea. This polysomnogram consisted of overnight recording of left and right EOG, submental EMG, left and right anterior EMG, central and occipital EEG, EKG, airflow measurement, respiratory effort and pulse oximetry. The test was done without supplemental oxygen. His latency to sleep onset was slightly prolonged at 28.5 minutes. Sleep efficiency was normal at 89.3% (413.5 minutes sleep time out of 463 minutes in bed).
During the first 71 minutes of sleep Mr. B____ manifested 83 obstructive apneas, 3 central apneas, 1 mixed apnea and 28 hypopneas, for an elevated apnea+hypopnea index (AHI) of 97 events/hr (*"severe" OSA). His lowest SaO2 during the pre-CPAP period was 72%. CPAP was then applied at 5 cm H2O, and sequentially titrated to a final pressure of 17 cm H2O. At this pressure his AHI was 4 events/hr. and the low SaO2 had increased to 89%. This final titration level occurred while he was in REM sleep. Mask used was a Respironics Classic nasal (medium-size).
In summary, this split night study shows severe OSA in the pre-CPAP period, with definite improvement on high levels of CPAP. At 17 cm H2O his AHI was normal at 4 events/hr. and low SaO2 was 89%. Based on this split night study I recommend he start on nasal CPAP 17 cm H2O along with heated humidity.
== See also ==
Polysomnographic technician
Respiratory monitoring
Sleep disorder
Sleep medicine
Sleep study
== References ==
== Further reading ==
Iber C, Ancoli-Israel S, Chesson A, and Quan SF for the American Academy of Sleep Medicine. The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications, 1st ed.: Westchester, Illinois: American Academy of Sleep Medicine, 2007.
Pressman MR (2002). Primer of Polysomnogram Interpretation. Boston: Butterworth Heinemann. ISBN 978-0-7506-9782-8.
Berry RB (2003). Sleep Medicine Pearls. Philadelphia: Hanley & Belfus. ISBN 978-1-56053-490-7.
Bowman TJ (2003). Review of Sleep Medicine. Boston: Butterworth Heinemann. ISBN 978-0-7506-7392-1.
Kryger MH, Roth T, Dement WC (2005). Principles and Practice of Sleep Medicine (4th ed.). Philadelphia: Elsevier Saunders. ISBN 978-0-7216-0797-9.
Kushida CA, Littner MR, Morgenthaler TM, et al. (2005). "Practice parameters for the indications for polysomnography and related procedures: An update for 2005". Sleep. 28 (4): 499–519. doi:10.1093/sleep/28.4.499. PMID 16171294.
== External links ==
Practical guide to Polysomnography
What is Polysomnography
What is a Sleep Study for Sleep Apnea?
Polysomnography by Carmel Armon, on Medscape Reference | Wikipedia/Polysomnography |
Brain positron emission tomography is a form of positron emission tomography (PET) that is used to measure brain metabolism and the distribution of exogenous radiolabeled chemical agents throughout the brain. PET measures emissions from radioactively labeled metabolically active chemicals that have been injected into the bloodstream. The emission data from brain PET are computer-processed to produce multi-dimensional images of the distribution of the chemicals throughout the brain.: 57
== Process ==
The positron emitting radioisotopes used are usually produced by a cyclotron, and chemicals are labeled with these radioactive atoms. The radioisotopes used in clinics are normally 18F (fluoride), 11C (carbon) and 15O (oxygen). The labeled compound, called a radiotracer or radioligand, is injected into the bloodstream and eventually makes its way to the brain through blood circulation. Detectors in the PET scanner detect the radioactivity as the compound charges in various regions of the brain. A computer uses the data gathered by the detectors to create multi-dimensional (normally 3-dimensional volumetric or 4-dimensional time-varying) images that show the distribution of the radiotracer in the brain following the time. Especially useful are a wide array of ligands used to map different aspects of neurotransmitter activity, with by far the most commonly used PET tracer being a labeled form of glucose, such as fluorodeoxyglucose (18F).
== Advantages and disadvantages ==
The greatest benefit of PET scanning is that different compounds can show flow and oxygen, and glucose metabolism in the tissues of the working brain. These measurements reflect the amount of brain activity in the various regions of the brain and allow us to learn more about how the brain works. PET scans were superior to all other metabolic imaging methods in terms of resolution and speed of completion (as little as 30 seconds), when they first became available. The improved resolution permitted better study to be made as to the area of the brain activated by a particular task. The biggest drawback of PET scanning is that because the radioactivity decays rapidly, it is limited to monitoring short tasks.: 60
== Uses ==
Before the use of functional magnetic resonance imaging (fMRI) became widespread, PET scanning was the preferred method of functional (as opposed to structural) brain imaging, and it still continues to make large contributions to neuroscience. PET scanning is also useful in PET-guided stereotactic surgery and radiosurgery for treatment of intracranial tumors, arteriovenous malformations and other surgically treatable conditions.
PET scanning is also used for diagnosis of brain disease, most notably because brain tumors, strokes, and neurondegenerative diseases (such as Alzheimer's disease and Parkinson's disease) all cause great changes in brain metabolism, which in turn causes detectable changes in PET scans. PET is probably most useful in early cases of certain dementias (with classic examples being Alzheimer's disease and Pick's disease) where the early damage is too diffuse and makes too little difference in brain volume and gross structure to change CT and standard MRI images enough to be able to reliably differentiate it from the "normal" range of cortical atrophy which occurs with aging (in many but not all) persons, and which does not cause clinical dementia.
PET is also actively used for multiple sclerosis and other acquired demyelinating syndromes, but mainly for research into pathogenesis instead of diagnosis. They use specific radioligands for microglial activity. Currently is widely used the 18-kDa translocator protein (TSPO). Also combined PET-CT are sometimes performed.
== Tracer types ==
PET imaging with oxygen-15 indirectly measures blood flow to the brain. In this method, increased radioactivity signal indicates increased blood flow which is assumed to correlate with increased brain activity. Because of its 2-minute half-life, O-15 must be piped directly from a medical cyclotron for such uses, which is difficult.
PET imaging with 18F-FDG takes advantage of the fact that the brain is normally a rapid user of glucose. Standard 18F-FDG PET of the brain measures regional glucose use and can be used in neuropathological diagnosis.
Example: Brain pathologies such as Alzheimer's disease greatly decrease brain metabolism of both glucose and oxygen in tandem. Therefore 18F-FDG PET of the brain may also be used to successfully differentiate Alzheimer's disease from other dementing processes, and also to make early diagnoses of Alzheimer's disease. The advantage of 18F-FDG PET for these uses is its much wider availability. Some radioactive tracers used for Alzheimer's are florbetapir 18F, flutemetamol F18, PiB and florbetaben 18F, which are all used to detect amyloid-beta plaques (a potential biomarker for Alzheimer's) in the brain.
Examples: PET imaging with FDG can also be used for localization of seizure focus: A seizure focus will appear as hypometabolic during an interictal scan. Several radiotracers (i.e. radioligands) have been developed for PET that are ligands for specific neuroreceptor subtypes such as [11C] raclopride, [18F] fallypride and [18F] desmethoxyfallypride for dopamine D2/D3 receptors, [11C] McN 5652 and [11C] DASB for serotonin transporters, [18F] Mefway for serotonin 5HT1A receptors, [18F] Nifene for nicotinic acetylcholine receptors or enzyme substrates (e.g. 6-FDOPA for the AADC enzyme). These agents permit the visualization of neuroreceptor pools in the context of a plurality of neuropsychiatric and neurologic illnesses.
Example: PET imaging with 18F-FDG can be used to estimate glucose metabolism in acute ischemic stroke. Some traces used for ischemic stroke are Oxygen-15 labelled water, [18F]FMISO.
The development of a number of novel probes for noninvasive, in vivo PET imaging of neuroaggregate in human brain has brought amyloid imaging to the doorstep of clinical use. The earliest amyloid imaging probes included 2-(1-{6-[(2-[18F]fluoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile ([18F]FDDNP) developed at the University of California, Los Angeles and N-methyl-[11C]2-(4'-methylaminophenyl)-6-hydroxybenzothiazole (termed Pittsburgh compound B) developed at the University of Pittsburgh. These amyloid imaging probes permit the visualization of amyloid plaques in the brains of Alzheimer's patients and could assist clinicians in making a positive clinical diagnosis of AD pre-mortem and aid in the development of novel anti-amyloid therapies. [11C]PMP (N-[11C]methylpiperidin-4-yl propionate) is a novel radiopharmaceutical used in PET imaging to determine the activity of the acetylcholinergic neurotransmitter system by acting as a substrate for acetylcholinesterase. Post-mortem examination of AD patients have shown decreased levels of acetylcholinesterase. [11C]PMP is used to map the acetylcholinesterase activity in the brain, which could allow for pre-mortem diagnoses of AD and help to monitor AD treatments. Avid Radiopharmaceuticals has developed and commercialized a compound called florbetapir that uses the longer-lasting radionuclide fluorine-18 to detect amyloid plaques using PET scans.
== Dedicated brain PET devices ==
In 2019 Catana et al. published an overview article about the "Development of Dedicated Brain PET Imaging Devices: Recent Advances and Future Perspectives". Various companies worldwide are working on developing a dedicated brain PET system either for pure research and/or clinical routine use. One of these companies is Positrigo which is working on the NeuroLF system.
== Challenges ==
One main challenge for developing new PET tracers for neuroimaging is that these tracers must cross the blood-brain barrier. Commonly, small molecules which are fat soluble have been used as they can pass the blood-brain barrier through lipid mediated passive diffusion.
However, as pharmaceutics move towards large biomolecules for therapies, new research has also focused on using biomolecules, such as antibodies, for PET tracers. These new larger PET tracers have increased difficulty passing the BBB as they are too large to passively diffuse across. Therefore, recent research is investigating methods to carry biomolecules across the BBB using endogenous transport systems including carrier-mediated transporters such as glucose and amino acid carriers, receptor-mediated transcytosis for insulin or transferrin.
== References == | Wikipedia/Brain_positron_emission_tomography |
A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or radiology technologists.
CT scanners use a rotating X-ray tube and a row of detectors placed in a gantry to measure X-ray attenuations by different tissues inside the body. The multiple X-ray measurements taken from different angles are then processed on a computer using tomographic reconstruction algorithms to produce tomographic (cross-sectional) images (virtual "slices") of a body. CT scans can be used in patients with metallic implants or pacemakers, for whom magnetic resonance imaging (MRI) is contraindicated.
Since its development in the 1970s, CT scanning has proven to be a versatile imaging technique. While CT is most prominently used in medical diagnosis, it can also be used to form images of non-living objects. The 1979 Nobel Prize in Physiology or Medicine was awarded jointly to South African-American physicist Allan MacLeod Cormack and British electrical engineer Godfrey Hounsfield "for the development of computer-assisted tomography".
== Types ==
On the basis of image acquisition and procedures, various type of scanners are available in the market.
=== Sequential CT ===
Sequential CT, also known as step-and-shoot CT, is a type of scanning method in which the CT table moves stepwise. The table increments to a particular location and then stops which is followed by the X-ray tube rotation and acquisition of a slice. The table then increments again, and another slice is taken. The table movement stops while taking slices. This results in an increased time of scanning.
=== Spiral CT ===
Spinning tube, commonly called spiral CT, or helical CT, is an imaging technique in which an entire X-ray tube is spun around the central axis of the area being scanned. These are the dominant type of scanners on the market because they have been manufactured longer and offer a lower cost of production and purchase. The main limitation of this type of CT is the bulk and inertia of the equipment (X-ray tube assembly and detector array on the opposite side of the circle) which limits the speed at which the equipment can spin. Some designs use two X-ray sources and detector arrays offset by an angle, as a technique to improve temporal resolution.
=== Electron beam tomography ===
Electron beam tomography (EBT) is a specific form of CT in which a large enough X-ray tube is constructed so that only the path of the electrons, travelling between the cathode and anode of the X-ray tube, are spun using deflection coils. This type had a major advantage since sweep speeds can be much faster, allowing for less blurry imaging of moving structures, such as the heart and arteries. Fewer scanners of this design have been produced when compared with spinning tube types, mainly due to the higher cost associated with building a much larger X-ray tube and detector array and limited anatomical coverage.
=== Dual energy CT ===
Dual energy CT, also known as spectral CT, is an advancement of computed Tomography in which two energies are used to create two sets of data. A dual energy CT may employ dual source, single source with dual detector layer, single source with energy switching methods to get two different sets of data.
Dual source CT is an advanced scanner with a two X-ray tube detector system, unlike conventional single tube systems. These two detector systems are mounted on a single gantry at 90° in the same plane. Dual source CT scanners allow fast scanning with higher temporal resolution by acquiring a full CT slice in only half a rotation. Fast imaging reduces motion blurring at high heart rates and potentially allowing for shorter breath-hold time. This is particularly useful for ill patients having difficulty holding their breath or unable to take heart-rate lowering medication.
Single source with energy switching is another mode of dual energy CT in which a single tube is operated at two different energies by switching the energies frequently.
=== CT perfusion imaging ===
CT perfusion imaging is a specific form of CT to assess flow through blood vessels whilst injecting a contrast agent. Blood flow, blood transit time, and organ blood volume, can all be calculated with reasonable sensitivity and specificity. This type of CT may be used on the heart, although sensitivity and specificity for detecting abnormalities are still lower than for other forms of CT. This may also be used on the brain, where CT perfusion imaging can often detect poor brain perfusion well before it is detected using a conventional spiral CT scan. This is better for stroke diagnosis than other CT types.
=== PET CT ===
Positron emission tomography–computed tomography is a hybrid CT modality which combines, in a single gantry, a positron emission tomography (PET) scanner and an X-ray computed tomography (CT) scanner, to acquire sequential images from both devices in the same session, which are combined into a single superposed (co-registered) image. Thus, functional imaging obtained by PET, which depicts the spatial distribution of metabolic or biochemical activity in the body can be more precisely aligned or correlated with anatomic imaging obtained by CT scanning.
PET-CT gives both anatomical and functional details of an organ under examination and is helpful in detecting different type of cancers.
== Medical use ==
Since its introduction in the 1970s, CT has become an important tool in medical imaging to supplement conventional X-ray imaging and medical ultrasonography. It has more recently been used for preventive medicine or screening for disease, for example, CT colonography for people with a high risk of colon cancer, or full-motion heart scans for people with a high risk of heart disease. Several institutions offer full-body scans for the general population although this practice goes against the advice and official position of many professional organizations in the field primarily due to the radiation dose applied.
The use of CT scans has increased dramatically over the last two decades in many countries. An estimated 72 million scans were performed in the United States in 2007 and more than 80 million in 2015.
=== Head ===
CT scanning of the head is typically used to detect infarction (stroke), tumors, calcifications, haemorrhage, and bone trauma. Of the above, hypodense (dark) structures can indicate edema and infarction, hyperdense (bright) structures indicate calcifications and haemorrhage and bone trauma can be seen as disjunction in bone windows. Tumors can be detected by the swelling and anatomical distortion they cause, or by surrounding edema. CT scanning of the head is also used in CT-guided stereotactic surgery and radiosurgery for treatment of intracranial tumors, arteriovenous malformations, and other surgically treatable conditions using a device known as the N-localizer.
=== Neck ===
Contrast CT is generally the initial study of choice for neck masses in adults. CT of the thyroid plays an important role in the evaluation of thyroid cancer. CT scan often incidentally finds thyroid abnormalities, and so is often the preferred investigation modality for thyroid abnormalities.
=== Lungs ===
A CT scan can be used for detecting both acute and chronic changes in the lung parenchyma, the tissue of the lungs. It is particularly relevant here because normal two-dimensional X-rays do not show such defects. A variety of techniques are used, depending on the suspected abnormality. For evaluation of chronic interstitial processes such as emphysema, and fibrosis, thin sections with high spatial frequency reconstructions are used; often scans are performed both on inspiration and expiration. This special technique is called high resolution CT that produces a sampling of the lung, and not continuous images.
Bronchial wall thickening can be seen on lung CTs and generally (but not always) implies inflammation of the bronchi.
An incidentally found nodule in the absence of symptoms (sometimes referred to as an incidentaloma) may raise concerns that it might represent a tumor, either benign or malignant. Perhaps persuaded by fear, patients and doctors sometimes agree to an intensive schedule of CT scans, sometimes up to every three months and beyond the recommended guidelines, in an attempt to do surveillance on the nodules. However, established guidelines advise that patients without a prior history of cancer and whose solid nodules have not grown over a two-year period are unlikely to have any malignant cancer. For this reason, and because no research provides supporting evidence that intensive surveillance gives better outcomes, and because of risks associated with having CT scans, patients should not receive CT screening in excess of those recommended by established guidelines.
=== Angiography ===
Computed tomography angiography (CTA) is a type of contrast CT to visualize the arteries and veins throughout the body. This ranges from arteries serving the brain to those bringing blood to the lungs, kidneys, arms and legs. An example of this type of exam is CT pulmonary angiogram (CTPA) used to diagnose pulmonary embolism (PE). It employs computed tomography and an iodine-based contrast agent to obtain an image of the pulmonary arteries. CT scans can reduce the risk of angiography by providing clinicians with more information about the positioning and number of clots prior to the procedure.
=== Cardiac ===
A CT scan of the heart is performed to gain knowledge about cardiac or coronary anatomy. Traditionally, cardiac CT scans are used to detect, diagnose, or follow up coronary artery disease. More recently CT has played a key role in the fast-evolving field of transcatheter structural heart interventions, more specifically in the transcatheter repair and replacement of heart valves.
The main forms of cardiac CT scanning are:
Coronary CT angiography (CCTA): the use of CT to assess the coronary arteries of the heart. The subject receives an intravenous injection of radiocontrast, and then the heart is scanned using a high-speed CT scanner, allowing radiologists to assess the extent of occlusion in the coronary arteries, usually to diagnose coronary artery disease.
Coronary CT calcium scan: also used for the assessment of severity of coronary artery disease. Specifically, it looks for calcium deposits in the coronary arteries that can narrow arteries and increase the risk of a heart attack. A typical coronary CT calcium scan is done without the use of radiocontrast, but it can possibly be done from contrast-enhanced images as well.
To better visualize the anatomy, post-processing of the images is common. Most common are multiplanar reconstructions (MPR) and volume rendering. For more complex anatomies and procedures, such as heart valve interventions, a true 3D reconstruction or a 3D print is created based on these CT images to gain a deeper understanding.
=== Abdomen and pelvis ===
CT is an accurate technique for diagnosis of abdominal diseases like Crohn's disease, GIT bleeding, and diagnosis and staging of cancer, as well as follow-up after cancer treatment to assess response. It is commonly used to investigate acute abdominal pain.
Non-contrast-enhanced CT scans are the gold standard for diagnosing kidney stone disease. They allow clinicians to estimate the size, volume, and density of stones, helping to guide further treatment; with size being especially important in predicting the time to spontaneous passage of a stone.
=== Axial skeleton and extremities ===
For the axial skeleton and extremities, CT is often used to image complex fractures, especially ones around joints, because of its ability to reconstruct the area of interest in multiple planes. Fractures, ligamentous injuries, and dislocations can easily be recognized with a 0.2 mm resolution. With modern dual-energy CT scanners, new areas of use have been established, such as aiding in the diagnosis of gout.
=== Biomechanical use ===
CT is used in biomechanics to quickly reveal the geometry, anatomy, density and elastic moduli of biological tissues.
== Other uses ==
=== Industrial use ===
Industrial CT scanning (industrial computed tomography) is a process which uses X-ray equipment to produce 3D representations of components both externally and internally. Industrial CT scanning has been used in many areas of industry for internal inspection of components. Some of the key uses for CT scanning have been flaw detection, failure analysis, metrology, assembly analysis, image-based finite element methods and reverse engineering applications. CT scanning is also employed in the imaging and conservation of museum artifacts.
=== Aviation security ===
CT scanning has also found an application in transport security (predominantly airport security) where it is currently used in a materials analysis context for explosives detection CTX (explosive-detection device) and is also under consideration for automated baggage/parcel security scanning using computer vision based object recognition algorithms that target the detection of specific threat items based on 3D appearance (e.g. guns, knives, liquid containers). Its usage in airport security pioneered at Shannon Airport in March 2022 has ended the ban on liquids over 100 ml there, a move that Heathrow Airport plans for a full roll-out on 1 December 2022 and the TSA spent $781.2 million on an order for over 1,000 scanners, ready to go live in the summer.
=== Geological use ===
X-ray CT is used in geological studies to quickly reveal materials inside a drill core. Dense minerals such as pyrite and barite appear brighter and less dense components such as clay appear dull in CT images.
=== Paleontological use ===
Traditional methods of studying fossils are often destructive, such as the use of thin sections and physical preparation. X-ray CT is used in paleontology to non-destructively visualize fossils in 3D. This has many advantages. For example, we can look at fragile structures that might never otherwise be able to be studied. In addition, one can freely move around models of fossils in virtual 3D space to inspect it without damaging the fossil.
=== Cultural heritage use ===
X-ray CT and micro-CT can also be used for the conservation and preservation of objects of cultural heritage. For many fragile objects, direct research and observation can be damaging and can degrade the object over time. Using CT scans, conservators and researchers are able to determine the material composition of the objects they are exploring, such as the position of ink along the layers of a scroll, without any additional harm. These scans have been optimal for research focused on the workings of the Antikythera mechanism or the text hidden inside the charred outer layers of the En-Gedi Scroll. However, they are not optimal for every object subject to these kinds of research questions, as there are certain artifacts like the Herculaneum papyri in which the material composition has very little variation along the inside of the object. After scanning these objects, computational methods can be employed to examine the insides of these objects, as was the case with the virtual unwrapping of the En-Gedi scroll and the Herculaneum papyri. Micro-CT has also proved useful for analyzing more recent artifacts such as still-sealed historic correspondence that employed the technique of letterlocking (complex folding and cuts) that provided a "tamper-evident locking mechanism". Further examples of use cases in archaeology is imaging the contents of sarcophagi or ceramics.
Recently, CWI in Amsterdam has collaborated with Rijksmuseum to investigate art object inside details in the framework called IntACT.
=== Microorganism research ===
Varied types of fungus can degrade wood to different degrees, one Belgium research group has been used X-ray CT 3 dimension with sub-micron resolution unveiled fungi can penetrate micropores of 0.6 μm under certain conditions.
=== Timber sawmill ===
Sawmills use industrial CT scanners to detect round defects, for instance knots, to improve total value of timber productions. Most sawmills are planning to incorporate this robust detection tool to improve productivity in the long run, however initial investment cost is high.
== Interpretation of results ==
=== Presentation ===
The result of a CT scan is a volume of voxels, which may be presented to a human observer by various methods, which broadly fit into the following categories:
Slices (of varying thickness). Thin slice is generally regarded as planes representing a thickness of less than 3 mm. Thick slice is generally regarded as planes representing a thickness between 3 mm and 5 mm.
Projection, including maximum intensity projection and average intensity projection
Volume rendering (VR)
Technically, all volume renderings become projections when viewed on a 2-dimensional display, making the distinction between projections and volume renderings a bit vague. The epitomes of volume rendering models feature a mix of for example coloring and shading in order to create realistic and observable representations.
Two-dimensional CT images are conventionally rendered so that the view is as though looking up at it from the patient's feet. Hence, the left side of the image is to the patient's right and vice versa, while anterior in the image also is the patient's anterior and vice versa. This left-right interchange corresponds to the view that physicians generally have in reality when positioned in front of patients.
==== Grayscale ====
Pixels in an image obtained by CT scanning are displayed in terms of relative radiodensity. The pixel itself is displayed according to the mean attenuation of the tissue(s) that it corresponds to on a scale from +3,071 (most attenuating) to −1,024 (least attenuating) on the Hounsfield scale. A pixel is a two dimensional unit based on the matrix size and the field of view. When the CT slice thickness is also factored in, the unit is known as a voxel, which is a three-dimensional unit. Water has an attenuation of 0 Hounsfield units (HU), while air is −1,000 HU, cancellous bone is typically +400 HU, and cranial bone can reach 2,000 HU. The attenuation of metallic implants depends on the atomic number of the element used: Titanium usually has an amount of +1000 HU, iron steel can completely block the X-ray and is, therefore, responsible for well-known line-artifacts in computed tomograms. Artifacts are caused by abrupt transitions between low- and high-density materials, which results in data values that exceed the dynamic range of the processing electronics.
==== Windowing ====
CT data sets have a very high dynamic range which must be reduced for display or printing. This is typically done via a process of "windowing", which maps a range (the "window") of pixel values to a grayscale ramp. For example, CT images of the brain are commonly viewed with a window extending from 0 HU to 80 HU. Pixel values of 0 and lower, are displayed as black; values of 80 and higher are displayed as white; values within the window are displayed as a gray intensity proportional to position within the window. The window used for display must be matched to the X-ray density of the object of interest, in order to optimize the visible detail. Window width and window level parameters are used to control the windowing of a scan.
==== Multiplanar reconstruction and projections ====
Multiplanar reconstruction (MPR) is the process of converting data from one anatomical plane (usually transverse) to other planes. It can be used for thin slices as well as projections. Multiplanar reconstruction is possible as present CT scanners provide almost isotropic resolution.
MPR is used almost in every scan. The spine is frequently examined with it. An image of the spine in axial plane can only show one vertebral bone at a time and cannot show its relation with other vertebral bones. By reformatting the data in other planes, visualization of the relative position can be achieved in sagittal and coronal plane.
New software allows the reconstruction of data in non-orthogonal (oblique) planes, which help in the visualization of organs which are not in orthogonal planes. It is better suited for visualization of the anatomical structure of the bronchi as they do not lie orthogonal to the direction of the scan.
Curved-plane reconstruction (or curved planar reformation = CPR) is performed mainly for the evaluation of vessels. This type of reconstruction helps to straighten the bends in a vessel, thereby helping to visualize a whole vessel in a single image or in multiple images. After a vessel has been "straightened", measurements such as cross-sectional area and length can be made. This is helpful in preoperative assessment of a surgical procedure.
For 2D projections used in radiation therapy for quality assurance and planning of external beam radiotherapy, including digitally reconstructed radiographs, see Beam's eye view.
==== Volume rendering ====
A threshold value of radiodensity is set by the operator (e.g., a level that corresponds to bone). With the help of edge detection image processing algorithms a 3D model can be constructed from the initial data and displayed on screen. Various thresholds can be used to get multiple models, each anatomical component such as muscle, bone and cartilage can be differentiated on the basis of different colours given to them. However, this mode of operation cannot show interior structures.
Surface rendering is limited technique as it displays only the surfaces that meet a particular threshold density, and which are towards the viewer. However, In volume rendering, transparency, colours and shading are used which makes it easy to present a volume in a single image. For example, Pelvic bones could be displayed as semi-transparent, so that, even viewing at an oblique angle one part of the image does not hide another.
=== Image quality ===
==== Dose versus image quality ====
An important issue within radiology today is how to reduce the radiation dose during CT examinations without compromising the image quality. In general, higher radiation doses result in higher-resolution images, while lower doses lead to increased image noise and unsharp images. However, increased dosage raises the adverse side effects, including the risk of radiation-induced cancer – a four-phase abdominal CT gives the same radiation dose as 300 chest X-rays. Several methods that can reduce the exposure to ionizing radiation during a CT scan exist.
New software technology can significantly reduce the required radiation dose. New iterative tomographic reconstruction algorithms (e.g., iterative Sparse Asymptotic Minimum Variance) could offer super-resolution without requiring higher radiation dose.
Individualize the examination and adjust the radiation dose to the body type and body organ examined. Different body types and organs require different amounts of radiation.
Higher resolution is not always suitable, such as detection of small pulmonary masses.
==== Artifacts ====
Although images produced by CT are generally faithful representations of the scanned volume, the technique is susceptible to a number of artifacts, such as the following:Chapters 3 and 5
Streak artifact
Streaks are often seen around materials that block most X-rays, such as metal or bone. Numerous factors contribute to these streaks: under sampling, photon starvation, motion, beam hardening, and Compton scatter. This type of artifact commonly occurs in the posterior fossa of the brain, or if there are metal implants. The streaks can be reduced using newer reconstruction techniques. Approaches such as metal artifact reduction (MAR) can also reduce this artifact. MAR techniques include spectral imaging, where CT images are taken with photons of different energy levels, and then synthesized into monochromatic images with special software such as GSI (Gemstone Spectral Imaging).
Partial volume effect
This appears as "blurring" of edges. It is due to the scanner being unable to differentiate between a small amount of high-density material (e.g., bone) and a larger amount of lower density (e.g., cartilage). The reconstruction assumes that the X-ray attenuation within each voxel is homogeneous; this may not be the case at sharp edges. This is most commonly seen in the z-direction (craniocaudal direction), due to the conventional use of highly anisotropic voxels, which have a much lower out-of-plane resolution, than in-plane resolution. This can be partially overcome by scanning using thinner slices, or an isotropic acquisition on a modern scanner.
Ring artifact
Probably the most common mechanical artifact, the image of one or many "rings" appears within an image. They are usually caused by the variations in the response from individual elements in a two dimensional X-ray detector due to defect or miscalibration. Ring artifacts can largely be reduced by intensity normalization, also referred to as flat field correction. Remaining rings can be suppressed by a transformation to polar space, where they become linear stripes. A comparative evaluation of ring artefact reduction on X-ray tomography images showed that the method of Sijbers and Postnov can effectively suppress ring artefacts.
Noise
This appears as grain on the image and is caused by a low signal to noise ratio. This occurs more commonly when a thin slice thickness is used. It can also occur when the power supplied to the X-ray tube is insufficient to penetrate the anatomy.
Windmill
Streaking appearances can occur when the detectors intersect the reconstruction plane. This can be reduced with filters or a reduction in pitch.
Beam hardening
This can give a "cupped appearance" when grayscale is visualized as height. It occurs because conventional sources, like X-ray tubes emit a polychromatic spectrum. Photons of higher photon energy levels are typically attenuated less. Because of this, the mean energy of the spectrum increases when passing the object, often described as getting "harder". This leads to an effect increasingly underestimating material thickness, if not corrected. Many algorithms exist to correct for this artifact. They can be divided into mono- and multi-material methods.
== Advantages ==
CT scanning has several advantages over traditional two-dimensional medical radiography. First, CT eliminates the superimposition of images of structures outside the area of interest. Second, CT scans have greater image resolution, enabling examination of finer details. CT can distinguish between tissues that differ in radiographic density by 1% or less. Third, CT scanning enables multiplanar reformatted imaging: scan data can be visualized in the transverse (or axial), coronal, or sagittal plane, depending on the diagnostic task.
The improved resolution of CT has permitted the development of new investigations. For example, CT angiography avoids the invasive insertion of a catheter. CT scanning can perform a virtual colonoscopy with greater accuracy and less discomfort for the patient than a traditional colonoscopy. Virtual colonography is far more accurate than a barium enema for detection of tumors and uses a lower radiation dose.
CT is a moderate-to-high radiation diagnostic technique. The radiation dose for a particular examination depends on multiple factors: volume scanned, patient build, number and type of scan protocol, and desired resolution and image quality. Two helical CT scanning parameters, tube current and pitch, can be adjusted easily and have a profound effect on radiation. CT scanning is more accurate than two-dimensional radiographs in evaluating anterior interbody fusion, although they may still over-read the extent of fusion.
== Adverse effects ==
=== Cancer ===
The radiation used in CT scans can damage body cells, including DNA molecules, which can lead to radiation-induced cancer. The radiation doses received from CT scans is variable. Compared to the lowest dose X-ray techniques, CT scans can have 100 to 1,000 times higher dose than conventional X-rays. However, a lumbar spine X-ray has a similar dose as a head CT. Articles in the media often exaggerate the relative dose of CT by comparing the lowest-dose X-ray techniques (chest X-ray) with the highest-dose CT techniques. In general, a routine abdominal CT has a radiation dose similar to three years of average background radiation.
Large scale population-based studies have consistently demonstrated that low dose radiation from CT scans has impacts on cancer incidence in a variety of cancers. For example, in a large population-based Australian cohort it was found that up to 3.7% of brain cancers were caused by CT scan radiation. Some experts project that in the future, between three and five percent of all cancers would result from medical imaging. An Australian study of 10.9 million people reported that the increased incidence of cancer after CT scan exposure in this cohort was mostly due to irradiation. In this group, one in every 1,800 CT scans was followed by an excess cancer. If the lifetime risk of developing cancer is 40% then the absolute risk rises to 40.05% after a CT. The risks of CT scan radiation are especially important in patients undergoing recurrent CT scans within a short time span of one to five years.
Some experts note that CT scans are known to be "overused," and "there is distressingly little evidence of better health outcomes associated with the current high rate of scans." On the other hand, a recent paper analyzing the data of patients who received high cumulative doses showed a high degree of appropriate use. This creates an important issue of cancer risk to these patients. Moreover, a highly significant finding that was previously unreported is that some patients received >100 mSv dose from CT scans in a single day, which counteracts existing criticisms some investigators may have on the effects of protracted versus acute exposure.
There are contrarian views and the debate is ongoing. Some studies have shown that publications indicating an increased risk of cancer from typical doses of body CT scans are plagued with serious methodological limitations and several highly improbable results, concluding that no evidence indicates such low doses cause any long-term harm.
One study estimated that as many as 0.4% of cancers in the United States resulted from CT scans, and that this may have increased to as much as 1.5 to 2% based on the rate of CT use in 2007. Others dispute this estimate, as there is no consensus that the low levels of radiation used in CT scans cause damage. Lower radiation doses are used in many cases, such as in the investigation of renal colic.
A person's age plays a significant role in the subsequent risk of cancer. Estimated lifetime cancer mortality risks from an abdominal CT of a one-year-old is 0.1%, or 1:1000 scans. The risk for someone who is 40 years old is half that of someone who is 20 years old with substantially less risk in the elderly. The International Commission on Radiological Protection estimates that the risk to a fetus being exposed to 10 mGy (a unit of radiation exposure) increases the rate of cancer before 20 years of age from 0.03% to 0.04% (for reference a CT pulmonary angiogram exposes a fetus to 4 mGy). A 2012 review did not find an association between medical radiation and cancer risk in children noting however the existence of limitations in the evidences over which the review is based. CT scans can be performed with different settings for lower exposure in children with most manufacturers of CT scans as of 2007 having this function built in. Furthermore, certain conditions can require children to be exposed to multiple CT scans.
Current recommendations are to inform patients of the risks of CT scanning. However, employees of imaging centers tend not to communicate such risks unless patients ask.
=== Contrast reactions ===
In the United States half of CT scans are contrast CTs using intravenously injected radiocontrast agents. The most common reactions from these agents are mild, including nausea, vomiting, and an itching rash. Severe life-threatening reactions may rarely occur. Overall reactions occur in 1 to 3% with nonionic contrast and 4 to 12% of people with ionic contrast. Skin rashes may appear within a week to 3% of people.
The old radiocontrast agents caused anaphylaxis in 1% of cases while the newer, low-osmolar agents cause reactions in 0.01–0.04% of cases. Death occurs in about 2 to 30 people per 1,000,000 administrations, with newer agents being safer.
There is a higher risk of mortality in those who are female, elderly or in poor health, usually secondary to either anaphylaxis or acute kidney injury.
The contrast agent may induce contrast-induced nephropathy. This occurs in 2 to 7% of people who receive these agents, with greater risk in those who have preexisting kidney failure, preexisting diabetes, or reduced intravascular volume. People with mild kidney impairment are usually advised to ensure full hydration for several hours before and after the injection. For moderate kidney failure, the use of iodinated contrast should be avoided; this may mean using an alternative technique instead of CT. Those with severe kidney failure requiring dialysis require less strict precautions, as their kidneys have so little function remaining that any further damage would not be noticeable and the dialysis will remove the contrast agent; it is normally recommended, however, to arrange dialysis as soon as possible following contrast administration to minimize any adverse effects of the contrast.
In addition to the use of intravenous contrast, orally administered contrast agents are frequently used when examining the abdomen. These are frequently the same as the intravenous contrast agents, merely diluted to approximately 10% of the concentration. However, oral alternatives to iodinated contrast exist, such as very dilute (0.5–1% w/v) barium sulfate suspensions. Dilute barium sulfate has the advantage that it does not cause allergic-type reactions or kidney failure, but cannot be used in patients with suspected bowel perforation or suspected bowel injury, as leakage of barium sulfate from damaged bowel can cause fatal peritonitis.
Side effects from contrast agents, administered intravenously in some CT scans, might impair kidney performance in patients with kidney disease, although this risk is now believed to be lower than previously thought.
=== Scan dose ===
The table reports average radiation exposures; however, there can be a wide variation in radiation doses between similar scan types, where the highest dose could be as much as 22 times higher than the lowest dose. A typical plain film X-ray involves radiation dose of 0.01 to 0.15 mGy, while a typical CT can involve 10–20 mGy for specific organs, and can go up to 80 mGy for certain specialized CT scans.
For purposes of comparison, the world average dose rate from naturally occurring sources of background radiation is 2.4 mSv per year, equal for practical purposes in this application to 2.4 mGy per year. While there is some variation, most people (99%) received less than 7 mSv per year as background radiation. Medical imaging as of 2007 accounted for half of the radiation exposure of those in the United States with CT scans making up two thirds of this amount. In the United Kingdom it accounts for 15% of radiation exposure. The average radiation dose from medical sources is ≈0.6 mSv per person globally as of 2007. Those in the nuclear industry in the United States are limited to doses of 50 mSv a year and 100 mSv every 5 years.
Lead is the main material used by radiography personnel for shielding against scattered X-rays.
==== Radiation dose units ====
The radiation dose reported in the gray or mGy unit is proportional to the amount of energy that the irradiated body part is expected to absorb, and the physical effect (such as DNA double strand breaks) on the cells' chemical bonds by X-ray radiation is proportional to that energy.
The sievert unit is used in the report of the effective dose. The sievert unit, in the context of CT scans, does not correspond to the actual radiation dose that the scanned body part absorbs but to another radiation dose of another scenario, the whole body absorbing the other radiation dose and the other radiation dose being of a magnitude, estimated to have the same probability to induce cancer as the CT scan. Thus, as is shown in the table above, the actual radiation that is absorbed by a scanned body part is often much larger than the effective dose suggests. A specific measure, termed the computed tomography dose index (CTDI), is commonly used as an estimate of the radiation absorbed dose for tissue within the scan region, and is automatically computed by medical CT scanners.
The equivalent dose is the effective dose of a case, in which the whole body would actually absorb the same radiation dose, and the sievert unit is used in its report. In the case of non-uniform radiation, or radiation given to only part of the body, which is common for CT examinations, using the local equivalent dose alone would overstate the biological risks to the entire organism.
==== Effects of radiation ====
Most adverse health effects of radiation exposure may be grouped in two general categories:
deterministic effects (harmful tissue reactions) due in large part to the killing/malfunction of cells following high doses;
stochastic effects, i.e., cancer and heritable effects involving either cancer development in exposed individuals owing to mutation of somatic cells or heritable disease in their offspring owing to mutation of reproductive (germ) cells.
The added lifetime risk of developing cancer by a single abdominal CT of 8 mSv is estimated to be 0.05%, or 1 one in 2,000.
Because of increased susceptibility of fetuses to radiation exposure, the radiation dosage of a CT scan is an important consideration in the choice of medical imaging in pregnancy.
==== Excess doses ====
In October, 2009, the US Food and Drug Administration (FDA) initiated an investigation of brain perfusion CT (PCT) scans, based on radiation burns caused by incorrect settings at one particular facility for this particular type of CT scan. Over 200 patients were exposed to radiation at approximately eight times the expected dose for an 18-month period; over 40% of them lost patches of hair. This event prompted a call for increased CT quality assurance programs. It was noted that "while unnecessary radiation exposure should be avoided, a medically needed CT scan obtained with appropriate acquisition parameter has benefits that outweigh the radiation risks." Similar problems have been reported at other centers. These incidents are believed to be due to human error.
== Procedure ==
CT scan procedure varies according to the type of the study and the organ being imaged. The patient lies on the CT table and the centering of the table is done according to the body part. The IV line is established in case of contrast-enhanced CT. After selecting proper and rate of contrast from the pressure injector, the scout is taken to localize and plan the scan. Once the plan is selected, the contrast is given. The raw data is processed according to the study and proper windowing is done to make scans easy to diagnose.
=== Preparation ===
Patient preparation may vary according to the type of scan. The general patient preparation includes.
Signing the informed consent.
Removal of metallic objects and jewelry from the region of interest.
Changing to the hospital gown according to hospital protocol.
Checking of kidney function, especially creatinine and urea levels (in case of CECT).
== Mechanism ==
Computed tomography operates by using an X-ray generator that rotates around the object; X-ray detectors are positioned on the opposite side of the circle from the X-ray source. As the X-rays pass through the patient, they are attenuated differently by various tissues according to the tissue density. A visual representation of the raw data obtained is called a sinogram, yet it is not sufficient for interpretation. Once the scan data has been acquired, the data must be processed using a form of tomographic reconstruction, which produces a series of cross-sectional images. These cross-sectional images are made up of small units of pixels or voxels.
Pixels in an image obtained by CT scanning are displayed in terms of relative radiodensity. The pixel itself is displayed according to the mean attenuation of the tissue(s) that it corresponds to on a scale from +3,071 (most attenuating) to −1,024 (least attenuating) on the Hounsfield scale. A pixel is a two dimensional unit based on the matrix size and the field of view. When the CT slice thickness is also factored in, the unit is known as a voxel, which is a three-dimensional unit.
Water has an attenuation of 0 Hounsfield units (HU), while air is −1,000 HU, cancellous bone is typically +400 HU, and cranial bone can reach 2,000 HU or more (os temporale) and can cause artifacts. The attenuation of metallic implants depends on the atomic number of the element used: Titanium usually has an amount of +1000 HU, iron steel can completely extinguish the X-ray and is, therefore, responsible for well-known line-artifacts in computed tomograms. Artifacts are caused by abrupt transitions between low- and high-density materials, which results in data values that exceed the dynamic range of the processing electronics. Two-dimensional CT images are conventionally rendered so that the view is as though looking up at it from the patient's feet. Hence, the left side of the image is to the patient's right and vice versa, while anterior in the image also is the patient's anterior and vice versa. This left-right interchange corresponds to the view that physicians generally have in reality when positioned in front of patients.
Initially, the images generated in CT scans were in the transverse (axial) anatomical plane, perpendicular to the long axis of the body. Modern scanners allow the scan data to be reformatted as images in other planes. Digital geometry processing can generate a three-dimensional image of an object inside the body from a series of two-dimensional radiographic images taken by rotation around a fixed axis. These cross-sectional images are widely used for medical diagnosis and therapy.
=== Contrast ===
Contrast media used for X-ray CT, as well as for plain film X-ray, are called radiocontrasts. Radiocontrasts for CT are, in general, iodine-based. This is useful to highlight structures such as blood vessels that otherwise would be difficult to delineate from their surroundings. Using contrast material can also help to obtain functional information about tissues. Often, images are taken both with and without radiocontrast.
== History ==
The history of X-ray computed tomography goes back to at least 1917 with the mathematical theory of the Radon transform. In October 1963, William H. Oldendorf received a U.S. patent for a "radiant energy apparatus for investigating selected areas of interior objects obscured by dense material". The first commercially viable CT scanner was invented by Godfrey Hounsfield in 1972.
It is often claimed that revenues from the sales of The Beatles' records in the 1960s helped fund the development of the first CT scanner at EMI. The first production X-ray CT machines were in fact called EMI scanners.
=== Etymology ===
The word tomography is derived from the Greek tome 'slice' and graphein 'to write'. Computed tomography was originally known as the "EMI scan" as it was developed in the early 1970s at a research branch of EMI, a company best known today for its music and recording business. It was later known as computed axial tomography (CAT or CT scan) and body section röntgenography.
The term CAT scan is no longer in technical use because current CT scans enable for multiplanar reconstructions. This makes CT scan the most appropriate term, which is used by radiologists in common vernacular as well as in textbooks and scientific papers.
In Medical Subject Headings (MeSH), computed axial tomography was used from 1977 to 1979, but the current indexing explicitly includes X-ray in the title.
The term sinogram was introduced by Paul Edholm and Bertil Jacobson in 1975.
== Society and culture ==
=== Campaigns ===
In response to increased concern by the public and the ongoing progress of best practices, the Alliance for Radiation Safety in Pediatric Imaging was formed within the Society for Pediatric Radiology. In concert with the American Society of Radiologic Technologists, the American College of Radiology and the American Association of Physicists in Medicine, the Society for Pediatric Radiology developed and launched the Image Gently Campaign which is designed to maintain high-quality imaging studies while using the lowest doses and best radiation safety practices available on pediatric patients. This initiative has been endorsed and applied by a growing list of various professional medical organizations around the world and has received support and assistance from companies that manufacture equipment used in Radiology.
Following upon the success of the Image Gently campaign, the American College of Radiology, the Radiological Society of North America, the American Association of Physicists in Medicine and the American Society of Radiologic Technologists have launched a similar campaign to address this issue in the adult population called Image Wisely.
The World Health Organization and International Atomic Energy Agency (IAEA) of the United Nations have also been working in this area and have ongoing projects designed to broaden best practices and lower patient radiation dose.
=== Prevalence ===
Use of CT has increased dramatically over the last two decades. An estimated 72 million scans were performed in the United States in 2007, accounting for close to half of the total per-capita dose rate from radiologic and nuclear medicine procedures. Of the CT scans, six to eleven percent are done in children, an increase of seven to eightfold from 1980. Similar increases have been seen in Europe and Asia. In Calgary, Canada, 12.1% of people who present to the emergency with an urgent complaint received a CT scan, most commonly either of the head or of the abdomen. The percentage who received CT, however, varied markedly by the emergency physician who saw them from 1.8% to 25%. In the emergency department in the United States, CT or MRI imaging is done in 15% of people who present with injuries as of 2007 (up from 6% in 1998).
The increased use of CT scans has been the greatest in two fields: screening of adults (screening CT of the lung in smokers, virtual colonoscopy, CT cardiac screening, and whole-body CT in asymptomatic patients) and CT imaging of children. Shortening of the scanning time to around 1 second, eliminating the strict need for the subject to remain still or be sedated, is one of the main reasons for the large increase in the pediatric population (especially for the diagnosis of appendicitis). As of 2007, in the United States a proportion of CT scans are performed unnecessarily. Some estimates place this number at 30%. There are a number of reasons for this including: legal concerns, financial incentives, and desire by the public. For example, some healthy people avidly pay to receive full-body CT scans as screening. In that case, it is not at all clear that the benefits outweigh the risks and costs. Deciding whether and how to treat incidentalomas is complex, radiation exposure is not negligible, and the money for the scans involves opportunity cost.
== Manufacturers ==
Major manufacturers of CT scanning devices and equipment are:
Canon Medical Systems Corporation
Fujifilm Healthcare
GE HealthCare
Neusoft Medical Systems
Philips
Siemens Healthineers
United Imaging
== Research ==
Photon-counting computed tomography is a CT technique currently under development. Typical CT scanners use energy integrating detectors; photons are measured as a voltage on a capacitor which is proportional to the X-rays detected. However, this technique is susceptible to noise and other factors which can affect the linearity of the voltage to X-ray intensity relationship. Photon counting detectors (PCDs) are still affected by noise but it does not change the measured counts of photons. PCDs have several potential advantages, including improving signal (and contrast) to noise ratios, reducing doses, improving spatial resolution, and through use of several energies, distinguishing multiple contrast agents. PCDs have only recently become feasible in CT scanners due to improvements in detector technologies that can cope with the volume and rate of data required. As of February 2016, photon counting CT is in use at three sites. Some early research has found the dose reduction potential of photon counting CT for breast imaging to be very promising. In view of recent findings of high cumulative doses to patients from recurrent CT scans, there has been a push for scanning technologies and techniques that reduce ionising radiation doses to patients to sub-milliSievert (sub-mSv in the literature) levels during the CT scan process, a goal that has been lingering.
== See also ==
== References ==
== External links ==
Development of CT imaging
CT Artefacts—PPT by David Platten
Filler A (2009-06-30). "The History, Development and Impact of Computed Imaging in Neurological Diagnosis and Neurosurgery: CT, MRI, and DTI". Nature Precedings: 1. doi:10.1038/npre.2009.3267.4. ISSN 1756-0357.
Boone JM, McCollough CH (2021). "Computed tomography turns 50". Physics Today. 74 (9): 34–40. Bibcode:2021PhT....74i..34B. doi:10.1063/PT.3.4834. ISSN 0031-9228. S2CID 239718717. | Wikipedia/X-ray_computed_tomography |
Plastic surgery is a surgical specialty involving restoration, reconstruction, or alteration of the human body. It can be divided into two main categories: reconstructive surgery and cosmetic surgery. Reconstructive surgery covers a wide range of specialties, including craniofacial surgery, hand surgery, microsurgery, and the treatment of burns. This kind of surgery focuses on restoring a body part or improving its function. In contrast, cosmetic (or aesthetic) surgery focuses solely on improving the physical appearance of the body. A comprehensive definition of plastic surgery has never been established, because it has no distinct anatomical object and thus overlaps with practically all other surgical specialties. An essential feature of plastic surgery is that it involves the treatment of conditions that require or may require tissue relocation skills.
== Etymology ==
The word plastic in plastic surgery refers to the concept of "reshaping" and comes from the Greek πλαστική (τέχνη), plastikē (tekhnē), "the art of modelling" of malleable flesh. This meaning in English is seen as early as 1598. In the surgical context, the word "plastic" first appeared in 1816 and was established in 1838 by Eduard Zeis, preceding the modern technical usage of the word as "engineering material made from petroleum" by 70 years.
== History ==
Treatments for the plastic repair of a broken nose are first mentioned in the c. 1600 BC Egyptian medical text called the Edwin Smith papyrus. The early trauma surgery textbook was named after the American Egyptologist, Edwin Smith. Reconstructive surgery techniques were being carried out in India by 800 BC. Sushruta was a physician who made contributions to the field of plastic and cataract surgery in the 6th century BC.
The Romans also performed plastic cosmetic surgery, using simple techniques, such as repairing damaged ears, from around the 1st century BC. For religious reasons, they did not dissect either human beings or animals, thus, their knowledge was based in its entirety on the texts of their Greek predecessors. Notwithstanding, Aulus Cornelius Celsus left some accurate anatomical descriptions, some of which—for instance, his studies on the genitalia and the skeleton—are of special interest to plastic surgery.
Arabs practiced the plastic surgery, during the Abbasid Caliphate in 750 AD. The Arabic translations made their way into Europe via intermediaries. In Italy, the Branca family of Sicily and Gaspare Tagliacozzi (Bologna) became familiar with the techniques of Sushruta.
In all fields of surgery, the Arab physician, surgeon, and chemist Al-Zahrawi talks of the use of silk thread sutures to achieve good cosmesis. He describes what is thought to be the first attempt at reduction mammaplasty for the management of gynaecomastia. He gives detailed descriptions of other basic surgical techniques such as cautery and wound management.
British physicians travelled to India to see rhinoplasties being performed by Indian methods. Reports on Indian rhinoplasty performed by a Kumhar (potter) vaidya were published in the Gentleman's Magazine by 1794. Joseph Constantine Carpue spent 20 years in India studying local plastic surgery methods. Carpue was able to perform the first major surgery in the Western world in the year 1815. Instruments described in the Sushruta Samhita were further modified in the Western world.
In 1465, Sabuncu's book, description, and classification of hypospadias were more informative and up to date. Localization of the urethral meatus was described in detail. Sabuncuoglu also detailed the description and classification of ambiguous genitalia. In mid-15th-century Europe, Heinrich von Pfolspeundt described a process "to make a new nose for one who lacks it entirely, and the dogs have devoured it" by removing skin from the back of the arm and suturing it in place. However, because of the dangers associated with surgery in any form, especially that involving the head or face, it was not until the 19th and 20th centuries that such surgery became common.
In 1814, Joseph Carpue successfully performed an operative procedure on a British military officer who had lost his nose to the toxic effects of mercury treatments. In 1818, German surgeon Carl Ferdinand von Graefe published his major work entitled Rhinoplastik. Von Graefe modified the Italian method using a free skin graft from the arm instead of the original delayed pedicle flap.
The first American plastic surgeon was John Peter Mettauer, who, in 1827, performed the first cleft palate operation with instruments that he designed himself.
Johann Friedrich Dieffenbach specialized in skin transplantation and early plastic surgery. His work in rhinoplastic and maxillofacial surgery established many modern techniques of reconstructive surgery. In 1845, Dieffenbach wrote a comprehensive text on rhinoplasty, titled Operative Chirurgie, and introduced the concept of reoperation to improve the cosmetic appearance of the reconstructed nose. Dieffenbach has been called the "father of plastic surgery".
Another case of plastic surgery for nose reconstruction from 1884 at Bellevue Hospital was described in Scientific American.
In 1891, American otorhinolaryngologist John Roe presented an example of his work: a young woman on whom he reduced a dorsal nasal hump for cosmetic indications. In 1892, Robert Weir experimented unsuccessfully with xenografts (duck sternum) in the reconstruction of sunken noses. In 1896, James Israel, a urological surgeon from Germany, and in 1889 George Monks of the United States each described the successful use of heterogeneous free-bone grafting to reconstruct saddle nose defects. In 1898, Jacques Joseph, the German orthopaedic-trained surgeon, published his first account of reduction rhinoplasty. In 1910, Alexander Ostroumov, the Russian pharmacist, and perfume and cosmetics manufacturer, founded a unique plastic surgery department in his Moscow Institute of Medical Cosmetics. In 1928, Jacques Joseph published Nasenplastik und Sonstige Gesichtsplastik.
== Nascency of maxillofacial surgery ==
The development of weapons such as machine guns and explosive shells during World War I created trench warfare, which led to a rapid increase in the number of mutilations to the faces and the heads of soldiers because the trenches mainly offered protection to the body. The surgeons, who were not prepared for these injuries, were even less prepared for a large number of injuries and had to react quickly and intelligently to treat the greatest number. Facial injuries were hard to treat on the front line, and because of the sanitary conditions, many infections could occur. Sometimes, some stitches were made on a jagged wound without considering the amount of flesh that had been lost, so the resulting scars were hideous and disfigured soldiers. Some of the wounded had severe injuries, and the stitches were not sufficient, so some became blind or were left with gaping holes instead of their nose. Harold Gillies, scared by the number of new facial injuries and the lack of good surgical techniques, decided to dedicate an entire hospital to the reconstruction of facial injuries as fully as possible. He took into account the psychological dimension. Gillies introduced skin grafts to the treatments of soldiers, so they would be less horrified by looking at themselves in the mirror.
It is the multidisciplinary approach to the treatment of facial lesions, bringing together plastic surgeons, dental surgeons, technicians, and specialized nurses, which has made it possible to develop techniques leading to the reconstruction of injured faces. Before the dentist Auguste Charles Valadier and then Gillies identified the need to advance the specialty of maxillofacial surgery, which would be directly dedicated to the management of war wounds at this time. Gillies developed a new technique using rotational and transposition flaps but also bone grafts from the ribs and tibia to reconstruct facial defects caused by the weapons during the war. He experimented with this technique so he knew that he had to start by moving back healthy tissue to its normal position, and then he would be able to fill with tissue from another place on the body of the soldier. One of the most successful techniques in skin grafting had the aim of not completely severing the connection to the body. It was possible by releasing and lifting a flap of skin from the wound. The flap of skin, still connected to the donor site, would then be swung over the site of the wound, allowing the maintenance of physical connection and ensuring that blood is supplied to the skin, increasing the chances of the skin graft being accepted by the body. At this time, we also assisted in improving treating infections also meant that important injuries had become survivable, mostly thanks to the new technique of Gillies. Some soldiers arrived at the hospital of Gillies without noses, chins, cheekbones, or even eyes. But for them, the most important trauma was psychological.
== Development of modern techniques ==
The father of modern plastic surgery is generally considered to have been Sir Harold Gillies. A New Zealand otolaryngologist working in London, he developed many of the techniques of modern facial surgery in caring for soldiers with disfiguring facial injuries during the First World War.
During World War I, he worked as a medical minder with the Royal Army Medical Corps. After working with the French oral and maxillofacial surgeon Hippolyte Morestin on skin grafts, he persuaded the army's chief surgeon, Arbuthnot-Lane, to establish a facial injury ward at the Cambridge Military Hospital, Aldershot, later upgraded to a new hospital for facial repairs at Sidcup in 1917. There, Gillies and his colleagues developed many techniques of plastic surgery; more than 11,000 operations were performed on more than 5,000 men (mostly soldiers with facial injuries, usually from gunshot wounds). After the war, Gillies developed a private practice with Rainsford Mowlem, including many famous patients, and travelled extensively to promote his advanced techniques worldwide.
In 1930, Gillies' cousin, Archibald McIndoe, joined the practice and became committed to plastic surgery. When World War II broke out, plastic surgery provision was largely divided between the different services of the armed forces, and Gillies and his team were split up. Gillies himself was sent to Rooksdown House near Basingstoke, which became the principal army plastic surgery unit; Tommy Kilner (who had worked with Gillies during the First World War, and who now has a surgical instrument named after him, the kilner cheek retractor) went to Queen Mary's Hospital, Roehampton; and Mowlem went to St Albans. McIndoe, consultant to the RAF, moved to the recently rebuilt Queen Victoria Hospital in East Grinstead, Sussex, and founded a Centre for Plastic and Jaw Surgery. There, he treated very deep burns and serious facial disfigurement, such as loss of eyelids, typical of those caused to aircrew by burning fuel.
McIndoe is often recognized for not only developing new techniques for treating badly burned faces and hands but also for recognising the importance of the rehabilitation of the casualties and particularly of social reintegration back into normal life. He disposed of the "convalescent uniforms" and let the patients use their service uniforms instead. With the help of two friends, Neville and Elaine Blond, he also convinced the locals to support the patients and invite them to their homes. McIndoe kept referring to them as "his boys" and the staff called him "The Boss" or "The Maestro".
His other important work included the development of the walking-stalk skin graft, and the discovery that immersion in saline promoted healing as well as improving survival rates for patients with extensive burns—this was a serendipitous discovery drawn from observation of differential healing rates in pilots who had come down on land and in the sea. His radical, experimental treatments led to the formation of the Guinea Pig Club at Queen Victoria Hospital, Sussex. Among the better-known members of his "club" were Richard Hillary, Bill Foxley and Jimmy Edwards.
== Sub-specialties ==
Plastic surgery is a broad field and may be subdivided further. In the United States, plastic surgeons are board certified by American Board of Plastic Surgery. Subdisciplines of plastic surgery may include:
=== Aesthetic surgery ===
Aesthetic surgery is a central component of plastic surgery and includes facial and body aesthetic surgery. Plastic surgeons use cosmetic surgical principles in all reconstructive surgical procedures as well as isolated operations to improve overall appearance.
=== Burn surgery ===
Burn surgery generally takes place in two phases. Acute burn surgery is the treatment immediately after a burn. Reconstructive burn surgery takes place after the burn wounds have healed.
=== Craniofacial surgery ===
Craniofacial surgery is divided into pediatric and adult craniofacial surgery. Pediatric craniofacial surgery mostly revolves around the treatment of congenital anomalies of the craniofacial skeleton and soft tissues, such as cleft lip and palate, microtia, craniosynostosis, and pediatric fractures. Adult craniofacial surgery deals mostly with reconstructive surgeries after trauma or cancer and revision surgeries, along with orthognathic surgery and facial feminization surgery. Craniofacial surgery is an important part of all plastic surgery training programs. Further training and subspecialisation are obtained via a craniofacial fellowship. Craniofacial surgery is also practiced by maxillofacial surgeons.
=== Ethnic plastic surgery ===
Ethnic plastic surgery is plastic surgery performed to change ethnic attributes, often considered used as a way of "passing".
=== Hand surgery ===
Hand surgery is concerned with acute injuries and chronic diseases of the hand and wrist, correction of congenital malformations of the upper extremities, and peripheral nerve problems (such as brachial plexus injuries or carpal tunnel syndrome). Hand surgery is an important part of training in plastic surgery, as well as microsurgery, which is necessary to replant an amputated extremity. The hand surgery field is also practiced by orthopedic surgeons and general surgeons. Scar tissue formation after surgery can be problematic on the delicate hand, causing loss of dexterity and digit function if severe enough. There have been cases of surgery on women's hands in order to correct perceived flaws to create the perfect engagement ring photo.
=== Microsurgery ===
Microsurgery is generally concerned with the reconstruction of missing tissues by transferring a piece of tissue to the reconstruction site and reconnecting blood vessels. Popular subspecialty areas are breast reconstruction, head and neck reconstruction, hand surgery/replantation, and brachial plexus surgery.
=== Pediatric plastic surgery ===
Children often face medical issues very different from the experiences of an adult patient. Many birth defects or syndromes present at birth are best treated in childhood, and pediatric plastic surgeons specialize in treating these conditions in children. Conditions commonly treated by pediatric plastic surgeons include craniofacial anomalies, Syndactyly (webbing of the fingers and toes), Polydactyly (excess fingers and toes at birth), cleft lip and palate, and congenital hand deformities.
=== Prison plastic surgery ===
Plastic surgery was performed on an incarcerated population in order to affect their recidivism rate, a practice instituted in the early 20th century that lasted until the mid-1990s. Separate from surgery performed for medical need.
== Techniques and procedures ==
In plastic surgery, the transfer of skin tissue (skin grafting) is a very common procedure. Skin grafts can be derived from the recipient or donors:
Autografts are taken from the recipient. If absent or deficient of natural tissue, alternatives can be cultured sheets of epithelial cells in vitro or synthetic compounds, such as integra, which consists of silicone and bovine tendon collagen with glycosaminoglycans.
Allografts are taken from a donor of the same species. Kidney transplants are an example of allograft transfer. Joseph Murray is credited for completing the first successful kidney transplantation in 1954.
Xenografts are taken from a donor of a different species.
Usually, good results would be expected from plastic surgery that emphasize careful planning of incisions so that they fall within the line of natural skin folds or lines, appropriate choice of wound closure, use of best available suture materials, and early removal of exposed sutures so that the wound is held closed by buried sutures.
== Cosmetic surgery procedures ==
Cosmetic surgery is a voluntary or elective surgery that is performed on normal parts of the body with the only purpose of improving a person's appearance or removing signs of aging. Some cosmetic surgeries such as breast reduction are also functional and can help to relieve symptoms of discomfort such as back ache or neck ache. Cosmetic surgeries are also undertaken following breast cancer and mastectomy to recreate the natural breast shape which has been lost during the process of removing the cancer. In 2014, nearly 16 million cosmetic procedures were performed in the United States alone. The number of cosmetic procedures performed in the United States has almost doubled since the start of the century. 92% of cosmetic procedures were performed on women in 2014, up from 88% in 2001. 15.6 million cosmetic procedures were performed in 2020, with the five most common surgeries being rhinoplasties, blepharoplasties, rhytidectomies, liposuctions, and breast augmentation. Breast augmentation continues to be one of the top 5 cosmetic surgical procedures and has been since 2006. Silicone implants were used in 84% and saline implants in 16% of all breast augmentations in 2020. The American Society for Aesthetic Plastic Surgery looked at the statistics for 34 different cosmetic procedures. Nineteen of the procedures were surgical, such as rhinoplasties or rhytidectomies. The nonsurgical procedures included botox and laser hair removal. In 2010, their survey revealed that there were 9,336,814 total procedures in the United States. Of those, 1,622,290 procedures were surgical (p. 5). They also found that a large majority, 81%, of the procedures were done on Caucasian people (p. 12).
In 1949, 15,000 Americans underwent cosmetic surgery procedures and by 1969 this number rose to almost half a million people. The American Society of Plastic Surgeons estimates that more than 333,000 cosmetic procedures were performed on patients 18 years of age or younger in the US in 2005 compared to approx. 14,000 in 1996. In 2018, more than 226,994 patients between the ages of 13 and 19 underwent plastic surgery compared to just over 218,900 patients in the same age group in 2010. Concerns about young people undergoing plastic surgery include the financial burden of additional surgical procedures needed to correct problems after the initial cosmetic surgery, long-term health complications from plastic surgery, and unaddressed mental health issues that may have led to surgery. The increased use of cosmetic procedures crosses racial and ethnic lines in the U.S., with increases seen among African-Americans, Asian Americans and Hispanic Americans as well as Caucasian Americans. In Asia, cosmetic surgery has become more popular, and countries such as China and India have become Asia's biggest cosmetic surgery markets. South Korea is also rising in popularity in Asian and Western countries due to their expertise in facial bone surgeries (see cosmetic surgery in South Korea).
Plastic surgery is increasing slowly, rising 115% from 2000 to 2015. "According to the annual plastic surgery procedural statistics, there were 15.9 million surgical and minimally-invasive cosmetic procedures performed in the United States in 2015, a 2 percent increase over 2014." A study from 2021 found that requests for cosmetic procedures had increased significantly since the beginning of the COVID-19 pandemic, possibly due to the increase in videoconferencing; cited estimates include a 10% increase in the United States and a 20% increase in France.
The most popular aesthetic/cosmetic procedures include:
Abdominoplasty ("tummy tuck"): reshaping and firming of the abdomen
Blepharoplasty ("eyelid surgery"): reshaping of upper/lower eyelids including Asian blepharoplasty
While blepharoplasty remains the most common procedure for modifying eyelid shape, non-surgical alternatives are increasingly sought after, especially in East Asia.
Methods such as double eyelid tape, eyelid glue, and structured eyelid training systems allow individuals to temporarily or semi-permanently create a double eyelid crease without surgery. Some of these products, such as D-UP Eyelid Tape, AB Mezical, and Optifold, use mechanical reinforcement to encourage crease retention over time.
Unlike traditional adhesive-based tapes, structured eyelid training tapes aim to replicate mechanotransduction—a biological process where skin tension encourages crease formation. Studies on long-term non-surgical crease retention remain limited, but anecdotal evidence suggests some users achieve lasting results after sustained use.
Phalloplasty ("penile surgery"): construction (or reconstruction) of a penis or, sometimes, artificial modification of the penis by surgery, often for cosmetic purposes
Mammoplasty:
Breast augmentations ("breast implant" or "boob job"): augmentation of the breasts by means of fat grafting, saline, or silicone gel prosthetics, which was initially performed for women with micromastia
Reduction mammoplasty ("breast reduction"): removal of skin and glandular tissue, which is done to reduce back and shoulder pain in women with gigantomastia and for men with gynecomastia
Mastopexy ("breast lift"): Lifting or reshaping of breasts to make them less saggy, often after weight loss (after a pregnancy, for example). It involves the removal of breast skin as opposed to glandular tissue
Augmentation mastopexy ("breast lift with breast implants"): Lifting breasts to make them less saggy, repositioning the nipple to a higher location, and increasing breast size with saline or silicone gel implants. Recent studies of a newer technique for simultaneous augmentation mastopexy (SAM) indicate that it is a safe surgical procedure with minimal medical complications. The SAM technique involves invaginating and tacking the tissues first, in order to previsualize the result, before making any surgical incisions to the breast.
Buttock augmentation ("butt implant"): enhancement of the buttocks using silicone implants or fat grafting ("Brazilian butt lift") where fat is transferred from other areas of the body
Cryolipolysis: refers to a medical device used to destroy fat cells. Its principle relies on controlled cooling for the non-invasive local reduction of fat deposits to reshape body contours.
Cryoneuromodulation: Treatment of superficial and subcutaneous tissue structures using gaseous nitrous oxide, including temporary wrinkle reduction, temporary pain reduction, treatment of dermatologic conditions, and focal cryo-treatment of tissue
Calf augmentation: done by silicone implants or fat transfer to add bulk to calf muscles
Labiaplasty: surgical reduction and reshaping of the labia
Lip augmentation: alters the appearance of the lips by increasing their fullness through surgical enlargement with lip implants or nonsurgical enhancement with injectable fillers
Cheiloplasty: surgical reconstruction of the lip
Rhinoplasty ("nose job"): reshaping of the nose sometimes used to correct breathing impaired by structural defects.
Otoplasty ("ear surgery"/"ear pinning"): reshaping of the ear, most often done by pinning the protruding ear closer to the head.
Rhytidectomy ("face lift"): removal of wrinkles and signs of aging from the face
Neck lift: tightening of lax tissues in the neck. This procedure is often combined with a facelift for lower face rejuvenation.
Browplasty ("brow lift" or "forehead lift"): elevates eyebrows, smoothens forehead skin
Midface lift ("cheek lift"): tightening of the cheeks
Genioplasty: augmentation of the chin with an individual's bones or with the use of an implant, usually silicone, by suture of the soft tissue
Mentoplasty: surgery to the chin. This can involve either enhancing or reducing the size of the chin. Enhancements are achieved with the use of facial implants. Reduction of the chin involves reducing the size of the chin bone.
Cheek augmentation ("cheek implant"): implants to the cheek
Orthognathic surgery: altering the upper and lower jaw bones (through osteotomy) to correct jaw alignment issues and correct the teeth alignment
Fillers injections: collagen, fat, and other tissue filler injections, such as hyaluronic acid
Brachioplasty ("Arm lift"): reducing excess skin and fat between the underarm and the elbow
Laser skin rejuvenation or laser resurfacing: the lessening of the depth of facial pores and exfoliation of dead or damaged skin cells
Liposuction ("suction lipectomy"): removal of fat deposits by traditional suction technique or ultrasonic energy to aid fat removal
Zygoma reduction plasty: reducing the facial width by performing osteotomy and resecting part of the zygomatic bone and arch
Jaw reduction: reduction of the mandible angle to smooth out an angular jaw and creating a slim jaw
Buccal fat extraction: extraction of the buccal pads
Body contouring: the removal of this excess skin and fat from numerous areas of the body, restoring the appearance of skin elasticity of the remaining skin. The surgery is prominent in those who have undergone significant weight loss, resulting in excess sagging skin being present around areas of the body. The skin loses elasticity (a condition called elastosis) once it has been stretched past capacity and is unable to recoil back to its standard position against the body and also with age.
Sclerotherapy: removing visible 'spider veins' (Telangiectasia), which appear on the surface of the skin.
Dermal fillers: Dermal fillers are injected below the skin to give a more fuller, more youthful appearance of a feature or section of the face. One type of dermal filler is hyaluronic acid. Hyaluronic acid is naturally found throughout the human body. It plays a vital role in moving nutrients to the cells of the skin from the blood. It is also commonly used in patients with arthritis as it acts like a cushion to the bones which have depleted the articular cartilage casing. Development within this field has occurred over time with synthetic forms of hyaluronic acid is being created, playing roles in other forms of cosmetic surgery such as facial augmentation.
Micropigmentation: is the creation of permanent makeup using natural pigments to places such as the eyes to create the effect of eye shadow, lips creating lipstick and cheek bones to create a blush like look. The pigment is inserted beneath the skin using a machine which injects a small needle at a very fast rate carrying pigment into the skin, creating a lasting colouration of the desired area.
In 2015, the most popular surgeries were botox, liposuction, blepharoplasties, breast implants, rhynoplasties, and rhytidectomies. According to the 2020 Plastic Surgery Statistics Report, which is published by the American Society of Plastic Surgeons, the most surgical procedure performed in the U.S. was rhinoplasty (nose reshaping) accounting for 15.2% of all cosmetic surgical procedures that year, followed by blepharoplasty (eyelid surgery), which accounted for 14% of all procedures. The third most populous procedure was rhytidectomy (facelift) (10% of all procedures), then liposuction (9.1% of all procedures).
== Complications, risks, and reversals ==
All surgery has risks. Common complications of cosmetic surgery includes hematoma, nerve injury, infection, scarring, implant failure and end organ damage. Breast implants can have many complications, including rupture. In a study of his 4761 augmentation mammaplasty patients, Eisenberg reported that overfilling saline breast implants 10–13% significantly reduced the rupture-deflation rate to 1.83% at 8-years post-implantation. In 2011 FDA stated that one in five patients who received implants for breast augmentation will need them removed within 10 years of implantation.
== Psychological disorders ==
Although media and advertising do play a large role in influencing many people's lives, such as by making people believe plastic surgery to be an acceptable course to change one's identity to their liking, researchers believe that plastic surgery obsession is linked to psychological disorders such as body dysmorphic disorder. There exists a correlation between those with BDD and the predilection toward cosmetic plastic surgery in order to correct a perceived defect in their appearance.
BDD is a disorder resulting in the individual becoming "preoccupied with what they regard as defects in their bodies or faces". Alternatively, where there is a slight physical anomaly, then the person's concern is markedly excessive. While 2% of people have body dysmorphic disorder in the United States, 15% of patients seeing a dermatologist and cosmetic surgeons have the disorder. Half of the patients with the disorder who have cosmetic surgery performed are not pleased with the aesthetic outcome. BDD can lead to suicide in some people with the condition. While many with BDD seek cosmetic surgery, the procedures do not treat BDD, and can ultimately worsen the problem. The psychological root of the problem is usually unidentified; therefore causing the treatment to be even more difficult. Some say that the fixation or obsession with correction of the area could be a sub-disorder such as anorexia or muscle dysmorphia. The increased use of body and facial reshaping applications such as Snapchat and Facetune have been identified as potential triggers of BDD. Recently, a phenomenon referred to as 'Snapchat dysmorphia' has appeared to describe people who request surgery to resemble the edited version of themselves as they appear through Snapchat filters. In response to the detrimental trend, Instagram banned all augmented reality (AR) filters that depict or promote cosmetic surgery.
In some cases, people whose physicians refuse to perform any further surgeries, have turned to "do it yourself" plastic surgery, injecting themselves and facing extreme safety risks.
== See also ==
Biomaterial
Body modification
Cosmetic surgery in Australia
Dental trauma
Dermatologic surgical procedure
Ethnic plastic surgery
List of plastic surgery flaps
Plastic and Reconstructive Surgery
Scalp reconstruction
Serdev suture
Rejuvenation
== References ==
== Further reading ==
Atkinson M (2008). "Exploring Male Femininity in the 'Crisis': Men and Cosmetic Surgery". Body & Society. 14: 67–87. doi:10.1177/1357034X07087531. S2CID 143604536.
Fraser S (2003). Cosmetic surgery, gender and culture. Palgrave. ISBN 978-1-4039-1299-2.
Gilman S (2005). Creating Beauty to Cure the Soul: Race and Psychology in the Shaping of Aesthetic Surgery. Duke University Press. ISBN 978-0-8223-2144-6.
Haiken E (1997). Venus Envy: A History of Cosmetic Surgery. Johns Hopkins University Press. ISBN 978-0-8018-5763-8.
Kolle FS (1911). Plastic and Cosmetic Surgery. D. Appleton and Company.
Kalaskar D, Butler P, Ghali S, eds. (2016). Textbook of Plastic and Reconstructive Surgery. UCL Press. ISBN 9781910634394.
== External links ==
Countries with the largest total number of cosmetic procedures, Statista, 2019
Cosmetic Surgery Statistics, American Cosmetic Association, 2023 | Wikipedia/Plastic_surgery |
Electrocorticography (ECoG), a type of intracranial electroencephalography (iEEG), is a type of electrophysiological monitoring that uses electrodes placed directly on the exposed surface of the brain to record electrical activity from the cerebral cortex. In contrast, conventional electroencephalography (EEG) electrodes monitor this activity from outside the skull. ECoG may be performed either in the operating room during surgery (intraoperative ECoG) or outside of surgery (extraoperative ECoG). Because a craniotomy (a surgical incision into the skull) is required to implant the electrode grid, ECoG is an invasive procedure.
== History ==
ECoG was pioneered in the early 1950s by Wilder Penfield and Herbert Jasper, neurosurgeons at the Montreal Neurological Institute. The two developed ECoG as part of their groundbreaking Montreal procedure, a surgical protocol used to treat patients with severe epilepsy. The cortical potentials recorded by ECoG were used to identify epileptogenic zones – regions of the cortex that generate epileptic seizures. These zones would then be surgically removed from the cortex during resectioning, thus destroying the brain tissue where epileptic seizures had originated. Penfield and Jasper also used electrical stimulation during ECoG recordings in patients undergoing epilepsy surgery under local anesthesia. This procedure was used to explore the functional anatomy of the brain, mapping speech areas and identifying the somatosensory and somatomotor cortex areas to be excluded from surgical removal.
A doctor named Robert Galbraith Heath was also an early researcher of the brain at the Tulane University School of Medicine.
== Electrophysiological basis ==
ECoG signals are composed of synchronized postsynaptic potentials (local field potentials), recorded directly from the exposed surface of the cortex. The potentials occur primarily in cortical pyramidal cells, and thus must be conducted through several layers of the cerebral cortex, cerebrospinal fluid (CSF), pia mater, and arachnoid mater before reaching subdural recording electrodes placed just below the dura mater (outer cranial membrane). However, to reach the scalp electrodes of a conventional electroencephalogram (EEG), electrical signals must also be conducted through the skull, where potentials rapidly attenuate due to the low conductivity of bone. For this reason, the spatial resolution of ECoG is much higher than EEG, a critical imaging advantage for presurgical planning. ECoG offers a temporal resolution of approximately 5 ms and spatial resolution as low as 1-100 μm.
Using depth electrodes, the local field potential gives a measure of a neural population in a sphere with a radius of 0.5–3 mm around the tip of the electrode. With a sufficiently high sampling rate (more than about 10 kHz), depth electrodes can also measure action potentials. In which case the spatial resolution is down to individual neurons, and the field of view of an individual electrode is approximately 0.05–0.35 mm.
== Procedure ==
The ECoG recording is performed from electrodes placed on the exposed cortex. In order to access the cortex, a surgeon must first perform a craniotomy, removing a part of the skull to expose the brain surface. This procedure may be performed either under general anesthesia or under local anesthesia if patient interaction is required for functional cortical mapping. Electrodes are then surgically implanted on the surface of the cortex, with placement guided by the results of preoperative EEG and magnetic resonance imaging (MRI). Electrodes may either be placed outside the dura mater (epidural) or under the dura mater (subdural). ECoG electrode arrays typically consist of sixteen sterile, disposable stainless steel, carbon tip, platinum, Platinum-iridium alloy or gold ball electrodes, each mounted on a ball and socket joint for ease in positioning. These electrodes are attached to an overlying frame in a "crown" or "halo" configuration. Subdural strip and grid electrodes are also widely used in various dimensions, having anywhere from 4 to 256 electrode contacts. The grids are transparent, flexible, and numbered at each electrode contact. Standard spacing between grid electrodes is 1 cm; individual electrodes are typically 5 mm in diameter. The electrodes sit lightly on the cortical surface, and are designed with enough flexibility to ensure that normal movements of the brain do not cause injury. A key advantage of strip and grid electrode arrays is that they may be slid underneath the dura mater into cortical regions not exposed by the craniotomy. Strip electrodes and crown arrays may be used in any combination desired. Depth electrodes may also be used to record activity from deeper structures such as the hippocampus.
== DCES ==
Direct cortical electrical stimulation (DCES), also known as cortical stimulation mapping, is frequently performed in concurrence with ECoG recording for functional mapping of the cortex and identification of critical cortical structures. When using a crown configuration, a handheld wand bipolar stimulator may be used at any location along the electrode array. However, when using a subdural strip, stimulation must be applied between pairs of adjacent electrodes due to the nonconductive material connecting the electrodes on the grid. Electrical stimulating currents applied to the cortex are relatively low, between 2 and 4 mA for somatosensory stimulation, and near 15 mA for cognitive stimulation. The stimulation frequency is usually 60 Hz in North America and 50 Hz in Europe, and any charge density more than 150 μC/cm2 causes tissue damage.
The functions most commonly mapped through DCES are primary motor, primary sensory, and language. The patient must be alert and interactive for mapping procedures, though patient involvement varies with each mapping procedure. Language mapping may involve naming, reading aloud, repetition, and oral comprehension; somatosensory mapping requires that the patient describe sensations experienced across the face and extremities as the surgeon stimulates different cortical regions.
== Clinical applications ==
Since its development in the 1950s, ECoG has been used to localize epileptogenic zones during presurgical planning, map out cortical functions, and to predict the success of epileptic surgical resectioning. ECoG offers several advantages over alternative diagnostic modalities:
Flexible placement of recording and stimulating electrodes
Can be performed at any stage before, during, and after a surgery
Allows for direct electrical stimulation of the brain, identifying critical regions of the cortex to be avoided during surgery
Greater precision and sensitivity than an EEG scalp recording – spatial resolution is higher and signal-to-noise ratio is superior due to closer proximity to neural activity
Limitations of ECoG include:
Limited sampling time – seizures (ictal events) may not be recorded during the ECoG recording period
Limited field of view – electrode placement is limited by the area of exposed cortex and surgery time, sampling errors may occur
Recording is subject to the influence of anesthetics, narcotic analgesics, and the surgery itself
=== Intractable epilepsy ===
Epilepsy is currently ranked as the third most commonly diagnosed neurological disorder, afflicting approximately 2.5 million people in the United States alone. Epileptic seizures are chronic and unrelated to any immediately treatable causes, such as toxins or infectious diseases, and may vary widely based on etiology, clinical symptoms, and site of origin within the brain. For patients with intractable epilepsy – epilepsy that is unresponsive to anticonvulsants – surgical treatment may be a viable treatment option. Partial epilepsy is the common intractable epilepsy and the partial seizure is difficult to locate.Treatment for such epilepsy is limited to attachment of vagus nerve stimulator. Epilepsy surgery is the cure for partial epilepsy provided that the brain region generating seizure is carefully and accurately removed.
Extraoperative ECoG
Before a patient can be identified as a candidate for resectioning surgery, MRI must be performed to demonstrate the presence of a structural lesion within the cortex, supported by EEG evidence of epileptogenic tissue. Once a lesion has been identified, ECoG may be performed to determine the location and extent of the lesion and surrounding irritative region. The scalp EEG, while a valuable diagnostic tool, lacks the precision necessary to localize the epileptogenic region. ECoG is considered to be the gold standard for assessing neuronal activity in patients with epilepsy, and is widely used for presurgical planning to guide surgical resection of the lesion and epileptogenic zone. The success of the surgery depends on accurate localization and removal of the epileptogenic zone. ECoG data is assessed with regard to ictal spike activity – "diffuse fast wave activity" recorded during a seizure – and interictal epileptiform activity (IEA), brief bursts of neuronal activity recorded between epileptic events. ECoG is also performed following the resectioning surgery to detect any remaining epileptiform activity, and to determine the success of the surgery. Residual spikes on the ECoG, unaltered by the resection, indicate poor seizure control, and incomplete neutralization of the epileptogenic cortical zone. Additional surgery may be necessary to completely eradicate seizure activity. Extraoperative ECoG is also used to localize functionally-important areas (also known as eloquent cortex) to be preserved during epilepsy surgery.
Motor, sensory, cognitive tasks during extraoperative ECoG are reported to increase the amplitude of high-frequency activity at 70–110 Hz in areas involved in execution of given tasks. Task-related high-frequency activity can animate 'when' and 'where' cerebral cortex is activated and inhibited in a 4D manner with a temporal resolution of 10 milliseconds or below and a spatial resolution of 10 mm or below.
Intraoperative ECoG
The objective of the resectioning surgery is to remove the epileptogenic tissue without causing unacceptable neurological consequences. In addition to identifying and localizing the extent of epileptogenic zones, ECoG used in conjunction with DCES is also a valuable tool for functional cortical mapping. It is vital to precisely localize critical brain structures, identifying which regions the surgeon must spare during resectioning (the "eloquent cortex") in order to preserve sensory processing, motor coordination, and speech. Functional mapping requires that the patient be able to interact with the surgeon, and thus is performed under local rather than general anesthesia. Electrical stimulation using cortical and acute depth electrodes is used to probe distinct regions of the cortex in order to identify centers of speech, somatosensory integration, and somatomotor processing. During the resectioning surgery, intraoperative ECoG may also be performed to monitor the epileptic activity of the tissue and ensure that the entire epileptogenic zone is resectioned.
Although the use of extraoperative and intraoperative ECoG in resectioning surgery has been an accepted clinical practice for several decades, recent studies have shown that the usefulness of this technique may vary based on the type of epilepsy a patient exhibits. Kuruvilla and Flink reported that while intraoperative ECoG plays a critical role in tailored temporal lobectomies, in multiple subpial transections (MST), and in the removal of malformations of cortical development (MCDs), it has been found impractical in standard resection of medial temporal lobe epilepsy (TLE) with MRI evidence of mesial temporal sclerosis (MTS). A study performed by Wennberg, Quesney, and Rasmussen demonstrated the presurgical significance of ECoG in frontal lobe epilepsy (FLE) cases.
== Research applications ==
ECoG has recently emerged as a promising recording technique for use in brain-computer interfaces (BCI). BCIs are direct neural interfaces that provide control of prosthetic, electronic, or communication devices via direct use of the individual's brain signals. Brain signals may be recorded either invasively, with recording devices implanted directly into the cortex, or noninvasively, using EEG scalp electrodes. ECoG serves to provide a partially invasive compromise between the two modalities – while ECoG does not penetrate the blood–brain barrier like invasive recording devices, it features a higher spatial resolution and higher signal-to-noise ratio than EEG. ECoG has gained attention recently for decoding imagined speech or music, which could lead to "literal" BCIs in which users simply imagine words, sentences, or music that the BCI can directly interpret.
In addition to clinical applications to localize functional regions to support neurosurgery, real-time functional brain mapping with ECoG has gained attention to support research into fundamental questions in neuroscience. For example, a 2017 study explored regions within face and color processing areas and found that these subregions made highly specific contributions to different aspects of vision. Another study found that high-frequency activity from 70 to 200 Hz reflected processes associated with both transient and sustained decision-making. Other work based on ECoG presented a new approach to interpreting brain activity, suggesting that both power and phase jointly influence instantaneous voltage potential, which directly regulates cortical excitability. Like the work toward decoding imagined speech and music, these research directions involving real-time functional brain mapping also have implications for clinical practice, including both neurosurgery and BCI systems. The system that was used in most of these real-time functional mapping publications, "CortiQ". has been used for both research and clinical applications.
== Recent advances ==
The electrocorticogram is still considered to be the "gold standard" for defining epileptogenic zones; however, this procedure is risky and highly invasive. Recent studies have explored the development of a noninvasive cortical imaging technique for presurgical planning that may provide similar information and resolution of the invasive ECoG.
In one novel approach, Lei Ding et al. seek to integrate the information provided by a structural MRI and scalp EEG to provide a noninvasive alternative to ECoG. This study investigated a high-resolution subspace source localization approach, FINE (first principle vectors) to image the locations and estimate the extents of current sources from the scalp EEG. A thresholding technique was applied to the resulting tomography of subspace correlation values in order to identify epileptogenic sources. This method was tested in three pediatric patients with intractable epilepsy, with encouraging clinical results. Each patient was evaluated using structural MRI, long-term video EEG monitoring with scalp electrodes, and subsequently with subdural electrodes. The ECoG data were then recorded from implanted subdural electrode grids placed directly on the surface of the cortex. MRI and computed tomography images were also obtained for each subject.
The epileptogenic zones identified from preoperative EEG data were validated by observations from postoperative ECoG data in all three patients. These preliminary results suggest that it is possible to direct surgical planning and locate epileptogenic zones noninvasively using the described imaging and integrating methods. EEG findings were further validated by the surgical outcomes of all three patients. After surgical resectioning, two patients are seizure-free and the third has experienced a significant reduction in seizures. Due to its clinical success, FINE offers a promising alternative to preoperative ECoG, providing information about both the location and extent of epileptogenic sources through a noninvasive imaging procedure.
== See also ==
== References == | Wikipedia/Electrocorticography |
Pediatric Neurosurgery is a subspecialty of neurosurgery; which includes surgical procedures that are related to the nervous system, brain and spinal cord; that treats children with operable neurological disorders.
== History ==
Boston Children's Hospital was the first hospital in the United States with a specialized neurosurgical service for children, established in 1929 by Harvey Cushing and Franc Ingraham.
As of 2009, there were fewer than 200 pediatric neurosurgeons in the United States. Approximately 80% of them were male. In the past 25 years, 391 doctors graduated from a pediatric neurosurgery program. Only 70% of them currently practice primarily pediatric rather than adult neurosurgery. Approximately 70% of them are in academic medicine.
== See also ==
Medical specialties
Pediatric neuropsychology
== References == | Wikipedia/Pediatric_neurosurgery |
A Bachelor of Medical Sciences (BMedSci, BMedSc, BSc(Med), BMSc) is an undergraduate academic degree involving study of a variety of disciplines related to human health leading to an in depth understanding of human biology and associated research skills such as study design, statistics and laboratory techniques. Such disciplines include biochemistry, cell biology, physiology, pharmacology or psychosocial aspects of health. It is an equivalent level qualification to the more commonly awarded Bachelor of Science (BSc). Graduates may enter a diverse range of roles including post-graduate study, higher education, the biotechnology industry, the pharmaceutical industry, consultancy roles, scientific communication, education or unrelated disciplines which make use of the broad range of transferable skills gained through this degree.
== Australia ==
In Australia, the Bachelor of Medical Sciences (BMedSc) degree is offered by The University of Adelaide, Griffith University, University of New South Wales, University of Sydney, Monash University, Australian National University, University of Western Sydney, University of Newcastle, Flinders University, Charles Sturt University, Macquarie University , Central Queensland University and The University of the Sunshine Coast.
== Canada ==
At the University of Western Ontario, BMSc is a four-year degree offered by the Schulich School of Medicine & Dentistry. It is differentiated from a BSc due to the advanced medical sciences orientation of the courses offered such as Anatomy and Pharmacology.
The University of Alberta offers a BMSc to Faculty of Medicine and Dentistry students who did not complete a bachelor's degree prior to entry into the program.
== India ==
In India, BMSc is an undergraduate degree offered by top universities like Panjab University, Punjabi University, Indian Institutes of Technology and the R. G. Kar Medical College and Hospital.
== United Kingdom ==
In the United Kingdom, the Bachelor of Medical Sciences degree can be awarded in four situations; firstly as a standalone 3-year first degree, secondly, as a consequence of taking an extra year during a medical or dental course (termed intercalating), thirdly as an additional part of a medical degree but without any additional years of study, and fourthly as an exit award if a student wishes to leave their primary medical or dental undergraduate course. When the degree is obtained without any additional years of study, it may not be viewed as an equivalent qualification. For example, the UK Foundation Programme Office (the British body which manages first jobs for new medical graduates) places less value on a BMedSc degree if an additional year of study has not been undertaken. Regardless of the way in which the degree is obtained, a research project typically forms a large component of the degree as well as formal teaching in medical science related disciplines.
Bachelor of Medical Sciences degrees are awarded as a standalone 3-year course by the University of Chester, University of Exeter, University of Birmingham, the University of Sheffield, Bangor University, Oxford Brookes University, De Montfort University, and the University of St Andrews. Medical schools which award an intercalated Bachelor of Medical Sciences after an additional year of study are Barts and The London School of Medicine and Dentistry, the University of Birmingham, the University of Dundee, the University of Edinburgh the University of Aberdeen and the University of Sheffield.
The University of Nottingham and the University of Southampton award the degree as a standard part of their undergraduate medicine courses without an additional year of study (students must undertake a research project).
== Egypt ==
In Egypt, the bachelor of medical sciences is awarded after four years of study in addition to an internship year in which interns are trained in multiple public and university hospitals.
The degree is offered in five universities in Egypt: October 6 University, Misr University for Science and Technology, Pharos University in Alexandria, Beni-Suef University and Menoufia University. Faculties of applied medical sciences offer various disciplines for students to choose from, including medical laboratories, radiology and medical imaging, therapeutic nutrition, and biomedical equipment.
In 2015, the Central Authority For Organization and Administration (CAOA) granted the holders of the bachelor of medical sciences the title of "specialist" in the corresponding specialty.
== Israel ==
BSc.Med is granted by all six medical schools in Israel: the Hebrew University, Tel Aviv University, Ben-Gurion University, the Technion, Bar-Ilan University and Ariel University. The full M.D. program consists of six years of studies and an additional year of internship. The first part of the program consists of three years of basic science (pre-clinical) studies, culminating in the award of a BSc.Med degree in medical sciences.
== References == | Wikipedia/Bachelor_of_Medical_Sciences |
Radiosurgery is surgery using radiation, that is, the destruction of precisely selected areas of tissue using ionizing radiation rather than excision with a blade. Like other forms of radiation therapy (also called radiotherapy), it is usually used to treat cancer. Radiosurgery was originally defined by the Swedish neurosurgeon Lars Leksell as "a single high dose fraction of radiation, stereotactically directed to an intracranial region of interest".
In stereotactic radiosurgery (SRS), the word "stereotactic" refers to a three-dimensional coordinate system that enables accurate correlation of a virtual target seen in the patient's diagnostic images with the actual target position in the patient. Stereotactic radiosurgery may also be called stereotactic body radiation therapy (SBRT) or stereotactic ablative radiotherapy (SABR) when used outside the central nervous system (CNS).
== History ==
Stereotactic radiosurgery was first developed in 1949 by the Swedish neurosurgeon Lars Leksell to treat small targets in the brain that were not amenable to conventional surgery. The initial stereotactic instrument he conceived used probes and electrodes. The first attempt to supplant the electrodes with radiation was made in the early fifties, with x-rays. The principle of this instrument was to hit the intra-cranial target with narrow beams of radiation from multiple directions. The beam paths converge in the target volume, delivering a lethal cumulative dose of radiation there, while limiting the dose to the adjacent healthy tissue. Ten years later significant progress had been made, due in considerable measure to the contribution of the physicists Kurt Liden and Börje Larsson. At this time, stereotactic proton beams had replaced the x-rays. The heavy particle beam presented as an excellent replacement for the surgical knife, but the synchrocyclotron was too clumsy. Leksell proceeded to develop a practical, compact, precise and simple tool which could be handled by the surgeon himself. In 1968 this resulted in the Gamma Knife, which was installed at the Karolinska Institute and consisted of several cobalt-60 radioactive sources placed in a kind of helmet with central channels for irradiation with gamma rays. This prototype was designed to produce slit-like radiation lesions for functional neurosurgical procedures to treat pain, movement disorders, or behavioral disorders that did not respond to conventional treatment. The success of this first unit led to the construction of a second device, containing 179 cobalt-60 sources. This second Gamma Knife unit was designed to produce spherical lesions to treat brain tumors and intracranial arteriovenous malformations (AVMs). Additional units were installed in the 1980s all with 201 cobalt-60 sources.
In parallel to these developments, a similar approach was designed for a linear particle accelerator or Linac. Installation of the first 4 MeV clinical linear accelerator began in June 1952 in the Medical Research Council (MRC) Radiotherapeutic Research Unit at the Hammersmith Hospital, London. The system was handed over for physics and other testing in February 1953 and began to treat patients on 7 September that year. Meanwhile, work at the Stanford Microwave Laboratory led to the development of a 6 MeV accelerator, which was installed at Stanford University Hospital, California, in 1956. Linac units quickly became favored devices for conventional fractionated radiotherapy but it lasted until the 1980s before dedicated Linac radiosurgery became a reality. In 1982, the Spanish neurosurgeon J. Barcia-Salorio began to evaluate the role of cobalt-generated and then Linac-based photon radiosurgery for the treatment of AVMs and epilepsy. In 1984, Betti and Derechinsky described a Linac-based radiosurgical system. Winston and Lutz further advanced Linac-based radiosurgical prototype technologies by incorporating an improved stereotactic positioning device and a method to measure the accuracy of various components. Using a modified Linac, the first patient in the United States was treated in Boston Brigham and Women's Hospital in February 1986.
=== 21st century ===
Technological improvements in medical imaging and computing have led to increased clinical adoption of stereotactic radiosurgery and have broadened its scope in the 21st century. The localization accuracy and precision that are implicit in the word "stereotactic" remain of utmost importance for radiosurgical interventions and are significantly improved via image-guidance technologies such as the N-localizer and Sturm-Pastyr localizer that were originally developed for stereotactic surgery.
In the 21st century the original concept of radiosurgery expanded to include treatments comprising up to five fractions, and stereotactic radiosurgery has been redefined as a distinct neurosurgical discipline that utilizes externally generated ionizing radiation to inactivate or eradicate defined targets, typically in the head or spine, without the need for a surgical incision. Irrespective of the similarities between the concepts of stereotactic radiosurgery and fractionated radiotherapy the mechanism to achieve treatment is subtly different, although both treatment modalities are reported to have identical outcomes for certain indications. Stereotactic radiosurgery has a greater emphasis on delivering precise, high doses to small areas, to destroy target tissue while preserving adjacent normal tissue. The same principle is followed in conventional radiotherapy although lower dose rates spread over larger areas are more likely to be used (for example as in VMAT treatments). Fractionated radiotherapy relies more heavily on the different radiosensitivity of the target and the surrounding normal tissue to the total accumulated radiation dose. Historically, the field of fractionated radiotherapy evolved from the original concept of stereotactic radiosurgery following discovery of the principles of radiobiology: repair, reassortment, repopulation, and reoxygenation. Today, both treatment techniques are complementary, as tumors that may be resistant to fractionated radiotherapy may respond well to radiosurgery, and tumors that are too large or too close to critical organs for safe radiosurgery may be suitable candidates for fractionated radiotherapy.
Today, both Gamma Knife and Linac radiosurgery programs are commercially available worldwide. While the Gamma Knife is dedicated to radiosurgery, many Linacs are built for conventional fractionated radiotherapy and require additional technology and expertise to become dedicated radiosurgery tools. There is not a clear difference in efficacy between these different approaches. The major manufacturers, Varian and Elekta offer dedicated radiosurgery Linacs as well as machines designed for conventional treatment with radiosurgery capabilities. Systems designed to complement conventional Linacs with beam-shaping technology, treatment planning, and image-guidance tools to provide. An example of a dedicated radiosurgery Linac is the CyberKnife, a compact Linac mounted onto a robotic arm that moves around the patient and irradiates the tumor from a large set of fixed positions, thereby mimicking the Gamma Knife concept.
== Mechanism of action ==
The fundamental principle of radiosurgery is that of selective ionization of tissue, by means of high-energy beams of radiation. Ionization is the production of ions and free radicals which are damaging to the cells. These ions and radicals, which may be formed from the water in the cell or biological materials, can produce irreparable damage to DNA, proteins, and lipids, resulting in the cell's death. Thus, biological inactivation is carried out in a volume of tissue to be treated, with a precise destructive effect. The radiation dose is usually measured in grays (one gray (Gy) is the absorption of one joule of energy per kilogram of mass). A unit that attempts to take into account both the different organs that are irradiated and the type of radiation is the sievert, a unit that describes both the amount of energy deposited and the biological effectiveness.
== Clinical applications ==
When used outside the CNS it may be called stereotactic body radiation therapy (SBRT) or stereotactic ablative radiotherapy (SABR).
=== Brain and spine ===
Radiosurgery is performed by a multidisciplinary team of neurosurgeons, radiation oncologists and medical physicists to operate and maintain highly sophisticated, highly precise and complex instruments, including medical linear accelerators, the Gamma Knife unit and the Cyberknife unit. The highly precise irradiation of targets within the brain and spine is planned using information from medical images that are obtained via computed tomography, magnetic resonance imaging, and angiography.
Radiosurgery is indicated primarily for the therapy of tumors, vascular lesions and functional disorders. Significant clinical judgment must be used with this technique and considerations must include lesion type, pathology if available, size, location and age and general health of the patient. General contraindications to radiosurgery include excessively large size of the target lesion, or lesions too numerous for practical treatment. Patients can be treated within one to five days as outpatients. By comparison, the average hospital stay for a craniotomy (conventional neurosurgery, requiring the opening of the skull) is about 15 days. The radiosurgery outcome may not be evident until months after the treatment. Since radiosurgery does not remove the tumor but inactivates it biologically, lack of growth of the lesion is normally considered to be treatment success. General indications for radiosurgery include many kinds of brain tumors, such as acoustic neuromas, germinomas, meningiomas, metastases, trigeminal neuralgia, arteriovenous malformations, and skull base tumors, among others.
Stereotatic radiosurgery of the spinal metastasis is efficient in controlling pain in up to 90% of the cases and ensures stability of the tumours on imaging evaluation in 95% of the cases, and is more efficient for spinal metastasis involving one or two segments. Meanwhile, conventional external beam radiotherapy is more suitable for multiple spinal involvement.
=== Combination therapy ===
SRS may be administered alone or in combination with other therapies. For brain metastases, these treatment options include whole brain radiation therapy (WBRT), surgery, and systemic therapies. However, a recent systematic review found no difference in the affects on overall survival or deaths due to brain metastases when comparing SRS treatment alone to SRS plus WBRT treatment or WBRT alone.
=== Other bodily organs ===
Expansion of stereotactic radiotherapy to other lesions is increasing, and includes liver cancer, lung cancer, pancreatic cancer, etc.
== Risks ==
The New York Times reported in December 2010 that radiation overdoses had occurred with the linear accelerator method of radiosurgery, due in large part to inadequate safeguards in equipment retrofitted for stereotactic radiosurgery. In the U.S. the Food and Drug Administration (FDA) regulates these devices, whereas the Gamma Knife is regulated by the Nuclear Regulatory Commission.
This is evidence that immunotherapy may be useful for treatment of radiation necrosis following stereotactic radiotherapy.
== Types of radiation source ==
The selection of the proper kind of radiation and device depends on many factors including lesion type, size, and location in relation to critical structures. Data suggest that similar clinical outcomes are possible with all of the various techniques. More important than the device used are issues regarding indications for treatment, total dose delivered, fractionation schedule and conformity of the treatment plan.
=== Gamma Knife ===
A Gamma Knife (also known as the Leksell Gamma Knife) is used to treat brain tumors by administering high-intensity gamma radiation therapy in a manner that concentrates the radiation over a small volume. The device was invented in 1967 at the Karolinska Institute in Stockholm, Sweden, by Lars Leksell, Romanian-born neurosurgeon Ladislau Steiner, and radiobiologist Börje Larsson from Uppsala University, Sweden.
A Gamma Knife typically contains 201 cobalt-60 sources of approximately 30 curies each (1.1 TBq), placed in a hemispheric array in a heavily shielded assembly. The device aims gamma radiation through a target point in the patient's brain. The patient wears a specialized helmet that is surgically fixed to the skull, so that the brain tumor remains stationary at the target point of the gamma rays. An ablative dose of radiation is thereby sent through the tumor in one treatment session, while surrounding brain tissues are relatively spared.
Gamma Knife therapy, like all radiosurgery, uses doses of radiation to kill cancer cells and shrink tumors, delivered precisely to avoid damaging healthy brain tissue. Gamma Knife radiosurgery is able to accurately focus many beams of gamma radiation on one or more tumors. Each individual beam is of relatively low intensity, so the radiation has little effect on intervening brain tissue and is concentrated only at the tumor itself.
Gamma Knife radiosurgery has proven effective for patients with benign or malignant brain tumors up to 4 cm (1.6 in) in size, vascular malformations such as an arteriovenous malformation (AVM), pain, and other functional problems. For treatment of trigeminal neuralgia the procedure may be used repeatedly on patients.
Acute complications following Gamma Knife radiosurgery are rare, and complications are related to the condition being treated.
=== Linear accelerator-based therapies ===
A linear accelerator (linac) produces x-rays from the impact of accelerated electrons striking a high z target, usually tungsten. The process is also referred to as "x-ray therapy" or "photon therapy." The emission head, or "gantry", is mechanically rotated around the patient in a full or partial circle. The table where the patient is lying, the "couch", can also be moved in small linear or angular steps. The combination of the movements of the gantry and of the couch allow the computerized planning of the volume of tissue that is going to be irradiated. Devices with a high energy of 6 MeV are commonly used for the treatment of the brain, due to the depth of the target. The diameter of the energy beam leaving the emission head can be adjusted to the size of the lesion by means of collimators. They may be interchangeable orifices with different diameters, typically varying from 5 to 40 mm in 5 mm steps, or multileaf collimators, which consist of a number of metal leaflets that can be moved dynamically during treatment in order to shape the radiation beam to conform to the mass to be ablated. As of 2017 Linacs were capable of achieving extremely narrow beam geometries, such as 0.15 to 0.3 mm. Therefore, they can be used for several kinds of surgeries which hitherto had been carried out by open or endoscopic surgery, such as for trigeminal neuralgia. Long-term follow-up data has shown it to be as effective as radiofrequency ablation, but inferior to surgery in preventing the recurrence of pain.
The first such systems were developed by John R. Adler, a Stanford University professor of neurosurgery and radiation oncology, and Russell and Peter Schonberg at Schonberg Research, and commercialized under the brand name CyberKnife.
=== Proton beam therapy ===
Protons may also be used in radiosurgery in a procedure called Proton Beam Therapy (PBT) or proton therapy. Protons are extracted from proton donor materials by a medical synchrotron or cyclotron, and accelerated in successive transits through a circular, evacuated conduit or cavity, using powerful magnets to shape their path, until they reach the energy required to just traverse a human body, usually about 200 MeV. They are then released toward the region to be treated in the patient's body, the irradiation target. In some machines, which deliver protons of only a specific energy, a custom mask made of plastic is interposed between the beam source and the patient to adjust the beam energy to provide the appropriate degree of penetration. The phenomenon of the Bragg peak of ejected protons gives proton therapy advantages over other forms of radiation, since most of the proton's energy is deposited within a limited distance, so tissue beyond this range (and to some extent also tissue inside this range) is spared from the effects of radiation. This property of protons, which has been called the "depth charge effect" by analogy to the explosive weapons used in anti-submarine warfare, allows for conformal dose distributions to be created around even very irregularly shaped targets, and for higher doses to targets surrounded or backstopped by radiation-sensitive structures such as the optic chiasm or brainstem. The development of "intensity modulated" techniques allowed similar conformities to be attained using linear accelerator radiosurgery.
As of 2013 there was no evidence that proton beam therapy is better than any other types of treatment in most cases, except for a "handful of rare pediatric cancers". Critics, responding to the increasing number of very expensive PBT installations, spoke of a "medical arms race" and "crazy medicine and unsustainable public policy".
== References ==
== External links ==
Treating Tumors that Move with Respiration Book on Radiosurgery to moving targets (July 2007)
Shaped Beam Radiosurgery Book on LINAC-based radiosurgery using multileaf collimation (March 2011) | Wikipedia/Novalis_radiosurgery |
Neurosurgery is a monthly peer-reviewed medical journal of neurosurgery and the official journal of the Congress of Neurological Surgeons. It is published by Lippincott Williams & Wilkins. The journal publishes original research, reviews, and editorials.
There are also two associated journals. The Operative Neurosurgery journal focuses on technical material that highlights operative procedures, anatomy, instrumentation, devices, and technology. There is also an online-only, open access journal Neurosurgery Practice (previously named "Neurosurgery Open") which was debuted in 2019.
== History ==
=== Founding (1970s) ===
Discussion about a new specialist journal began in 1973 at a Southern Neurosurgical Society meeting, held in New Orleans, Louisiana. For the next three years, negotiations took place to either purchase an existing journal or start a new one. In July 1976, during a meeting of the executive committee of the Congress of Neurological Surgeons, the decision to begin a new publication was made at the recommendation of the Congress' Publication Committee.
President Robert G. Ojemann made the announcement of its launch at the 26th Annual Meeting of the Congress of Neurological Surgeons on October 27, 1976 and the inaugural issue of Neurosurgery was published in July 1977 as a bimonthly publication. The journal shifted to monthly publication in 1979.
=== Recent years (2000–2023) ===
The magazine in recent years is published by Lippincott Williams & Wilkins.
The first supplement to Neurosurgery, named the Millennium Supplement, was published in September 2000.
Two associated journals debuted afterwards. The Operative Neurosurgery journal focuses on technical material that highlights operative procedures, anatomy, instrumentation, devices, and technology.
There is also an online-only, open access journal Neurosurgery Practice (previously named Neurosurgery Open) which was debuted in 2019.
== Editors-in-chief ==
The following individuals have been editor-in-chief of the journal:
Robert Wilkins, 1977–1982
Clark Watts, 1982–1987
Edward Laws, Jr., 1987–1992
Michael Apuzzo, 1992–2009
Nelson Oyesiku, 2009–2022
Douglas Kondziolka, 2022–present
== Impact factor ==
Neurosurgery has a 2021 impact factor of 5.315. It was ranked 26 out of 211 journals in the category "Surgery" and 52 out of 212 in the category "Clinical Neurology".
== Associated works ==
=== Podcast ===
In May 2010, the international podcast series was introduced with article abstracts from the current issue translated and read in eight languages (Spanish, French, Italian, Korean, Chinese, Japanese, Portuguese, and Russian).
=== Associated journals ===
Operative Neurosurgery
Neurosurgery Practice
== References ==
== External links ==
Official website | Wikipedia/Neurosurgery_(journal) |
Digestive system surgery, or gastrointestinal surgery, can be divided into upper GI surgery and lower GI surgery.
== Subtypes ==
=== Upper gastrointestinal ===
Upper gastrointestinal surgery, often referred to as upper GI surgery, refers to a practise of surgery that focuses on the upper parts of the gastrointestinal tract. There are many operations relevant to the upper gastrointestinal tract that are best done only by those who keep constant practise, owing to their complexity. Consequently, a general surgeon may specialise in 'upper GI' by attempting to maintain currency in those skills.
Upper GI surgeons would have an interest in, and may exclusively perform, the following operations:
Pancreaticoduodenectomy
Esophagectomy
Liver resection
=== Lower gastrointestinal ===
Lower gastrointestinal surgery includes colorectal surgery as well as surgery of the small intestine.
Academically, it refers to a sub-specialisation of medical practise whereby a general surgeon focuses on the lower gastrointestinal tract.
In the U.S., a student wanting to specialize and practice in adult lower GI surgery would generally have to go through four years of undergraduate college pre-medical education and get a bachelor's degree, then finish the four years of medical school, then finish a typically five-year-long residency in general surgery, and then perform a subsequent one-year-long (minimum) residency in surgery of the small intestine or large intestine (the colon- specifically, the cecum, the vermiform appendix, the ascending colon, the transverse colon, the hepatic flexure and the splenic flexure, the descending colon, and the sigmoid colon; and also the rectum and the anus).
A fellowship (in surgery of the small intestine or of the large bowel, or in pediatric/neonatal lower GI surgery, or in surgery of congenital abnormalities or rare disorders of the lower GI tract, or in emergency/trauma surgery or in cancer surgery of the area), would add on approximately one to three more years.
A lower GI surgeon might specialise in the following operations:
Colectomy
Low (anterior) (LAR) or ultra-low (anterior) resections (ULAR) for rectal cancer, etc.
Pelvic exenteration for advanced or recurrent cancer; usually performed in conjunction with other surgeons (e.g., urologists, obstetricians and gynecologists)
== References == | Wikipedia/Digestive_system_surgery |
The Master of Surgery (Latin: Magister Chirurgiae) is an advanced qualification in surgery. Depending upon the degree, it may be abbreviated ChM, MCh, MChir or MS. At a typical medical school the program lasts two to three years. The possession of a medical degree is a prerequisite. The ChM can be awarded on clinical and academic or academic competency. The regulations may ask for surgical experience and a thesis topic that is not purely medical.
There are number of Master of Surgery Courses across the UK and Internationally, these are level 7 programmes (UK/Wales). Whilst most MS/MChir courses distinguish target professional practicing clinicians, there is not a harmonised definition of the qualification and different courses target different cohorts of students with different learning objectives, e.g., to prepare advanced surgical trainees for their FRCS examination, professional development of the surgeon approaching independent consultancy, engagement with surgical research or developing specialist surgical skills.
== References == | Wikipedia/Master_of_Surgery |
Computed tomography of the head uses a series of X-rays in a CT scan of the head taken from many different directions; the resulting data is transformed into a series of cross sections of the brain using a computer program. CT images of the head are used to investigate and diagnose brain injuries and other neurological conditions, as well as other conditions involving the skull or sinuses; it used to guide some brain surgery procedures as well. CT scans expose the person getting them to ionizing radiation which has a risk of eventually causing cancer; some people have allergic reactions to contrast agents that are used in some CT procedures.
== Uses ==
Computed tomography (CT) has become the diagnostic modality of choice for head trauma due to its accuracy, reliability, safety, and wide availability. The changes in microcirculation, impaired auto-regulation, cerebral edema, and axonal injury start as soon as head injury occurs and manifest as clinical, biochemical, and radiological changes. Proper therapeutic management of brain injury is based on correct diagnosis and appreciation of the temporal course of the disease process. CT scan detects and precisely localizes the intracranial hematomas, cerebral contusions, edema and foreign bodies.
Even in emergency situations, when a head injury is minor as determined by a physician's evaluation and based on established guidelines, CT of the head should be avoided for adults and delayed pending clinical observation in the emergency department for children. Many people visit emergency departments for minor head injuries. CT scans of the head can confirm a diagnosis of skull fracture or brain bleeding, but even in the emergency department, such things are uncommon and not minor injuries, so CT of the head is usually not necessary. Clinical trials have shown the efficacy and safety of using CT of the head in emergency settings only when indicated, which would be at the indication of evidence-based guidelines following the physical examination and a review of the person's history.
Concussion is not a routine indication for having brain CT or brain MRI and can be diagnosed by a healthcare provider trained to manage concussions. People with concussions usually do not have relevant abnormalities about which brain imaging could give insight, so brain imaging should not routinely be ordered for people with concussions. If there is concern about a skull fracture, focal neurological symptoms present or worsening symptoms, then CT imaging may be useful. MRI may be useful for people whose symptoms worsen over time or when structural pathology is suspected.
CT of the head is sometimes used for people who have sudden hearing loss. However, when there are not other neurological findings, a history of trauma, or a history of ear disease, CT scans are not useful and should not be used in response to sudden hearing loss.
CT of the head is also used in CT-guided stereotactic surgery and radiosurgery for treatment of intracranial tumors, arteriovenous malformations and other surgically treatable conditions.
== Orbital views for eye-related disorders ==
Special views focusing on the orbit of the eye may be taken to investigate concerns relating to the eye. CT scans are used by physicians specializing in treating the eye (ophthalmologists) to detect foreign bodies (especially metallic objects), fractures, abscesses, cellulitis, sinusitis, bleeding within the skull (intracranial bleeding), proptosis, Graves disease changes in the eye, and evaluation of the orbital apex and cavernous sinus.
== Comparison with MRI ==
Magnetic resonance imaging (MRI) of the head provides superior information as compared to CT scans when seeking information about headache to confirm a diagnosis of neoplasm, vascular disease, posterior cranial fossa lesions, cervicomedullary lesions, or intracranial pressure disorders. It also does not carry the risks of exposing the person to ionizing radiation. CT scans may be used to diagnose headaches when neuroimaging is indicated and MRI is not available, or in emergency settings when hemorrhage, stroke, or traumatic brain injury is suspected.
MRI (magnetic resonance imaging) provides more sensitivity in the evaluation of the cavernous sinus and the orbital apex.
One advantage over a brain MRI is in the evaluation of intracerebral calcifications.
== Cautions ==
Several different views of the head are available, including axial, coronal, reformatted coronal, and reformatted sagittal images. However, coronal images require the person to hyperextend their neck, which must be avoided if any possibility of neck injury exists.
CT scans of the head increase the risk of brain cancer, especially for children. As of 2018, it appeared that there was a risk of one excess cancer per 3,000–10,000 head CT exams in children under the age of 10.
== See also ==
Neuroimaging
== References == | Wikipedia/Computed_tomography_of_the_head |
Image-guided surgery (IGS) is any surgical procedure where the surgeon uses tracked surgical instruments in conjunction with preoperative or intraoperative images in order to directly or indirectly guide the procedure. Image guided surgery systems use cameras, ultrasonic, electromagnetic or a combination of fields to capture and relay the patient's anatomy and the surgeon's precise movements in relation to the patient, to computer monitors in the operating room or to augmented reality headsets (augmented reality surgical navigation technology). This is generally performed in real-time though there may be delays of seconds or minutes depending on the modality and application.
Image-guided surgery helps surgeons perform safer and less invasive procedures and has become a recognized standard of care in managing disorders including cranial, otorhinolaryngology, spine, orthopedic, and cardiovascular.
== Benefits ==
The benefits of Image-guided surgery include greater control of the surgical procedure, real-time feedback on the effect of the intervention, reduced tissue trauma and disruption in gaining access to the anatomical structure. Image-guided surgery allows for: reduced post-operative neural deficits and adverse events associated with endovenous laser ablative procedures, and more effective removal of brain tumors that were once considered inoperable due to their size or location.
== Applications ==
During image-guided surgery, the procedure is guided by preoperative or intraoperative imaging. Image-guided surgery has been applied to procedures involving on multiple organs such as the brain, spine, pelvis/hip, knee, lung, breast, liver, and prostate.
Part of the wider field of computer-assisted surgery, image-guided surgery can take place in hybrid operating rooms using intraoperative imaging. A hybrid operating room is a surgical theatre that is equipped with advanced medical imaging devices such as fixed C-Arms, CT scanners or MRI scanners. Most image-guided surgical procedures are minimally invasive. A field of medicine that pioneered and specializes in minimally invasive image-guided surgery is interventional radiology.
A hand-held surgical probe is an essential component of any image-guided surgery system as it provides the surgeon with a map of the designated area. During the surgical procedure, the IGS tracks the probe position and displays the anatomy beneath it as, for example, three orthogonal image slices on a workstation-based 3D imaging system. Existing IGS systems use different tracking techniques including mechanical, optical, ultrasonic, and electromagnetic.
When fluorescence modality is adopted to such devices, the technique is also called fluorescence image-guided surgery.
Image-guided surgery using medical ultrasound utilises sounds waves and as such does not require the protection and safety precautions necessary with ionising radiation modalities such as fluoroscopy, CT, X-Ray and tomography. Optical topographic imaging using structured light and machine vision stereoscopic cameras has been applied in neurosurgical navigation systems to reduce the use of intraoperative ionising radiation as well.
Modern image-guided surgery systems are often combined with robotics.
=== Neurosurgery ===
The various applications of navigation for neurosurgery have been widely used and reported for almost two decades. According to a study in 2000, researchers were already anticipating that a significant portion of neurosurgery would be performed using computer-based interventions. Recent advancements in ultrasound, including intravascular ultrasound (IVUS) allow for real-time cross sectional mapping of vessels and lateral tissues providing calibrated measurements of vessel diameters, contours and morphology.
Image-guided surgery was originally developed for treatment of brain tumors using stereotactic surgery and radiosurgery that are guided by computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET) via technologies such as the N-localizer and Sturm-Pastyr localizer.
Image-guided surgery systems are also used in spine surgery to guide the placement of implants and avoid damaging the nearby neurovascular structures.
=== Orthopedics ===
A mini-optical navigation system has been developed that makes real-time measurements to guide surgeons during total hip arthroplasty procedures. This image-guide surgery system involves a patient-mounted camera and a tracker for positional detection by the camera when mounted on surgical instruments or anatomical locations.
=== Urology ===
Image-guided surgery based on MRI is used to guide prostatic biopsy. Image guidance is used to assist surgeons with identifying anatomic landmarks and surgical planes between the prostate and neurovascular bundles during nerve-sparing procedures. This can help reduce negative effects of the procedure like sexual dysfunction and urinary incontinence.
== See also ==
Computer assisted surgery
Interventional radiology
Intraoperative MRI
Microsoft Hololens
Radiosurgery
Stereotactic surgery
== References ==
== Further reading == | Wikipedia/Image-guided_surgery |
Cardiac surgery, or cardiovascular surgery, is a surgery on the heart or great vessels performed by cardiac surgeons. It is often used to treat complications of ischemic heart disease (for example, with coronary artery bypass grafting); to correct congenital heart disease; or to treat valvular heart disease from various causes, including endocarditis, rheumatic heart disease, and atherosclerosis. It also includes heart transplantation.
== History ==
=== 19th century ===
The earliest operations on the pericardium (the sac that surrounds the heart) took place in the 19th century and were performed by Francisco Romero (1801) in the city of Almería (Spain), Dominique Jean Larrey (1810), Henry Dalton (1891), and Daniel Hale Williams (1893). The first surgery on the heart itself was performed by Axel Cappelen on 4 September 1895 at Rikshospitalet in Kristiania, now Oslo. Cappelen ligated a bleeding coronary artery in a 24-year-old man who had been stabbed in the left axilla and was in deep shock upon arrival. Access was through a left thoracotomy. The patient awoke and seemed fine for 24 hours but became ill with a fever and died three days after the surgery from mediastinitis.
=== 20th century ===
Surgery on the great vessels (e.g., aortic coarctation repair, Blalock–Thomas–Taussig shunt creation, closure of patent ductus arteriosus) became common after the turn of the century. However, operations on the heart valves were unknown until, in 1925, Henry Souttar operated successfully on a young woman with mitral valve stenosis. He made an opening in the appendage of the left atrium and inserted a finger in order to palpate and explore the damaged mitral valve. The patient survived for several years, but Souttar's colleagues considered the procedure unjustified, and he could not continue.
Alfred Blalock, Helen Taussig, and Vivien Thomas performed the first successful palliative pediatric cardiac operation at Johns Hopkins Hospital on 29 November 1944, in a one-year-old girl with Tetralogy of Fallot. Their work on patient Eileen Saxon was dramatically portrayed by HBO in the 2004 television film Something The Lord Made as the birth of modern cardiac surgery.
Cardiac surgery changed significantly after World War II. In 1947, Thomas Sellors of Middlesex Hospital in London operated on a Tetralogy of Fallot patient with pulmonary stenosis and successfully divided the stenosed pulmonary valve. In 1948, Russell Brock, probably unaware of Sellors's work, used a specially designed dilator in three cases of pulmonary stenosis. Later that year, he designed a punch to resect a stenosed infundibulum, which is often associated with Tetralogy of Fallot. Many thousands of these "blind" operations were performed until the introduction of cardiopulmonary bypass made direct surgery on valves possible.
Also in 1948, four surgeons carried out successful operations for mitral valve stenosis resulting from rheumatic fever. Horace Smithy of Charlotte used a valvulotome to remove a portion of a patient's mitral valve, while three other doctors—Charles Bailey of Hahnemann University Hospital in Philadelphia; Dwight Harken in Boston; and Russell Brock of Guy's Hospital in London—adopted Souttar's method. All four men began their work independently of one another within a period of a few months. This time, Souttar's technique was widely adopted, with some modifications.
The first successful intracardiac correction of a congenital heart defect using hypothermia was performed by lead surgeon Dr. F. John Lewis (Dr. C. Walton Lillehei assisted) at the University of Minnesota on 2 September 1952. In 1953, Alexander Alexandrovich Vishnevsky conducted the first cardiac surgery under local anesthesia. In 1956, Dr. John Carter Callaghan performed the first documented open-heart surgery in Canada.
== Types of cardiac surgery ==
=== Open-heart surgery ===
Open-heart surgery is any kind of surgery in which a surgeon makes a large incision (cut) in the chest to open the rib cage and operate on the heart. "Open" refers to the chest, not the heart. Depending on the type of surgery, the surgeon also may open the heart.
Dr. Wilfred G. Bigelow of the University of Toronto found that procedures involving opening the patient's heart could be performed better in a bloodless and motionless environment. Therefore, during such surgery, the heart is temporarily stopped, and the patient is placed on cardiopulmonary bypass, meaning a machine pumps their blood and oxygen. Because the machine cannot function the same way as the heart, surgeons try to minimize the time a patient spends on it.
Cardiopulmonary bypass was developed after surgeons realized the limitations of hypothermia in cardiac surgery: Complex intracardiac repairs take time, and the patient needs blood flow to the body (particularly to the brain), as well as heart and lung function. In July 1952, Forest Dodrill was the first to use a mechanical pump in a human to bypass the left side of the heart whilst allowing the patient's lungs to oxygenate the blood, in order to operate on the mitral valve. In 1953, Dr. John Heysham Gibbon of Jefferson Medical School in Philadelphia reported the first successful use of extracorporeal circulation by means of an oxygenator, but he abandoned the method after subsequent failures. In 1954, Dr. Lillehei performed a series of successful operations with the controlled cross-circulation technique, in which the patient's mother or father was used as a "heart-lung machine". Dr. John W. Kirklin at the Mayo Clinic was the first to use a Gibbon-type pump-oxygenator. Russell M. Nelson became the first surgeon to perform an open heart surgery in Utah in 1955.
Nazih Zuhdi performed the first total intentional hemodilution open-heart surgery on Terry Gene Nix, age 7, on 25 February 1960 at Mercy Hospital in Oklahoma City. The operation was a success; however, Nix died three years later. In March 1961, Zuhdi, Carey, and Greer performed open-heart surgery on a child, aged 3+1⁄2, using the total intentional hemodilution machine.
==== Modern beating-heart surgery ====
In the early 1990s, surgeons began to perform off-pump coronary artery bypass, done without cardiopulmonary bypass. In these operations, the heart continues beating during surgery, but is stabilized to provide an almost still work area in which to connect a conduit vessel that bypasses a blockage. The conduit vessel that is often used is the saphenous vein. This vein is harvested using a technique known as endoscopic vein harvesting (EVH).
=== Heart transplant ===
In 1945, the Soviet pathologist Nikolai Sinitsyn successfully transplanted a heart from one frog to another frog and from one dog to another dog.
Norman Shumway is widely regarded as the father of human heart transplantation, although the world's first adult heart transplant was performed by a South African cardiac surgeon, Christiaan Barnard, using techniques developed by Shumway and Richard Lower. Barnard performed the first transplant on Louis Washkansky on 3 December 1967 at Groote Schuur Hospital in Cape Town. Adrian Kantrowitz performed the first pediatric heart transplant on 6 December 1967 at Maimonides Hospital (now Maimonides Medical Center) in Brooklyn, New York, barely three days later. Shumway performed the first adult heart transplant in the United States on 6 January 1968 at Stanford University Hospital.
=== Coronary artery bypass grafting ===
Coronary artery bypass grafting (CABG), also called revascularization, is a common surgical procedure to create an alternative path to deliver blood supply to the heart and body, with the goal of preventing clot formation. This can be done in many ways, and the arteries used can be taken from several areas of the body. Arteries are typically harvested from the chest, arm, or wrist and then attached to a portion of the coronary artery, relieving pressure and limiting clotting factors in that area of the heart.
The procedure is typically performed because of coronary artery disease (CAD), in which a plaque-like substance builds up in the coronary artery, the main pathway carrying oxygen-rich blood to the heart. This can cause a blockage and/or a rupture, which can lead to a heart attack.
=== Minimally invasive surgery ===
As an alternative to open-heart surgery, which involves a five- to eight-inch incision in the chest wall, a surgeon may perform an endoscopic procedure by making very small incisions through which a camera and specialized tools are inserted.
In robot-assisted heart surgery, a machine controlled by a cardiac surgeon is used to perform a procedure. The main advantage to this is the size of the incision required: three small port holes instead of an incision big enough for the surgeon's hands. The use of robotics in heart surgery continues to be evaluated, but early research has shown it to be a safe alternative to traditional techniques.
== Post-surgical procedures ==
As with any surgical procedure, cardiac surgery requires postoperative precautions to avoid complications. Incision care is needed to avoid infection and minimize scarring. Swelling and loss of appetite are common.
Recovery from open-heart surgery begins with about 48 hours in an intensive care unit, where heart rate, blood pressure, and oxygen levels are closely monitored. Chest tubes are inserted to drain blood around the heart and lungs. After discharge from the hospital, compression socks may be recommended in order to regulate blood flow.
== Risks ==
The advancement of cardiac surgery and cardiopulmonary bypass techniques has greatly reduced the mortality rates of these procedures. For instance, repairs of congenital heart defects are currently estimated to have 4–6% mortality rates.
A major concern with cardiac surgery is neurological damage. Stroke occurs in 2–3% of all people undergoing cardiac surgery, and the rate is higher in patients with other risk factors for stroke. A more subtle complication attributed to cardiopulmonary bypass is postperfusion syndrome, sometimes called "pumphead". The neurocognitive symptoms of postperfusion syndrome were initially thought to be permanent, but turned out to be transient, with no permanent neurological impairment.
In order to assess the performance of surgical units and individual surgeons, a popular risk model has been created called the EuroSCORE. It takes a number of health factors from a patient and, using precalculated logistic regression coefficients, attempts to quantify the probability that they will survive to discharge. Within the United Kingdom, the EuroSCORE was used to give a breakdown of all cardiothoracic surgery centres and to indicate whether the units and their individuals surgeons performed within an acceptable range. The results are available on the Care Quality Commission website.
Another important source of complications are the neuropsychological and psychopathologic changes following open-heart surgery. One example is Skumin syndrome, described by Victor Skumin in 1978, which is a "cardioprosthetic psychopathological syndrome" associated with mechanical heart valve implants and characterized by irrational fear, anxiety, depression, sleep disorder, and weakness.
=== Risk reduction ===
Pharmacological and non-pharmacological prevention approaches may reduce the risk of atrial fibrillation after an operation and reduce the length of hospital stays, however there is no evidence that this improves mortality.
==== Non-pharmacologic approaches ====
Preoperative physical therapy may reduce postoperative pulmonary complications, such as pneumonia and atelectasis, in patients undergoing elective cardiac surgery and may decrease the length of hospital stay by more than three days on average. There is evidence that quitting smoking at least four weeks before surgery may reduce the risk of postoperative complications.
==== Pharmacological approaches ====
Beta-blocking medication is sometimes prescribed during cardiac surgery. There is some low certainty evidence that this perioperative blockade of beta-adrenergic receptors may reduce the incidence of atrial fibrillation and ventricular arrhythmias in patients undergoing cardiac surgery.
== See also ==
Frank Gerbode (surgeon)
== References ==
== Further reading ==
Cohn, Lawrence H.; Edmunds, L. Henry Jr., eds. (2003). Cardiac surgery in the adult. New York: McGraw-Hill, Medical Pub. Division. ISBN 978-0-07-139129-0. Archived from the original on 14 June 2016.
== External links ==
Media related to Cardiac surgery at Wikimedia Commons | Wikipedia/Cardiac_surgery |
Epilepsy surgery involves a neurosurgical procedure where an area of the brain involved in seizures is either resected, ablated, disconnected or stimulated. The goal is to eliminate seizures or significantly reduce seizure burden. Approximately 60% of all people with epilepsy (0.4% of the population of industrialized countries) have focal epilepsy syndromes. In 20% to 30% of these patients, the condition is not adequately controlled with adequate trials of two anticonvulsive drugs, termed drug resistant epilepsy, or refractory epilepsy. Such patients are potential candidates for surgical epilepsy treatment.
First line therapy for epilepsy involves treatment with anticonvulsive drugs, also called antiepileptic drugs– most patients will respond to trials of one or two different medications. The goal of treatment is the elimination of seizures, since uncontrolled seizures carry significant risks, including injury and sudden unexpected death in epilepsy. In patients with refractory epilepsy, surgery is considered the only curative option. Epilepsy surgery has been performed for more than a century, but its use dramatically increased in the 1980s and 1990s, reflecting advancement in technique and improved efficacy in selected patients.
== Evaluation ==
The pre-surgical evaluation for epilepsy is designed to locate the "epileptic focus" or the "epileptogenic zone" (the location where the epilepsy originates in the brain) and to determine if/how surgery could affect normal brain function. Defining the epileptogenic zone has a fundamental role in determining the boundaries of the area that needs to be removed in order to relieve seizures but also to avoid harming the "eloquent cortex" or areas of the brain that control functions such as language, motor control, or vision. Resective surgery involves cutting away or disconnecting areas of the brain that are generating or propagating seizures. Epileptologists, neurologists with special training in epilepsy, will also confirm the diagnosis of epilepsy to make sure that seizure-like activity is truly due to epilepsy as opposed to non-epileptic seizures.
The evaluation typically includes neurological physical examination, routine electroencephalography (EEG), Long-term video-EEG monitoring, neuropsychological evaluation, and neuroimaging such as MRI, functional magnetic resonance imaging (fMRI), single photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetoencephalography (MEG). Neuroimaging can help identify if there is a structural cause for the seizures, such as a tumor or abnormal blood vessels such as arteriovenous malformations (AVMs). Several imaging techniques including MRI, SPECT, and PET have been found to identify the epileptogenic zone in anywhere from 50% to 80% of cases. Some epilepsy centers use intracarotid sodium amobarbital test (Wada test) and fMRI when evaluating temporal lobe epilepsy surgery, as surgeries in this area of the brain can affect memory. Recent studies note fMRI outperforming the Wada test for memory and language localization. Current research into pre-surgical evaluation includes computer models of seizure generation, high-frequency oscillations as biomarkers of epilepsy, and magnetoencephalography for repeat epilepsy surgeries.
If noninvasive testing was inadequate in identifying the epileptic focus or in distinguishing the surgical target from normal brain tissue and function, then long-term video-EEG monitoring with the use of intracranial electrodes may be required for evaluation. Brain mapping by the technique of cortical electrical stimulation or electrocorticography are other procedures used in the process of invasive testing for certain patients.
Once the epilepsy focus is located, the specific surgery involved in treatment is decided on. The type of surgery depends on the location of the seizure focal point. Surgeries for epilepsy treatment include, but are not limited to: temporal lobe resection, hemispherectomy, ground temporal and extratemporal resection, parietal resection, occipital resection, frontal resection, extratemporal resection, and callosotomy.
== Hemispherectomy ==
Hemispherectomy or hemispherotomy involves removal or a functional disconnection of most, or all of, one half of the brain typically leaving the basal ganglia and thalamus. It is reserved for people with the most catastrophic epilepsies, such as those due to Rasmussen's encephalitis. If the surgery is performed on very young patients (2–5 years old), then the remaining hemisphere may acquire some motor control of the ipsilateral body due to neuroplasticity; in older patients, paralysis results on the side of the body opposite to the part of the brain that was removed with less prospect for recovery. A visual field defect is an unavoidable side effect, typically involving a homonymous hemianopia involving loss of the half of the visual field on the same side of the disconnected brain. Because of these and other side-effects, it is usually reserved for patients having exhausted other treatment options, including for children under 3 years of age who have drug-resistant epilepsy.
Hemispherectomies can be divided into three main types: anatomic, functional, and hemidecortication. Anatomic hemispherectomy involves the surgical removal of an entire cerebral hemisphere excluding deep structures such as the basal ganglia, thalamus, and brainstem to preserve vital functions. WE Dandy recorded the first anatomic hemispherectomy in 1928 for glioma resection and the first surgery for epilepsy was performed by McKenzie ten years later. This approach is less commonly performed due to high risks of complications, such as hydrocephalus due to blockage of the foramen of Monro, one of the passages that drains cerebrospinal fluid in the brain and spine, and superficial cerebral hemosiderosis (SCH). The procedure became less popular with the introduction of new antiepileptic drugs in the 1960s.
Functional hemispherectomies differ in that they disconnect the affected hemisphere from the rest of the brain to prevent spread from the epileptogenic focus to other parts of the brain. Structures involved can include the corpus callosum and thalamocortical fibers, as they are implicated in relaying information between the brain's hemispheres. Many approaches are available and overall are described according to their surgical plane including vertical (between the two hemispheres) and lateral (along the Sylvian fissure). Depending on each patient case, alternate procedures such as hemidecortication or peri-insular hemispherectomies are available to disrupt the epilepsy signal but remain less invasive to minimize risks.
== Temporal lobe resection ==
Temporal lobe resection acts as a treatment option for patients with temporal lobe epilepsy, or those whose seizure focus is in the temporal lobe. Temporal lobe seizures are the most common type (approximately 30% of diagnoses) of seizures for teens and young adults. The procedure involves resecting, or cutting away, brain tissue within the region of the temporal lobe in order to remove the seizure focus. Specific evaluation for temporal lobe resection requires convergent clinical, MRI, and EEG data in order to precisely pinpoint the focal area and boundaries of the focal area.
The surgery has produced successful outcomes, controlling seizures in as much as 70 percent of temporal lobe epilepsy patients. Follow-up studies suggest that the procedure also has produced positive long-term effects that illustrate 63 percent of patients still remaining seizure-free. Although the procedure produces positive outcomes for patients regarding seizure control, it can also produce negative outcomes such as memory impairment, visual disturbance, and cognitive dysfunction. Hemispheric dominance can determine the likelihood of certain complications of surgery in the temporal lobe; for the majority of right-handed people, the left hemisphere is dominant and is associated with the brain's language centers (most notably Wernicke's area) and the right (non-dominant) hemisphere is associated with memory and learning of non verbal information such as vision. Thus, temporal lobe resection of the dominant hemisphere often causes verbal memory impairment while resection of the non-dominant hemisphere often causes visual memory impairment.
Important structures implicated in temporal lobectomies include the auditory cortex, hippocampus, Wernicke's area, and amygdala; the latter three broadly affecting memory, language, and emotion, respectively. The hippocampus, amygdala, and parahippocampal gyrus are collectively termed the mesial temporal structures and are frequently targeted for resection in epilepsy.
Types of temporal lobectomy include anterior temporal lobectomy (ATL) and selective amygdalohippocampectomy (SAH). The ATL resection is the most common technique where the lateral and polar cortex are removed along with the aforementioned mesial temporal structures as well as the posterior part depending on which hemisphere the epileptogenic zone lies. The most common complication after ATL is a defect in vision known as a homonymous superior quadrantanopia, wherein the upper quarter field of vision on both eyes is altered, known as the "pie in the sky defect", with a frequency from 1.5% to 22%. ATL surgery resection encompasses the amygdala, hippocampus as well as surrounding tissue or neocortex whereas SAH is more targeted to the former two structures to be as minimally disruptive as possible. The SAH approach goes through a space on the lateral side of the brain known as the Sylvian fissure to reach the amygdala and hippocampus which are deeper in the middle of the brain. These structures may also be targeted through the middle temporal gyrus, below the Sylvian fissure, to avoid the visual pathways that course near the top of the temporal lobe.
The decision between ATL and SAH should include a multidisciplinary team involving an epileptologist and neurosurgeon and tailored to each patient's specific case. Both have varying rates of seizure freedom depending on how well the epileptogenic zone is localized. One meta-analysis found that there is no significant difference in seizure freedom but visual complications after surgery were less frequent in SAH.
== Extratemporal resection ==
Extratemporal lobe resection acts as a treatment option for patients with extratemporal epilepsy, or epilepsy patients whose seizure focus is outside of the temporal lobe, and stems from either the occipital lobes, parietal lobe, frontal lobe, or in multiple lobes. The evaluation for the procedure often requires more than clinical, MRI, and EEG convergence due to the variability of the seizure focus. Along with additional imaging techniques such as PET and SPECT, invasive studies may be needed to pinpoint the seizure focus. The efficacy of extratemporal lobe resection generally is less than resection of the temporal lobe. For example, in frontal lobe resections seizure freedom has been achieved in 38-44 percent of patients.
== Tumor Resection ==
If a benign or malignant brain tumor is suspected to be the cause of seizure activity, surgical removal of the tumor may be indicated. The approach and technique is case-dependent. One study of supratentorial brain tumors in children less observed a dramatic reduction in the severity and frequency of seizures at one and four year follow-up.
See also Brain tumors.
== Laser Interstitial Thermal Therapy (LITT) ==
LITT is a minimally invasive technique under imaging guidance (typically MRI) where a small hole is drilled through the skull (a Burr hole) and a precise laser targets structures that are causing seizures, known as laser ablation. Ablative procedures are appropriate options for patients who otherwise would not be good surgical candidates due to other medical problems or specific anatomical reasons that would make targeting their epilepsy difficult with a traditional surgery. Outcomes for each type of surgery vary widely depending on seizure localization, epilepsy specifics, and surgeon approach. Given that this is a new technique, more research into comparing outcomes is necessary but preliminary studies suggest lower seizure freedom.
See also ablative brain surgery.
== See also ==
Engel classification
Anticonvulsant
Temporal lobe
Temporal lobe epilepsy
Epilepsy syndromes
Rasmussen Encephalitis
Sturge–Weber syndrome
Hippocampal sclerosis
== References == | Wikipedia/Epilepsy_surgery |
A therapy or medical treatment is the attempted remediation of a health problem, usually following a medical diagnosis. Both words, treatment and therapy, are often abbreviated tx, Tx, or Tx.
As a rule, each therapy has indications and contraindications. There are many different types of therapy. Not all therapies are effective. Many therapies can produce unwanted adverse effects.
Treatment and therapy are often synonymous, especially in the usage of health professionals. However, in the context of mental health, the term therapy may refer specifically to psychotherapy.
== Semantic field ==
The words care, therapy, treatment, and intervention overlap in a semantic field, and thus they can be synonymous depending on context. Moving rightward through that order, the connotative level of holism decreases and the level of specificity (to concrete instances) increases. Thus, in health-care contexts (where its senses are always noncount), the word care tends to imply a broad idea of everything done to protect or improve someone's health (for example, as in the terms preventive care and primary care, which connote ongoing action), although it sometimes implies a narrower idea (for example, in the simplest cases of wound care or postanesthesia care, a few particular steps are sufficient, and the patient's interaction with the provider of such care is soon finished). In contrast, the word intervention tends to be specific and concrete, and thus the word is often countable; for example, one instance of cardiac catheterization is one intervention performed, and coronary care (noncount) can require a series of interventions (count). At the extreme, the piling on of such countable interventions amounts to interventionism, a flawed model of care lacking holistic circumspection—merely treating discrete problems (in billable increments) rather than maintaining health. Therapy and treatment, in the middle of the semantic field, can connote either the holism of care or the discreteness of intervention, with context conveying the intent in each use. Accordingly, they can be used in both noncount and count senses (for example, therapy for chronic kidney disease can involve several dialysis treatments per week).
The words aceology and iamatology are obscure and obsolete synonyms referring to the study of therapies.
The English word therapy comes via Latin therapīa from Ancient Greek: θεραπεία and literally means "curing" or "healing". The term therapeusis is a somewhat archaic doublet of the word therapy.
== Types of therapies ==
Therapy as a treatment for physical or mental condition is based on knowledge usually from one of three separate fields (or a combination of them): conventional medicine (allopathic, Western biomedicine, relying on scientific approach and evidence-based practice), traditional medicine (age-old cultural practices), and alternative medicine (healthcare procedures "not readily integrated into the dominant healthcare model").
=== By chronology, priority, or intensity ===
==== Levels of care ====
Levels of care classify health care into categories of chronology, priority, or intensity, as follows:
Urgent care handles health issues that need to be handled today but are not necessarily emergencies; the urgent care venue can send a patient to the emergency care level if it turns out to be needed.
In the United States (and possibly various other countries), urgent care centers also serve another function as their other main purpose: U.S. primary care practices have evolved in recent decades into a configuration whereby urgent care centers provide portions of primary care that cannot wait a month, because getting an appointment with the primary care practitioner is often subject to a waitlist of 2 to 8 weeks.
Emergency care handles medical emergencies and is a first point of contact or intake for less serious problems, which can be referred to other levels of care as appropriate. This therapy is often given to patients before a definitive diagnosis is made.
Intensive care, also called critical care, is care for extremely ill or injured patients. It thus requires high resource intensity, knowledge, and skill, as well as quick decision making.
Ambulatory care is care provided on an outpatient basis. Typically patients can walk into and out of the clinic under their own power (hence "ambulatory"), usually on the same day. This care type also involves surgery which, according to recent research, offers "generally superior 30-day outcomes relative to inpatient-based care".
Home care is care at home, including care from providers (such as physicians, nurses, and home health aides) making house calls, care from caregivers such as family members, and patient self-care.
Primary care is meant to be the main kind of care in general, and ideally a medical home that unifies care across referred providers. The current trend in this area is digitalization aiming to ensure open access to information about therapy, issues, and recent progress on biomedical research.
Secondary care is care provided by medical specialists and other health professionals who generally do not have first contact with patients, for example, cardiologists, urologists and dermatologists. A patient reaches secondary care as a next step from primary care, typically by provider referral although sometimes by patient self-initiative. According to a systematic review, fields for development secondary care from patients' viewpoint may be classified into four domains that should usefully guide future improvement of this care stage: "barriers to care, communication, coordination, and relationships and personal value".
Tertiary care is specialized consultative care, usually for inpatients and on referral from a primary or secondary health professional, in a facility that has personnel and facilities for advanced medical investigation and treatment, such as a tertiary referral hospital.
Follow-up care is additional care during or after convalescence. Aftercare is generally synonymous with follow-up care. One of the key areas of development–Telehealth, including non-clinical services: provider training, administrative meetings, and continuing medical education–offers opportunities to improve access to care, increase provider and patient productivity through reduced travel, potential expenses savings, and the ability to expand services.
End-of-life care is care near the end of one's life. It often includes the following:
Palliative care is supportive care, most especially (but not necessarily) near the end of life.
Hospice care is palliative care very near the end of life when cure is very unlikely. Its main goal is comfort, both physical and mental. A systematic meta review showed that the most cost-efficient one relates to home-based end-of-life care, including reduced overall "resource use and improved patient and carer outcomes".
==== Lines of therapy ====
Treatment decisions often follow formal or informal algorithmic guidelines. Treatment options can often be ranked or prioritized into lines of therapy: first-line therapy, second-line therapy, third-line therapy, and so on. First-line therapy (sometimes referred to as induction therapy, primary therapy, or front-line therapy) is the first therapy that will be tried. Its priority over other options is usually either: (1) formally recommended on the basis of clinical trial evidence for its best-available combination of efficacy, safety, and tolerability or (2) chosen based on the clinical experience of the physician. If a first-line therapy either fails to resolve the issue or produces intolerable side effects, additional (second-line) therapies may be substituted or added to the treatment regimen, followed by third-line therapies, and so on.
An example of a context in which the formalization of treatment algorithms and the ranking of lines of therapy is very extensive is chemotherapy regimens. Because of the great difficulty in successfully treating some forms of cancer, one line after another may be tried. In oncology the count of therapy lines may reach 10 or even 20.
Often multiple therapies may be tried simultaneously (combination therapy or polytherapy). Thus combination chemotherapy is also called polychemotherapy, whereas chemotherapy with one agent at a time is called single-agent therapy or monotherapy. Single-agent therapy is a care algorithm that focuses on one specific drug or procedure. It utilizes a single therapeutic agent rather than combining multiple ones. Multiagent Therapy is a treatment by two or more drugs or procedures. Comprehensive therapy combines various forms of medical treatment to provide the most effective care for patients.
Adjuvant therapy is therapy given in addition to the primary, main, or initial treatment, but simultaneously (as opposed to second-line therapy). Neoadjuvant therapy is therapy that is begun before the main therapy. Thus one can consider surgical excision of a tumor as the first-line therapy for a certain type and stage of cancer even though radiotherapy is used before it; the radiotherapy is neoadjuvant (chronologically first but not primary in the sense of the main event). Premedication is conceptually not far from this, but the words are not interchangeable; cytotoxic drugs to put a tumor "on the ropes" before surgery delivers the "knockout punch" are called neoadjuvant chemotherapy, not premedication, whereas things like anesthetics or prophylactic antibiotics before dental surgery are called premedication.
Step therapy or stepladder therapy is a specific type of prioritization by lines of therapy. It is controversial in American health care because unlike conventional decision-making about what constitutes first-line, second-line, and third-line therapy, which in the U.S. reflects safety and efficacy first and cost only according to the patient's wishes, step therapy attempts to mix cost containment by someone other than the patient (third-party payers) into the algorithm.
Therapy freedom refers to prescription for use of an unlicensed medicine (without a marketing authorization issued by the licensing authority of the country) and the negotiation between individual and group rights are involved. A comprehensive research in Australia, Czech Republic, India, Israel, Italy, Netherlands, Spain, Serbia, Sweden, UK, and USA showed that the rate of the unlicensed medicine prescription has been reported to range from 0.3 to 35% depending on the country. In many jurisdictions, therapy freedom is limited to cases of no treatment existing that is both well-established and more efficacious.
=== By intent ===
=== By intervention ===
Invasive therapy is achieved either through surgery or through the use of drugs. Medical invasive treatments can be divided into two main categories: pharmacotherapy and surgery.
Noninvasive therapies are medical treatments that do not involve entry into the body. It can be classified into five main categories: neurotherapy, physical therapy, occupational therapy, radiation therapy, and psychotherapy.
=== By therapy composition ===
Treatments can be classified according to the method of treatment:
==== By matter ====
by drugs: pharmacotherapy, chemotherapy (also, medical therapy often means specifically pharmacotherapy)
by medical devices: implantation
cardiac resynchronization therapy
by specific molecules: molecular therapy (although most drugs are specific molecules, molecular medicine refers in particular to medicine relying on molecular biology)
by specific biomolecular targets: targeted therapy
molecular chaperone therapy
by chelation: chelation therapy
by specific chemical elements:
by metals:
by heavy metals:
by gold: chrysotherapy (aurotherapy)
by platinum-containing drugs: platin therapy
by biometals
by lithium: lithium therapy
by potassium: potassium supplementation
by magnesium: magnesium supplementation
by chromium: chromium supplementation; phonemic neurological hypochromium therapy
by copper: copper supplementation
by nonmetals:
by diatomic oxygen: oxygen therapy, hyperbaric oxygen therapy (hyperbaric medicine)
transdermal continuous oxygen therapy
by triatomic oxygen (ozone): ozone therapy
by fluoride: fluoride therapy
by other gases: medical gas therapy
by water:
hydrotherapy
aquatic therapy
rehydration therapy
oral rehydration therapy
water cure (therapy)
by biological materials (biogenic substances, biomolecules, biotic materials, natural products), including their synthetic equivalents: biotherapy
by whole organisms
by viruses: virotherapy
by bacteriophages: phage therapy
by animal interaction: see animal interaction section
by constituents or products of organisms
by plant parts or extracts (but many drugs are derived from plants, even when the term phytotherapy is not used)
scientific type: phytotherapy
traditional (prescientific) type: herbalism
by animal parts: quackery involving shark fins, tiger parts, and so on, often driving threat or endangerment of species
by genes: gene therapy
gene therapy for epilepsy
gene therapy for osteoarthritis
gene therapy for color blindness
gene therapy of the human retina
gene therapy in Parkinson's disease
by epigenetics: epigenetic therapy
by proteins: protein therapy (but many drugs are proteins despite not being called protein therapy)
by enzymes: enzyme replacement therapy
by hormones: hormone therapy
hormonal therapy (oncology)
hormone replacement therapy
estrogen replacement therapy
androgen replacement therapy
hormone replacement therapy (menopause)
transgender hormone therapy
feminizing hormone therapy
masculinizing hormone therapy
antihormone therapy
androgen deprivation therapy
by whole cells: cell therapy (cytotherapy)
by stem cells: stem cell therapy
by immune cells: see immune system products below
by immune system products: immunotherapy, host modulatory therapy
by immune cells:
T-cell vaccination
cell transfer therapy
autologous immune enhancement therapy
TK cell therapy
by humoral immune factors: antibody therapy
by whole serum: serotherapy, including antiserum therapy
by immunoglobulins: immunoglobulin therapy
by monoclonal antibodies: monoclonal antibody therapy
by urine: urine therapy (some scientific forms; many prescientific or pseudoscientific forms)
by food and dietary choices:
medical nutrition therapy
grape therapy (quackery)
by salts (but many drugs are the salts of organic acids, even when drug therapy is not called by names reflecting that)
by salts in the air
by natural dry salt air: "taking the cure" in desert locales (especially common in prescientific medicine; for example, one 19th-century way to treat tuberculosis)
by artificial dry salt air:
low-humidity forms of speleotherapy
negative air ionization therapy
by moist salt air:
by natural moist salt air: seaside cure (especially common in prescientific medicine)
by artificial moist salt air: water vapor forms of speleotherapy
by salts in the water
by mineral water: spa cure ("taking the waters") (especially common in prescientific medicine)
by seawater: seaside cure (especially common in prescientific medicine)
by aroma: aromatherapy
by other materials with mechanism of action unknown
by occlusion with duct tape: duct tape occlusion therapy
==== By energy ====
by electric energy as electric current: electrotherapy, electroconvulsive therapy
Transcranial magnetic stimulation
Vagus nerve stimulation
by magnetic energy:
magnet therapy
pulsed electromagnetic field therapy
magnetic resonance therapy
by electromagnetic radiation (EMR):
by light: light therapy (phototherapy)
ultraviolet light therapy
PUVA therapy
photodynamic therapy
photothermal therapy
cytoluminescent therapy
blood irradiation therapy
by darkness: dark therapy
by lasers: laser therapy
low level laser therapy
by gamma rays: radiosurgery
Gamma Knife radiosurgery
stereotactic radiation therapy
cobalt therapy
by radiation generally: radiation therapy (radiotherapy)
intraoperative radiation therapy
by EMR particles:
particle therapy
proton therapy
electron therapy
intraoperative electron radiation therapy
Auger therapy
neutron therapy
fast neutron therapy
neutron capture therapy of cancer
by radioisotopes emitting EMR:
by nuclear medicine
by brachytherapy
quackery type: electromagnetic therapy (alternative medicine)
by mechanical: manual therapy as massotherapy and therapy by exercise as in physical therapy
inversion therapy
by sound:
by ultrasound:
ultrasonic lithotripsy
extracorporeal shockwave therapy
sonodynamic therapy
by music: music therapy
by temperature
by heat: heat therapy (thermotherapy)
by moderately elevated ambient temperatures: hyperthermia therapy
by dry warm surroundings: Waon therapy
by dry or humid warm surroundings: sauna, including infrared sauna, for sweat therapy
by cold:
by extreme cold to specific tissue volumes: cryotherapy
by ice and compression: cold compression therapy
by ambient cold:
hypothermia therapy for neonatal encephalopathy (in newborns)
targeted temperature management (therapeutic hypothermia, protective hypothermia)
by hot and cold alternation: contrast bath therapy
==== By procedure and human interaction ====
Surgery
by counseling, such as psychotherapy (see also: list of psychotherapies)
systemic therapy
by group psychotherapy
by cognitive behavioral therapy
by cognitive therapy
by behaviour therapy
by dialectical behavior therapy
by cognitive emotional behavioral therapy
by cognitive rehabilitation therapy
by family therapy
by education
by psychoeducation
by information therapy
by speech therapy, physical therapy, occupational therapy, vision therapy, massage therapy, chiropractic or acupuncture
by lifestyle modifications, such as avoiding unhealthy food or maintaining a predictable sleep schedule
by coaching
==== By animal interaction ====
by pets, assistance animals, or working animals: animal-assisted therapy
by horses: equine therapy, hippotherapy
by dogs: pet therapy with therapy dogs, including grief therapy dogs
by cats: pet therapy with therapy cats
by fish: ichthyotherapy (wading with fish), aquarium therapy (watching fish)
by maggots: maggot therapy
by worms:
by internal worms: helminthic therapy
by leeches: leech therapy
by immersion: animal bath
==== By meditation ====
by mindfulness: mindfulness-based cognitive therapy
==== By reading ====
by bibliotherapy
==== By creativity ====
by expression: expressive therapy
by writing: writing therapy
journal therapy
by play: play therapy
by art: art therapy
sensory art therapy
comic book therapy
by gardening: horticultural therapy
by dance: dance therapy
by drama: drama therapy
by recreation: recreational therapy
by music: music therapy
==== By sleeping and waking ====
by deep sleep: deep sleep therapy
by sleep deprivation: wake therapy
== See also ==
== References ==
== External links ==
The dictionary definition of therapy at Wiktionary
"Chapter Nine of the Book of Medicine Dedicated to Mansur, with the Commentary of Sillanus de Nigris" is a Latin book by Rhazes, from 1483, that is known for its ninth chapter, which is about therapeutics | Wikipedia/Medical_treatment |
Hand surgery deals with both surgical and non-surgical treatment of conditions and problems that may take place in the hand or upper extremity (commonly from the tip of the hand to the shoulder) including injury and infection. Hand surgery may be practiced by post graduates of orthopedic surgery and plastic surgery and MCh Hand surgery.
Plastic surgeons and orthopedic surgeons receive significant training in hand surgery during their residency training. Also, some graduates do an additional one-year hand fellowship. Board certified general, plastic, or orthopedics surgeons who have completed approved fellowship training in hand surgery and have met a number of other practice requirements are qualified to take the "Certificate of Added Qualifications in Surgery of the Hand" examination, formerly known as the CAQSH, it is now known as the SOTH." Now super speciatity training called MCh Hand Surgery required to be a qualified hand surgeon. Regardless of their original field of training, once candidates have completed an approved fellowship in hand surgery, all hand surgeons have received training in treating all injuries both to the bones and soft tissues of the hand and upper extremity. Among those without additional hand training, plastic surgeons have usually received training to handle traumatic hand and digit amputations that require a "replant" operation. Orthopedic surgeons are trained to reconstruct all aspects to salvage the appendage: tendons, muscle, bone. As well, orthopedic surgeons are trained to handle complex fractures of the hand and injuries to the carpal bones that alter the mechanics of the wrist.
== History ==
The historical context for the three qualifying fields is that both plastic surgery and orthopedic surgery are more recent branches off the general surgery main trunk. Modern hand surgery began in World War II as a military planning decision. US Army Surgeon General, Major General Norman T. Kirk, knew that hand injuries in World War I had poor outcomes in part because there was no formal system to deal with them. Kirk also knew that his civilian general surgical colleague Dr. Sterling Bunnell had a special interest and experience in hand reconstruction. Kirk tapped Bunnell to train military surgeons in the management of hand injuries to treat the war casualties, and at that time hand surgery became a formal specialty.
Orthopedic surgeons continued to develop special techniques to manage small bones, as found in the wrist and hand. Pioneering plastic surgeons developed microsurgical techniques for repairing the small nerves and arteries of the hand. Surgeons from all three specialties have contributed to the development of techniques for repairing tendons and managing a broad range of acute and chronic hand injuries. Hand surgery incorporates techniques from orthopaedics, plastic surgery, general surgery, neurosurgery, vascular and microvascular surgery and psychiatry. A recent advance is the progression to 'wide awake hand surgery.'
In a few countries such as Sweden, Finland and Singapore, hand surgery is recognized as a clinical specialty in its own right, with a formal four to six years hand surgery resident training program. Hand surgeons going through these programs are trained in all aspects of hand surgery, combining and mastering all the skills traditionally associated with "Orthopedic hand surgeons" and "Plastic hand surgeons" to become equally adept at handling tendon, ligament and bone injuries as well as microsurgical reconstruction such as reattachment of severed parts or free tissue transfers and transplants.
== Scope of field ==
Hand surgeons perform a wide variety of operations such as fracture repairs, releases, transfer and repairs of tendons and reconstruction of injuries, rheumatoid deformities and congenital defects. They also perform microsurgical reattachment of amputated digits and limbs, microsurgical reconstruction of soft tissues and bone, nerve reconstruction, and surgery to improve function in paralysed upper limbs. There are two medical societies that exist in the United States to provide continuing medical education to hand surgeons: the American Society for Surgery of the Hand and the American Association for Hand Surgery. In Britain, the medical society for hand surgeons is the: British Society for Surgery of the Hand (BSSH). In Europe, several societies are brought together by the Federation of European Societies for Surgery of the Hand (FESSH).
== Indications ==
The following conditions can be indications for hand surgery:
Hand and Wrist injuries
Tendon conditions e.g. trigger finger
Nerve Compression Disorders e.g. Carpal tunnel syndrome, Cubital tunnel syndrome
Carpometacarpal bossing
Rheumatoid arthritis
Dupuytren's contracture
Congenital defects
== Complications ==
Some complications of hand surgery include:
Infection - sometimes termed surgical site infection, infection is the most common and costly complication of surgery. This is equally true within the hand whereby the overall risk is ~5%.
Bleeding is uncommon and the available evidence indicates that the risk of bleeding is not related to the use of oral antiplatelet or anticoagulants.
Stiffness
Contractures
Complex Regional Pain Syndrome
== See also ==
Tetraplegic upper limb surgery
== References == | Wikipedia/Hand_surgery |
Transsphenoidal surgery is a type of surgery in which an endoscope or surgical instruments are inserted into part of the brain by going through the nose and the sphenoid bone (a butterfly-shaped bone forming the anterior inferior portion of the brain case) into the sphenoidal sinus cavity. Transsphenoidal surgery is used to remove tumors of the pituitary gland. (Such tumours, although within the skull, are outside the brain itself).
== History ==
The transsphenoidal approach was first attempted by Hermann Schloffer in 1907. Use of the procedure grew in the 1950s and 1960s with the introduction of intraoperative fluoroscopy and operating microscope.
== See also ==
Pituitary adenoma
Endoscopic endonasal surgery, particularly Surgical approaches to the anterior skull base
== References ==
== External links ==
Transsphenoidal surgery entry in the public domain NCI Dictionary of Cancer Terms.
Endoscopic transsphenoidal pituitary adenoma resection (IPG32) – National Institute for Clinical Excellence, United Kingdom.
This article incorporates public domain material from Dictionary of Cancer Terms. U.S. National Cancer Institute. | Wikipedia/Transsphenoidal_surgery |
Bienenstock–Cooper–Munro (BCM) theory, BCM synaptic modification, or the BCM rule, named after Elie Bienenstock, Leon Cooper, and Paul Munro, is a physical theory of learning in the visual cortex developed in 1981.
The BCM model proposes a sliding threshold for long-term potentiation (LTP) or long-term depression (LTD) induction, and states that synaptic plasticity is stabilized by a dynamic adaptation of the time-averaged postsynaptic activity. According to the BCM model, when a pre-synaptic neuron fires, the post-synaptic neurons will tend to undergo LTP if it is in a high-activity state (e.g., is firing at high frequency, and/or has high internal calcium concentrations), or LTD if it is in a lower-activity state (e.g., firing in low frequency, low internal calcium concentrations). This theory is often used to explain how cortical neurons can undergo both LTP or LTD depending on different conditioning stimulus protocols applied to pre-synaptic neurons (usually high-frequency stimulation, or HFS, for LTP, or low-frequency stimulation, LFS, for LTD).
== Development ==
In 1949, Donald Hebb proposed a working mechanism for memory and computational adaption in the brain now called Hebbian learning, or the maxim that cells that fire together, wire together. This notion is foundational in the modern understanding of the brain as a neural network, and though not universally true, remains a good first approximation supported by decades of evidence.
However, Hebb's rule has problems, namely that it has no mechanism for connections to get weaker and no upper bound for how strong they can get. In other words, the model is unstable, both theoretically and computationally. Later modifications gradually improved Hebb's rule, normalizing it and allowing for decay of synapses, where no activity or unsynchronized activity between neurons results in a loss of connection strength. New biological evidence brought this activity to a peak in the 1970s, where theorists formalized various approximations in the theory, such as the use of firing frequency instead of potential in determining neuron excitation, and the assumption of ideal and, more importantly, linear synaptic integration of signals. That is, there is no unexpected behavior in the adding of input currents to determine whether or not a cell will fire.
These approximations resulted in the basic form of BCM below in 1979, but the final step came in the form of mathematical analysis to prove stability and computational analysis to prove applicability, culminating in Bienenstock, Cooper, and Munro's 1982 paper.
Since then, experiments have shown evidence for BCM behavior in both the visual cortex and the hippocampus, the latter of which plays an important role in the formation and storage of memories. Both of these areas are well-studied experimentally, but both theory and experiment have yet to establish conclusive synaptic behavior in other areas of the brain. It has been proposed that in the cerebellum, the parallel-fiber to Purkinje cell synapse follows an "inverse BCM rule", meaning that at the time of parallel fiber activation, a high calcium concentration in the Purkinje cell results in LTD, while a lower concentration results in LTP. Furthermore, the biological implementation for synaptic plasticity in BCM has yet to be established.
== Theory ==
The basic BCM rule takes the form
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)
{\displaystyle c(t)={\textbf {w}}(t){\textbf {d}}(t)=\sum _{j}w_{j}(t)d_{j}(t)}
is the inner product of weights and input currents (weighted sum of inputs),
ϕ
(
c
)
{\displaystyle \phi (c)}
is a non-linear function. This function must change sign at some threshold
θ
M
{\displaystyle \theta _{M}}
, that is,
ϕ
(
c
)
<
0
{\displaystyle \phi (c)<0}
if and only if
c
<
θ
M
{\displaystyle c<\theta _{M}}
. See below for details and properties.
and
ϵ
{\displaystyle \epsilon }
is the (often negligible) time constant of uniform decay of all synapses.
This model is a modified form of the Hebbian learning rule,
m
j
˙
=
c
d
j
{\displaystyle {\dot {m_{j}}}=cd_{j}}
, and requires a suitable choice of function
ϕ
{\displaystyle \phi }
to avoid the Hebbian problems of instability.
Bienenstock at al. rewrite
ϕ
(
c
)
{\displaystyle \phi (c)}
as a function
ϕ
(
c
,
c
¯
)
{\displaystyle \phi (c,{\bar {c}})}
where
c
¯
{\displaystyle {\bar {c}}}
is the time average of
c
{\displaystyle c}
. With this modification and discarding the uniform decay the rule takes the vectorial form:
m
˙
(
t
)
=
ϕ
(
c
(
t
)
,
c
¯
(
t
)
)
d
(
t
)
{\displaystyle {\dot {\mathbf {m} }}(t)=\phi (c(t),{\bar {c}}(t))\mathbf {d} (t)}
The conditions for stable learning are derived rigorously in BCM noting that with
c
(
t
)
=
m
(
t
)
⋅
d
(
t
)
{\displaystyle c(t)={\textbf {m}}(t)\cdot {\textbf {d}}(t)}
and with the approximation of the average output
c
¯
(
t
)
≈
m
(
t
)
d
¯
{\displaystyle {\bar {c}}(t)\approx {\textbf {m}}(t){\bar {\mathbf {d} }}}
, it is sufficient that
sgn
ϕ
(
c
,
c
¯
)
=
sgn
(
c
−
(
c
¯
c
0
)
p
c
¯
)
for
c
>
0
,
and
{\displaystyle \,\operatorname {sgn} \phi (c,{\bar {c}})=\operatorname {sgn} \left(c-\left({\frac {\bar {c}}{c_{0}}}\right)^{p}{\bar {c}}\right)~~{\textrm {for}}~c>0,~{\textrm {and}}}
ϕ
(
0
,
c
¯
)
=
0
for
all
c
¯
,
{\displaystyle \,\phi (0,{\bar {c}})=0~~{\textrm {for}}~{\textrm {all}}~{\bar {c}},}
or equivalently, that the threshold
θ
M
(
c
¯
)
=
(
c
¯
/
c
0
)
p
c
¯
{\displaystyle \theta _{M}({\bar {c}})=({\bar {c}}/c_{0})^{p}{\bar {c}}}
, where
p
{\displaystyle p}
and
c
0
{\displaystyle c_{0}}
are fixed positive constants.
When implemented, the theory is often taken such that
ϕ
(
c
,
c
¯
)
=
c
(
c
−
θ
M
)
and
θ
M
=
c
¯
2
=
1
τ
∫
−
∞
t
c
2
(
t
′
)
e
−
(
t
−
t
′
)
/
τ
d
t
′
,
{\displaystyle \,\phi (c,{\bar {c}})=c(c-\theta _{M})~~~{\textrm {and}}~~~\theta _{M}={\bar {c}}^{2}={\frac {1}{\tau }}\int _{-\infty }^{t}c^{2}(t^{\prime })e^{-(t-t^{\prime })/\tau }dt^{\prime },}
where
τ
{\displaystyle \tau }
is a time constant of selectivity.
The model has drawbacks, as it requires both long-term potentiation and long-term depression, or increases and decreases in synaptic strength, something which has not been observed in all cortical systems. Further, it requires a variable activation threshold and depends strongly on stability of the selected fixed points
c
0
{\displaystyle c_{0}}
and
p
{\displaystyle p}
. However, the model's strength is that it incorporates all these requirements from independently derived rules of stability, such as normalizability and a decay function with time proportional to the square of the output.
== Example ==
This example is a particular case of the one at chapter "Mathematical results" of Bienenstock at al. work, assuming
p
=
2
{\displaystyle p=2}
and
c
0
=
1
{\displaystyle c_{0}=1}
. With these values
θ
M
=
(
c
¯
/
c
0
)
p
c
¯
=
c
¯
3
{\displaystyle \theta _{M}=({\bar {c}}/c_{0})^{p}{\bar {c}}={\bar {c}}^{3}}
and we decide
ϕ
(
c
,
c
¯
)
=
c
(
c
−
θ
M
)
{\displaystyle \phi (c,{\bar {c}})=c(c-\theta _{M})}
that fulfills the stability conditions said in previous chapter.
Assume two presynaptic neurons that provides inputs
d
1
{\displaystyle d_{1}}
and
d
2
{\displaystyle d_{2}}
, its activity a repetitive cycle with half of time
d
=
(
d
1
,
d
2
)
=
(
0.9
,
0.1
)
{\displaystyle \mathbf {d} =(d_{1},d_{2})=(0.9,0.1)}
and remainder time
d
=
(
0.2
,
0.7
)
{\displaystyle \mathbf {d} =(0.2,0.7)}
.
c
¯
{\displaystyle {\bar {c}}}
time average will be the average of
c
{\displaystyle c}
value in first and second half of a cycle.
Let initial value of weights
m
=
(
0.1
,
0.05
)
{\displaystyle \mathbf {m} =(0.1,0.05)}
. In the first half of time
d
=
(
0.9
,
0.1
)
{\displaystyle \mathbf {d} =(0.9,0.1)}
and
m
=
(
0.1
,
0.05
)
{\displaystyle \mathbf {m} =(0.1,0.05)}
, the weighted sum
c
{\displaystyle c}
is equal to 0.095 and we use same value as initial average
c
¯
{\displaystyle {\bar {c}}}
. That means
θ
M
=
0.001
{\displaystyle \theta _{M}=0.001}
,
ϕ
=
0.009
{\displaystyle \phi =0.009}
,
m
˙
=
(
0.008
,
0.001
)
{\displaystyle {\dot {m}}=(0.008,0.001)}
. Adding 10% of the derivative to the weights we obtain new ones
m
=
(
0.101
,
0.051
)
{\displaystyle \mathbf {m} =(0.101,0.051)}
.
In next half of time, inputs are
d
=
(
0.2
,
0.7
)
{\displaystyle \mathbf {d} =(0.2,0.7)}
and weights
m
=
(
0.101
,
0.051
)
{\displaystyle \mathbf {m} =(0.101,0.051)}
. That means
c
=
0.055
{\displaystyle c=0.055}
,
c
¯
{\displaystyle {\bar {c}}}
of full cycle is 0.075,
θ
M
=
0.000
{\displaystyle \theta _{M}=0.000}
,
ϕ
=
0.003
{\displaystyle \phi =0.003}
,
m
˙
=
(
0.001
,
0.002
)
{\displaystyle {\dot {m}}=(0.001,0.002)}
. Adding 10% of the derivative to the weights we obtain new ones
m
=
(
0.110
,
0.055
)
{\displaystyle \mathbf {m} =(0.110,0.055)}
.
Repeating previous cycle we obtain, after several hundred of iterations, that stability is reached with
m
=
(
3.246
,
−
0.927
)
{\displaystyle \mathbf {m} =(3.246,-0.927)}
,
c
=
8
=
2.828
{\displaystyle c={\sqrt {8}}=2.828}
(first half) and
c
=
0.000
{\displaystyle c=0.000}
(remainder time),
c
¯
=
8
/
2
=
1.414
{\displaystyle {\bar {c}}={\sqrt {8}}/2=1.414}
,
θ
M
=
8
=
2.828
{\displaystyle \theta _{M}={\sqrt {8}}=2.828}
,
ϕ
=
0.000
{\displaystyle \phi =0.000}
and
m
˙
=
(
0.000
,
0.000
)
{\displaystyle {\dot {m}}=(0.000,0.000)}
.
Note how, as predicted, the final weight vector
m
{\displaystyle m}
has become orthogonal to one of the input patterns, being the final values of
c
{\displaystyle c}
in both intervals zeros of the function
ϕ
{\displaystyle \phi }
.
== Experiment ==
The first major experimental confirmation of BCM came in 1992 in investigating LTP and LTD in the hippocampus. Serena Dudek's experimental work showed qualitative agreement with the final form of the BCM activation function. This experiment was later replicated in the visual cortex, which BCM was originally designed to model. This work provided further evidence of the necessity for a variable threshold function for stability in Hebbian-type learning (BCM or others).
Experimental evidence has been non-specific to BCM until Rittenhouse et al. confirmed BCM's prediction of synapse modification in the visual cortex when one eye is selectively closed. Specifically,
log
(
m
c
l
o
s
e
d
(
t
)
m
c
l
o
s
e
d
(
0
)
)
∼
−
n
2
¯
t
,
{\displaystyle \log \left({\frac {m_{\rm {closed}}(t)}{m_{\rm {closed}}(0)}}\right)\sim -{\overline {n^{2}}}t,}
where
n
2
¯
{\displaystyle {\overline {n^{2}}}}
describes the variance in spontaneous activity or noise in the closed eye and
t
{\displaystyle t}
is time since closure. Experiment agreed with the general shape of this prediction and provided an explanation for the dynamics of monocular eye closure (monocular deprivation) versus binocular eye closure. The experimental results are far from conclusive, but so far have favored BCM over competing theories of plasticity.
== Applications ==
While the algorithm of BCM is too complicated for large-scale parallel distributed processing, it has been put to use in lateral networks with some success. Furthermore, some existing computational network learning algorithms have been made to correspond to BCM learning.
== References ==
== External links ==
Scholarpedia article | Wikipedia/BCM_theory |
An artificial neuron is a mathematical function conceived as a model of a biological neuron in a neural network. The artificial neuron is the elementary unit of an artificial neural network.
The design of the artificial neuron was inspired by biological neural circuitry. Its inputs are analogous to excitatory postsynaptic potentials and inhibitory postsynaptic potentials at neural dendrites, or activation. Its weights are analogous to synaptic weights, and its output is analogous to a neuron's action potential which is transmitted along its axon.
Usually, each input is separately weighted, and the sum is often added to a term known as a bias (loosely corresponding to the threshold potential), before being passed through a nonlinear function known as an activation function. Depending on the task, these functions could have a sigmoid shape (e.g. for binary classification), but they may also take the form of other nonlinear functions, piecewise linear functions, or step functions. They are also often monotonically increasing, continuous, differentiable, and bounded. Non-monotonic, unbounded, and oscillating activation functions with multiple zeros that outperform sigmoidal and ReLU-like activation functions on many tasks have also been recently explored. The threshold function has inspired building logic gates referred to as threshold logic; applicable to building logic circuits resembling brain processing. For example, new devices such as memristors have been extensively used to develop such logic.
The artificial neuron activation function should not be confused with a linear system's transfer function.
An artificial neuron may be referred to as a semi-linear unit, Nv neuron, binary neuron, linear threshold function, or McCulloch–Pitts (MCP) neuron, depending on the structure used.
Simple artificial neurons, such as the McCulloch–Pitts model, are sometimes described as "caricature models", since they are intended to reflect one or more neurophysiological observations, but without regard to realism. Artificial neurons can also refer to artificial cells in neuromorphic engineering that are similar to natural physical neurons.
== Basic structure ==
For a given artificial neuron
k
{\displaystyle k}
, let there be
m
+
1
{\displaystyle m+1}
inputs with signals
x
0
{\displaystyle x_{0}}
through
x
m
{\displaystyle x_{m}}
and weights
w
k
0
{\displaystyle w_{k0}}
through
w
k
m
{\displaystyle w_{km}}
. Usually, the input
x
0
{\displaystyle x_{0}}
is assigned the value +1, which makes it a bias input with
w
k
0
=
b
k
{\displaystyle w_{k0}=b_{k}}
. This leaves only
m
{\displaystyle m}
actual inputs to the neuron:
x
1
{\displaystyle x_{1}}
to
x
m
{\displaystyle x_{m}}
.
The output of the
k
{\displaystyle k}
-th neuron is:
y
k
=
φ
(
∑
j
=
0
m
w
k
j
x
j
)
{\displaystyle y_{k}=\varphi \left(\sum _{j=0}^{m}w_{kj}x_{j}\right)}
,
where
φ
{\displaystyle \varphi }
(phi) is the activation function.
The output is analogous to the axon of a biological neuron, and its value propagates to the input of the next layer, through a synapse. It may also exit the system, possibly as part of an output vector.
It has no learning process as such. Its activation function weights are calculated, and its threshold value is predetermined.
== McCulloch–Pitts (MCP) neuron ==
An MCP neuron is a kind of restricted artificial neuron which operates in discrete time-steps. Each has zero or more inputs, and are written as
x
1
,
.
.
.
,
x
n
{\displaystyle x_{1},...,x_{n}}
. It has one output, written as
y
{\displaystyle y}
. Each input can be either excitatory or inhibitory. The output can either be quiet or firing. An MCP neuron also has a threshold
b
∈
{
0
,
1
,
2
,
.
.
.
}
{\displaystyle b\in \{0,1,2,...\}}
.
In an MCP neural network, all the neurons operate in synchronous discrete time-steps of
t
=
0
,
1
,
2
,
3
,
.
.
.
{\displaystyle t=0,1,2,3,...}
. At time
t
+
1
{\displaystyle t+1}
, the output of the neuron is
y
(
t
+
1
)
=
1
{\displaystyle y(t+1)=1}
if the number of firing excitatory inputs is at least equal to the threshold, and no inhibitory inputs are firing;
y
(
t
+
1
)
=
0
{\displaystyle y(t+1)=0}
otherwise.
Each output can be the input to an arbitrary number of neurons, including itself (i.e., self-loops are possible). However, an output cannot connect more than once with a single neuron. Self-loops do not cause contradictions, since the network operates in synchronous discrete time-steps.
As a simple example, consider a single neuron with threshold 0, and a single inhibitory self-loop. Its output would oscillate between 0 and 1 at every step, acting as a "clock".
Any finite state machine can be simulated by a MCP neural network. Furnished with an infinite tape, MCP neural networks can simulate any Turing machine.
== Biological models ==
Artificial neurons are designed to mimic aspects of their biological counterparts. However a significant performance gap exists between biological and artificial neural networks. In particular single biological neurons in the human brain with oscillating activation function capable of learning the XOR function have been discovered.
Dendrites – in biological neurons, dendrites act as the input vector. These dendrites allow the cell to receive signals from a large (>1000) number of neighboring neurons. As in the above mathematical treatment, each dendrite is able to perform "multiplication" by that dendrite's "weight value." The multiplication is accomplished by increasing or decreasing the ratio of synaptic neurotransmitters to signal chemicals introduced into the dendrite in response to the synaptic neurotransmitter. A negative multiplication effect can be achieved by transmitting signal inhibitors (i.e. oppositely charged ions) along the dendrite in response to the reception of synaptic neurotransmitters.
Soma – in biological neurons, the soma acts as the summation function, seen in the above mathematical description. As positive and negative signals (exciting and inhibiting, respectively) arrive in the soma from the dendrites, the positive and negative ions are effectively added in summation, by simple virtue of being mixed together in the solution inside the cell's body.
Axon – the axon gets its signal from the summation behavior which occurs inside the soma. The opening to the axon essentially samples the electrical potential of the solution inside the soma. Once the soma reaches a certain potential, the axon will transmit an all-in signal pulse down its length. In this regard, the axon behaves as the ability for us to connect our artificial neuron to other artificial neurons.
Unlike most artificial neurons, however, biological neurons fire in discrete pulses. Each time the electrical potential inside the soma reaches a certain threshold, a pulse is transmitted down the axon. This pulsing can be translated into continuous values. The rate (activations per second, etc.) at which an axon fires converts directly into the rate at which neighboring cells get signal ions introduced into them. The faster a biological neuron fires, the faster nearby neurons accumulate electrical potential (or lose electrical potential, depending on the "weighting" of the dendrite that connects to the neuron that fired). It is this conversion that allows computer scientists and mathematicians to simulate biological neural networks using artificial neurons which can output distinct values (often from −1 to 1).
=== Encoding ===
Research has shown that unary coding is used in the neural circuits responsible for birdsong production. The use of unary in biological networks is presumably due to the inherent simplicity of the coding. Another contributing factor could be that unary coding provides a certain degree of error correction.
== Physical artificial cells ==
There is research and development into physical artificial neurons – organic and inorganic.
For example, some artificial neurons can receive and release dopamine (chemical signals rather than electrical signals) and communicate with natural rat muscle and brain cells, with potential for use in BCIs/prosthetics.
Low-power biocompatible memristors may enable construction of artificial neurons which function at voltages of biological action potentials and could be used to directly process biosensing signals, for neuromorphic computing and/or direct communication with biological neurons.
Organic neuromorphic circuits made out of polymers, coated with an ion-rich gel to enable a material to carry an electric charge like real neurons, have been built into a robot, enabling it to learn sensorimotorically within the real world, rather than via simulations or virtually. Moreover, artificial spiking neurons made of soft matter (polymers) can operate in biologically relevant environments and enable the synergetic communication between the artificial and biological domains.
== History ==
The first artificial neuron was the Threshold Logic Unit (TLU), or Linear Threshold Unit, first proposed by Warren McCulloch and Walter Pitts in 1943 in A logical calculus of the ideas immanent in nervous activity. The model was specifically targeted as a computational model of the "nerve net" in the brain. As an activation function, it employed a threshold, equivalent to using the Heaviside step function. Initially, only a simple model was considered, with binary inputs and outputs, some restrictions on the possible weights, and a more flexible threshold value. Since the beginning it was already noticed that any Boolean function could be implemented by networks of such devices, what is easily seen from the fact that one can implement the AND and OR functions, and use them in the disjunctive or the conjunctive normal form.
Researchers also soon realized that cyclic networks, with feedbacks through neurons, could define dynamical systems with memory, but most of the research concentrated (and still does) on strictly feed-forward networks because of the smaller difficulty they present.
One important and pioneering artificial neural network that used the linear threshold function was the perceptron, developed by Frank Rosenblatt. This model already considered more flexible weight values in the neurons, and was used in machines with adaptive capabilities. The representation of the threshold values as a bias term was introduced by Bernard Widrow in 1960 – see ADALINE.
In the late 1980s, when research on neural networks regained strength, neurons with more continuous shapes started to be considered. The possibility of differentiating the activation function allows the direct use of the gradient descent and other optimization algorithms for the adjustment of the weights. Neural networks also started to be used as a general function approximation model. The best known training algorithm called backpropagation has been rediscovered several times but its first development goes back to the work of Paul Werbos.
== Types of activation function ==
The activation function of a neuron is chosen to have a number of properties which either enhance or simplify the network containing the neuron. Crucially, for instance, any multilayer perceptron using a linear activation function has an equivalent single-layer network; a non-linear function is therefore necessary to gain the advantages of a multi-layer network.
Below,
u
{\displaystyle u}
refers in all cases to the weighted sum of all the inputs to the neuron, i.e. for
n
{\displaystyle n}
inputs,
u
=
∑
i
=
1
n
w
i
x
i
{\displaystyle u=\sum _{i=1}^{n}w_{i}x_{i}}
where
w
{\displaystyle w}
is a vector of synaptic weights and
x
{\displaystyle x}
is a vector of inputs.
=== Step function ===
The output
y
{\displaystyle y}
of this activation function is binary, depending on whether the input meets a specified threshold,
θ
{\displaystyle \theta }
(theta). The "signal" is sent, i.e. the output is set to 1, if the activation meets or exceeds the threshold.
y
=
{
1
if
u
≥
θ
0
if
u
<
θ
{\displaystyle y={\begin{cases}1&{\text{if }}u\geq \theta \\0&{\text{if }}u<\theta \end{cases}}}
This function is used in perceptrons, and appears in many other models. It performs a division of the space of inputs by a hyperplane. It is specially useful in the last layer of a network, intended for example to perform binary classification of the inputs.
=== Linear combination ===
In this case, the output unit is simply the weighted sum of its inputs, plus a bias term. A number of such linear neurons perform a linear transformation of the input vector. This is usually more useful in the early layers of a network. A number of analysis tools exist based on linear models, such as harmonic analysis, and they can all be used in neural networks with this linear neuron. The bias term allows us to make affine transformations to the data.
=== Sigmoid ===
A fairly simple nonlinear function, the sigmoid function such as the logistic function also has an easily calculated derivative, which can be important when calculating the weight updates in the network. It thus makes the network more easily manipulable mathematically, and was attractive to early computer scientists who needed to minimize the computational load of their simulations. It was previously commonly seen in multilayer perceptrons. However, recent work has shown sigmoid neurons to be less effective than rectified linear neurons. The reason is that the gradients computed by the backpropagation algorithm tend to diminish towards zero as activations propagate through layers of sigmoidal neurons, making it difficult to optimize neural networks using multiple layers of sigmoidal neurons.
=== Rectifier ===
In the context of artificial neural networks, the rectifier or ReLU (Rectified Linear Unit) is an activation function defined as the positive part of its argument:
f
(
x
)
=
x
+
=
max
(
0
,
x
)
,
{\displaystyle f(x)=x^{+}=\max(0,x),}
where
x
{\displaystyle x}
is the input to a neuron. This is also known as a ramp function and is analogous to half-wave rectification in electrical engineering. This activation function was first introduced to a dynamical network by Hahnloser et al. in a 2000 paper in Nature with strong biological motivations and mathematical justifications. It has been demonstrated for the first time in 2011 to enable better training of deeper networks, compared to the widely used activation functions prior to 2011, i.e., the logistic sigmoid (which is inspired by probability theory; see logistic regression) and its more practical counterpart, the hyperbolic tangent.
A commonly used variant of the ReLU activation function is the Leaky ReLU which allows a small, positive gradient when the unit is not active:
f
(
x
)
=
{
x
if
x
>
0
,
a
x
otherwise
.
{\displaystyle f(x)={\begin{cases}x&{\text{if }}x>0,\\ax&{\text{otherwise}}.\end{cases}}}
where
x
{\displaystyle x}
is the input to the neuron and
a
{\displaystyle a}
is a small positive constant (set to 0.01 in the original paper).
== Pseudocode algorithm ==
The following is a simple pseudocode implementation of a single Threshold Logic Unit (TLU) which takes Boolean inputs (true or false), and returns a single Boolean output when activated. An object-oriented model is used. No method of training is defined, since several exist. If a purely functional model were used, the class TLU below would be replaced with a function TLU with input parameters threshold, weights, and inputs that returned a Boolean value.
class TLU defined as:
data member threshold : number
data member weights : list of numbers of size X
function member fire(inputs : list of booleans of size X) : boolean defined as:
variable T : number
T ← 0
for each i in 1 to X do
if inputs(i) is true then
T ← T + weights(i)
end if
end for each
if T > threshold then
return true
else:
return false
end if
end function
end class
== See also ==
Binding neuron
Connectionism
== References ==
== Further reading ==
== External links ==
Artifical [sic] neuron mimicks function of human cells
McCulloch-Pitts Neurons (Overview) | Wikipedia/Artificial_neurons |
In mathematics, a function from a set X to a set Y assigns to each element of X exactly one element of Y. The set X is called the domain of the function and the set Y is called the codomain of the function.
Functions were originally the idealization of how a varying quantity depends on another quantity. For example, the position of a planet is a function of time. Historically, the concept was elaborated with the infinitesimal calculus at the end of the 17th century, and, until the 19th century, the functions that were considered were differentiable (that is, they had a high degree of regularity). The concept of a function was formalized at the end of the 19th century in terms of set theory, and this greatly increased the possible applications of the concept.
A function is often denoted by a letter such as f, g or h. The value of a function f at an element x of its domain (that is, the element of the codomain that is associated with x) is denoted by f(x); for example, the value of f at x = 4 is denoted by f(4). Commonly, a specific function is defined by means of an expression depending on x, such as
f
(
x
)
=
x
2
+
1
;
{\displaystyle f(x)=x^{2}+1;}
in this case, some computation, called function evaluation, may be needed for deducing the value of the function at a particular value; for example, if
f
(
x
)
=
x
2
+
1
,
{\displaystyle f(x)=x^{2}+1,}
then
f
(
4
)
=
4
2
+
1
=
17.
{\displaystyle f(4)=4^{2}+1=17.}
Given its domain and its codomain, a function is uniquely represented by the set of all pairs (x, f (x)), called the graph of the function, a popular means of illustrating the function. When the domain and the codomain are sets of real numbers, each such pair may be thought of as the Cartesian coordinates of a point in the plane.
Functions are widely used in science, engineering, and in most fields of mathematics. It has been said that functions are "the central objects of investigation" in most fields of mathematics.
The concept of a function has evolved significantly over centuries, from its informal origins in ancient mathematics to its formalization in the 19th century. See History of the function concept for details.
== Definition ==
A function f from a set X to a set Y is an assignment of one element of Y to each element of X. The set X is called the domain of the function and the set Y is called the codomain of the function.
If the element y in Y is assigned to x in X by the function f, one says that f maps x to y, and this is commonly written
y
=
f
(
x
)
.
{\displaystyle y=f(x).}
In this notation, x is the argument or variable of the function.
A specific element x of X is a value of the variable, and the corresponding element of Y is the value of the function at x, or the image of x under the function. The image of a function, sometimes called its range, is the set of the images of all elements in the domain.
A function f, its domain X, and its codomain Y are often specified by the notation
f
:
X
→
Y
.
{\displaystyle f:X\to Y.}
One may write
x
↦
y
{\displaystyle x\mapsto y}
instead of
y
=
f
(
x
)
{\displaystyle y=f(x)}
, where the symbol
↦
{\displaystyle \mapsto }
(read 'maps to') is used to specify where a particular element x in the domain is mapped to by f. This allows the definition of a function without naming. For example, the square function is the function
x
↦
x
2
.
{\displaystyle x\mapsto x^{2}.}
The domain and codomain are not always explicitly given when a function is defined. In particular, it is common that one might only know, without some (possibly difficult) computation, that the domain of a specific function is contained in a larger set. For example, if
f
:
R
→
R
{\displaystyle f:\mathbb {R} \to \mathbb {R} }
is a real function, the determination of the domain of the function
x
↦
1
/
f
(
x
)
{\displaystyle x\mapsto 1/f(x)}
requires knowing the zeros of f. This is one of the reasons for which, in mathematical analysis, "a function from X to Y " may refer to a function having a proper subset of X as a domain. For example, a "function from the reals to the reals" may refer to a real-valued function of a real variable whose domain is a proper subset of the real numbers, typically a subset that contains a non-empty open interval. Such a function is then called a partial function.
A function f on a set S means a function from the domain S, without specifying a codomain. However, some authors use it as shorthand for saying that the function is f : S → S.
=== Formal definition ===
The above definition of a function is essentially that of the founders of calculus, Leibniz, Newton and Euler. However, it cannot be formalized, since there is no mathematical definition of an "assignment". It is only at the end of the 19th century that the first formal definition of a function could be provided, in terms of set theory. This set-theoretic definition is based on the fact that a function establishes a relation between the elements of the domain and some (possibly all) elements of the codomain. Mathematically, a binary relation between two sets X and Y is a subset of the set of all ordered pairs
(
x
,
y
)
{\displaystyle (x,y)}
such that
x
∈
X
{\displaystyle x\in X}
and
y
∈
Y
.
{\displaystyle y\in Y.}
The set of all these pairs is called the Cartesian product of X and Y and denoted
X
×
Y
.
{\displaystyle X\times Y.}
Thus, the above definition may be formalized as follows.
A function with domain X and codomain Y is a binary relation R between X and Y that satisfies the two following conditions:
For every
x
{\displaystyle x}
in
X
{\displaystyle X}
there exists
y
{\displaystyle y}
in
Y
{\displaystyle Y}
such that
(
x
,
y
)
∈
R
.
{\displaystyle (x,y)\in R.}
If
(
x
,
y
)
∈
R
{\displaystyle (x,y)\in R}
and
(
x
,
z
)
∈
R
,
{\displaystyle (x,z)\in R,}
then
y
=
z
.
{\displaystyle y=z.}
This definition may be rewritten more formally, without referring explicitly to the concept of a relation, but using more notation (including set-builder notation):
A function is formed by three sets, the domain
X
,
{\displaystyle X,}
the codomain
Y
,
{\displaystyle Y,}
and the graph
R
{\displaystyle R}
that satisfy the three following conditions.
R
⊆
{
(
x
,
y
)
∣
x
∈
X
,
y
∈
Y
}
{\displaystyle R\subseteq \{(x,y)\mid x\in X,y\in Y\}}
∀
x
∈
X
,
∃
y
∈
Y
,
(
x
,
y
)
∈
R
{\displaystyle \forall x\in X,\exists y\in Y,\left(x,y\right)\in R\qquad }
(
x
,
y
)
∈
R
∧
(
x
,
z
)
∈
R
⟹
y
=
z
{\displaystyle (x,y)\in R\land (x,z)\in R\implies y=z\qquad }
=== Partial functions ===
Partial functions are defined similarly to ordinary functions, with the "total" condition removed. That is, a partial function from X to Y is a binary relation R between X and Y such that, for every
x
∈
X
,
{\displaystyle x\in X,}
there is at most one y in Y such that
(
x
,
y
)
∈
R
.
{\displaystyle (x,y)\in R.}
Using functional notation, this means that, given
x
∈
X
,
{\displaystyle x\in X,}
either
f
(
x
)
{\displaystyle f(x)}
is in Y, or it is undefined.
The set of the elements of X such that
f
(
x
)
{\displaystyle f(x)}
is defined and belongs to Y is called the domain of definition of the function. A partial function from X to Y is thus an ordinary function that has as its domain a subset of X called the domain of definition of the function. If the domain of definition equals X, one often says that the partial function is a total function.
In several areas of mathematics, the term "function" refers to partial functions rather than to ordinary (total) functions. This is typically the case when functions may be specified in a way that makes difficult or even impossible to determine their domain.
In calculus, a real-valued function of a real variable or real function is a partial function from the set
R
{\displaystyle \mathbb {R} }
of the real numbers to itself. Given a real function
f
:
x
↦
f
(
x
)
{\displaystyle f:x\mapsto f(x)}
its multiplicative inverse
x
↦
1
/
f
(
x
)
{\displaystyle x\mapsto 1/f(x)}
is also a real function. The determination of the domain of definition of a multiplicative inverse of a (partial) function amounts to compute the zeros of the function, the values where the function is defined but not its multiplicative inverse.
Similarly, a function of a complex variable is generally a partial function whose domain of definition is a subset of the complex numbers
C
{\displaystyle \mathbb {C} }
. The difficulty of determining the domain of definition of a complex function is illustrated by the multiplicative inverse of the Riemann zeta function: the determination of the domain of definition of the function
z
↦
1
/
ζ
(
z
)
{\displaystyle z\mapsto 1/\zeta (z)}
is more or less equivalent to the proof or disproof of one of the major open problems in mathematics, the Riemann hypothesis.
In computability theory, a general recursive function is a partial function from the integers to the integers whose values can be computed by an algorithm (roughly speaking). The domain of definition of such a function is the set of inputs for which the algorithm does not run forever. A fundamental theorem of computability theory is that there cannot exist an algorithm that takes an arbitrary general recursive function as input and tests whether 0 belongs to its domain of definition (see Halting problem).
=== Multivariate functions ===
A multivariate function, multivariable function, or function of several variables is a function that depends on several arguments. Such functions are commonly encountered. For example, the position of a car on a road is a function of the time travelled and its average speed.
Formally, a function of n variables is a function whose domain is a set of n-tuples. For example, multiplication of integers is a function of two variables, or bivariate function, whose domain is the set of all ordered pairs (2-tuples) of integers, and whose codomain is the set of integers. The same is true for every binary operation. The graph of a bivariate surface over a two-dimensional real domain may be interpreted as defining a parametric surface, as used in, e.g., bivariate interpolation.
Commonly, an n-tuple is denoted enclosed between parentheses, such as in
(
1
,
2
,
…
,
n
)
.
{\displaystyle (1,2,\ldots ,n).}
When using functional notation, one usually omits the parentheses surrounding tuples, writing
f
(
x
1
,
…
,
x
n
)
{\displaystyle f(x_{1},\ldots ,x_{n})}
instead of
f
(
(
x
1
,
…
,
x
n
)
)
.
{\displaystyle f((x_{1},\ldots ,x_{n})).}
Given n sets
X
1
,
…
,
X
n
,
{\displaystyle X_{1},\ldots ,X_{n},}
the set of all n-tuples
(
x
1
,
…
,
x
n
)
{\displaystyle (x_{1},\ldots ,x_{n})}
such that
x
1
∈
X
1
,
…
,
x
n
∈
X
n
{\displaystyle x_{1}\in X_{1},\ldots ,x_{n}\in X_{n}}
is called the Cartesian product of
X
1
,
…
,
X
n
,
{\displaystyle X_{1},\ldots ,X_{n},}
and denoted
X
1
×
⋯
×
X
n
.
{\displaystyle X_{1}\times \cdots \times X_{n}.}
Therefore, a multivariate function is a function that has a Cartesian product or a proper subset of a Cartesian product as a domain.
f
:
U
→
Y
,
{\displaystyle f:U\to Y,}
where the domain U has the form
U
⊆
X
1
×
⋯
×
X
n
.
{\displaystyle U\subseteq X_{1}\times \cdots \times X_{n}.}
If all the
X
i
{\displaystyle X_{i}}
are equal to the set
R
{\displaystyle \mathbb {R} }
of the real numbers or to the set
C
{\displaystyle \mathbb {C} }
of the complex numbers, one talks respectively of a function of several real variables or of a function of several complex variables.
== Notation ==
There are various standard ways for denoting functions. The most commonly used notation is functional notation, which is the first notation described below.
=== Functional notation ===
The functional notation requires that a name is given to the function, which, in the case of a unspecified function is often the letter f. Then, the application of the function to an argument is denoted by its name followed by its argument (or, in the case of a multivariate functions, its arguments) enclosed between parentheses, such as in
f
(
x
)
,
sin
(
3
)
,
or
f
(
x
2
+
1
)
.
{\displaystyle f(x),\quad \sin(3),\quad {\text{or}}\quad f(x^{2}+1).}
The argument between the parentheses may be a variable, often x, that represents an arbitrary element of the domain of the function, a specific element of the domain (3 in the above example), or an expression that can be evaluated to an element of the domain (
x
2
+
1
{\displaystyle x^{2}+1}
in the above example). The use of a unspecified variable between parentheses is useful for defining a function explicitly such as in "let
f
(
x
)
=
sin
(
x
2
+
1
)
{\displaystyle f(x)=\sin(x^{2}+1)}
".
When the symbol denoting the function consists of several characters and no ambiguity may arise, the parentheses of functional notation might be omitted. For example, it is common to write sin x instead of sin(x).
Functional notation was first used by Leonhard Euler in 1734. Some widely used functions are represented by a symbol consisting of several letters (usually two or three, generally an abbreviation of their name). In this case, a roman type is customarily used instead, such as "sin" for the sine function, in contrast to italic font for single-letter symbols.
The functional notation is often used colloquially for referring to a function and simultaneously naming its argument, such as in "let
f
(
x
)
{\displaystyle f(x)}
be a function". This is an abuse of notation that is useful for a simpler formulation.
=== Arrow notation ===
Arrow notation defines the rule of a function inline, without requiring a name to be given to the function. It uses the ↦ arrow symbol, pronounced "maps to". For example,
x
↦
x
+
1
{\displaystyle x\mapsto x+1}
is the function which takes a real number as input and outputs that number plus 1. Again, a domain and codomain of
R
{\displaystyle \mathbb {R} }
is implied.
The domain and codomain can also be explicitly stated, for example:
sqr
:
Z
→
Z
x
↦
x
2
.
{\displaystyle {\begin{aligned}\operatorname {sqr} \colon \mathbb {Z} &\to \mathbb {Z} \\x&\mapsto x^{2}.\end{aligned}}}
This defines a function sqr from the integers to the integers that returns the square of its input.
As a common application of the arrow notation, suppose
f
:
X
×
X
→
Y
;
(
x
,
t
)
↦
f
(
x
,
t
)
{\displaystyle f:X\times X\to Y;\;(x,t)\mapsto f(x,t)}
is a function in two variables, and we want to refer to a partially applied function
X
→
Y
{\displaystyle X\to Y}
produced by fixing the second argument to the value t0 without introducing a new function name. The map in question could be denoted
x
↦
f
(
x
,
t
0
)
{\displaystyle x\mapsto f(x,t_{0})}
using the arrow notation. The expression
x
↦
f
(
x
,
t
0
)
{\displaystyle x\mapsto f(x,t_{0})}
(read: "the map taking x to f of x comma t nought") represents this new function with just one argument, whereas the expression f(x0, t0) refers to the value of the function f at the point (x0, t0).
=== Index notation ===
Index notation may be used instead of functional notation. That is, instead of writing f (x), one writes
f
x
.
{\displaystyle f_{x}.}
This is typically the case for functions whose domain is the set of the natural numbers. Such a function is called a sequence, and, in this case the element
f
n
{\displaystyle f_{n}}
is called the nth element of the sequence.
The index notation can also be used for distinguishing some variables called parameters from the "true variables". In fact, parameters are specific variables that are considered as being fixed during the study of a problem. For example, the map
x
↦
f
(
x
,
t
)
{\displaystyle x\mapsto f(x,t)}
(see above) would be denoted
f
t
{\displaystyle f_{t}}
using index notation, if we define the collection of maps
f
t
{\displaystyle f_{t}}
by the formula
f
t
(
x
)
=
f
(
x
,
t
)
{\displaystyle f_{t}(x)=f(x,t)}
for all
x
,
t
∈
X
{\displaystyle x,t\in X}
.
=== Dot notation ===
In the notation
x
↦
f
(
x
)
,
{\displaystyle x\mapsto f(x),}
the symbol x does not represent any value; it is simply a placeholder, meaning that, if x is replaced by any value on the left of the arrow, it should be replaced by the same value on the right of the arrow. Therefore, x may be replaced by any symbol, often an interpunct " ⋅ ". This may be useful for distinguishing the function f (⋅) from its value f (x) at x.
For example,
a
(
⋅
)
2
{\displaystyle a(\cdot )^{2}}
may stand for the function
x
↦
a
x
2
{\displaystyle x\mapsto ax^{2}}
, and
∫
a
(
⋅
)
f
(
u
)
d
u
{\textstyle \int _{a}^{\,(\cdot )}f(u)\,du}
may stand for a function defined by an integral with variable upper bound:
x
↦
∫
a
x
f
(
u
)
d
u
{\textstyle x\mapsto \int _{a}^{x}f(u)\,du}
.
=== Specialized notations ===
There are other, specialized notations for functions in sub-disciplines of mathematics. For example, in linear algebra and functional analysis, linear forms and the vectors they act upon are denoted using a dual pair to show the underlying duality. This is similar to the use of bra–ket notation in quantum mechanics. In logic and the theory of computation, the function notation of lambda calculus is used to explicitly express the basic notions of function abstraction and application. In category theory and homological algebra, networks of functions are described in terms of how they and their compositions commute with each other using commutative diagrams that extend and generalize the arrow notation for functions described above.
=== Functions of more than one variable ===
In some cases the argument of a function may be an ordered pair of elements taken from some set or sets. For example, a function f can be defined as mapping any pair of real numbers
(
x
,
y
)
{\displaystyle (x,y)}
to the sum of their squares,
x
2
+
y
2
{\displaystyle x^{2}+y^{2}}
. Such a function is commonly written as
f
(
x
,
y
)
=
x
2
+
y
2
{\displaystyle f(x,y)=x^{2}+y^{2}}
and referred to as "a function of two variables". Likewise one can have a function of three or more variables, with notations such as
f
(
w
,
x
,
y
)
{\displaystyle f(w,x,y)}
,
f
(
w
,
x
,
y
,
z
)
{\displaystyle f(w,x,y,z)}
.
== Other terms ==
A function may also be called a map or a mapping, but some authors make a distinction between the term "map" and "function". For example, the term "map" is often reserved for a "function" with some sort of special structure (e.g. maps of manifolds). In particular map may be used in place of homomorphism for the sake of succinctness (e.g., linear map or map from G to H instead of group homomorphism from G to H). Some authors reserve the word mapping for the case where the structure of the codomain belongs explicitly to the definition of the function.
Some authors, such as Serge Lang, use "function" only to refer to maps for which the codomain is a subset of the real or complex numbers, and use the term mapping for more general functions.
In the theory of dynamical systems, a map denotes an evolution function used to create discrete dynamical systems. See also Poincaré map.
Whichever definition of map is used, related terms like domain, codomain, injective, continuous have the same meaning as for a function.
== Specifying a function ==
Given a function
f
{\displaystyle f}
, by definition, to each element
x
{\displaystyle x}
of the domain of the function
f
{\displaystyle f}
, there is a unique element associated to it, the value
f
(
x
)
{\displaystyle f(x)}
of
f
{\displaystyle f}
at
x
{\displaystyle x}
. There are several ways to specify or describe how
x
{\displaystyle x}
is related to
f
(
x
)
{\displaystyle f(x)}
, both explicitly and implicitly. Sometimes, a theorem or an axiom asserts the existence of a function having some properties, without describing it more precisely. Often, the specification or description is referred to as the definition of the function
f
{\displaystyle f}
.
=== By listing function values ===
On a finite set a function may be defined by listing the elements of the codomain that are associated to the elements of the domain. For example, if
A
=
{
1
,
2
,
3
}
{\displaystyle A=\{1,2,3\}}
, then one can define a function
f
:
A
→
R
{\displaystyle f:A\to \mathbb {R} }
by
f
(
1
)
=
2
,
f
(
2
)
=
3
,
f
(
3
)
=
4.
{\displaystyle f(1)=2,f(2)=3,f(3)=4.}
=== By a formula ===
Functions are often defined by an expression that describes a combination of arithmetic operations and previously defined functions; such a formula allows computing the value of the function from the value of any element of the domain.
For example, in the above example,
f
{\displaystyle f}
can be defined by the formula
f
(
n
)
=
n
+
1
{\displaystyle f(n)=n+1}
, for
n
∈
{
1
,
2
,
3
}
{\displaystyle n\in \{1,2,3\}}
.
When a function is defined this way, the determination of its domain is sometimes difficult. If the formula that defines the function contains divisions, the values of the variable for which a denominator is zero must be excluded from the domain; thus, for a complicated function, the determination of the domain passes through the computation of the zeros of auxiliary functions. Similarly, if square roots occur in the definition of a function from
R
{\displaystyle \mathbb {R} }
to
R
,
{\displaystyle \mathbb {R} ,}
the domain is included in the set of the values of the variable for which the arguments of the square roots are nonnegative.
For example,
f
(
x
)
=
1
+
x
2
{\displaystyle f(x)={\sqrt {1+x^{2}}}}
defines a function
f
:
R
→
R
{\displaystyle f:\mathbb {R} \to \mathbb {R} }
whose domain is
R
,
{\displaystyle \mathbb {R} ,}
because
1
+
x
2
{\displaystyle 1+x^{2}}
is always positive if x is a real number. On the other hand,
f
(
x
)
=
1
−
x
2
{\displaystyle f(x)={\sqrt {1-x^{2}}}}
defines a function from the reals to the reals whose domain is reduced to the interval [−1, 1]. (In old texts, such a domain was called the domain of definition of the function.)
Functions can be classified by the nature of formulas that define them:
A quadratic function is a function that may be written
f
(
x
)
=
a
x
2
+
b
x
+
c
,
{\displaystyle f(x)=ax^{2}+bx+c,}
where a, b, c are constants.
More generally, a polynomial function is a function that can be defined by a formula involving only additions, subtractions, multiplications, and exponentiation to nonnegative integer powers. For example,
f
(
x
)
=
x
3
−
3
x
−
1
{\displaystyle f(x)=x^{3}-3x-1}
and
f
(
x
)
=
(
x
−
1
)
(
x
3
+
1
)
+
2
x
2
−
1
{\displaystyle f(x)=(x-1)(x^{3}+1)+2x^{2}-1}
are polynomial functions of
x
{\displaystyle x}
.
A rational function is the same, with divisions also allowed, such as
f
(
x
)
=
x
−
1
x
+
1
,
{\displaystyle f(x)={\frac {x-1}{x+1}},}
and
f
(
x
)
=
1
x
+
1
+
3
x
−
2
x
−
1
.
{\displaystyle f(x)={\frac {1}{x+1}}+{\frac {3}{x}}-{\frac {2}{x-1}}.}
An algebraic function is the same, with nth roots and roots of polynomials also allowed.
An elementary function is the same, with logarithms and exponential functions allowed.
=== Inverse and implicit functions ===
A function
f
:
X
→
Y
,
{\displaystyle f:X\to Y,}
with domain X and codomain Y, is bijective, if for every y in Y, there is one and only one element x in X such that y = f(x). In this case, the inverse function of f is the function
f
−
1
:
Y
→
X
{\displaystyle f^{-1}:Y\to X}
that maps
y
∈
Y
{\displaystyle y\in Y}
to the element
x
∈
X
{\displaystyle x\in X}
such that y = f(x). For example, the natural logarithm is a bijective function from the positive real numbers to the real numbers. It thus has an inverse, called the exponential function, that maps the real numbers onto the positive numbers.
If a function
f
:
X
→
Y
{\displaystyle f:X\to Y}
is not bijective, it may occur that one can select subsets
E
⊆
X
{\displaystyle E\subseteq X}
and
F
⊆
Y
{\displaystyle F\subseteq Y}
such that the restriction of f to E is a bijection from E to F, and has thus an inverse. The inverse trigonometric functions are defined this way. For example, the cosine function induces, by restriction, a bijection from the interval [0, π] onto the interval [−1, 1], and its inverse function, called arccosine, maps [−1, 1] onto [0, π]. The other inverse trigonometric functions are defined similarly.
More generally, given a binary relation R between two sets X and Y, let E be a subset of X such that, for every
x
∈
E
,
{\displaystyle x\in E,}
there is some
y
∈
Y
{\displaystyle y\in Y}
such that x R y. If one has a criterion allowing selecting such a y for every
x
∈
E
,
{\displaystyle x\in E,}
this defines a function
f
:
E
→
Y
,
{\displaystyle f:E\to Y,}
called an implicit function, because it is implicitly defined by the relation R.
For example, the equation of the unit circle
x
2
+
y
2
=
1
{\displaystyle x^{2}+y^{2}=1}
defines a relation on real numbers. If −1 < x < 1 there are two possible values of y, one positive and one negative. For x = ± 1, these two values become both equal to 0. Otherwise, there is no possible value of y. This means that the equation defines two implicit functions with domain [−1, 1] and respective codomains [0, +∞) and (−∞, 0].
In this example, the equation can be solved in y, giving
y
=
±
1
−
x
2
,
{\displaystyle y=\pm {\sqrt {1-x^{2}}},}
but, in more complicated examples, this is impossible. For example, the relation
y
5
+
y
+
x
=
0
{\displaystyle y^{5}+y+x=0}
defines y as an implicit function of x, called the Bring radical, which has
R
{\displaystyle \mathbb {R} }
as domain and range. The Bring radical cannot be expressed in terms of the four arithmetic operations and nth roots.
The implicit function theorem provides mild differentiability conditions for existence and uniqueness of an implicit function in the neighborhood of a point.
=== Using differential calculus ===
Many functions can be defined as the antiderivative of another function. This is the case of the natural logarithm, which is the antiderivative of 1/x that is 0 for x = 1. Another common example is the error function.
More generally, many functions, including most special functions, can be defined as solutions of differential equations. The simplest example is probably the exponential function, which can be defined as the unique function that is equal to its derivative and takes the value 1 for x = 0.
Power series can be used to define functions on the domain in which they converge. For example, the exponential function is given by
e
x
=
∑
n
=
0
∞
x
n
n
!
{\textstyle e^{x}=\sum _{n=0}^{\infty }{x^{n} \over n!}}
. However, as the coefficients of a series are quite arbitrary, a function that is the sum of a convergent series is generally defined otherwise, and the sequence of the coefficients is the result of some computation based on another definition. Then, the power series can be used to enlarge the domain of the function. Typically, if a function for a real variable is the sum of its Taylor series in some interval, this power series allows immediately enlarging the domain to a subset of the complex numbers, the disc of convergence of the series. Then analytic continuation allows enlarging further the domain for including almost the whole complex plane. This process is the method that is generally used for defining the logarithm, the exponential and the trigonometric functions of a complex number.
=== By recurrence ===
Functions whose domain are the nonnegative integers, known as sequences, are sometimes defined by recurrence relations.
The factorial function on the nonnegative integers (
n
↦
n
!
{\displaystyle n\mapsto n!}
) is a basic example, as it can be defined by the recurrence relation
n
!
=
n
(
n
−
1
)
!
for
n
>
0
,
{\displaystyle n!=n(n-1)!\quad {\text{for}}\quad n>0,}
and the initial condition
0
!
=
1.
{\displaystyle 0!=1.}
== Representing a function ==
A graph is commonly used to give an intuitive picture of a function. As an example of how a graph helps to understand a function, it is easy to see from its graph whether a function is increasing or decreasing. Some functions may also be represented by bar charts.
=== Graphs and plots ===
Given a function
f
:
X
→
Y
,
{\displaystyle f:X\to Y,}
its graph is, formally, the set
G
=
{
(
x
,
f
(
x
)
)
∣
x
∈
X
}
.
{\displaystyle G=\{(x,f(x))\mid x\in X\}.}
In the frequent case where X and Y are subsets of the real numbers (or may be identified with such subsets, e.g. intervals), an element
(
x
,
y
)
∈
G
{\displaystyle (x,y)\in G}
may be identified with a point having coordinates x, y in a 2-dimensional coordinate system, e.g. the Cartesian plane. Parts of this may create a plot that represents (parts of) the function. The use of plots is so ubiquitous that they too are called the graph of the function. Graphic representations of functions are also possible in other coordinate systems. For example, the graph of the square function
x
↦
x
2
,
{\displaystyle x\mapsto x^{2},}
consisting of all points with coordinates
(
x
,
x
2
)
{\displaystyle (x,x^{2})}
for
x
∈
R
,
{\displaystyle x\in \mathbb {R} ,}
yields, when depicted in Cartesian coordinates, the well known parabola. If the same quadratic function
x
↦
x
2
,
{\displaystyle x\mapsto x^{2},}
with the same formal graph, consisting of pairs of numbers, is plotted instead in polar coordinates
(
r
,
θ
)
=
(
x
,
x
2
)
,
{\displaystyle (r,\theta )=(x,x^{2}),}
the plot obtained is Fermat's spiral.
=== Tables ===
A function can be represented as a table of values. If the domain of a function is finite, then the function can be completely specified in this way. For example, the multiplication function
f
:
{
1
,
…
,
5
}
2
→
R
{\displaystyle f:\{1,\ldots ,5\}^{2}\to \mathbb {R} }
defined as
f
(
x
,
y
)
=
x
y
{\displaystyle f(x,y)=xy}
can be represented by the familiar multiplication table
On the other hand, if a function's domain is continuous, a table can give the values of the function at specific values of the domain. If an intermediate value is needed, interpolation can be used to estimate the value of the function. For example, a portion of a table for the sine function might be given as follows, with values rounded to 6 decimal places:
Before the advent of handheld calculators and personal computers, such tables were often compiled and published for functions such as logarithms and trigonometric functions.
=== Bar chart ===
A bar chart can represent a function whose domain is a finite set, the natural numbers, or the integers. In this case, an element x of the domain is represented by an interval of the x-axis, and the corresponding value of the function, f(x), is represented by a rectangle whose base is the interval corresponding to x and whose height is f(x) (possibly negative, in which case the bar extends below the x-axis).
== General properties ==
This section describes general properties of functions, that are independent of specific properties of the domain and the codomain.
=== Standard functions ===
There are a number of standard functions that occur frequently:
For every set X, there is a unique function, called the empty function, or empty map, from the empty set to X. The graph of an empty function is the empty set. The existence of empty functions is needed both for the coherency of the theory and for avoiding exceptions concerning the empty set in many statements. Under the usual set-theoretic definition of a function as an ordered triplet (or equivalent ones), there is exactly one empty function for each set, thus the empty function
∅
→
X
{\displaystyle \varnothing \to X}
is not equal to
∅
→
Y
{\displaystyle \varnothing \to Y}
if and only if
X
≠
Y
{\displaystyle X\neq Y}
, although their graphs are both the empty set.
For every set X and every singleton set {s}, there is a unique function from X to {s}, which maps every element of X to s. This is a surjection (see below) unless X is the empty set.
Given a function
f
:
X
→
Y
,
{\displaystyle f:X\to Y,}
the canonical surjection of f onto its image
f
(
X
)
=
{
f
(
x
)
∣
x
∈
X
}
{\displaystyle f(X)=\{f(x)\mid x\in X\}}
is the function from X to f(X) that maps x to f(x).
For every subset A of a set X, the inclusion map of A into X is the injective (see below) function that maps every element of A to itself.
The identity function on a set X, often denoted by idX, is the inclusion of X into itself.
=== Function composition ===
Given two functions
f
:
X
→
Y
{\displaystyle f:X\to Y}
and
g
:
Y
→
Z
{\displaystyle g:Y\to Z}
such that the domain of g is the codomain of f, their composition is the function
g
∘
f
:
X
→
Z
{\displaystyle g\circ f:X\rightarrow Z}
defined by
(
g
∘
f
)
(
x
)
=
g
(
f
(
x
)
)
.
{\displaystyle (g\circ f)(x)=g(f(x)).}
That is, the value of
g
∘
f
{\displaystyle g\circ f}
is obtained by first applying f to x to obtain y = f(x) and then applying g to the result y to obtain g(y) = g(f(x)). In this notation, the function that is applied first is always written on the right.
The composition
g
∘
f
{\displaystyle g\circ f}
is an operation on functions that is defined only if the codomain of the first function is the domain of the second one. Even when both
g
∘
f
{\displaystyle g\circ f}
and
f
∘
g
{\displaystyle f\circ g}
satisfy these conditions, the composition is not necessarily commutative, that is, the functions
g
∘
f
{\displaystyle g\circ f}
and
f
∘
g
{\displaystyle f\circ g}
need not be equal, but may deliver different values for the same argument. For example, let f(x) = x2 and g(x) = x + 1, then
g
(
f
(
x
)
)
=
x
2
+
1
{\displaystyle g(f(x))=x^{2}+1}
and
f
(
g
(
x
)
)
=
(
x
+
1
)
2
{\displaystyle f(g(x))=(x+1)^{2}}
agree just for
x
=
0.
{\displaystyle x=0.}
The function composition is associative in the sense that, if one of
(
h
∘
g
)
∘
f
{\displaystyle (h\circ g)\circ f}
and
h
∘
(
g
∘
f
)
{\displaystyle h\circ (g\circ f)}
is defined, then the other is also defined, and they are equal, that is,
(
h
∘
g
)
∘
f
=
h
∘
(
g
∘
f
)
.
{\displaystyle (h\circ g)\circ f=h\circ (g\circ f).}
Therefore, it is usual to just write
h
∘
g
∘
f
.
{\displaystyle h\circ g\circ f.}
The identity functions
id
X
{\displaystyle \operatorname {id} _{X}}
and
id
Y
{\displaystyle \operatorname {id} _{Y}}
are respectively a right identity and a left identity for functions from X to Y. That is, if f is a function with domain X, and codomain Y, one has
f
∘
id
X
=
id
Y
∘
f
=
f
.
{\displaystyle f\circ \operatorname {id} _{X}=\operatorname {id} _{Y}\circ f=f.}
=== Image and preimage ===
Let
f
:
X
→
Y
.
{\displaystyle f:X\to Y.}
The image under f of an element x of the domain X is f(x). If A is any subset of X, then the image of A under f, denoted f(A), is the subset of the codomain Y consisting of all images of elements of A, that is,
f
(
A
)
=
{
f
(
x
)
∣
x
∈
A
}
.
{\displaystyle f(A)=\{f(x)\mid x\in A\}.}
The image of f is the image of the whole domain, that is, f(X). It is also called the range of f, although the term range may also refer to the codomain.
On the other hand, the inverse image or preimage under f of an element y of the codomain Y is the set of all elements of the domain X whose images under f equal y. In symbols, the preimage of y is denoted by
f
−
1
(
y
)
{\displaystyle f^{-1}(y)}
and is given by the equation
f
−
1
(
y
)
=
{
x
∈
X
∣
f
(
x
)
=
y
}
.
{\displaystyle f^{-1}(y)=\{x\in X\mid f(x)=y\}.}
Likewise, the preimage of a subset B of the codomain Y is the set of the preimages of the elements of B, that is, it is the subset of the domain X consisting of all elements of X whose images belong to B. It is denoted by
f
−
1
(
B
)
{\displaystyle f^{-1}(B)}
and is given by the equation
f
−
1
(
B
)
=
{
x
∈
X
∣
f
(
x
)
∈
B
}
.
{\displaystyle f^{-1}(B)=\{x\in X\mid f(x)\in B\}.}
For example, the preimage of
{
4
,
9
}
{\displaystyle \{4,9\}}
under the square function is the set
{
−
3
,
−
2
,
2
,
3
}
{\displaystyle \{-3,-2,2,3\}}
.
By definition of a function, the image of an element x of the domain is always a single element of the codomain. However, the preimage
f
−
1
(
y
)
{\displaystyle f^{-1}(y)}
of an element y of the codomain may be empty or contain any number of elements. For example, if f is the function from the integers to themselves that maps every integer to 0, then
f
−
1
(
0
)
=
Z
{\displaystyle f^{-1}(0)=\mathbb {Z} }
.
If
f
:
X
→
Y
{\displaystyle f:X\to Y}
is a function, A and B are subsets of X, and C and D are subsets of Y, then one has the following properties:
A
⊆
B
⟹
f
(
A
)
⊆
f
(
B
)
{\displaystyle A\subseteq B\Longrightarrow f(A)\subseteq f(B)}
C
⊆
D
⟹
f
−
1
(
C
)
⊆
f
−
1
(
D
)
{\displaystyle C\subseteq D\Longrightarrow f^{-1}(C)\subseteq f^{-1}(D)}
A
⊆
f
−
1
(
f
(
A
)
)
{\displaystyle A\subseteq f^{-1}(f(A))}
C
⊇
f
(
f
−
1
(
C
)
)
{\displaystyle C\supseteq f(f^{-1}(C))}
f
(
f
−
1
(
f
(
A
)
)
)
=
f
(
A
)
{\displaystyle f(f^{-1}(f(A)))=f(A)}
f
−
1
(
f
(
f
−
1
(
C
)
)
)
=
f
−
1
(
C
)
{\displaystyle f^{-1}(f(f^{-1}(C)))=f^{-1}(C)}
The preimage by f of an element y of the codomain is sometimes called, in some contexts, the fiber of y under f.
If a function f has an inverse (see below), this inverse is denoted
f
−
1
.
{\displaystyle f^{-1}.}
In this case
f
−
1
(
C
)
{\displaystyle f^{-1}(C)}
may denote either the image by
f
−
1
{\displaystyle f^{-1}}
or the preimage by f of C. This is not a problem, as these sets are equal. The notation
f
(
A
)
{\displaystyle f(A)}
and
f
−
1
(
C
)
{\displaystyle f^{-1}(C)}
may be ambiguous in the case of sets that contain some subsets as elements, such as
{
x
,
{
x
}
}
.
{\displaystyle \{x,\{x\}\}.}
In this case, some care may be needed, for example, by using square brackets
f
[
A
]
,
f
−
1
[
C
]
{\displaystyle f[A],f^{-1}[C]}
for images and preimages of subsets and ordinary parentheses for images and preimages of elements.
=== Injective, surjective and bijective functions ===
Let
f
:
X
→
Y
{\displaystyle f:X\to Y}
be a function.
The function f is injective (or one-to-one, or is an injection) if f(a) ≠ f(b) for every two different elements a and b of X. Equivalently, f is injective if and only if, for every
y
∈
Y
,
{\displaystyle y\in Y,}
the preimage
f
−
1
(
y
)
{\displaystyle f^{-1}(y)}
contains at most one element. An empty function is always injective. If X is not the empty set, then f is injective if and only if there exists a function
g
:
Y
→
X
{\displaystyle g:Y\to X}
such that
g
∘
f
=
id
X
,
{\displaystyle g\circ f=\operatorname {id} _{X},}
that is, if f has a left inverse. Proof: If f is injective, for defining g, one chooses an element
x
0
{\displaystyle x_{0}}
in X (which exists as X is supposed to be nonempty), and one defines g by
g
(
y
)
=
x
{\displaystyle g(y)=x}
if
y
=
f
(
x
)
{\displaystyle y=f(x)}
and
g
(
y
)
=
x
0
{\displaystyle g(y)=x_{0}}
if
y
∉
f
(
X
)
.
{\displaystyle y\not \in f(X).}
Conversely, if
g
∘
f
=
id
X
,
{\displaystyle g\circ f=\operatorname {id} _{X},}
and
y
=
f
(
x
)
,
{\displaystyle y=f(x),}
then
x
=
g
(
y
)
,
{\displaystyle x=g(y),}
and thus
f
−
1
(
y
)
=
{
x
}
.
{\displaystyle f^{-1}(y)=\{x\}.}
The function f is surjective (or onto, or is a surjection) if its range
f
(
X
)
{\displaystyle f(X)}
equals its codomain
Y
{\displaystyle Y}
, that is, if, for each element
y
{\displaystyle y}
of the codomain, there exists some element
x
{\displaystyle x}
of the domain such that
f
(
x
)
=
y
{\displaystyle f(x)=y}
(in other words, the preimage
f
−
1
(
y
)
{\displaystyle f^{-1}(y)}
of every
y
∈
Y
{\displaystyle y\in Y}
is nonempty). If, as usual in modern mathematics, the axiom of choice is assumed, then f is surjective if and only if there exists a function
g
:
Y
→
X
{\displaystyle g:Y\to X}
such that
f
∘
g
=
id
Y
,
{\displaystyle f\circ g=\operatorname {id} _{Y},}
that is, if f has a right inverse. The axiom of choice is needed, because, if f is surjective, one defines g by
g
(
y
)
=
x
,
{\displaystyle g(y)=x,}
where
x
{\displaystyle x}
is an arbitrarily chosen element of
f
−
1
(
y
)
.
{\displaystyle f^{-1}(y).}
The function f is bijective (or is a bijection or a one-to-one correspondence) if it is both injective and surjective. That is, f is bijective if, for every
y
∈
Y
,
{\displaystyle y\in Y,}
the preimage
f
−
1
(
y
)
{\displaystyle f^{-1}(y)}
contains exactly one element. The function f is bijective if and only if it admits an inverse function, that is, a function
g
:
Y
→
X
{\displaystyle g:Y\to X}
such that
g
∘
f
=
id
X
{\displaystyle g\circ f=\operatorname {id} _{X}}
and
f
∘
g
=
id
Y
.
{\displaystyle f\circ g=\operatorname {id} _{Y}.}
(Contrarily to the case of surjections, this does not require the axiom of choice; the proof is straightforward).
Every function
f
:
X
→
Y
{\displaystyle f:X\to Y}
may be factorized as the composition
i
∘
s
{\displaystyle i\circ s}
of a surjection followed by an injection, where s is the canonical surjection of X onto f(X) and i is the canonical injection of f(X) into Y. This is the canonical factorization of f.
"One-to-one" and "onto" are terms that were more common in the older English language literature; "injective", "surjective", and "bijective" were originally coined as French words in the second quarter of the 20th century by the Bourbaki group and imported into English. As a word of caution, "a one-to-one function" is one that is injective, while a "one-to-one correspondence" refers to a bijective function. Also, the statement "f maps X onto Y" differs from "f maps X into B", in that the former implies that f is surjective, while the latter makes no assertion about the nature of f. In a complicated reasoning, the one letter difference can easily be missed. Due to the confusing nature of this older terminology, these terms have declined in popularity relative to the Bourbakian terms, which have also the advantage of being more symmetrical.
=== Restriction and extension ===
If
f
:
X
→
Y
{\displaystyle f:X\to Y}
is a function and S is a subset of X, then the restriction of
f
{\displaystyle f}
to S, denoted
f
|
S
{\displaystyle f|_{S}}
, is the function from S to Y defined by
f
|
S
(
x
)
=
f
(
x
)
{\displaystyle f|_{S}(x)=f(x)}
for all x in S. Restrictions can be used to define partial inverse functions: if there is a subset S of the domain of a function
f
{\displaystyle f}
such that
f
|
S
{\displaystyle f|_{S}}
is injective, then the canonical surjection of
f
|
S
{\displaystyle f|_{S}}
onto its image
f
|
S
(
S
)
=
f
(
S
)
{\displaystyle f|_{S}(S)=f(S)}
is a bijection, and thus has an inverse function from
f
(
S
)
{\displaystyle f(S)}
to S. One application is the definition of inverse trigonometric functions. For example, the cosine function is injective when restricted to the interval [0, π]. The image of this restriction is the interval [−1, 1], and thus the restriction has an inverse function from [−1, 1] to [0, π], which is called arccosine and is denoted arccos.
Function restriction may also be used for "gluing" functions together. Let
X
=
⋃
i
∈
I
U
i
{\textstyle X=\bigcup _{i\in I}U_{i}}
be the decomposition of X as a union of subsets, and suppose that a function
f
i
:
U
i
→
Y
{\displaystyle f_{i}:U_{i}\to Y}
is defined on each
U
i
{\displaystyle U_{i}}
such that for each pair
i
,
j
{\displaystyle i,j}
of indices, the restrictions of
f
i
{\displaystyle f_{i}}
and
f
j
{\displaystyle f_{j}}
to
U
i
∩
U
j
{\displaystyle U_{i}\cap U_{j}}
are equal. Then this defines a unique function
f
:
X
→
Y
{\displaystyle f:X\to Y}
such that
f
|
U
i
=
f
i
{\displaystyle f|_{U_{i}}=f_{i}}
for all i. This is the way that functions on manifolds are defined.
An extension of a function f is a function g such that f is a restriction of g. A typical use of this concept is the process of analytic continuation, that allows extending functions whose domain is a small part of the complex plane to functions whose domain is almost the whole complex plane.
Here is another classical example of a function extension that is encountered when studying homographies of the real line. A homography is a function
h
(
x
)
=
a
x
+
b
c
x
+
d
{\displaystyle h(x)={\frac {ax+b}{cx+d}}}
such that ad − bc ≠ 0. Its domain is the set of all real numbers different from
−
d
/
c
,
{\displaystyle -d/c,}
and its image is the set of all real numbers different from
a
/
c
.
{\displaystyle a/c.}
If one extends the real line to the projectively extended real line by including ∞, one may extend h to a bijection from the extended real line to itself by setting
h
(
∞
)
=
a
/
c
{\displaystyle h(\infty )=a/c}
and
h
(
−
d
/
c
)
=
∞
{\displaystyle h(-d/c)=\infty }
.
== In calculus ==
The idea of function, starting in the 17th century, was fundamental to the new infinitesimal calculus. At that time, only real-valued functions of a real variable were considered, and all functions were assumed to be smooth. But the definition was soon extended to functions of several variables and to functions of a complex variable. In the second half of the 19th century, the mathematically rigorous definition of a function was introduced, and functions with arbitrary domains and codomains were defined.
Functions are now used throughout all areas of mathematics. In introductory calculus, when the word function is used without qualification, it means a real-valued function of a single real variable. The more general definition of a function is usually introduced to second or third year college students with STEM majors, and in their senior year they are introduced to calculus in a larger, more rigorous setting in courses such as real analysis and complex analysis.
=== Real function ===
A real function is a real-valued function of a real variable, that is, a function whose codomain is the field of real numbers and whose domain is a set of real numbers that contains an interval. In this section, these functions are simply called functions.
The functions that are most commonly considered in mathematics and its applications have some regularity, that is they are continuous, differentiable, and even analytic. This regularity insures that these functions can be visualized by their graphs. In this section, all functions are differentiable in some interval.
Functions enjoy pointwise operations, that is, if f and g are functions, their sum, difference and product are functions defined by
(
f
+
g
)
(
x
)
=
f
(
x
)
+
g
(
x
)
(
f
−
g
)
(
x
)
=
f
(
x
)
−
g
(
x
)
(
f
⋅
g
)
(
x
)
=
f
(
x
)
⋅
g
(
x
)
.
{\displaystyle {\begin{aligned}(f+g)(x)&=f(x)+g(x)\\(f-g)(x)&=f(x)-g(x)\\(f\cdot g)(x)&=f(x)\cdot g(x)\\\end{aligned}}.}
The domains of the resulting functions are the intersection of the domains of f and g. The quotient of two functions is defined similarly by
f
g
(
x
)
=
f
(
x
)
g
(
x
)
,
{\displaystyle {\frac {f}{g}}(x)={\frac {f(x)}{g(x)}},}
but the domain of the resulting function is obtained by removing the zeros of g from the intersection of the domains of f and g.
The polynomial functions are defined by polynomials, and their domain is the whole set of real numbers. They include constant functions, linear functions and quadratic functions. Rational functions are quotients of two polynomial functions, and their domain is the real numbers with a finite number of them removed to avoid division by zero. The simplest rational function is the function
x
↦
1
x
,
{\displaystyle x\mapsto {\frac {1}{x}},}
whose graph is a hyperbola, and whose domain is the whole real line except for 0.
The derivative of a real differentiable function is a real function. An antiderivative of a continuous real function is a real function that has the original function as a derivative. For example, the function
x
↦
1
x
{\textstyle x\mapsto {\frac {1}{x}}}
is continuous, and even differentiable, on the positive real numbers. Thus one antiderivative, which takes the value zero for x = 1, is a differentiable function called the natural logarithm.
A real function f is monotonic in an interval if the sign of
f
(
x
)
−
f
(
y
)
x
−
y
{\displaystyle {\frac {f(x)-f(y)}{x-y}}}
does not depend of the choice of x and y in the interval. If the function is differentiable in the interval, it is monotonic if the sign of the derivative is constant in the interval. If a real function f is monotonic in an interval I, it has an inverse function, which is a real function with domain f(I) and image I. This is how inverse trigonometric functions are defined in terms of trigonometric functions, where the trigonometric functions are monotonic. Another example: the natural logarithm is monotonic on the positive real numbers, and its image is the whole real line; therefore it has an inverse function that is a bijection between the real numbers and the positive real numbers. This inverse is the exponential function.
Many other real functions are defined either by the implicit function theorem (the inverse function is a particular instance) or as solutions of differential equations. For example, the sine and the cosine functions are the solutions of the linear differential equation
y
″
+
y
=
0
{\displaystyle y''+y=0}
such that
sin
0
=
0
,
cos
0
=
1
,
∂
sin
x
∂
x
(
0
)
=
1
,
∂
cos
x
∂
x
(
0
)
=
0.
{\displaystyle \sin 0=0,\quad \cos 0=1,\quad {\frac {\partial \sin x}{\partial x}}(0)=1,\quad {\frac {\partial \cos x}{\partial x}}(0)=0.}
=== Vector-valued function ===
When the elements of the codomain of a function are vectors, the function is said to be a vector-valued function. These functions are particularly useful in applications, for example modeling physical properties. For example, the function that associates to each point of a fluid its velocity vector is a vector-valued function.
Some vector-valued functions are defined on a subset of
R
n
{\displaystyle \mathbb {R} ^{n}}
or other spaces that share geometric or topological properties of
R
n
{\displaystyle \mathbb {R} ^{n}}
, such as manifolds. These vector-valued functions are given the name vector fields.
== Function space ==
In mathematical analysis, and more specifically in functional analysis, a function space is a set of scalar-valued or vector-valued functions, which share a specific property and form a topological vector space. For example, the real smooth functions with a compact support (that is, they are zero outside some compact set) form a function space that is at the basis of the theory of distributions.
Function spaces play a fundamental role in advanced mathematical analysis, by allowing the use of their algebraic and topological properties for studying properties of functions. For example, all theorems of existence and uniqueness of solutions of ordinary or partial differential equations result of the study of function spaces.
== Multi-valued functions ==
Several methods for specifying functions of real or complex variables start from a local definition of the function at a point or on a neighbourhood of a point, and then extend by continuity the function to a much larger domain. Frequently, for a starting point
x
0
,
{\displaystyle x_{0},}
there are several possible starting values for the function.
For example, in defining the square root as the inverse function of the square function, for any positive real number
x
0
,
{\displaystyle x_{0},}
there are two choices for the value of the square root, one of which is positive and denoted
x
0
,
{\displaystyle {\sqrt {x_{0}}},}
and another which is negative and denoted
−
x
0
.
{\displaystyle -{\sqrt {x_{0}}}.}
These choices define two continuous functions, both having the nonnegative real numbers as a domain, and having either the nonnegative or the nonpositive real numbers as images. When looking at the graphs of these functions, one can see that, together, they form a single smooth curve. It is therefore often useful to consider these two square root functions as a single function that has two values for positive x, one value for 0 and no value for negative x.
In the preceding example, one choice, the positive square root, is more natural than the other. This is not the case in general. For example, let consider the implicit function that maps y to a root x of
x
3
−
3
x
−
y
=
0
{\displaystyle x^{3}-3x-y=0}
(see the figure on the right). For y = 0 one may choose either
0
,
3
,
or
−
3
{\displaystyle 0,{\sqrt {3}},{\text{ or }}-{\sqrt {3}}}
for x. By the implicit function theorem, each choice defines a function; for the first one, the (maximal) domain is the interval [−2, 2] and the image is [−1, 1]; for the second one, the domain is [−2, ∞) and the image is [1, ∞); for the last one, the domain is (−∞, 2] and the image is (−∞, −1]. As the three graphs together form a smooth curve, and there is no reason for preferring one choice, these three functions are often considered as a single multi-valued function of y that has three values for −2 < y < 2, and only one value for y ≤ −2 and y ≥ −2.
Usefulness of the concept of multi-valued functions is clearer when considering complex functions, typically analytic functions. The domain to which a complex function may be extended by analytic continuation generally consists of almost the whole complex plane. However, when extending the domain through two different paths, one often gets different values. For example, when extending the domain of the square root function, along a path of complex numbers with positive imaginary parts, one gets i for the square root of −1; while, when extending through complex numbers with negative imaginary parts, one gets −i. There are generally two ways of solving the problem. One may define a function that is not continuous along some curve, called a branch cut. Such a function is called the principal value of the function. The other way is to consider that one has a multi-valued function, which is analytic everywhere except for isolated singularities, but whose value may "jump" if one follows a closed loop around a singularity. This jump is called the monodromy.
== In the foundations of mathematics ==
The definition of a function that is given in this article requires the concept of set, since the domain and the codomain of a function must be a set. This is not a problem in usual mathematics, as it is generally not difficult to consider only functions whose domain and codomain are sets, which are well defined, even if the domain is not explicitly defined. However, it is sometimes useful to consider more general functions.
For example, the singleton set may be considered as a function
x
↦
{
x
}
.
{\displaystyle x\mapsto \{x\}.}
Its domain would include all sets, and therefore would not be a set. In usual mathematics, one avoids this kind of problem by specifying a domain, which means that one has many singleton functions. However, when establishing foundations of mathematics, one may have to use functions whose domain, codomain or both are not specified, and some authors, often logicians, give precise definitions for these weakly specified functions.
These generalized functions may be critical in the development of a formalization of the foundations of mathematics. For example, Von Neumann–Bernays–Gödel set theory, is an extension of the set theory in which the collection of all sets is a class. This theory includes the replacement axiom, which may be stated as: If X is a set and F is a function, then F[X] is a set.
In alternative formulations of the foundations of mathematics using type theory rather than set theory, functions are taken as primitive notions rather than defined from other kinds of object. They are the inhabitants of function types, and may be constructed using expressions in the lambda calculus.
== In computer science ==
In computer programming, a function is, in general, a subroutine which implements the abstract concept of function. That is, it is a program unit that produces an output for each input. Functional programming is the programming paradigm consisting of building programs by using only subroutines that behave like mathematical functions, meaning that they have no side effects and depend only on their arguments: they are referentially transparent. For example, if_then_else is a function that takes three (nullary) functions as arguments, and, depending on the value of the first argument (true or false), returns the value of either the second or the third argument. An important advantage of functional programming is that it makes easier program proofs, as being based on a well founded theory, the lambda calculus (see below). However, side effects are generally necessary for practical programs, ones that perform input/output. There is a class of purely functional languages, such as Haskell, which encapsulate the possibility of side effects in the type of a function. Others, such as the ML family, simply allow side effects.
In many programming languages, every subroutine is called a function, even when there is no output but only side effects, and when the functionality consists simply of modifying some data in the computer memory.
Outside the context of programming languages, "function" has the usual mathematical meaning in computer science. In this area, a property of major interest is the computability of a function. For giving a precise meaning to this concept, and to the related concept of algorithm, several models of computation have been introduced, the old ones being general recursive functions, lambda calculus, and Turing machine. The fundamental theorem of computability theory is that these three models of computation define the same set of computable functions, and that all the other models of computation that have ever been proposed define the same set of computable functions or a smaller one. The Church–Turing thesis is the claim that every philosophically acceptable definition of a computable function defines also the same functions.
General recursive functions are partial functions from integers to integers that can be defined from
constant functions,
successor, and
projection functions
via the operators
composition,
primitive recursion, and
minimization.
Although defined only for functions from integers to integers, they can model any computable function as a consequence of the following properties:
a computation is the manipulation of finite sequences of symbols (digits of numbers, formulas, etc.),
every sequence of symbols may be coded as a sequence of bits,
a bit sequence can be interpreted as the binary representation of an integer.
Lambda calculus is a theory that defines computable functions without using set theory, and is the theoretical background of functional programming. It consists of terms that are either variables, function definitions (𝜆-terms), or applications of functions to terms. Terms are manipulated by interpreting its axioms (the α-equivalence, the β-reduction, and the η-conversion) as rewriting rules, which can be used for computation.
In its original form, lambda calculus does not include the concepts of domain and codomain of a function. Roughly speaking, they have been introduced in the theory under the name of type in typed lambda calculus. Most kinds of typed lambda calculi can define fewer functions than untyped lambda calculus.
== See also ==
=== Subpages ===
=== Generalizations ===
=== Related topics ===
== Notes ==
== References ==
== Sources ==
== Further reading ==
== External links ==
The Wolfram Functions – website giving formulae and visualizations of many mathematical functions
NIST Digital Library of Mathematical Functions | Wikipedia/Mathematical_functions |
A cultured neuronal network is a cell culture of neurons that is used as a model to study the central nervous system, especially the brain. Often, cultured neuronal networks are connected to an input/output device such as a multi-electrode array (MEA), thus allowing two-way communication between the researcher and the network. This model has proved to be an invaluable tool to scientists studying the underlying principles behind neuronal learning, memory, plasticity, connectivity, and information processing.
Cultured neurons are often connected via computer to a real or simulated robotic component, creating a hybrot or animat, respectively. Researchers can then thoroughly study learning and plasticity in a realistic context, where the neuronal networks are able to interact with their environment and receive at least some artificial sensory feedback. One example of this can be seen in the Multielectrode Array Art (MEART) system developed by the Potter Research Group at the Georgia Institute of Technology in collaboration with SymbioticA, The Centre for Excellence in Biological Art, at the University of Western Australia. Another example can be seen in the neurally controlled animat.
== Use as a model ==
=== Advantages ===
The use of cultured neuronal networks as a model for their in vivo counterparts has been an indispensable resource for decades. It allows researchers to investigate neuronal activity in a much more controlled environment than would be possible in a live organism. Through this mechanism researchers have gleaned important information about the mechanisms behind learning and memory.
A cultured neuronal network allows researchers to observe neuronal activity from several vantage points. Electrophysiological recording and stimulation can take place either across the network or locally via an MEA, and the network development can be visually observed using microscopy techniques. Moreover, chemical analysis of the neurons and their environment is more easily accomplished than in an in vivo setting.
=== Disadvantages ===
Cultured neuronal networks are by definition disembodied cultures of neurons. Thus by being outside their natural environment, the neurons are influenced in ways that are not biologically normal. Foremost among these abnormalities is the fact that the neurons are usually harvested as neural stem cells from a fetus and are therefore disrupted at a critical stage in network development. When the neurons are suspended in solution and subsequently dispensed, the connections previously made are destroyed and new ones formed. Ultimately, the connectivity (and consequently the functionality) of the tissue is changed from what the original template suggested.
Another disadvantage lies in the fact that the cultured neurons lack a body and are thus severed from sensory input as well as the ability to express behavior – a crucial characteristic in learning and memory experiments. It is believed that such sensory deprivation has adverse effects on the development of these cultures and may result in abnormal patterns of behavior throughout the network.
Cultured networks on traditional MEAs are flat, single-layer sheets of cells with connectivity only two dimensions. Most in vivo neuronal systems, to the contrary, are large three-dimensional structures with much greater interconnectivity. This remains one of the most striking differences between the model and the reality, and this fact probably plays a large role in skewing some of the conclusions derived from experiments based on this model.
== Growing a neuronal network ==
=== Neurons used ===
Because of their wide availability, neuronal networks are typically cultured from dissociated rat neurons. Studies commonly employ rat cortical, hippocampal, and spinal neurons, although lab mouse neurons have also been used. Currently, relatively little research has been conducted on growing primate or other animal neuronal networks. Harvesting neural stem cells requires sacrificing the developing fetus, a process considered too costly to perform on many mammals that are valuable in other studies.
One study, however, did make use of human neural stem cells grown into a network to control a robotic actuator. These cells were acquired from a fetus that spontaneously aborted after ten weeks in gestation.
=== Long-term culture ===
One of the most formidable problems associated with cultured neuronal networks is their lack of longevity. Like most cell cultures, neuron cultures are highly susceptible to infection. They are also susceptible to hyperosmolality from medium evaporation. The long timelines associated with studying neuronal plasticity (usually on the scale of months) makes extending the lifespan of neurons in vitro paramount.
One solution to this problem involves growing cells on an MEA inside a sealed chamber. This chamber serves as a non-humidified incubator that is enclosed by a fluorinated ethylene propylene (FEP) membrane that is permeable to select gases (i.e. gases necessary for metabolism) but impermeable to water and microbes. Other solutions entail an incubator with an impermeable membrane that has a specific mix of gases (air with 5% CO2 is typical) sealed inside.
=== Microelectrode arrays (MEAs) ===
A microelectrode array (MEA), also commonly called a multielectrode array, is a patterned array of electrodes laid out in a transparent substrate used for communication with neurons in contact with it. The communication can be, and usually is, bidirectional; researchers can both record electrophysiological data from a live network and stimulate it.
This device has been an essential biosensor for more than thirty years. It has been used not only in the study of neuronal plasticity and information processing but also in drug and toxin effects on neurons. Additionally, when coupled with a sealed incubation chamber this device greatly reduces the risk of culture contamination by nearly eliminating the need to expose it to air.
Currently, commonly used MEAs have relatively poor spatial resolution. They employ approximately sixty electrodes for recording and stimulation in varying patterns in a dish with a typical culture of 50,000 cells or more (or a density of 5,000 cells/mm2). It follows that each electrode in the array services a large cluster of neurons and cannot provide resolute information regarding signal origin and destination; such MEAs are only capable of region-specific data acquisition and stimulation.
Ideally it would be possible to record and stimulate from a single or a few neurons at a time. Indeed, companies such as Axion Biosystems are working to provide MEAs with much higher spatial resolution to this end (a maximum of 768 input/output electrodes). Another study investigates establishing a stable one-to-one connection between neurons and electrodes. The goal was to meet the ideal interface situation by establishing a correspondence with every neuron in the network. They do so by caging individual neurons while still allowing the axons and dendrites to extend and make connections. Neurons are contained within neurocages or other sorts of containers, and the device itself could be referred to as the caged neuron MEA or neurochip.
Other research suggests alternative techniques to stimulating neurons in vitro. One study investigates the use of a laser beam to free caged compounds such as neurotransmitters and neuromodulators. A laser beam with wavelength in the UV spectrum would have extremely high spatial accuracy and, by releasing the caged compounds, could be used to influence a very select set of neurons.
== Network behavior ==
=== Spontaneous network activity ===
Spontaneous network bursts are a commonplace feature of neuronal networks both in vitro and in vivo. In vitro, this activity is particularly important in studies on learning and plasticity. Such experiments look intensely at the network-wide activity both before and after experiments in order to discern any changes that might implicate plasticity or even learning. However, confounding this experimental technique is the fact that normal neuronal development induces change in array-wide bursts that could easily skew data. In vivo, however, it has been suggested that these network bursts may form the basis for memories.
Depending on experimental perspective, network-wide bursts can be viewed either positively or negatively. In a pathological sense, spontaneous network activity can be attributed to the disembodiment of the neurons; one study saw a marked difference between array-wide firing frequency in cultures that received continuous input versus those that did not. To eliminate aberrant activity, researchers commonly use magnesium or synaptic blockers to quiet the network. However, this approach has great costs; quieted networks have little capacity for plasticity due to a diminished ability to create action potentials. A different and perhaps more effective approach is the use of low frequency stimulation that emulates sensory background activity.
In a different light, network bursts can be thought of as benign and even good. Any given network demonstrates non-random, structured bursts. Some studies have suggested that these bursts represent information carriers, expression of memory, a means for the network to form appropriate connections, and learning when their pattern changes.
==== Array-wide burst stability ====
Stegenga et al. set out to establish the stability of spontaneous network bursts as a function of time. They saw bursts throughout the lifetime of the cell cultures, beginning at 4–7 days in vitro (DIV) and continuing until culture death. They gathered network burst profiles (BPs) through a mathematical observation of array-wide spiking rate (AWSR), which is the summation of action potentials over all electrodes in an MEA. This analysis yielded the conclusion that, in their culture of Wistar rat neocortical cells, the AWSR has long rise and fall times during early development and sharper, more intense profiles after approximately 25 DIV. However, the use of BPs has an inherent shortcoming; BPs are an average of all network activity over time, and therefore only contain temporal information. In order to attain data about the spatial pattern of network activity they developed what they call phase profiles (PPs), which contain electrode specific data.
Data was gathered using these PPs on timescales of milliseconds up through days. Their goal was to establish the stability of network burst profiles on the timescale of minutes to hours and to establish stability or developmental changes over the course of days. In summary, they were successful in demonstrating stability over minutes to hours, but the PPs gathered over the course of days displayed significant variability. These finding imply that studies of plasticity of neurons can only be conducted over the course of minutes or hours without bias in network activity introduced by normal development.
=== Learning vs. plasticity ===
There is much controversy in the field of neuroscience surrounding whether or not a cultured neuronal network can learn. A crucial step in finding the answer to this problem lies in establishing the difference between learning and plasticity. One definition suggests that learning is "the acquisition of novel behavior through experience". Corollary to this argument is the necessity for interaction with the environment around it, something that cultured neurons are virtually incapable of without sensory systems. Plasticity, on the other hand, is simply the reshaping of an existing network by changing connections between neurons: formation and elimination of synapses or extension and retraction of neurites and dendritic spines. But these two definitions are not mutually exclusive; in order for learning to take place, plasticity must also take place.
In order to establish learning in a cultured network, researchers have attempted to re-embody the dissociated neuronal networks in either simulated or real environments (see MEART and animat). Through this method the networks are able to interact with their environment and, therefore, have the opportunity to learn in a more realistic setting. Other studies have attempted to imprint signal patterns onto the networks via artificial stimulation. This can be done by inducing network bursts or by inputting specific patterns to the neurons, from which the network is expected to derive some meaning (as in experiments with animats, where an arbitrary signal to the network indicates that the simulated animal has run into a wall or is moving in a direction, etc.). The latter technique attempts to take advantage of the inherent ability of neuronal networks to make sense of patterns. However, experiments have had limited success in demonstrating a definition of learning that is widely agreed upon. Nevertheless, plasticity in neuronal networks is a phenomenon that is well-established in the neuroscience community, and one that is thought to play a very large role in learning.
== See also ==
== References == | Wikipedia/Cultured_neuronal_networks |
A cognitive model is a representation of one or more cognitive processes in humans or other animals for the purposes of comprehension and prediction. There are many types of cognitive models, and they can range from box-and-arrow diagrams to a set of equations to software programs that interact with the same tools that humans use to complete tasks (e.g., computer mouse and keyboard). In terms of information processing, cognitive modeling is modeling of human perception, reasoning, memory and action.
== Relationship to cognitive architectures ==
Cognitive models can be developed within or without a cognitive architecture, though the two are not always easily distinguishable. In contrast to cognitive architectures, cognitive models tend to be focused on a single cognitive phenomenon or process (e.g., list learning), how two or more processes interact (e.g., visual search and decision making), or making behavioral predictions for a specific task or tool (e.g., how instituting a new software package will affect productivity). Cognitive architectures tend to be focused on the structural properties of the modeled system, and help constrain the development of cognitive models within the architecture. Likewise, model development helps to inform limitations and shortcomings of the architecture. Some of the most popular architectures for cognitive modeling include ACT-R, Clarion, LIDA, and Soar.
== History ==
Cognitive modeling historically developed within cognitive psychology/cognitive science (including human factors), and has received contributions from the fields of machine learning and artificial intelligence among others.
== Box-and-arrow models ==
A number of key terms are used to describe the processes involved in the perception, storage, and production of speech. Typically, they are used by speech pathologists while treating a child patient. The input signal is the speech signal heard by the child, usually assumed to come from an adult speaker. The output signal is the utterance produced by the child. The unseen psychological events that occur between the arrival of an input signal and the production of speech are the focus of psycholinguistic models. Events that process the input signal are referred to as input processes, whereas events that process the production of speech are referred to as output processes. Some aspects of speech processing are thought to happen online—that is, they occur during the actual perception
or production of speech and thus require a share of the attentional resources dedicated to the speech task. Other processes, thought to happen offline, take place as part of the child's background mental processing rather than during the time dedicated to the speech task.
In this sense, online processing is sometimes defined as occurring in real-time, whereas offline processing is said to be time-free (Hewlett, 1990). In box-and-arrow psycholinguistic models, each hypothesized level of representation or processing can be represented in a diagram by a “box,” and the relationships between them by “arrows,” hence the name. Sometimes (as in the models of Smith, 1973, and Menn, 1978, described later in this paper) the arrows represent processes additional to those shown in boxes. Such models make explicit the hypothesized information-
processing activities carried out in a particular cognitive function (such as language), in a manner analogous to computer flowcharts that depict the processes and decisions carried out by a computer program. Box-and-arrow models differ widely in the number of unseen psychological processes they describe and thus in the number of boxes they contain. Some have only one or two boxes between the input and output signals (e.g., Menn, 1978; Smith, 1973), whereas others have multiple boxes representing complex relationships between a number of different information-processing events (e.g., Hewlett, 1990; Hewlett, Gibbon, & Cohen- McKenzie, 1998; Stackhouse & Wells, 1997). The most important box, however, and the source of much ongoing debate, is that representing the underlying representation (or UR). In essence, an underlying representation captures information stored in a child's mind about a word he or she knows and uses. As the following description of several models will illustrate, the nature of this information and thus the type(s) of representation present in the child's knowledge base have captured the attention of researchers for some time. (Elise Baker et al. Psycholinguistic Models of Speech Development and Their Application to Clinical Practice. Journal of Speech, Language, and Hearing Research. June 2001. 44. p 685–702.)
== Computational models ==
A computational model is a mathematical model in computational science that requires extensive computational resources to study the behavior of a complex system by computer simulation. Computational cognitive models examine cognition and cognitive functions by developing process-based computational models formulated as sets of mathematical equations or computer simulations. The system under study is often a complex nonlinear system for which simple, intuitive analytical solutions are not readily available. Rather than deriving a mathematical analytical solution to the problem, experimentation with the model is done by changing the parameters of the system in the computer, and studying the differences in the outcome of the experiments. Theories of operation of the model can be derived/deduced from these computational experiments.
Examples of common computational models are weather forecasting models, earth simulator models, flight simulator models, molecular protein folding models, and neural network models.
=== Symbolic ===
A symbolic model is expressed in characters, usually non-numeric ones, that require translation before they can be used.
=== Subsymbolic ===
A cognitive model is subsymbolic if it is made by constituent entities that are not representations in their turn, e.g., pixels, sound images as perceived by the ear, signal samples; subsymbolic units in neural networks can be considered particular cases of this category.
=== Hybrid ===
Hybrid computers are computers that exhibit features of analog computers and digital computers. The digital component normally serves as the controller and provides logical operations, while the analog component normally serves as a solver of differential equations. See more details at hybrid intelligent system.
== Dynamical systems ==
In the traditional computational approach, representations are viewed as static structures of discrete symbols. Cognition takes place by transforming static symbol structures in discrete, sequential steps. Sensory information is transformed into symbolic inputs, which produce symbolic outputs that get transformed into motor outputs. The entire system operates in an ongoing cycle.
What is missing from this traditional view is that human cognition happens continuously and in real time. Breaking down the processes into discrete time steps may not fully capture this behavior. An alternative approach is to define a system with (1) a state of the system at any given time, (2) a behavior, defined as the change over time in overall state, and (3) a state set or state space, representing the totality of overall states the system could be in. The system is distinguished by the fact that a change in any aspect of the system state depends on other aspects of the same or other system states.
A typical dynamical model is formalized by several differential equations that describe how the system's state changes over time. By doing so, the form of the space of possible trajectories and the internal and external forces that shape a specific trajectory that unfold over time, instead of the physical nature of the underlying mechanisms that manifest this dynamics, carry explanatory force. On this dynamical view, parametric inputs alter the system's intrinsic dynamics, rather than specifying an internal state that describes some external state of affairs.
=== Early dynamical systems ===
==== Associative memory ====
Early work in the application of dynamical systems to cognition can be found in the model of Hopfield networks. These networks were proposed as a model for associative memory. They represent the neural level of memory, modeling systems of around 30 neurons which can be in either an on or off state. By letting the network learn on its own, structure and computational properties naturally arise. Unlike previous models, “memories” can be formed and recalled by inputting a small portion of the entire memory. Time ordering of memories can also be encoded. The behavior of the system is modeled with vectors which can change values, representing different states of the system. This early model was a major step toward a dynamical systems view of human cognition, though many details had yet to be added and more phenomena accounted for.
==== Language acquisition ====
By taking into account the evolutionary development of the human nervous system and the similarity of the brain to other organs, Elman proposed that language and cognition should be treated as a dynamical system rather than a digital symbol processor. Neural networks of the type Elman implemented have come to be known as Elman networks. Instead of treating language as a collection of static lexical items and grammar rules that are learned and then used according to fixed rules, the dynamical systems view defines the lexicon as regions of state space within a dynamical system. Grammar is made up of attractors and repellers that constrain movement in the state space. This means that representations are sensitive to context, with mental representations viewed as trajectories through mental space instead of objects that are constructed and remain static. Elman networks were trained with simple sentences to represent grammar as a dynamical system. Once a basic grammar had been learned, the networks could then parse complex sentences by predicting which words would appear next according to the dynamical model.
==== Cognitive development ====
A classic developmental error has been investigated in the context of dynamical systems: The A-not-B error is proposed to be not a distinct error occurring at a specific age (8 to 10 months), but a feature of a dynamic learning process that is also present in older children. Children 2 years old were found to make an error similar to the A-not-B error when searching for toys hidden in a sandbox. After observing the toy being hidden in location A and repeatedly searching for it there, the 2-year-olds were shown a toy hidden in a new location B. When they looked for the toy, they searched in locations that were biased toward location A. This suggests that there is an ongoing representation of the toy's location that changes over time. The child's past behavior influences its model of locations of the sandbox, and so an account of behavior and learning must take into account how the system of the sandbox and the child's past actions is changing over time.
==== Locomotion ====
One proposed mechanism of a dynamical system comes from analysis of continuous-time recurrent neural networks (CTRNNs). By focusing on the output of the neural networks rather than their states and examining fully interconnected networks, three-neuron central pattern generator (CPG) can be used to represent systems such as leg movements during walking. This CPG contains three motor neurons to control the foot, backward swing, and forward swing effectors of the leg. Outputs of the network represent whether the foot is up or down and how much force is being applied to generate torque in the leg joint. One feature of this pattern is that neuron outputs are either off or on most of the time. Another feature is that the states are quasi-stable, meaning that they will eventually transition to other states. A simple pattern generator circuit like this is proposed to be a building block for a dynamical system. Sets of neurons that simultaneously transition from one quasi-stable state to another are defined as a dynamic module. These modules can in theory be combined to create larger circuits that comprise a complete dynamical system. However, the details of how this combination could occur are not fully worked out.
=== Modern dynamical systems ===
==== Behavioral dynamics ====
Modern formalizations of dynamical systems applied to the study of cognition vary. One such formalization, referred to as “behavioral dynamics”, treats the agent and the environment as a pair of coupled dynamical systems based on classical dynamical systems theory. In this formalization, the information from the environment informs the agent's behavior and the agent's actions modify the environment. In the specific case of perception-action cycles, the coupling of the environment and the agent is formalized by two functions. The first transforms the representation of the agents action into specific patterns of muscle activation that in turn produce forces in the environment. The second function transforms the information from the environment (i.e., patterns of stimulation at the agent's receptors that reflect the environment's current state) into a representation that is useful for controlling the agents actions. Other similar dynamical systems have been proposed (although not developed into a formal framework) in which the agent's nervous systems, the agent's body, and the environment are coupled together
===== Adaptive behaviors =====
Behavioral dynamics have been applied to locomotive behavior. Modeling locomotion with behavioral dynamics demonstrates that adaptive behaviors could arise from the interactions of an agent and the environment. According to this framework, adaptive behaviors can be captured by two levels of analysis. At the first level of perception and action, an agent and an environment can be conceptualized as a pair of dynamical systems coupled together by the forces the agent applies to the environment and by the structured information provided by the environment. Thus, behavioral dynamics emerge from the agent-environment interaction. At the second level of time evolution, behavior can be expressed as a dynamical system represented as a vector field. In this vector field, attractors reflect stable behavioral solutions, where as bifurcations reflect changes in behavior. In contrast to previous work on central pattern generators, this framework suggests that stable behavioral patterns are an emergent, self-organizing property of the agent-environment system rather than determined by the structure of either the agent or the environment.
==== Open dynamical systems ====
In an extension of classical dynamical systems theory, rather than coupling the environment's and the agent's dynamical systems to each other, an “open dynamical system” defines a “total system”, an “agent system”, and a mechanism to relate these two systems. The total system is a dynamical system that models an agent in an environment, whereas the agent system is a dynamical system that models an agent's intrinsic dynamics (i.e., the agent's dynamics in the absence of an environment). Importantly, the relation mechanism does not couple the two systems together, but rather continuously modifies the total system into the decoupled agent's total system. By distinguishing between total and agent systems, it is possible to investigate an agent's behavior when it is isolated from the environment and when it is embedded within an environment. This formalization can be seen as a generalization from the classical formalization, whereby the agent system can be viewed as the agent system in an open dynamical system, and the agent coupled to the environment and the environment can be viewed as the total system in an open dynamical system.
===== Embodied cognition =====
In the context of dynamical systems and embodied cognition, representations can be conceptualized as indicators or mediators. In the indicator view, internal states carry information about the existence of an object in the environment, where the state of a system during exposure to an object is the representation of that object. In the mediator view, internal states carry information about the environment which is used by the system in obtaining its goals. In this more complex account, the states of the system carries information that mediates between the information the agent takes in from the environment, and the force exerted on the environment by the agents behavior. The application of open dynamical systems have been discussed for four types of classical embodied cognition examples:
Instances where the environment and agent must work together to achieve a goal, referred to as "intimacy". A classic example of intimacy is the behavior of simple agents working to achieve a goal (e.g., insects traversing the environment). The successful completion of the goal relies fully on the coupling of the agent to the environment.
Instances where the use of external artifacts improves the performance of tasks relative to performance without these artifacts. The process is referred to as "offloading". A classic example of offloading is the behavior of Scrabble players; people are able to create more words when playing Scrabble if they have the tiles in front of them and are allowed to physically manipulate their arrangement. In this example, the Scrabble tiles allow the agent to offload working memory demands on to the tiles themselves.
Instances where a functionally equivalent external artifact replaces functions that are normally performed internally by the agent, which is a special case of offloading. One famous example is that of human (specifically the agents Otto and Inga) navigation in a complex environment with or without assistance of an artifact.
Instances where there is not a single agent. The individual agent is part of larger system that contains multiple agents and multiple artifacts. One famous example, formulated by Ed Hutchins in his book Cognition in the Wild, is that of navigating a naval ship.
The interpretations of these examples rely on the following logic: (1) the total system captures embodiment; (2) one or more agent systems capture the intrinsic dynamics of individual agents; (3) the complete behavior of an agent can be understood as a change to the agent's intrinsic dynamics in relation to its situation in the environment; and (4) the paths of an open dynamical system can be interpreted as representational processes. These embodied cognition examples show the importance of studying the emergent dynamics of an agent-environment systems, as well as the intrinsic dynamics of agent systems. Rather than being at odds with traditional cognitive science approaches, dynamical systems are a natural extension of these methods and should be studied in parallel rather than in competition.
== See also ==
Computational cognition
Computational models of language acquisition
Computational-representational understanding of mind
MindModeling@Home
Memory-prediction framework
Space mapping
== References ==
== External links ==
Cognitive modeling at CMU
Cognitive modeling at RPI (HCI)
Cognitive modeling at RPI (CLARION)
Cognitive modeling at the University of Memphis (LIDA)
Cognitive modeling at UMich | Wikipedia/Cognitive_modelling |
Adaptive resonance theory (ART) is a theory developed by Stephen Grossberg and Gail Carpenter on aspects of how the brain processes information. It describes a number of artificial neural network models which use supervised and unsupervised learning methods, and address problems such as pattern recognition and prediction.
The primary intuition behind the ART model is that object identification and recognition generally occur as a result of the interaction of 'top-down' observer expectations with 'bottom-up' sensory information. The model postulates that 'top-down' expectations take the form of a memory template or prototype that is then compared with the actual features of an object as detected by the senses. This comparison gives rise to a measure of category belongingness. As long as this difference between sensation and expectation does not exceed a set threshold called the 'vigilance parameter', the sensed object will be considered a member of the expected class. The system thus offers a solution to the 'plasticity/stability' problem, i.e. the problem of acquiring new knowledge without disrupting existing knowledge that is also called incremental learning.
== Learning model ==
The basic ART system is an unsupervised learning model. It typically consists of a comparison field and a recognition field composed of neurons, a vigilance parameter (threshold of recognition), and a reset module.
The comparison field takes an input vector (a one-dimensional array of values) and transfers it to its best match in the recognition field.
Its best match is the single neuron whose set of weights (weight vector) most closely matches the input vector.
Each recognition field neuron outputs a negative signal (proportional to that neuron's quality of match to the input vector) to each of the other recognition field neurons and thus inhibits their output.
In this way the recognition field exhibits lateral inhibition, allowing each neuron in it to represent a category to which input vectors are classified.
After the input vector is classified, the reset module compares the strength of the recognition match to the vigilance parameter.
If the vigilance parameter is overcome (i.e. the input vector is within the normal range seen on previous input vectors), then training commences:
The weights of the winning recognition neuron are adjusted towards the features of the input vector
Otherwise, if the match level is below the vigilance parameter (i.e. the input vector's match is outside the normal expected range for that neuron) the winning recognition neuron is inhibited and a search procedure is carried out.
In this search procedure, recognition neurons are disabled one by one by the reset function until the vigilance parameter is overcome by a recognition match.
In particular, at each cycle of the search procedure the most active recognition neuron is selected and then switched off, if its activation is below the vigilance parameter
(note that it thus releases the remaining recognition neurons from its inhibition).
If no committed recognition neuron's match overcomes the vigilance parameter, then an uncommitted neuron is committed and its weights are adjusted towards matching the input vector.
The vigilance parameter has considerable influence on the system: higher vigilance produces highly detailed memories (many, fine-grained categories), while lower vigilance results in more general memories (fewer, more-general categories).
== Training ==
There are two basic methods of training ART-based neural networks: slow and fast. In the slow learning method, the degree of training of the recognition neuron's weights towards the input vector is calculated to continuous values with differential equations and is thus dependent on the length of time the input vector is presented. With fast learning, algebraic equations are used to calculate degree of weight adjustments to be made, and binary values are used. While fast learning is effective and efficient for a variety of tasks, the slow learning method is more biologically plausible and can be used with continuous-time networks (i.e. when the input vector can vary continuously).
== Types ==
ART 1 is the simplest variety of ART networks, accepting only binary inputs.
ART 2 extends network capabilities to support continuous inputs.
ART 2-A is a streamlined form of ART-2 with a drastically accelerated runtime, and with qualitative results being only rarely inferior to the full ART-2 implementation.
ART 3 builds on ART-2 by simulating rudimentary neurotransmitter regulation of synaptic activity by incorporating simulated sodium (Na+) and calcium (Ca2+) ion concentrations into the system's equations, which results in a more physiologically realistic means of partially inhibiting categories that trigger mismatch resets.
ARTMAP also known as Predictive ART, combines two slightly modified ART-1 or ART-2 units into a supervised learning structure where the first unit takes the input data and the second unit takes the correct output data, then used to make the minimum possible adjustment of the vigilance parameter in the first unit in order to make the correct classification.
Fuzzy ART implements fuzzy logic into ART's pattern recognition, thus enhancing generalizability. An optional (and very useful) feature of fuzzy ART is complement coding, a means of incorporating the absence of features into pattern classifications, which goes a long way towards preventing inefficient and unnecessary category proliferation. The applied similarity measures are based on the L1 norm. Fuzzy ART is known to be very sensitive to noise.
Fuzzy ARTMAP is merely ARTMAP using fuzzy ART units, resulting in a corresponding increase in efficacy.
Simplified Fuzzy ARTMAP (SFAM) constitutes a strongly simplified variant of fuzzy ARTMAP dedicated to classification tasks.
Gaussian ART and Gaussian ARTMAP use Gaussian activation functions and computations based on probability theory. Therefore, they have some similarity with Gaussian mixture models. In comparison to fuzzy ART and fuzzy ARTMAP, they are less sensitive to noise. But the stability of learnt representations is reduced which may lead to category proliferation in open-ended learning tasks.
Fusion ART and related networks extend ART and ARTMAP to multiple pattern channels. They support several learning paradigms, including unsupervised learning, supervised learning and reinforcement learning.
TopoART combines fuzzy ART with topology learning networks such as the growing neural gas. Furthermore, it adds a noise reduction mechanism. There are several derived neural networks which extend TopoART to further learning paradigms.
Hypersphere ART and Hypersphere ARTMAP are closely related to fuzzy ART and fuzzy ARTMAP, respectively. But as they use a different type of category representation (namely hyperspheres), they do not require their input to be normalised to the interval [0, 1]. They apply similarity measures based on the L2 norm.
LAPART The Laterally Primed Adaptive Resonance Theory (LAPART) neural networks couple two Fuzzy ART algorithms to create a mechanism for making predictions based on learned associations. The coupling of the two Fuzzy ARTs has a unique stability that allows the system to converge rapidly towards a clear solution. Additionally, it can perform logical inference and supervised learning similar to fuzzy ARTMAP.
== Criticism ==
It has been noted that results of Fuzzy ART and ART 1 (i.e., the learnt categories) depend critically upon the order in which the training data are processed. The effect can be reduced to some extent by using a slower learning rate, but is present regardless of the size of the input data set. Hence Fuzzy ART and ART 1 estimates do not possess the statistical property of consistency. This problem can be considered as a side effect of the respective mechanisms ensuring stable learning in both networks.
More advanced ART networks such as TopoART and Hypersphere TopoART that summarise categories to clusters may solve this problem as the shapes of the clusters do not depend on the order of creation of the associated categories. (cf. Fig. 3(g, h) and Fig. 4 of )
== References ==
Wasserman, Philip D. (1989), Neural computing: theory and practice, New York: Van Nostrand Reinhold, ISBN 0-442-20743-3
== External links ==
Stephen Grossberg's website
ART's implementation for unsupervised learning (ART 1, ART 2A, ART 2A-C and ART distance)
Summary of the ART algorithm
LibTopoART — TopoART implementations for supervised and unsupervised learning (TopoART, TopoART-AM, TopoART-C, TopoART-R, Episodic TopoART, Hypersphere TopoART, and Hypersphere TopoART-C) | Wikipedia/Adaptive_resonance_theory |
A mycorrhizal network (also known as a common mycorrhizal network or CMN) is an underground network found in forests and other plant communities, created by the hyphae of mycorrhizal fungi joining with plant roots. This network connects individual plants together. Mycorrhizal relationships are most commonly mutualistic, with both partners benefiting, but can be commensal or parasitic, and a single partnership may change between any of the three types of symbiosis at different times. Mycorrhizal networks were discovered in 1997 by Suzanne Simard, professor of forest ecology at the University of British Columbia in Canada. Simard grew up in Canadian forests where her family had made a living as foresters for generations. Her field studies revealed that trees are linked to neighboring trees by an underground network of fungi that resembles the neural networks in the brain. In one study, Simard watched as a Douglas fir that had been injured by insects appeared to send chemical warning signals to a ponderosa pine growing nearby. The pine tree then produced defense enzymes to protect against the insect.
The formation and nature of these networks is context-dependent, and can be influenced by factors such as soil fertility, resource availability, host or mycosymbiont genotype, disturbance and seasonal variation. Some plant species, such as buckhorn plantain, a common lawn and agricultural weed, benefit from mycorrhizal relationships in conditions of low soil fertility, but are harmed in higher soil fertility. Both plants and fungi associate with multiple symbiotic partners at once, and both plants and fungi are capable of preferentially allocating resources to one partner over another.
Mycorrhizal associations have profoundly impacted the evolution of plant life on Earth ever since the initial adaptation of plant life to land. In evolutionary biology, mycorrhizal symbiosis has prompted inquiries into the possibility that symbiosis, not competition, is the main driver of evolution.
Referencing an analogous function served by the World Wide Web in human communities, the many roles that mycorrhizal networks appear to play in woodland have earned them a colloquial nickname: the "Wood Wide Web". Many of the claims made about common mycorrhizal networks, including that they are ubiquitous in forests, that resources are transferred between plants through them, and that they are used to transfer warnings between trees, have been criticised as being not strongly supported by evidence.
== Definitions and types ==
As a scientific term, mycorrhizal network has broad meanings and usage. Scientific understandings and thus publications utilize more specific definitions arising from the term common mycorrhizal network (CMN). The keyword "common" requires that two or more individual plants are connected by the same underground fungal network, through which matter of various types and functions may flow. The plants themselves may be individuals of the same or different species. In turn, the fungal network that is composed of threadlike hyphae may be limited to a single type or entail several. The kinds of evidence deemed necessary for supporting scientific conclusions, along with the tendency for disputes to arise, depend in part on the definitions used.
There are two main types of mycorrhizal networks. These are determined by the two main categories of fungal growth forms. Arbuscular mycorrhizal networks are those in which fungal hyphae not only enter the plant's roots but also penetrate into the cells themselves. Ectomycorrhizal networks send hyphae into the roots where they thread their way between the plant cells but do not penetrate cell walls. The arbuscular type is the most common among land plants and is regarded as the ancestral type. However, tree species comprising the canopy of temperate and especially boreal forests in the Northern Hemisphere tend to associate with ectomycorrhizal fungi.
Plant and fungal partners within a network may enact a variety of symbiotic relationships. Earliest attention was given to mutualistic networks by which the plant and fungal partners both benefit. Commensal and parasitic relationships are also found in mycorrhizal networks. A single partnership may change between any of the three types at different times.
== Knowns, unknowns, and controversies ==
The mycorrhizal symbiosis between plants and fungi is fundamental to terrestrial ecosystems, with evolutionary origins before the colonization of land by plants. In the mycorrhizal symbiosis, a plant and a fungus become physically linked to one another and establish an exchange of resources between one another. The plant provides to the fungus up to 30% of the carbon it fixes by photosynthesis, while the fungus provides the plant with nutrients that are limiting in terrestrial environments, such as nitrogen and phosphorus.
As this relationship has been better investigated and understood by science, interest has emerged in its potential influence on interactions between different plants, particularly in the possibility that connectivity through the mycorrhizal network may allow plants to positively impact the survival of other plants. Evidence and potential mechanisms for a variety of plant-plant interactions mediated by the mycorrhizal symbiosis have been presented, but their validity and significance is still controversial.
=== Proposed effects and functions of the mycorrhizal network ===
==== Potential nutrient and photosynthate transfer between plants ====
Since multiple plants can be simultaneously colonized by the same fungus, there has been interest in the possibility that inter-plant transfer of nutrients may occur via mycorrhizal networks, with photosynthates moving from a 'donor' plant to a 'recipient' plant. Numerous studies have reported that carbon, nitrogen and phosphorus are transferred between conspecific and heterospecific plants via AM and ECM networks. Other nutrients may also be transferred, as strontium and rubidium, which are calcium and potassium analogs respectively, have also been reported to move via an AM network between conspecific plants. It is possible that in this way, mycorrhizal networks could alter the behavior of receiving plants by inducing physiological or biochemical changes, and there is evidence that these changes have improved nutrition, growth and survival of receiving plants.
==== Potential signaling and communication between plants ====
Reports discuss the ongoing debate within the scientific community regarding what constitutes communication, but the extent of communication influences how a biologist perceives behaviors. Communication is commonly defined as imparting or exchanging information. Biological communication, however, is often defined by how fitness in an organism is affected by the transfer of information in both the sender and the receiver. Signals are the result of evolved behavior in the sender and effect a change in the receiver by imparting information about the sender's environment. Cues are similar in origin but only effect the fitness of the receiver. Both signals and cues are important elements of communication, but workers maintain caution as to when it can be determined that transfer of information benefits both senders and receivers. Thus, the extent of biological communication can be in question without rigorous experimentation. It has, therefore, been suggested that the term infochemical be used for chemical substances which can travel from one organism to another and elicit changes. This is important to understanding biological communication where it is not clearly delineated that communication involves a signal that can be adaptive to both sender and receiver.
==== Behavior and information transfer ====
A morphological or physiological change in a plant due to a signal or cue from its environment constitutes behavior in plants, and plants connected by a mycorrhizal network have the ability to alter their behavior based on the signals or cues they receive from other plants. These signals or cues can be biochemical, electrical, or can involve nutrient transfer. Plants release chemicals both above and below the ground to communicate with their neighbors to reduce damage from their environment. Changes in plant behavior invoked by the transfer of infochemicals vary depending on environmental factors, the types of plants involved and the type of mycorrhizal network. In a study of trifoliate orange seedlings, mycorrhizal networks acted to transfer infochemicals, and the presence of a mycorrhizal network affected the growth of plants and enhanced production of signaling molecules. One argument in support of the claim mycorrhizal can transfer various infochemicals is that they have been shown to transfer molecules such as lipids, carbohydrates and amino acids. Thus, transfer of infochemicals via mycorrhizal networks can act to influence plant behavior.
There are three main types of infochemicals shown to act as response inducing signals or cues by plants in mycorrhizal networks, as evidenced by increased effects on plant behavior: allelochemicals, defensive chemicals and nutrients.
==== Allelopathic communication ====
Allelopathy is the process by which plants produce secondary metabolites known as allelochemicals, which can interfere with the development of other plants or organisms. Allelochemicals can affect nutrient uptake, photosynthesis and growth; furthermore, they can down regulate defense genes, affect mitochondrial function, and disrupt membrane permeability leading to issues with respiration.
Plants produce many types of allelochemicals, such as thiophenes and juglone, which can be volatilized or exuded by the roots into the rhizosphere. Plants release allelochemicals due to biotic and abiotic stresses in their environment and often release them in conjunction with defensive compounds. In order for allelochemicals to have a detrimental effect on a target plant, they must exist in high enough concentrations to be toxic, but, much like animal pheromones, allelochemicals are released in very small amounts and rely on the reaction of the target plant to amplify their effects. Due to their lower concentrations and the ease in which they are degraded in the environment, the toxicity of allelochemicals is limited by soil moisture, soil structure, and organic matter types and microbes present in soils. The effectiveness of allelopathic interactions has been called into question in native habitats due to the effects of them passing through soils, but studies have shown that mycorrhizal networks make their transfer more efficient. These infochemicals are hypothesized to be able to travel faster via mycorrhizal networks, because the networks protect them from some hazards of being transmitted through the soil, such as leaching and degradation. This increased transfer speed is hypothesized to occur if the allelochemicals move via water on hyphal surfaces or by cytoplasmic streaming. Studies have reported concentrations of allelochemicals two to four times higher in plants connected by mycorrhizal networks. Thus, mycorrhizal networks can facilitate the transfer of these infochemicals.
Studies have demonstrated correlations between increased levels of allelochemicals in target plants and the presence of mycorrhizal networks. These studies strongly suggest that mycorrhizal networks increase the transfer of allelopathic chemicals and expand the range, called the bioactive zone, in which they can disperse and maintain their function. Furthermore, studies indicate increased bioactive zones aid in the effectiveness of the allelochemicals because these infochemicals cannot travel very far without a mycorrhizal network. There was greater accumulation of allelochemicals, such as thiopenes and the herbicide imazamox, in target plants connected to a supplier plant via a mycorrhizal network than without that connection, supporting the conclusion that the mycorrhizal network increased the bioactive zone of the allelochemical. Allelopathic chemicals have also been demonstrated to inhibit target plant growth when target and supplier are connected via AM networks. The black walnut is one of the earliest studied examples of allelopathy and produces juglone, which inhibits growth and water uptake in neighboring plants. In studies of juglone in black walnuts and their target species, the presence of mycorrhizal networks caused target plants to exhibit reduced growth by increasing the transfer of the infochemical. Spotted knapweed, an allelopathic invasive species, provides further evidence of the ability of mycorrhizal networks to contribute to the transfer of allelochemicals. Spotted knapweed can alter which plant species a certain AM fungus prefers to connect to, changing the structure of the network so that the invasive plant shares a network with its target. These and other studies provide evidence that mycorrhizal networks can facilitate the effects on plant behavior caused by allelochemicals.
==== Defensive communication ====
Mycorrhizal networks can connect many different plants and provide shared pathways by which plants can transfer infochemicals related to attacks by pathogens or herbivores, allowing receiving plants to react in the same way as the infected or infested plants. A variety of plant derived substances act as these infochemicals.
When plants are attacked they can manifest physical changes, such as strengthening their cell walls, depositing callose, or forming cork. They can also manifest biochemical changes, including the production of volatile organic compounds (VOCs) or the upregulation of genes producing other defensive enzymes, many of which are toxic to pathogens or herbivores. Salicylic acid (SA) and its derivatives, like methyl salicylate, are VOCs which help plants to recognize infection or attack and to organize other plant defenses, and exposure to them in animals can cause pathological processes. Terpenoids are produced constituently in many plants or are produced as a response to stress and act much like methyl salicylate. Jasmonates are a class of VOCs produced by the jasmonic acid (JA) pathway. Jasmonates are used in plant defense against insects and pathogens and can cause the expression of proteases, which defend against insect attack. Plants have many ways to react to attack, including the production of VOCs, which studies report can coordinate defenses among plants connected by mycorrhizal networks.
Many studies report that mycorrhizal networks facilitate the coordination of defenses between connected plants using volatile organic compounds and other plant defensive enzymes acting as infochemicals.
Priming occurs when a plant's defenses are activated before an attack. Studies have shown that priming of plant defenses among plants in mycorrhizal networks may be activated by the networks, as they make it easier for these infochemicals to propagate among the connected plants. The defenses of uninfected plants are primed by their response via the network to the terpenoids produced by the infected plants. AM networks can prime plant defensive reactions by causing them to increase the production of terpenoids.
In a study of tomato plants connected via an AM mycorrhizal network, a plant not infected by a fungal pathogen showed evidence of defensive priming when another plant in the network was infected, causing the uninfected plant to upregulate genes for the SA and JA pathways. Similarly, aphid-free plants were shown to only be able to express the SA pathways when a mycorrhizal network connected them to infested plants. Furthermore, only then did they display resistance to the herbivore, showing that the plants were able to transfer defensive infochemicals via the mycorrhizal network.
Many insect herbivores are drawn to their food by VOCs. When the plant is consumed, however, the composition of the VOCs change, which can then cause them to repel the herbivores and attract insect predators, such as parasitoid wasps. Methyl salicylate was shown to be the primary VOC produced by beans in a study which demonstrated this effect. It was found to be in high concentrations in infested and uninfested plants, which were only connected via a mycorrhizal network. A plant sharing a mycorrhizal network with another that is attacked will display similar defensive strategies, and its defenses will be primed to increase the production of toxins or chemicals which repel attackers or attract defensive species.
In another study, introduction of budworm to Douglas fir trees led to increased production of defensive enzymes in uninfested ponderosa pines connected to the damaged tree by an ECM network. This effect demonstrates that defensive infochemicals transferred through such a network can cause rapid increases in resistance and defense in uninfested plants of a different species.
The results of these studies support the conclusion that both ECM and AM networks provide pathways for defensive infochemicals from infected or infested hosts to induce defensive changes in uninfected or uninfested conspecific and heterospecific plants, and that some recipient species generally receive less damage from infestation or infection.
=== Limits and challenges to research ===
Because natural environments contain many different plant and fungal species as well as various other biotic and abiotic factors interacting with one another, it is difficult to verify the effect of interactions occurring via the mycorrhizal network in a field setting. On the other hand, controlled experiments that isolate simple interactions between a few species do not replicate anything found in nature. In a natural ecosystem, plants simultaneously participate in symbiotic relationships with multiple fungi, and some of these relationships may be commensal or parasitic.
The connectivity between plants believed to share a common mycorrhizal network is also difficult to verify in a natural ecosystem. Field observations cannot easily rule out the possibility that effects attributed to physical connection between plants via mycorrhizal networks could be happening due to other interactions.
While movement of resources between plants connected to the same mycorrhizal network has been shown, it is often unclear whether the transfer is direct, as though the mycelium is forming a literal “pipeline,” or indirect, such as nutrients being released into the soil by fungi and then picked up by neighboring plants. It is furthermore unclear whether apparent nutrient transfer between plants has a significant impact on plant fitness.
=== Research tools and methods ===
==== Isotopic labeling ====
Carbon transfer has been demonstrated by experiments using carbon-14 (14C) isotopic labeling and following the pathway from ectomycorrhizal conifer seedlings to another using mycorrhizal networks. The experiment showed a bidirectional movement of the 14C within ectomycorrhizal species. Further investigation of bidirectional movement and the net transfer was analyzed using pulse labeling technique with 13C and 14C in ectomycorrhizal Douglas fir and Betula payrifera seedlings. Results displayed an overall net balance of carbon transfer between the two, until the second year where the Douglas fir received carbon from B. payrifera. Detection of the isotopes was found in receiver plant shoots, expressing carbon transfer from fungus to plant tissues.
Plants sense carbon through a receptor in their guard cells that measure carbon dioxide concentrations in the leaf and environment. Carbon information is integrated using proteins known as carbonic anhydrases, in which the plant then responds by utilizing or disregarding the carbon resources from the mycorrhizal networks. One case study follows a CMN shared by a paper birch and Douglas fir tree. By using carbon-13 and carbon-14 labels, researchers found that both tree species were trading carbon–that is to say, carbon was moving from tree to tree in both directions. The rate of carbon transfer varied based on the physiological factors such as total biomass, age, nutrient status, and photosynthetic rate. At the end of the experiment, the Douglas fir was found to have a 2% to 3% net gain in carbon. This gain may seem small, but in the past a carbon gain of less than 1% has been shown to coincide with a four-fold increase in the establishment of new seedlings. Both plants showed a threefold increase in carbon received from the CMN when compared to the soil pathway.
=== Proposed models ===
Several models have been proposed to explain the movement of nutrients between plants connected by a mycorrhizal network, including source-sink relationships, "market" analogies, preferential transfer and kin related mechanisms.
==== Source-sink model ====
Transfer of nutrients can follow a source–sink relationship where nutrients move from areas of higher concentration to areas of lower concentration. An experiment with grasses and forbs from a California oak woodland showed that nutrients were transferred between plant species via an AM mycorrhizal network, with different species acting as sources and sinks for different elements. Nitrogen has also been shown to flow from nitrogen-fixing plants to non-nitrogen fixing plants through a mycorrhizal network following a source-sink relationship.
The direction carbon resources flow through the mycorrhizal network has been observed to shift seasonally, with carbon flowing toward the parts of the network that need it the most. For example, in a network that includes Acer saccharinum (sugar maple) and Erythronium americanum (trout lily), carbon moves to young sugar maple saplings in spring when leaves are unfurling, and shifts to move to the trout lilies in fall when the lilies are developing their roots. A further study with paper birch and Douglas fir demonstrated that the flow of carbon shifts direction more than once per season: in spring, newly budding birch receives carbon from green Douglas fir, in summer, stressed Douglas fir in the forest understory receives carbon from birch in full leaf, and in fall, birch again receives carbon from Douglas fir as birch trees shed their leaves and evergreen Douglas firs continue photosynthesizing.
When the ectomycorrhizal fungus-receiving end of the plant has limited sunlight availability, there was an increase in carbon transfer, indicating a source–sink gradient of carbon among plants and shade surface area regulates carbon transfer.
It has been demonstrated that mechanisms exist by which mycorrhizal fungi can preferentially allocate nutrients to certain plants without a source–sink relationship. Studies have also detailed bidirectional transfer of nutrients between plants connected by a network, and evidence indicates that carbon can be shared between plants unequally, sometimes to the benefit of one species over another.
Kinship can act as another transfer mechanism. More carbon has been found to be exchanged between the roots of more closely related Douglas firs sharing a network than more distantly related roots. Evidence is also mounting that micronutrients transferred via mycorrhizal networks can communicate relatedness between plants. Carbon transfer between Douglas fir seedlings led workers to hypothesize that micronutrient transfer via the network may have increased carbon transfer between related plants.
These transfer mechanisms can facilitate movement of nutrients via mycorrhizal networks and result in behavioral modifications in connected plants, as indicated by morphological or physiological changes, due to the infochemicals being transmitted. One study reported a threefold increase in photosynthesis in a paper birch transferring carbon to a Douglas fir, indicating a physiological change in the tree which produced the signal. Photosynthesis was also shown to be increased in Douglas fir seedlings by the transport of carbon, nitrogen and water from an older tree connected by a mycorrhizal network. Furthermore, nutrient transfer from older to younger trees on a network can dramatically increase growth rates of the younger receivers. Physiological changes due to environmental stress have also initiated nutrient transfer by causing the movement of carbon from the roots of the stressed plant to the roots of a conspecific plant over a mycorrhizal network. Thus, nutrients transferred through mychorrhizal networks act as signals and cues to change the behavior of the connected plants.
=== Evolutionary and adaptational perspectives ===
Several positive effects of mycorrhizal networks on plants have been reported. These include increased establishment success, higher growth rate and survivorship of seedlings; improved inoculum availability for mycorrhizal infection; transfer of water, carbon, nitrogen and other limiting resources increasing the probability for colonization in less favorable conditions. These benefits have also been identified as the primary drivers of positive interactions and feedbacks between plants and mycorrhizal fungi that influence plant species abundance.
The formation and nature of these networks is context-dependent, and can be influenced by factors such as soil fertility, resource availability, host or mycosymbiont genotype, disturbance and seasonal variation. Some plant species, such as buckhorn plantain, a common lawn and agricultural weed, benefit from mycorrhizal relationships in conditions of low soil fertility, but are harmed in higher soil fertility. Both plants and fungi associate with multiple symbiotic partners at once, and both plants and fungi are capable of preferentially allocating resources to one partner over another.
It is hypothesized that fitness is improved by the transfer of infochemicals through common mycorrhizal networks, as these signals and cues can induce responses which can help the receiver survive in its environment. Plants and fungus have evolved heritable genetic traits which influence their interactions with each other, and experiments, such as one which revealed the heritability of mycorrhizal colonization in cowpeas, provide evidence. Furthermore, changes in behavior of one partner in a mycorrhizal network can affect others in the network; thus, the mycorrhizal network can provide selective pressure to increase the fitness of its members.
==== Adaptive mechanisms ====
Although they remain to be vigorously demonstrated, researchers have suggested mechanisms which might explain how transfer of infochemicals via mycorrhizal networks may influence the fitness of the connected plants and fungi.
A fungus may preferentially allocate carbon and defensive infochemicals to plants that supply it more carbon, as this would help to maximize its carbon uptake. This may happen in ecosystems where environmental stresses, such as climate change, cause fluctuations in the types of plants in the mycorrhizal network. A fungus might also benefit its own survival by taking carbon from one host with a surplus and giving it to another in need, thus it would ensure the survival of more potential hosts and leave itself with more carbon sources should a particular host species suffer. Thus, preferential transfer could improve fungal fitness.
Plant fitness may also be increased in several ways. Relatedness may be a factor, as plants in a network are more likely to be related; therefore, kin selection might improve inclusive fitness and explain why a plant might support a fungus that helps other plants to acquire nutrients. Receipt of defensive signals or cues from an infested plant would be adaptive, as the receiving plant would be able to prime its own defenses in advance of an attack by herbivores. Allelopathic chemicals transferred via CMNs could also affect which plants are selected for survival by limiting the growth of competitors through a reduction of their access to nutrients and light. Therefore, transfer of the different classes of infochemicals might prove adaptive for plants.
==== Seedling establishment ====
Seedling establishment research often is focused on forest level communities with similar fungal species. However mycorrhizal networks may shift intraspecific and interspecific interactions that may alter preestablished plants' physiology. Shifting competition can alter the evenness and dominance of the plant community. Discovery of seedling establishment showed seedling preference is near existing plants of conspecific or heterospecific species and seedling amount is abundant. Many believe the process of new seedlings becoming infected with existing mycorrhizae expedite their establishment within the community. The seedling inherit tremendous benefits from their new formed symbiotic relation with the fungi. The new influx of nutrients and water availability, help the seedling with growth but more importantly help ensure survival when in a stressed state. Mycorrhizal networks aid in regeneration of seedlings when secondary succession occurs, seen in temperate and boreal forests. Seedling benefits from infecting mycorrhizae include increased infectivity range of diverse mycorrhizal fungi, increased carbon inputs from mycorrhizal networks with other plants, increased area meaning greater access to nutrients and water, and increased exchange rates of nutrients and water from other plants.
Several studies have focused on relationships between mycorrhizal networks and plants, specifically their performance and establishment rate. Douglas fir seedlings' growth expanded when planted with hardwood trees compared to unamended soils in the mountains of Oregon. Douglas firs had higher rates of ectomycorrhizal fungal diversity, richness, and photosynthetic rates when planted alongside root systems of mature Douglas firs and Betula papyrifera than compared to those seedlings who exhibited no or little growth when isolated from mature trees. The Douglas fir was the focus of another study to understand its preference for establishing in an ecosystem. Two shrub species, Arctostaphylos and Adenostoma both had the opportunity to colonize the seedlings with their ectomycorrhizae fungi. Arctostaphylos shrubs colonized Douglas fir seedlings who also had higher survival rates. The mycorrhizae joining the pair had greater net carbon transfer toward the seedling. The researchers were able to minimize environmental factors they encountered in order to avoid swaying readers in opposite directions.
In burned and salvaged forest, Quercus rubrum establishment was facilitated when acorns were planted near Q. montana but did not grow when near arbuscular mycorrhizae Acer rubrum Seedlings deposited near Q. montana had a greater diversity of ectomycorrhizal fungi, and a more significant net transfer of nitrogen and phosphorus content, demonstrating that ectomycorrhizal fungi formation with the seedling helped with their establishment. Results demonstrated with increasing density; mycorrhizal benefits decrease due to an abundance of resources that overwhelmed their system resulting in little growth as seen in Q. rubrum.
Mycorrhizal networks decline with increasing distance from parents, but the rate of survival was unaffected. This indicated that seedling survival has a positive relation with decreasing competition as networks move out farther.
One study displayed the effects of ectomycorrhizal networks in plants which face primary succession. In an experiment, Nara (2006) transplanted Salix reinii seedlings inoculated with different ectomycorrhizal species. It was found that mycorrhizal networks are the connection of ectomycorrhizal fungi colonization and plant establishment. Results showed increased biomass and survival of germinates near the inoculated seedlings compared to inoculated seedlings.
Studies have found that association with mature plants correlates with higher survival of the plant and greater diversity and species richness of the mycorrhizal fungi.
== See also ==
Suzanne Simard
"Finding the Mother Tree" (book)
"Entangled Life (book)
Forest ecology
Plant communication
== References ==
== External links ==
Radiolab: From Tree to Shining Tree
BBC News: How trees secretly talk to each other
NOVA: The Wood Wide Web | Wikipedia/Mycorrhizal_network |
A knowledge-based system (KBS) is a computer program that reasons and uses a knowledge base to solve complex problems. Knowledge-based systems were the focus of early artificial intelligence researchers in the 1980s. The term can refer to a broad range of systems. However, all knowledge-based systems have two defining components: an attempt to represent knowledge explicitly, called a knowledge base, and a reasoning system that allows them to derive new knowledge, known as an inference engine.
== Components ==
The knowledge base contains domain-specific facts and rules about a problem domain (rather than knowledge implicitly embedded in procedural code, as in a conventional computer program). In addition, the knowledge may be structured by means of a subsumption ontology, frames, conceptual graph, or logical assertions.
The inference engine uses general-purpose reasoning methods to infer new knowledge and to solve problems in the problem domain. Most commonly, it employs forward chaining or backward chaining. Other approaches include the use of automated theorem proving, logic programming, blackboard systems, and term rewriting systems such as Constraint Handling Rules (CHR). These more formal approaches are covered in detail in the Wikipedia article on knowledge representation and reasoning.
== Aspects and development of early systems ==
=== Knowledge-based vs. expert systems ===
The term "knowledge-based system" was often used interchangeably with "expert system", possibly because almost all of the earliest knowledge-based systems were designed for expert tasks. However, these terms tell us about different aspects of a system:
expert: describes only the task the system is designed for – its purpose is to aid replace a human expert in a task typically requiring specialised knowledge
knowledge-based: refers only to the system's architecture – it represents knowledge explicitly, rather than as procedural code
Today, virtually all expert systems are knowledge-based, whereas knowledge-based system architecture is used in a wide range of types of system designed for a variety of tasks.
=== Rule-based systems ===
The first knowledge-based systems were primarily rule-based expert systems. These represented facts about the world as simple assertions in a flat database and used domain-specific rules to reason about these assertions, and then to add to them. One of the most famous of these early systems was Mycin, a program for medical diagnosis.
Representing knowledge explicitly via rules had several advantages:
Acquisition and maintenance. Using rules meant that domain experts could often define and maintain the rules themselves rather than via a programmer.
Explanation. Representing knowledge explicitly allowed systems to reason about how they came to a conclusion and use this information to explain results to users. For example, to follow the chain of inferences that led to a diagnosis and use these facts to explain the diagnosis.
Reasoning. Decoupling the knowledge from the processing of that knowledge enabled general purpose inference engines to be developed. These systems could develop conclusions that followed from a data set that the initial developers may not have even been aware of.
=== Meta-reasoning ===
Later architectures for knowledge-based reasoning, such as the BB1 blackboard architecture (a blackboard system), allowed the reasoning process itself to be affected by new inferences, providing meta-level reasoning. BB1 allowed the problem-solving process itself to be monitored. Different kinds of problem-solving (e.g., top-down, bottom-up, and opportunistic problem-solving) could be selectively mixed based on the current state of problem solving. Essentially, the problem-solver was being used both to solve a domain-level problem along with its own control problem, which could depend on the former.
Other examples of knowledge-based system architectures supporting meta-level reasoning are MRS and SOAR.
=== Widening of application ===
In the 1980s and 1990s, in addition to expert systems, other applications of knowledge-based systems included real-time process control, intelligent tutoring systems, and problem-solvers for specific domains such as protein structure analysis, construction-site layout, and computer system fault diagnosis.
=== Advances driven by enhanced architecture ===
As knowledge-based systems became more complex, the techniques used to represent the knowledge base became more sophisticated and included logic, term-rewriting systems, conceptual graphs, and frames.
Frames, for example, are a way representing world knowledge using techniques that can be seen as analogous to object-oriented programming, specifically classes and subclasses, hierarchies and relations between classes, and behavior of objects. With the knowledge base more structured, reasoning could now occur not only by independent rules and logical inference, but also based on interactions within the knowledge base itself. For example, procedures stored as daemons on objects could fire and could replicate the chaining behavior of rules.
=== Advances in automated reasoning ===
Another advancement in the 1990s was the development of special purpose automated reasoning systems called classifiers. Rather than statically declare the subsumption relations in a knowledge-base, a classifier allows the developer to simply declare facts about the world and let the classifier deduce the relations. In this way a classifier also can play the role of an inference engine.
The most recent advancement of knowledge-based systems was to adopt the technologies, especially a kind of logic called description logic, for the development of systems that use the internet. The internet often has to deal with complex, unstructured data that cannot be relied on to fit a specific data model. The technology of knowledge-based systems, and especially the ability to classify objects on demand, is ideal for such systems. The model for these kinds of knowledge-based internet systems is known as the Semantic Web.
== See also ==
Knowledge representation and reasoning
Knowledge modeling
Knowledge engine
Information retrieval
Reasoning system
Case-based reasoning
Conceptual graph
Neural networks
== References ==
== Further reading ==
Rajendra, Akerkar; Sajja, Priti (2009). Knowledge-Based Systems. Jones & Bartlett Learning. ISBN 9780763776473. | Wikipedia/Knowledge-based_systems |
A neural network, also called a neuronal network, is an interconnected population of neurons (typically containing multiple neural circuits). Biological neural networks are studied to understand the organization and functioning of nervous systems.
Closely related are artificial neural networks, machine learning models inspired by biological neural networks. They consist of artificial neurons, which are mathematical functions that are designed to be analogous to the mechanisms used by neural circuits.
== Overview ==
A biological neural network is composed of a group of chemically connected or functionally associated neurons. A single neuron may be connected to many other neurons and the total number of neurons and connections in a network may be extensive. Connections, called synapses, are usually formed from axons to dendrites, though dendrodendritic synapses and other connections are possible. Apart from electrical signalling, there are other forms of signalling that arise from neurotransmitter diffusion.
Artificial intelligence, cognitive modelling, and artificial neural networks are information processing paradigms inspired by how biological neural systems process data. Artificial intelligence and cognitive modelling try to simulate some properties of biological neural networks. In the artificial intelligence field, artificial neural networks have been applied successfully to speech recognition, image analysis and adaptive control, in order to construct software agents (in computer and video games) or autonomous robots.
Neural network theory has served to identify better how the neurons in the brain function and provide the basis for efforts to create artificial intelligence.
== History ==
The preliminary theoretical base for contemporary neural networks was independently proposed by Alexander Bain (1873) and William James (1890). In their work, both thoughts and body activity resulted from interactions among neurons within the brain.
For Bain, every activity led to the firing of a certain set of neurons. When activities were repeated, the connections between those neurons strengthened. According to his theory, this repetition was what led to the formation of memory. The general scientific community at the time was skeptical of Bain's theory because it required what appeared to be an inordinate number of neural connections within the brain. It is now apparent that the brain is exceedingly complex and that the same brain “wiring” can handle multiple problems and inputs.
James' theory was similar to Bain's; however, he suggested that memories and actions resulted from electrical currents flowing among the neurons in the brain. His model, by focusing on the flow of electrical currents, did not require individual neural connections for each memory or action.
C. S. Sherrington (1898) conducted experiments to test James' theory. He ran electrical currents down the spinal cords of rats. However, instead of demonstrating an increase in electrical current as projected by James, Sherrington found that the electrical current strength decreased as the testing continued over time. Importantly, this work led to the discovery of the concept of habituation.
McCulloch and Pitts (1943) also created a computational model for neural networks based on mathematics and algorithms. They called this model threshold logic. These early models paved the way for neural network research to split into two distinct approaches. One approach focused on biological processes in the brain and the other focused on the application of neural networks to artificial intelligence.
The parallel distributed processing of the mid-1980s became popular under the name connectionism. The text by Rumelhart and McClelland (1986) provided a full exposition on the use of connectionism in computers to simulate neural processes.
Artificial neural networks, as used in artificial intelligence, have traditionally been viewed as simplified models of neural processing in the brain, even though the relation between this model and brain biological architecture is debated, as it is not clear to what degree artificial neural networks mirror brain function.
== Neuroscience ==
Theoretical and computational neuroscience is the field concerned with the analysis and computational modeling of biological neural systems.
Since neural systems are intimately related to cognitive processes and behaviour, the field is closely related to cognitive and behavioural modeling.
The aim of the field is to create models of biological neural systems in order to understand how biological systems work. To gain this understanding, neuroscientists strive to make a link between observed biological processes (data), biologically plausible mechanisms for neural processing and learning (neural network models) and theory (statistical learning theory and information theory).
=== Types of models ===
Many models are used; defined at different levels of abstraction, and modeling different aspects of neural systems. They range from models of the short-term behaviour of individual neurons, through models of the dynamics of neural circuitry arising from interactions between individual neurons, to models of behaviour arising from abstract neural modules that represent complete subsystems. These include models of the long-term and short-term plasticity of neural systems and their relation to learning and memory, from the individual neuron to the system level.
=== Connectivity ===
In August 2020 scientists reported that bi-directional connections, or added appropriate feedback connections, can accelerate and improve communication between and in modular neural networks of the brain's cerebral cortex and lower the threshold for their successful communication. They showed that adding feedback connections between a resonance pair can support successful propagation of a single pulse packet throughout the entire network. The connectivity of a neural network stems from its biological structures and is usually challenging to map out experimentally. Scientists used a variety of statistical tools to infer the connectivity of a network based on the observed neuronal activities, i.e., spike trains. Recent research has shown that statistically inferred neuronal connections in subsampled neural networks strongly correlate with spike train covariances, providing deeper insights into the structure of neural circuits and their computational properties.
== Recent improvements ==
While initially research had been concerned mostly with the electrical characteristics of neurons, a particularly important part of the investigation in recent years has been the exploration of the role of neuromodulators such as dopamine, acetylcholine, and serotonin on behaviour and learning.
Biophysical models, such as BCM theory, have been important in understanding mechanisms for synaptic plasticity, and have had applications in both computer science and neuroscience.
== See also ==
Adaptive resonance theory
Biological cybernetics
Cognitive architecture
Cognitive science
Connectomics
Cultured neuronal networks
Parallel constraint satisfaction processes
Wood Wide Web
== References == | Wikipedia/Biological_neural_networks |
An orthography is a set of conventions for writing a language, including norms of spelling, punctuation, word boundaries, capitalization, hyphenation, and emphasis.
Most national and international languages have an established writing system that has undergone substantial standardization, thus exhibiting less dialect variation than the spoken language. These processes can fossilize pronunciation patterns that are no longer routinely observed in speech (e.g. would and should); they can also reflect deliberate efforts to introduce variability for the sake of national identity, as seen in Noah Webster's efforts to introduce easily noticeable differences between American and British spelling (e.g. honor and honour).
Orthographic norms develop through social and political influence at various levels, such as encounters with print in education, the workplace, and the state. Some nations have established language academies in an attempt to regulate aspects of the national language, including its orthography—such as the Académie Française in France and the Royal Spanish Academy in Spain. No such authority exists for most languages, including English. Some non-state organizations, such as newspapers of record and academic journals, choose greater orthographic homogeneity by enforcing a particular style guide or spelling standard such as Oxford spelling.
== Terminology ==
The English word orthography is first attested in the 15th century, ultimately from Ancient Greek: ὀρθός (orthós 'correct') and γράφειν (gráphein 'to write').
Orthography in phonetic writing systems is often concerned with matters of spelling, i.e. the correspondence between written graphemes and the phonemes found in speech. Other elements that may be considered part of orthography include hyphenation, capitalization, word boundaries, emphasis, and punctuation. Thus, orthography describes or defines the symbols used in writing, and the conventions that regulate their use.
Most natural languages developed as oral languages and writing systems have usually been crafted or adapted as ways of representing the spoken language. The rules for doing this tend to become standardized for a given language, leading to the development of an orthography that is generally considered "correct". In linguistics, orthography often refers to any method of writing a language without judgement as to right and wrong, with a scientific understanding that orthographic standardization exists on a spectrum of strength of convention. The original sense of the word, though, implies a dichotomy of correct and incorrect, and the word is still most often used to refer specifically to a standardized prescriptive manner of writing. A distinction is made between emic and etic viewpoints, with the emic approach taking account of perceptions of correctness among language users, and the etic approach being purely descriptive, considering only the empirical qualities of any system as used.
== Units and notation ==
Orthographic units, such as letters of an alphabet, are conceptualized as graphemes. These are a type of abstraction, analogous to the phonemes of spoken languages; different physical forms of written symbols are considered to represent the same grapheme if the differences between them are not significant for meaning. Thus, a grapheme can be regarded as an abstraction of a collection of glyphs that are all functionally equivalent. For example, in written English (or other languages using the Latin alphabet), there are two different physical representations (glyphs) of the lowercase Latin letter a: ⟨a⟩ and ⟨ɑ⟩. Since the substitution of either of them for the other cannot change the meaning of a word, they are considered to be allographs of the same grapheme, which can be written |a|. The italic and boldface forms are also allographic.
Graphemes or sequences of them are sometimes placed between angle brackets, as in |b| or |back|. This distinguishes them from phonemic transcription, which is placed between slashes (/b/, /bæk/), and from phonetic transcription, which is placed between square brackets ([b], [bæk]).
== Types ==
The writing systems on which orthographies are based can be divided into a number of types, depending on what type of unit each symbol serves to represent. The principal types are logographic (with symbols representing words or morphemes), syllabic (with symbols representing syllables), and alphabetic (with symbols roughly representing phonemes). Many writing systems combine features of more than one of these types, and a number of detailed classifications have been proposed. Japanese is an example of a writing system that can be written using a combination of logographic kanji characters and syllabic hiragana and katakana characters; as with many non-alphabetic languages, alphabetic romaji characters may also be used as needed.
== Correspondence with pronunciation ==
Orthographies that use alphabets and syllabaries are based on the principle that written graphemes correspond to units of sound of the spoken language: phonemes in the former case, and syllables in the latter. In virtually all cases, this correspondence is not exact. Different languages' orthographies offer different degrees of correspondence between spelling and pronunciation. English, French, Danish, and Thai orthographies, for example, are highly irregular, whereas the orthographies of languages such as Russian, German, Spanish, Finnish, Turkish, and Serbo-Croatian represent pronunciation much more faithfully.
An orthography in which the correspondences between spelling and pronunciation are highly complex or inconsistent is called a deep orthography (or less formally, the language is said to have irregular spelling). An orthography with relatively simple and consistent correspondences is called shallow (and the language has regular spelling).
One of the main reasons why spelling and pronunciation diverge is that sound changes taking place in the spoken language are not always reflected in the orthography, and hence spellings correspond to historical rather than present-day pronunciation. One consequence of this is that many spellings come to reflect a word's morphophonemic structure rather than its purely phonemic structure (for example, the English regular past tense morpheme is consistently spelled -ed in spite of its different pronunciations in various words). This is discussed further at Phonemic orthography § Morphophonemic features.
The syllabaries in the Japanese writing system (hiragana and katakana) are examples of almost perfectly shallow orthographies—the kana correspond with almost perfect consistency to the spoken syllables, although with a few exceptions where symbols reflect historical or morphophonemic features: notably the use of ぢ ji and づ zu (rather than じ ji and ず zu, their pronunciation in standard Tokyo dialect) when the character is a voicing of an underlying ち or つ (see rendaku), and the use of は, を, and へ to represent the sounds わ, お, and え, as relics of historical kana usage.
Korean hangul and Tibetan scripts were also originally extremely shallow orthographies, but as a representation of the modern language those frequently also reflect morphophonemic features.
=== Defective orthographies ===
An orthography based on a correspondence to phonemes may sometimes lack characters to represent all the phonemic distinctions in the language. This is called a defective orthography. An example in English is the lack of any indication of stress. Another is the digraph |th|, which represents two different phonemes (as in then and thin) and replaced the old letters |ð| and |þ|. A more systematic example is that of abjads like the Arabic and Hebrew alphabets, in which the short vowels are normally left unwritten and must be inferred by the reader.
When an alphabet is borrowed from its original language for use with a new language—as has been done with the Latin alphabet for many languages, or Japanese katakana for non-Japanese words—it often proves defective in representing the new language's phonemes. Sometimes this problem is addressed by the use of such devices as digraphs (such as |sh| and |ch| in English, where pairs of letters represent single sounds), diacritics (like the caron on the letters |š| and |č|, which represent those same sounds in Czech), or the addition of completely new symbols (as some languages have introduced the letter |w| to the Latin alphabet) or of symbols from another alphabet, such as the rune |þ| in Icelandic.
After the classical period, Greek developed a lowercase letter system with diacritics to enable foreigners to learn pronunciation and grammatical features. As pronunciation of letters changed over time, the diacritics were reduced to representing the stressed syllable. In Modern Greek typesetting, this system has been simplified to only have a single accent to indicate which syllable is stressed.
== See also ==
Cursive
Keyboard layout
Lateral masking
List of language disorders
Palaeography
Penmanship
Prescription and description
== References ==
=== Works cited ===
== Further reading ==
== External links == | Wikipedia/Orthography |
Baddeley's model of working memory is a model of human memory proposed by Alan Baddeley and Graham Hitch in 1974, in an attempt to present a more accurate model of primary memory (often referred to as short-term memory). Working memory splits primary memory into multiple components, rather than considering it to be a single, unified construct.
Baddeley and Hitch proposed their three-part working memory model as an alternative to the short-term store in Atkinson and Shiffrin's 'multi-store' memory model (1968). This model is later expanded upon by Baddeley and other co-workers to add a fourth component, and has become the dominant view in the field of working memory. However, alternative models are developing, providing a different perspective on the working memory system.
The original model of Baddeley & Hitch was composed of three main components: the central executive which acts as a supervisory system and controls the flow of information from and to its slave systems: the phonological loop and the visuo-spatial sketchpad. The phonological loop stores verbal content, whereas the visuo-spatial sketchpad caters to visuo-spatial data. Both the slave systems only function as short-term storage centers.
Baddeley and Hitch's argument for the distinction of two domain-specific slave systems in the older model was derived from experimental findings with dual-task paradigms. Performance of two simultaneous tasks requiring the use of two separate perceptual domains (i.e. a visual and a verbal task) is nearly as efficient as performance of the tasks individually. In contrast, when a person tries to carry out two tasks simultaneously that use the same perceptual domain, performance is less efficient than when performing the tasks individually.
A fourth component of Baddeley's model was added 25 years later to complement the central executive system. It was designated as episodic buffer. It is considered a limited-capacity system that provides temporary storage of information by conjoining information from the subsidiary systems, and long-term memory, into a single episodic representation.
== Components ==
=== Central executive ===
The central executive is a flexible system responsible for the control and regulation of cognitive processes. It directs focus and targets information, making working memory and long-term memory work together. It can be thought of as a supervisory system that controls cognitive processes, making sure the short-term store is actively working, and intervenes when they go astray and prevents distractions.
It has the following functions:
Updating and coding incoming information and replacing old information
Binding information from a number of sources into coherent episodes
Coordination of the slave systems
Shifting between tasks or retrieval strategies
Inhibition, suppressing dominant or automatic responses
Selective attention
The central executive has two main systems: the visuo-spatial sketchpad, for visual information, and the phonological loop, for verbal information.
Using the dual-task paradigm, Baddeley and Della Salla have found, for instance, that patients with Alzheimer's dementia are impaired when performing multiple tasks simultaneously, even when the difficulty of the individual tasks is adapted to their abilities. Two tasks include a memory tasks and a tracking task. Individual actions are completed well, but as the Alzheimer's becomes more prominent in a patient, performing two or more actions becomes more and more difficult. This research has shown the deteriorating of the central executive in individuals with Alzheimer's.
Recent research on executive functions suggests that the 'central' executive is not as central as conceived in the Baddeley & Hitch model. Rather, there seem to be separate executive functions that can vary largely independently between individuals and can be selectively impaired or spared by brain damage.
=== Phonological loop ===
The phonological loop (or articulatory loop) as a whole deals with sound or phonological information. It consists of two parts: a short-term phonological store with auditory memory traces that are subject to rapid decay and an articulatory rehearsal component (sometimes called the articulatory loop) that can revive the memory traces.
Any auditory verbal information is assumed to enter automatically into the phonological store. Visually presented language can be transformed into phonological code by silent articulation and thereby be encoded into the phonological store. This transformation is facilitated by the articulatory control process. The phonological store acts as an "inner ear", remembering speech sounds in their temporal order, whilst the articulatory process acts as an "inner voice" and repeats the series of words (or other speech elements) on a loop to prevent them from decaying. The phonological loop may play a key role in the acquisition of vocabulary, particularly in the early childhood years. It may also be vital for learning a second language.
Five main findings provide evidence for the phonological loop:
The effect of phonological similarity:Lists of words that sound similar are more difficult to remember than words that sound different. Semantic similarity (similarity of meaning) has comparatively little effect, supporting the assumption that verbal information is coded largely phonologically in working memory.
The effect of articulatory suppression:Memory for verbal material is impaired when people are asked to say something irrelevant aloud. This is assumed to block the articulatory rehearsal process, leading memory traces in the phonological loop to decay.
Transfer of information between codes:With visually presented items, adults usually name and sub-vocally rehearse them, so the information is transferred from a visual to an auditory encoding. Articulatory suppression prevents this transfer, and in that case the above-mentioned effect of phonological similarity is erased for visually presented items.
Neuropsychological evidence:A defective phonological store explains the behavior of patients with a specific deficit in phonological short-term memory. Aphasic patients with developmental verbal dyspraxia are unable to set up the speech motor codes necessary for articulation, caused by a deficiency of the articulatory rehearsal process.
On the other hand, patients with dysarthria, whose speech problems are secondary, show a normal capacity for rehearsal. This suggests that it is the subvocal rehearsing that is crucial.
==== Evidence in support of a phonological short-term store ====
An accumulation of literature across decades has lent strong support to the theory of phonological STS. In a 1971 study, Stephen Madigan demonstrated that a larger recency effect is seen during forward serial recall when people are presented a list auditorally as opposed to visually. (A smaller effect is seen in backwards serial recall.) In his study, auditory presentation led to greater recall of the most recently studied items. Catherine Penney expanded on this discovery to observe that modality effects can also be found in the case of free recall tasks. In 1965, Dallett had discovered that this observed modality effect is greatly reduced by the addition of a "suffix" item to the presented list; this suffix is a distractor item that is not to be recalled. Robert Greene utilized this observation in 1987 to discover that this suffix effect has a larger impact on lists learned auditorally as opposed to visually. The culmination of all of these findings results in strong support of the theory that there is a short-term store that phonologically stores recently learned items. In addition, Bloom and Watkins found that the suffix effect is greatly diminished when the suffix is not interpreted as linguistic sound, which agrees with the phonological short term store theory as it would be largely unaffected by non-linguistic distractors.
=== Visuo-spatial working memory ===
Alan Baddeley's theory of working memory has yet another aspect to which memory can be stored short term. The visuo-spatial sketchpad is the store that holds visual information for manipulation. The visuo-spatial sketchpad is thought to be its own storage of working memory in that it does not interfere with the short term processes of the phonological loop. In research, it has been found that the visuo-spatial sketchpad can work simultaneously with the phonological loop to process both auditory and visual stimuli without either of the processes affecting the efficacy of the other. Baddeley re-defined the theory of short-term memory as a working memory to explain this phenomenon. In the original theory of short-term memory, it is understood that a person only has one store of immediate information processing which could only hold a total of 7 items plus or minus two items to be stored in a very short period of time, sometimes a matter of seconds. The digit-span test is a perfect example of a measurement for classically defined short-term memory. Essentially, if one is not able to encode the 7 plus or minus two items within a few minutes by finding an existing association for the information to be transferred into long-term memory, then the information is lost and never encoded.
However, visuo-spatial short-term memory can retain visual and/or spatial information over brief periods of time. When this memory is in use, individuals are able to momentarily create and revisit a mental image that can be manipulated in complex or difficult tasks of spatial orientation. There are some who have disparities in the areas of the brain that allow for this to happen from different types of brain damage. There can also be a misunderstanding here in the differences between transient memories such as the visual sensory memory. A transient memory is merely a fleeting type of sensory memory; therefore, as the visual sensory memory is a type of sensory memory, there is a store for the information, but the store lasts for only a second or so. A common effect of the visual sensory memory is that individuals may remember seeing things that weren't really there or not remembering particular things that were in their line of sight. The memory is only momentary, and if it isn't attended to within a matter of seconds, it is gone.
There are two different pathways in the brain that control different functions of what is known inclusively as the visuo-spatial sketchpad. The sketchpad consists of the spatial short-term memory and the object memory. The spatial short-term memory is how one is able to learn and thus remember "where" they are in comparative representation to other objects. The object memory of the visuo-spatial sketchpad is essential in learning and remembering "what" an object is. The differences between these two differing visual abilities is due in large part because of different pathways of each of the abilities in the brain. The visual pathway in the brain that detects spatial representation of a person to and within their environment is the dorsal stream. The visual pathway that determines objects shapes, sizes, colors and other definitive characteristics is called the ventral stream. Each of these two streams runs independent of one another so that the visual system may process one without the other (like in brain damage for instance) or both simultaneously. The two streams do not depend on one another, so if one is functioning manipulatively, the other can still send its information through.
==== Logie's elaboration of the visuospatial sketchpad ====
Logie has proposed that the visuo-spatial sketchpad can be further subdivided into two components:
The visual cache, which stores information about form and color.
The inner scribe, which deals with spatial and movement information. It also rehearses information in the visual cache and transfers information to the central executive.
Three main findings provide evidence for the distinction between visual and spatial parts of the visuospatial sketchpad:
There is less interference between visual and spatial tasks than between two visual tasks or two spatial tasks.
Brain damage can influence one of the components without influencing the other.
Results from brain-imaging show that working memory tasks with visual objects activate mostly areas in the left hemisphere, whereas tasks with spatial information activate more areas in the right hemisphere.
=== Episodic buffer ===
In 2000 Baddeley added a fourth component to the model, the episodic buffer. This component is a limited capacity passive system, dedicated to linking information across domains to form integrated units of visual, spatial, and verbal information with time sequencing (or episodic chronological ordering), such as the memory of a story or a movie scene. The episodic buffer is also assumed to have links to long-term memory and semantic meaning.
The episodic buffer "acts as a buffer store, not only between the components of Working Memory, but also linking Working Memory to perception and Long-Term Memory". Baddeley assumes that "retrieval from the buffer occurred through conscious awareness". It allows individuals to use integrated units of information they already have to imagine new concepts. Since this is likely "an attention-demanding process...the buffer would depend heavily on the Central Executive".
The main motivation for introducing this component was the observation that some (in particular, highly intelligent) patients with amnesia, who presumably have no ability to encode new information in long-term memory, nevertheless have good short-term recall of stories, recalling much more information than could be held in the phonological loop. "The episodic buffer appears...capable of storing bound features and making them available to conscious awareness but not itself responsible for the process of binding".
It is assumed that "conscious access to the phonological loop or sketchpad may operate via the buffer". This is based on the assumption that both the visuo-spatial sketchpad and phonological loop act as minor buffers, combining information within their sensory area. The episodic buffer may also interact with smell and taste.
== Biology/neuroscience ==
There is much evidence for a brief memory buffer, as distinct from the long term store. The phonological loop seems to be connected to activation in the left hemisphere, more specifically the temporal lobe. The visuo-spatial sketchpad activates different areas depending on task difficulty; less intense tasks seem to activate in the occipital lobe, whereas more complex tasks appear in the parietal lobe. The central executive is still a mystery, although it would seem to be more or less located in the frontal lobes of the brain. The episodic buffer seems to be in both hemispheres (bilateral) with activations in both the frontal and temporal lobes, and even the left portion of the hippocampus. In terms of genetics, the gene ROBO1 has been associated with phonological buffer integrity or length.
== Validity of the model ==
The strength of Baddeley's model is its ability to integrate a large number of findings from work on short-term and working memory. Additionally, the mechanisms of the slave systems, especially the phonological loop, has inspired a wealth of research in experimental psychology, neuropsychology, and cognitive neuroscience.
However, criticisms have been raised, for instance of the phonological-loop component, because some details of the findings are not easily explained by the original Baddeley and Hitch model, including the controversy regarding the 7±2 rule.
The episodic buffer is seen as a helpful addition to the model of working memory, but it has not been investigated extensively and its functions remain unclear.
== See also ==
Echoic memory
Prefrontal cortex § Attention and memory
The Magical Number Seven, Plus or Minus Two
Working memory
== References ==
=== Notes ===
=== Bibliography === | Wikipedia/Baddeley's_model_of_working_memory |
Logic Theorist is a computer program written in 1956 by Allen Newell, Herbert A. Simon, and Cliff Shaw. It was the first program deliberately engineered to perform automated reasoning, and has been described as "the first artificial intelligence program". Logic Theorist proved 38 of the first 52 theorems in chapter two of Whitehead and Bertrand Russell's Principia Mathematica, and found new and shorter proofs for some of them.
== History ==
In 1955, when Newell and Simon began to work on the Logic Theorist, the field of artificial intelligence did not yet exist; the term "artificial intelligence" would not be coined until the following summer.
Simon was a political scientist who had previously studied the way bureaucracies function as well as developing his theory of bounded rationality (for which he would later win a Nobel Prize). He believed the study of business organizations requires, like artificial intelligence, an insight into the nature of human problem solving and decision making. Simon has stated that when consulting at RAND Corporation in the early 1950s, he saw a printer typing out a map, using ordinary letters and punctuation as symbols. This led him to think that a machine that could manipulate symbols could simulate decision making and possibly even the process of human thought.
The program that printed the map had been written by Newell, a RAND scientist studying logistics and organization theory. For Newell, the decisive moment was in 1954 when Oliver Selfridge came to RAND to describe his work on pattern matching. Watching the presentation, Newell suddenly understood how the interaction of simple, programmable units could accomplish complex behavior, including the intelligent behavior of human beings. "It all happened in one afternoon," he would later say. It was a rare moment of scientific epiphany.
"I had such a sense of clarity that this was a new path, and one I was going to go down. I haven't had that sensation very many times. I'm pretty skeptical, and so I don't normally go off on a toot, but I did on that one. Completely absorbed in it—without existing with the two or three levels consciousness so that you're working, and aware that you're working, and aware of the consequences and implications, the normal mode of thought. No. Completely absorbed for ten to twelve hours."
Newell and Simon began to talk about the possibility of teaching machines to think. Their first project was a program that could prove mathematical theorems like the ones used in Bertrand Russell and Alfred North Whitehead's Principia Mathematica. They enlisted the help of computer programmer Cliff Shaw, also from RAND, to develop the program. (Newell says "Cliff was the genuine computer scientist of the three".)
The first version was hand-simulated: they wrote the program onto 3x5 cards and, as Simon recalled:In January 1956, we assembled my wife and three children together with some graduate students. To each member of the group, we gave one of the cards, so that each one became, in effect, a component of the computer program ... Here was nature imitating art imitating nature.
They succeeded in showing that the program could successfully prove theorems as well as a talented mathematician. Eventually Shaw was able to run the program on the computer at RAND's Santa Monica facility.
In the summer of 1956, John McCarthy, Marvin Minsky, Claude Shannon and Nathan Rochester organized a conference on the subject of what they called "artificial intelligence" (a term coined by McCarthy for the occasion). Newell and Simon proudly presented the group with the Logic Theorist. It was met with a lukewarm reception. Pamela McCorduck writes "the evidence is that nobody save Newell and Simon themselves sensed the long-range significance of what they were doing." Simon confides that "we were probably fairly arrogant about it all" and adds:
They didn't want to hear from us, and we sure didn't want to hear from them: we had something to show them! ... In a way it was ironic because we already had done the first example of what they were after; and second, they didn't pay much attention to it.
Logic Theorist soon proved 38 of the first 52 theorems in chapter 2 of the Principia Mathematica. The proof of theorem 2.85 was actually more elegant than the proof produced laboriously by hand by Russell and Whitehead. Simon was able to show the new proof to Russell himself who "responded with delight". They attempted to publish the new proof in The Journal of Symbolic Logic, but it was rejected on the grounds that a new proof of an elementary mathematical theorem was not notable, apparently overlooking the fact that one of the authors was a computer program.
Newell and Simon formed a lasting partnership, founding one of the first AI laboratories at the Carnegie Institute of Technology and developing a series of influential artificial intelligence programs and ideas, including the General Problem Solver, Soar, and their unified theory of cognition.
== Architecture ==
The Logic Theorist is a program that performs logical processes on logical expressions. The Logic Theorist operates on the following principles:
=== Expressions ===
An expression is made of elements.
There are two kinds of memories: working and storage.
Each working memory contains a single element. The Logic Theorist usually uses 1 to 3 working memories.
Each storage memory is a list representing a full expression or a set of elements. In particular, it contains all the axioms and proven logical theorems.
An expression is an abstract syntax tree, each node being an element with up to 11 attributes.
For example, the logical expression
¬
P
→
(
Q
∧
¬
P
)
{\displaystyle \neg P\to (Q\wedge \neg P)}
is represented as a tree with a root element representing
→
{\displaystyle \to }
. Among the attributes of the root element are pointers to the two elements representing the subexpressions
¬
P
{\displaystyle \neg P}
and
Q
∧
¬
P
{\displaystyle Q\wedge \neg P}
.
=== Processes ===
There are four kinds of processes, from the lowest to the highest level.
Instruction: These are similar to assembly code. They may either perform a primitive operation on an expression in working memory, or perform a conditional jump to another instruction. An example is "put the right sub-element of working-memory 1 to working-memory 2"
Elementary process: These are similar to subroutines. A sequence of instructions that can be called.
Method: A sequence of elementary processes. There are 4 methods:
substitution: given an expression, it attempts to transform it to a proven theorem or axiom by substitutions of variables and logical connectives.
detachment: given expression
B
{\displaystyle B}
, it attempts to find a proven theorem or axiom of form
A
→
B
′
{\displaystyle A\to B'}
, where
B
′
{\displaystyle B'}
yields
B
{\displaystyle B}
after substitution, then attempts to prove
A
{\displaystyle A}
by substitution.
chaining forward: given expression
A
→
C
{\displaystyle A\to C}
, it attempts to find for a proven theorem or axiom of form
A
→
B
{\displaystyle A\to B}
, then attempt to prove
B
→
C
{\displaystyle B\to C}
by substitution.
chaining backward: given expression
A
→
C
{\displaystyle A\to C}
, it attempts to find for a proven theorem or axiom of form
B
→
C
{\displaystyle B\to C}
, then attempt to prove
A
→
B
{\displaystyle A\to B}
by substitution.
executive control method: This method applies each of the 4 methods in sequence to each theorem to be proved.
== Logic Theorist's influence on AI ==
Logic Theorist introduced several concepts that would be central to AI research:
Reasoning as search
Logic Theorist explored a search tree: the root was the initial hypothesis, each branch was a deduction based on the rules of logic. Somewhere in the tree was the goal: the proposition the program intended to prove. The pathway along the branches that led to the goal was a proof – a series of statements, each deduced using the rules of logic, that led from the hypothesis to the proposition to be proved.
Heuristics
Newell and Simon realized that the search tree would grow exponentially and that they needed to "trim" some branches, using "rules of thumb" to determine which pathways were unlikely to lead to a solution. They called these ad hoc rules "heuristics", using a term introduced by George Pólya in his classic book on mathematical proof, How to Solve It. (Newell had taken courses from Pólya at Stanford). Heuristics would become an important area of research in artificial intelligence and remains an important method to overcome the intractable combinatorial explosion of exponentially growing searches.
List processing
To implement Logic Theorist on a computer, the three researchers developed a programming language, IPL, which used the same form of symbolic list processing that would later form the basis of McCarthy's Lisp programming language, an important language still used by AI researchers.
== Philosophical implications ==
Pamela McCorduck writes that the Logic Theorist was "proof positive that a machine could perform tasks heretofore considered intelligent, creative and uniquely human". And, as such, it represents a milestone in the development of artificial intelligence and our understanding of intelligence in general.
Simon told a graduate class in January 1956, "Over Christmas, Al Newell and I invented a thinking machine,"
and would write:
[We] invented a computer program capable of thinking non-numerically, and thereby solved the venerable mind-body problem, explaining how a system composed of matter can have the properties of mind.
This statement, that machines can have minds just as people do, would be later named "Strong AI" by philosopher John Searle. It remains a serious subject of debate up to the present day.
Pamela McCorduck also sees in the Logic Theorist the debut of a new theory of the mind, the information processing model (sometimes called computationalism or cognitivism). She writes that "this view would come to be central to their later work, and in their opinion, as central to understanding mind in the 20th century as Darwin's principle of natural selection had been to understanding biology in the nineteenth century." Newell and Simon would later formalize this proposal as the physical symbol systems hypothesis.
== Notes ==
== Citations ==
== References ==
Crevier, Daniel (1993). AI: The Tumultuous Search for Artificial Intelligence. New York, NY: BasicBooks. ISBN 0-465-02997-3., pp. 44–46.
McCorduck, Pamela (2004), Machines Who Think (2nd ed.), Natick, Massachusetts: A. K. Peters, ISBN 1-5688-1205-1, pp. 161–170.
Russell, Stuart J.; Norvig, Peter. (2021). Artificial Intelligence: A Modern Approach (4th ed.). Hoboken: Pearson. ISBN 9780134610993. LCCN 20190474.
== External links ==
Newell and Simon's RAND Corporation report on the Logic Theorist
Full length version of Newell and Simon's RAND Corporation report on the Logic Theorist
CMU Libraries: Human and Machine Minds
Source code as PDF on Github | Wikipedia/Logic_Theory_Machine |
Daniel Dennett's multiple drafts model (MDM) of consciousness is a physicalist theory of consciousness based upon cognitivism, which views the mind in terms of information processing. The theory is described in depth in his book, Consciousness Explained, published in 1991. As the title states, the book proposes a high-level explanation of consciousness which is consistent with support for the possibility of strong AI.
Dennett describes the theory as first-person operationalism. As he states it:
The Multiple Drafts model makes [the procedure of] "writing it down" in memory criterial for consciousness: that is what it is for the "given" to be "taken" ... There is no reality of conscious experience independent of the effects of various vehicles of content on subsequent action (and hence, of course, on memory).
== The thesis of multiple drafts ==
Dennett's thesis is that our modern understanding of consciousness is unduly influenced by the ideas of René Descartes. To show why, he starts with a description of the phi illusion. In this experiment, two different coloured lights, with an angular separation of a few degrees at the eye, are flashed in succession. If the interval between the flashes is less than a second or so, the first light that is flashed appears to move across to the position of the second light. Furthermore, the light seems to change colour as it moves across the visual field. A green light will appear to turn red as it seems to move across to the position of a red light. Dennett asks how we could see the light change colour before the second light is observed.
Dennett claims that conventional explanations of the colour change boil down to either Orwellian or Stalinesque hypotheses, which he says are the result of Descartes' continued influence on our vision of the mind. In an Orwellian hypothesis, the subject comes to one conclusion, then goes back and changes that memory in light of subsequent events. This is akin to George Orwell's Nineteen Eighty-Four, where records of the past are routinely altered. In a Stalinesque hypothesis, the two events would be reconciled prior to entering the subject's consciousness, with the final result presented as fully resolved. This is akin to Joseph Stalin's show trials, where the verdict has been decided in advance and the trial is just a rote presentation.
[W]e can suppose, both theorists have exactly the same theory of what happens in your brain; they agree about just where and when in the brain the mistaken content enters the causal pathways; they just disagree about whether that location is to be deemed pre-experiential or post-experiential. ... [T]hey even agree about how it ought to "feel" to subjects: Subjects should be unable to tell the difference between misbegotten experiences and immediately misremembered experiences. [p. 125, original emphasis.]
Dennett argues that there is no principled basis for picking one of these theories over the other, because they share a common error in supposing that there is a special time and place where unconscious processing becomes consciously experienced, entering into what Dennett calls the "Cartesian theatre". Both theories require us to cleanly divide a sequence of perceptions and reactions into before and after the instant that they reach the seat of consciousness, but he denies that there is any such moment, as it would lead to infinite regress. Instead, he asserts that there is no privileged place in the brain where consciousness happens. Dennett states that, "[t]here does not exist ... a process such as 'recruitment of consciousness' (into what?), nor any place where the 'vehicle's arrival' is recognized (by whom?)"
Cartesian materialism is the view that there is a crucial finish line or boundary somewhere in the brain, marking a place where the order of arrival equals the order of "presentation" in experience because what happens there is what you are conscious of. ... Many theorists would insist that they have explicitly rejected such an obviously bad idea. But ... the persuasive imagery of the Cartesian Theater keeps coming back to haunt us—laypeople and scientists alike—even after its ghostly dualism has been denounced and exorcized. [p. 107, original emphasis.]
With no theatre, there is no screen, hence no reason to re-present data after it has already been analysed. Dennett says that, "the Multiple Drafts model goes on to claim that the brain does not bother 'constructing' any representations that go to the trouble of 'filling in' the blanks. That would be a waste of time and (shall we say?) paint. The judgement is already in so we can get on with other tasks!"
According to the model, there are a variety of sensory inputs from a given event and also a variety of interpretations of these inputs. The sensory inputs arrive in the brain and are interpreted at different times, so a given event can give rise to a succession of discriminations, constituting the equivalent of multiple drafts of a story. As soon as each discrimination is accomplished, it becomes available for eliciting a behaviour; it does not have to wait to be presented at the theatre.
Like a number of other theories, the Multiple Drafts model understands conscious experience as taking time to occur, such that percepts do not instantaneously arise in the mind in their full richness. The distinction is that Dennett's theory denies any clear and unambiguous boundary separating conscious experiences from all other processing. According to Dennett, consciousness is to be found in the actions and flows of information from place to place, rather than some singular view containing our experience. There is no central experiencer who confers a durable stamp of approval on any particular draft.
Different parts of the neural processing assert more or less control at different times. For something to reach consciousness is akin to becoming famous, in that it must leave behind consequences by which it is remembered. To put it another way, consciousness is the property of having enough influence to affect what the mouth will say and the hands will do. Which inputs are "edited" into our drafts is not an exogenous act of supervision, but part of the self-organizing functioning of the network, and at the same level as the circuitry that conveys information bottom-up.
The conscious self is taken to exist as an abstraction visible at the level of the intentional stance, akin to a body of mass having a "centre of gravity". Analogously, Dennett refers to the self as the "centre of narrative gravity", a story we tell ourselves about our experiences. Consciousness exists, but not independently of behaviour and behavioural disposition, which can be studied through heterophenomenology.
The origin of this operationalist approach can be found in Dennett's immediately preceding work. Dennett (1988) explains consciousness in terms of access consciousness alone, denying the independent existence of what Ned Block has labeled phenomenal consciousness. He argues that "Everything real has properties, and since I don't deny the reality of conscious experience, I grant that conscious experience has properties". Having related all consciousness to properties, he concludes that they cannot be meaningfully distinguished from our judgements about them. He writes:
The infallibilist line on qualia treats them as properties of one's experience one cannot in principle misdiscover, and this is a mysterious doctrine (at least as mysterious as papal infallibility) unless we shift the emphasis a little and treat qualia as logical constructs out of subjects' qualia-judgments: a subject's experience has the quale F if and only if the subject judges his experience to have quale F. We can then treat such judgings as constitutive acts, in effect, bringing the quale into existence by the same sort of license as novelists have to determine the hair color of their characters by fiat. We do not ask how Dostoevski knows that Raskolnikov's hair is light brown.
In other words, once we've explained a perception fully in terms of how it affects us, there is nothing left to explain. In particular, there is no such thing as a perception which may be considered in and of itself (a quale). Instead, the subject's honest reports of how things seem to them are inherently authoritative on how things seem to them, but not on the matter of how things actually are.
So when we look one last time at our original characterization of qualia, as ineffable, intrinsic, private, directly apprehensible properties of experience, we find that there is nothing to fill the bill. In their place are relatively or practically ineffable public properties we can refer to indirectly via reference to our private property-detectors—private only in the sense of idiosyncratic. And insofar as we wish to cling to our subjective authority about the occurrence within us of states of certain types or with certain properties, we can have some authority—not infallibility or incorrigibility, but something better than sheer guessing—but only if we restrict ourselves to relational, extrinsic properties like the power of certain internal states of ours to provoke acts of apparent re-identification. So contrary to what seems obvious at first blush, there simply are no qualia at all.
The key to the multiple drafts model is that, after removing qualia, explaining consciousness boils down to explaining the behaviour we recognise as conscious. Consciousness is as consciousness does.
== Critical responses ==
Psychobiologist John Staddon contrasts a simple "new behaviorism" interpretation of color phi with Dennett and Kinsbourne's account. The basic idea is that because of well-known processes such as lateral inhibition, the internal states created by the two stimuli are identical, hence are so reported. Bogen (1992) points out that the brain is bilaterally symmetrical. That being the case, if Cartesian materialism is true, there might be two Cartesian theatres, so arguments against only one are flawed. Velmans (1992) argues that the phi effect and the cutaneous rabbit illusion demonstrate that there is a delay whilst modelling occurs and that this delay was discovered by Benjamin Libet.
It has also been claimed that the argument in the multiple drafts model does not support its conclusion.
=== "Straw man" ===
Much of the criticism asserts that Dennett's theory attacks the wrong target, failing to explain what it claims to. Chalmers (1996) maintains that Dennett has produced no more than a theory of how subjects report events. Some even parody the title of the book as "Consciousness Explained Away", accusing him of greedy reductionism. Another line of criticism disputes the accuracy of Dennett's characterisations of existing theories:
The now standard response to Dennett's project is that he has picked a fight with a straw man. Cartesian materialism, it is alleged, is an impossibly naive account of phenomenal consciousness held by no one currently working in cognitive science or the philosophy of mind. Consequently, whatever the effectiveness of Dennett's demolition job, it is fundamentally misdirected (see, e.g., Block, 1993, 1995; Shoemaker, 1993; and Tye, 1993).
=== Unoriginality ===
Multiple drafts is also attacked for making a claim to novelty. It may be the case, however, that such attacks mistake which features Dennett is claiming as novel. Korb states that, "I believe that the central thesis will be relatively uncontentious for most cognitive scientists, but that its use as a cleaning solvent for messy puzzles will be viewed less happily in most quarters." (Korb 1993) In this way, Dennett uses uncontroversial ideas towards more controversial ends, leaving him open to claims of unoriginality when uncontroversial parts are focused upon.
Even the notion of consciousness as drafts is not unique to Dennett. According to Hankins, Dieter Teichert suggests that Paul Ricoeur's theories agree with Dennett's on the notion that "the self is basically a narrative entity, and that any attempt to give it a free-floating independent status is misguided." [Hankins] Others see Derrida's (1982) representationalism as consistent with the notion of a mind that has perceptually changing content without a definitive present instant.
To those who believe that consciousness entails something more than behaving in all ways conscious, Dennett's view is seen as eliminativist, since it denies the existence of qualia and the possibility of philosophical zombies. However, Dennett is not denying the existence of the mind or of consciousness, only what he considers a naive view of them. The point of contention is whether Dennett's own definitions are indeed more accurate: whether what we think of when we speak of perceptions and consciousness can be understood in terms of nothing more than their effect on behaviour.
=== Information processing and consciousness ===
The role of information processing in consciousness has been criticised by John Searle who, in his Chinese room argument, states that he cannot find anything that could be recognised as conscious experience in a system that relies solely on motions of things from place to place. Dennett sees this argument as misleading, arguing that consciousness is not to be found in a specific part of the system, but in the actions of the whole. In essence, he denies that consciousness requires something in addition to capacity for behaviour, saying that philosophers such as Searle, "just can't imagine how understanding could be a property that emerges from lots of distributed quasi-understanding in a large system".
== See also ==
Artificial consciousness
Cognitive model
Conceptual space
Global Workspace Theory
Image schema
== References ==
== Bibliography ==
== Further reading == | Wikipedia/Multiple_drafts_model |
Computer simulation is the running of a mathematical model on a computer, the model being designed to represent the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be determined by comparing their results to the real-world outcomes they aim to predict. Computer simulations have become a useful tool for the mathematical modeling of many natural systems in physics (computational physics), astrophysics, climatology, chemistry, biology and manufacturing, as well as human systems in economics, psychology, social science, health care and engineering. Simulation of a system is represented as the running of the system's model. It can be used to explore and gain new insights into new technology and to estimate the performance of systems too complex for analytical solutions.
Computer simulations are realized by running computer programs that can be either small, running almost instantly on small devices, or large-scale programs that run for hours or days on network-based groups of computers. The scale of events being simulated by computer simulations has far exceeded anything possible (or perhaps even imaginable) using traditional paper-and-pencil mathematical modeling. In 1997, a desert-battle simulation of one force invading another involved the modeling of 66,239 tanks, trucks and other vehicles on simulated terrain around Kuwait, using multiple supercomputers in the DoD High Performance Computer Modernization Program.
Other examples include a 1-billion-atom model of material deformation; a 2.64-million-atom model of the complex protein-producing organelle of all living organisms, the ribosome, in 2005;
a complete simulation of the life cycle of Mycoplasma genitalium in 2012; and the Blue Brain project at EPFL (Switzerland), begun in May 2005 to create the first computer simulation of the entire human brain, right down to the molecular level.
Because of the computational cost of simulation, computer experiments are used to perform inference such as uncertainty quantification.
== Simulation versus model ==
A model consists of the equations used to capture the behavior of a system. By contrast, computer simulation is the actual running of the program that perform algorithms which solve those equations, often in an approximate manner. Simulation, therefore, is the process of running a model. Thus one would not "build a simulation"; instead, one would "build a model (or a simulator)", and then either "run the model" or equivalently "run a simulation".
== History ==
Computer simulation developed hand-in-hand with the rapid growth of the computer, following its first large-scale deployment during the Manhattan Project in World War II to model the process of nuclear detonation. It was a simulation of 12 hard spheres using a Monte Carlo algorithm. Computer simulation is often used as an adjunct to, or substitute for, modeling systems for which simple closed form analytic solutions are not possible. There are many types of computer simulations; their common feature is the attempt to generate a sample of representative scenarios for a model in which a complete enumeration of all possible states of the model would be prohibitive or impossible.
== Data preparation ==
The external data requirements of simulations and models vary widely. For some, the input might be just a few numbers (for example, simulation of a waveform of AC electricity on a wire), while others might require terabytes of information (such as weather and climate models).
Input sources also vary widely:
Sensors and other physical devices connected to the model;
Control surfaces used to direct the progress of the simulation in some way;
Current or historical data entered by hand;
Values extracted as a by-product from other processes;
Values output for the purpose by other simulations, models, or processes.
Lastly, the time at which data is available varies:
"invariant" data is often built into the model code, either because the value is truly invariant (e.g., the value of π) or because the designers consider the value to be invariant for all cases of interest;
data can be entered into the simulation when it starts up, for example by reading one or more files, or by reading data from a preprocessor;
data can be provided during the simulation run, for example by a sensor network.
Because of this variety, and because diverse simulation systems have many common elements, there are a large number of specialized simulation languages. The best-known may be Simula. There are now many others.
Systems that accept data from external sources must be very careful in knowing what they are receiving. While it is easy for computers to read in values from text or binary files, what is much harder is knowing what the accuracy (compared to measurement resolution and precision) of the values are. Often they are expressed as "error bars", a minimum and maximum deviation from the value range within which the true value (is expected to) lie. Because digital computer mathematics is not perfect, rounding and truncation errors multiply this error, so it is useful to perform an "error analysis" to confirm that values output by the simulation will still be usefully accurate.
== Types ==
Models used for computer simulations can be classified according to several independent pairs of attributes, including:
Stochastic or deterministic (and as a special case of deterministic, chaotic) – see external links below for examples of stochastic vs. deterministic simulations
Steady-state or dynamic
Continuous or discrete (and as an important special case of discrete, discrete event or DE models)
Dynamic system simulation, e.g. electric systems, hydraulic systems or multi-body mechanical systems (described primarily by DAE:s) or dynamics simulation of field problems, e.g. CFD of FEM simulations (described by PDE:s).
Local or distributed.
Another way of categorizing models is to look at the underlying data structures. For time-stepped simulations, there are two main classes:
Simulations which store their data in regular grids and require only next-neighbor access are called stencil codes. Many CFD applications belong to this category.
If the underlying graph is not a regular grid, the model may belong to the meshfree method class.
For steady-state simulations, equations define the relationships between elements of the modeled system and attempt to find a state in which the system is in equilibrium. Such models are often used in simulating physical systems, as a simpler modeling case before dynamic simulation is attempted.
Dynamic simulations attempt to capture changes in a system in response to (usually changing) input signals.
Stochastic models use random number generators to model chance or random events;
A discrete event simulation (DES) manages events in time. Most computer, logic-test and fault-tree simulations are of this type. In this type of simulation, the simulator maintains a queue of events sorted by the simulated time they should occur. The simulator reads the queue and triggers new events as each event is processed. It is not important to execute the simulation in real time. It is often more important to be able to access the data produced by the simulation and to discover logic defects in the design or the sequence of events.
A continuous dynamic simulation performs numerical solution of differential-algebraic equations or differential equations (either partial or ordinary). Periodically, the simulation program solves all the equations and uses the numbers to change the state and output of the simulation. Applications include flight simulators, construction and management simulation games, chemical process modeling, and simulations of electrical circuits. Originally, these kinds of simulations were actually implemented on analog computers, where the differential equations could be represented directly by various electrical components such as op-amps. By the late 1980s, however, most "analog" simulations were run on conventional digital computers that emulate the behavior of an analog computer.
A special type of discrete simulation that does not rely on a model with an underlying equation, but can nonetheless be represented formally, is agent-based simulation. In agent-based simulation, the individual entities (such as molecules, cells, trees or consumers) in the model are represented directly (rather than by their density or concentration) and possess an internal state and set of behaviors or rules that determine how the agent's state is updated from one time-step to the next.
Distributed models run on a network of interconnected computers, possibly through the Internet. Simulations dispersed across multiple host computers like this are often referred to as "distributed simulations". There are several standards for distributed simulation, including Aggregate Level Simulation Protocol (ALSP), Distributed Interactive Simulation (DIS), the High Level Architecture (simulation) (HLA) and the Test and Training Enabling Architecture (TENA).
== Visualization ==
Formerly, the output data from a computer simulation was sometimes presented in a table or a matrix showing how data were affected by numerous changes in the simulation parameters. The use of the matrix format was related to traditional use of the matrix concept in mathematical models. However, psychologists and others noted that humans could quickly perceive trends by looking at graphs or even moving-images or motion-pictures generated from the data, as displayed by computer-generated-imagery (CGI) animation. Although observers could not necessarily read out numbers or quote math formulas, from observing a moving weather chart they might be able to predict events (and "see that rain was headed their way") much faster than by scanning tables of rain-cloud coordinates. Such intense graphical displays, which transcended the world of numbers and formulae, sometimes also led to output that lacked a coordinate grid or omitted timestamps, as if straying too far from numeric data displays. Today, weather forecasting models tend to balance the view of moving rain/snow clouds against a map that uses numeric coordinates and numeric timestamps of events.
Similarly, CGI computer simulations of CAT scans can simulate how a tumor might shrink or change during an extended period of medical treatment, presenting the passage of time as a spinning view of the visible human head, as the tumor changes.
Other applications of CGI computer simulations are being developed to graphically display large amounts of data, in motion, as changes occur during a simulation run.
== In science ==
Generic examples of types of computer simulations in science, which are derived from an underlying mathematical description:
a numerical simulation of differential equations that cannot be solved analytically, theories that involve continuous systems such as phenomena in physical cosmology, fluid dynamics (e.g., climate models, roadway noise models, roadway air dispersion models), continuum mechanics and chemical kinetics fall into this category.
a stochastic simulation, typically used for discrete systems where events occur probabilistically and which cannot be described directly with differential equations (this is a discrete simulation in the above sense). Phenomena in this category include genetic drift, biochemical or gene regulatory networks with small numbers of molecules. (see also: Monte Carlo method).
multiparticle simulation of the response of nanomaterials at multiple scales to an applied force for the purpose of modeling their thermoelastic and thermodynamic properties. Techniques used for such simulations are Molecular dynamics, Molecular mechanics, Monte Carlo method, and Multiscale Green's function.
Specific examples of computer simulations include:
statistical simulations based upon an agglomeration of a large number of input profiles, such as the forecasting of equilibrium temperature of receiving waters, allowing the gamut of meteorological data to be input for a specific locale. This technique was developed for thermal pollution forecasting.
agent based simulation has been used effectively in ecology, where it is often called "individual based modeling" and is used in situations for which individual variability in the agents cannot be neglected, such as population dynamics of salmon and trout (most purely mathematical models assume all trout behave identically).
time stepped dynamic model. In hydrology there are several such hydrology transport models such as the SWMM and DSSAM Models developed by the U.S. Environmental Protection Agency for river water quality forecasting.
computer simulations have also been used to formally model theories of human cognition and performance, e.g., ACT-R.
computer simulation using molecular modeling for drug discovery.
computer simulation to model viral infection in mammalian cells.
computer simulation for studying the selective sensitivity of bonds by mechanochemistry during grinding of organic molecules.
Computational fluid dynamics simulations are used to simulate the behaviour of flowing air, water and other fluids. One-, two- and three-dimensional models are used. A one-dimensional model might simulate the effects of water hammer in a pipe. A two-dimensional model might be used to simulate the drag forces on the cross-section of an aeroplane wing. A three-dimensional simulation might estimate the heating and cooling requirements of a large building.
An understanding of statistical thermodynamic molecular theory is fundamental to the appreciation of molecular solutions. Development of the Potential Distribution Theorem (PDT) allows this complex subject to be simplified to down-to-earth presentations of molecular theory.
Notable, and sometimes controversial, computer simulations used in science include: Donella Meadows' World3 used in the Limits to Growth, James Lovelock's Daisyworld and Thomas Ray's Tierra.
In social sciences, computer simulation is an integral component of the five angles of analysis fostered by the data percolation methodology, which also includes qualitative and quantitative methods, reviews of the literature (including scholarly), and interviews with experts, and which forms an extension of data triangulation. Of course, similar to any other scientific method, replication is an important part of computational modeling
== In practical contexts ==
Computer simulations are used in a wide variety of practical contexts, such as:
analysis of air pollutant dispersion using atmospheric dispersion modeling
As a possible humane alternative to live animal testing in respect to animal rights.
design of complex systems such as aircraft and also logistics systems.
design of noise barriers to effect roadway noise mitigation
modeling of application performance
flight simulators to train pilots
weather forecasting
forecasting of risk
simulation of electrical circuits
Power system simulation
simulation of other computers is emulation.
forecasting of prices on financial markets (for example Adaptive Modeler)
behavior of structures (such as buildings and industrial parts) under stress and other conditions
design of industrial processes, such as chemical processing plants
strategic management and organizational studies
reservoir simulation for the petroleum engineering to model the subsurface reservoir
process engineering simulation tools.
robot simulators for the design of robots and robot control algorithms
urban simulation models that simulate dynamic patterns of urban development and responses to urban land use and transportation policies.
traffic engineering to plan or redesign parts of the street network from single junctions over cities to a national highway network to transportation system planning, design and operations. See a more detailed article on Simulation in Transportation.
modeling car crashes to test safety mechanisms in new vehicle models.
crop-soil systems in agriculture, via dedicated software frameworks (e.g. BioMA, OMS3, APSIM)
The reliability and the trust people put in computer simulations depends on the validity of the simulation model, therefore verification and validation are of crucial importance in the development of computer simulations. Another important aspect of computer simulations is that of reproducibility of the results, meaning that a simulation model should not provide a different answer for each execution. Although this might seem obvious, this is a special point of attention in stochastic simulations, where random numbers should actually be semi-random numbers. An exception to reproducibility are human-in-the-loop simulations such as flight simulations and computer games. Here a human is part of the simulation and thus influences the outcome in a way that is hard, if not impossible, to reproduce exactly.
Vehicle manufacturers make use of computer simulation to test safety features in new designs. By building a copy of the car in a physics simulation environment, they can save the hundreds of thousands of dollars that would otherwise be required to build and test a unique prototype. Engineers can step through the simulation milliseconds at a time to determine the exact stresses being put upon each section of the prototype.
Computer graphics can be used to display the results of a computer simulation. Animations can be used to experience a simulation in real-time, e.g., in training simulations. In some cases animations may also be useful in faster than real-time or even slower than real-time modes. For example, faster than real-time animations can be useful in visualizing the buildup of queues in the simulation of humans evacuating a building. Furthermore, simulation results are often aggregated into static images using various ways of scientific visualization.
In debugging, simulating a program execution under test (rather than executing natively) can detect far more errors than the hardware itself can detect and, at the same time, log useful debugging information such as instruction trace, memory alterations and instruction counts. This technique can also detect buffer overflow and similar "hard to detect" errors as well as produce performance information and tuning data.
== Pitfalls ==
Although sometimes ignored in computer simulations, it is very important to perform a sensitivity analysis to ensure that the accuracy of the results is properly understood. For example, the probabilistic risk analysis of factors determining the success of an oilfield exploration program involves combining samples from a variety of statistical distributions using the Monte Carlo method. If, for instance, one of the key parameters (e.g., the net ratio of oil-bearing strata) is known to only one significant figure, then the result of the simulation might not be more precise than one significant figure, although it might (misleadingly) be presented as having four significant figures.
== See also ==
== References ==
== Further reading ==
Young, Joseph and Findley, Michael. 2014. "Computational Modeling to Study Conflicts and Terrorism." Routledge Handbook of Research Methods in Military Studies edited by Soeters, Joseph; Shields, Patricia and Rietjens, Sebastiaan. pp. 249–260. New York: Routledge,
R. Frigg and S. Hartmann, Models in Science. Entry in the Stanford Encyclopedia of Philosophy.
E. Winsberg Simulation in Science. Entry in the Stanford Encyclopedia of Philosophy.
S. Hartmann, The World as a Process: Simulations in the Natural and Social Sciences, in: R. Hegselmann et al. (eds.), Modelling and Simulation in the Social Sciences from the Philosophy of Science Point of View, Theory and Decision Library. Dordrecht: Kluwer 1996, 77–100.
E. Winsberg, Science in the Age of Computer Simulation. Chicago: University of Chicago Press, 2010.
P. Humphreys, Extending Ourselves: Computational Science, Empiricism, and Scientific Method. Oxford: Oxford University Press, 2004.
James J. Nutaro (2011). Building Software for Simulation: Theory and Algorithms, with Applications in C++. John Wiley & Sons. ISBN 978-1-118-09945-2.
Desa, W. L. H. M., Kamaruddin, S., & Nawawi, M. K. M. (2012). Modeling of Aircraft Composite Parts Using Simulation. Advanced Material Research, 591–593, 557–560.
== External links ==
Guide to the Computer Simulation Oral History Archive 2003-2018 | Wikipedia/Computational_modelling |
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. Model organisms are widely used to research human disease when human experimentation would be unfeasible or unethical. This strategy is made possible by the common descent of all living organisms, and the conservation of metabolic and developmental pathways and genetic material over the course of evolution.
Research using animal models has been central to most of the achievements of modern medicine. It has contributed most of the basic knowledge in fields such as human physiology and biochemistry, and has played significant roles in fields such as neuroscience and infectious disease. The results have included the near-eradication of polio and the development of organ transplantation, and have benefited both humans and animals. From 1910 to 1927, Thomas Hunt Morgan's work with the fruit fly Drosophila melanogaster identified chromosomes as the vector of inheritance for genes, and Eric Kandel wrote that Morgan's discoveries "helped transform biology into an experimental science". Research in model organisms led to further medical advances, such as the production of the diphtheria antitoxin and the 1922 discovery of insulin and its use in treating diabetes, which had previously meant death. Modern general anaesthetics such as halothane were also developed through studies on model organisms, and are necessary for modern, complex surgical operations. Other 20th-century medical advances and treatments that relied on research performed in animals include organ transplant techniques, the heart-lung machine, antibiotics, and the whooping cough vaccine.
In researching human disease, model organisms allow for better understanding the disease process without the added risk of harming an actual human. The species of the model organism is usually chosen so that it reacts to disease or its treatment in a way that resembles human physiology, even though care must be taken when generalizing from one organism to another. However, many drugs, treatments and cures for human diseases are developed in part with the guidance of animal models. Treatments for animal diseases have also been developed, including for rabies, anthrax, glanders, feline immunodeficiency virus (FIV), tuberculosis, Texas cattle fever, classical swine fever (hog cholera), heartworm, and other parasitic infections. Animal experimentation continues to be required for biomedical research, and is used with the aim of solving medical problems such as Alzheimer's disease, AIDS, multiple sclerosis, spinal cord injury, many headaches, and other conditions in which there is no useful in vitro model system available.
Model organisms are drawn from all three domains of life, as well as viruses. One of the first model systems for molecular biology was the bacterium Escherichia coli (E. coli), a common constituent of the human digestive system. The mouse (Mus musculus) has been used extensively as a model organism and is associated with many important biological discoveries of the 20th and 21st centuries. Other examples include baker's yeast (Saccharomyces cerevisiae), the T4 phage virus, the fruit fly Drosophila melanogaster, the flowering plant Arabidopsis thaliana, and guinea pigs (Cavia porcellus). Several of the bacterial viruses (bacteriophage) that infect E. coli also have been very useful for the study of gene structure and gene regulation (e.g. phages Lambda and T4). Disease models are divided into three categories: homologous animals have the same causes, symptoms and treatment options as would humans who have the same disease, isomorphic animals share the same symptoms and treatments, and predictive models are similar to a particular human disease in only a couple of aspects, but are useful in isolating and making predictions about mechanisms of a set of disease features.
== History ==
The use of animals in research dates back to ancient Greece, with Aristotle (384–322 BCE) and Erasistratus (304–258 BCE) among the first to perform experiments on living animals. Discoveries in the 18th and 19th centuries included Antoine Lavoisier's use of a guinea pig in a calorimeter to prove that respiration was a form of combustion, and Louis Pasteur's demonstration of the germ theory of disease in the 1880s using anthrax in sheep.
Research using animal models has been central to most of the achievements of modern medicine. It has contributed most of the basic knowledge in fields such as human physiology and biochemistry, and has played significant roles in fields such as neuroscience and infectious disease. For example, the results have included the near-eradication of polio and the development of organ transplantation, and have benefited both humans and animals. From 1910 to 1927, Thomas Hunt Morgan's work with the fruit fly Drosophila melanogaster identified chromosomes as the vector of inheritance for genes. Drosophila became one of the first, and for some time the most widely used, model organisms, and Eric Kandel wrote that Morgan's discoveries "helped transform biology into an experimental science". D. melanogaster remains one of the most widely used eukaryotic model organisms. During the same time period, studies on mouse genetics in the laboratory of William Ernest Castle in collaboration with Abbie Lathrop led to generation of the DBA ("dilute, brown and non-agouti") inbred mouse strain and the systematic generation of other inbred strains. The mouse has since been used extensively as a model organism and is associated with many important biological discoveries of the 20th and 21st centuries.
In the late 19th century, Emil von Behring isolated the diphtheria toxin and demonstrated its effects in guinea pigs. He went on to develop an antitoxin against diphtheria in animals and then in humans, which resulted in the modern methods of immunization and largely ended diphtheria as a threatening disease. The diphtheria antitoxin is famously commemorated in the Iditarod race, which is modeled after the delivery of antitoxin in the 1925 serum run to Nome. The success of animal studies in producing the diphtheria antitoxin has also been attributed as a cause for the decline of the early 20th-century opposition to animal research in the United States.
Subsequent research in model organisms led to further medical advances, such as Frederick Banting's research in dogs, which determined that the isolates of pancreatic secretion could be used to treat dogs with diabetes. This led to the 1922 discovery of insulin (with John Macleod) and its use in treating diabetes, which had previously meant death. John Cade's research in guinea pigs discovered the anticonvulsant properties of lithium salts, which revolutionized the treatment of bipolar disorder, replacing the previous treatments of lobotomy or electroconvulsive therapy. Modern general anaesthetics, such as halothane and related compounds, were also developed through studies on model organisms, and are necessary for modern, complex surgical operations.
In the 1940s, Jonas Salk used rhesus monkey studies to isolate the most virulent forms of the polio virus, which led to his creation of a polio vaccine. The vaccine, which was made publicly available in 1955, reduced the incidence of polio 15-fold in the United States over the following five years. Albert Sabin improved the vaccine by passing the polio virus through animal hosts, including monkeys; the Sabin vaccine was produced for mass consumption in 1963, and had virtually eradicated polio in the United States by 1965. It has been estimated that developing and producing the vaccines required the use of 100,000 rhesus monkeys, with 65 doses of vaccine produced from each monkey. Sabin wrote in 1992, "Without the use of animals and human beings, it would have been impossible to acquire the important knowledge needed to prevent much suffering and premature death not only among humans, but also among animals."
Other 20th-century medical advances and treatments that relied on research performed in animals include organ transplant techniques, the heart-lung machine, antibiotics, and the whooping cough vaccine. Treatments for animal diseases have also been developed, including for rabies, anthrax, glanders, feline immunodeficiency virus (FIV), tuberculosis, Texas cattle fever, classical swine fever (hog cholera), heartworm, and other parasitic infections. Animal experimentation continues to be required for biomedical research, and is used with the aim of solving medical problems such as Alzheimer's disease, AIDS, multiple sclerosis, spinal cord injury, many headaches, and other conditions in which there is no useful in vitro model system available.
== Selection ==
Models are those organisms with a wealth of biological data that make them attractive to study as examples for other species and/or natural phenomena that are more difficult to study directly. Continual research on these organisms focuses on a wide variety of experimental techniques and goals from many different levels of biology—from ecology, behavior and biomechanics, down to the tiny functional scale of individual tissues, organelles and proteins. Inquiries about the DNA of organisms are classed as genetic models (with short generation times, such as the fruitfly and nematode worm), experimental models, and genomic parsimony models, investigating pivotal position in the evolutionary tree. Historically, model organisms include a handful of species with extensive genomic research data, such as the NIH model organisms.
Often, model organisms are chosen on the basis that they are amenable to experimental manipulation. This usually will include characteristics such as short life-cycle, techniques for genetic manipulation (inbred strains, stem cell lines, and methods of transformation) and non-specialist living requirements. Sometimes, the genome arrangement facilitates the sequencing of the model organism's genome, for example, by being very compact or having a low proportion of junk DNA (e.g. yeast, arabidopsis, or pufferfish).
When researchers look for an organism to use in their studies, they look for several traits. Among these are size, generation time, accessibility, manipulation, genetics, conservation of mechanisms, and potential economic benefit. As comparative molecular biology has become more common, some researchers have sought model organisms from a wider assortment of lineages on the tree of life.
=== Phylogeny and genetic relatedness ===
The primary reason for the use of model organisms in research is the evolutionary principle that all organisms share some degree of relatedness and genetic similarity due to common ancestry. The study of taxonomic human relatives, then, can provide a great deal of information about mechanism and disease within the human body that can be useful in medicine.
Various phylogenetic trees for vertebrates have been constructed using comparative proteomics, genetics, genomics as well as the geochemical and fossil record. These estimations tell us that humans and chimpanzees last shared a common ancestor about 6 million years ago (mya). As our closest relatives, chimpanzees have a lot of potential to tell us about mechanisms of disease (and what genes may be responsible for human intelligence). However, chimpanzees are rarely used in research and are protected from highly invasive procedures. Rodents are the most common animal models. Phylogenetic trees estimate that humans and rodents last shared a common ancestor ~80-100mya. Despite this distant split, humans and rodents have far more similarities than they do differences. This is due to the relative stability of large portions of the genome, making the use of vertebrate animals particularly productive.
Genomic data is used to make close comparisons between species and determine relatedness. Humans share about 99% of their genome with chimpanzees (98.7% with bonobos) and over 90% with the mouse. With so much of the genome conserved across species, it is relatively impressive that the differences between humans and mice can be accounted for in approximately six thousand genes (of ~30,000 total). Scientists have been able to take advantage of these similarities in generating experimental and predictive models of human disease.
== Use ==
There are many model organisms. One of the first model systems for molecular biology was the bacterium Escherichia coli, a common constituent of the human digestive system. Several of the bacterial viruses (bacteriophage) that infect E. coli also have been very useful for the study of gene structure and gene regulation (e.g. phages Lambda and T4). However, it is debated whether bacteriophages should be classified as organisms, because they lack metabolism and depend on functions of the host cells for propagation.
In eukaryotes, several yeasts, particularly Saccharomyces cerevisiae ("baker's" or "budding" yeast), have been widely used in genetics and cell biology, largely because they are quick and easy to grow. The cell cycle in a simple yeast is very similar to the cell cycle in humans and is regulated by homologous proteins. The fruit fly Drosophila melanogaster is studied, again, because it is easy to grow for an animal, has various visible congenital traits and has a polytene (giant) chromosome in its salivary glands that can be examined under a light microscope. The roundworm Caenorhabditis elegans is studied because it has very defined development patterns involving fixed numbers of cells, and it can be rapidly assayed for abnormalities.
== Disease models ==
Animal models serving in research may have an existing, inbred or induced disease or injury that is similar to a human condition. These test conditions are often termed as animal models of disease. The use of animal models allows researchers to investigate disease states in ways which would be inaccessible in a human patient, performing procedures on the non-human animal that imply a level of harm that would not be considered ethical to inflict on a human.
The best models of disease are similar in etiology (mechanism of cause) and phenotype (signs and symptoms) to the human equivalent. However complex human diseases can often be better understood in a simplified system in which individual parts of the disease process are isolated and examined. For instance, behavioral analogues of anxiety or pain in laboratory animals can be used to screen and test new drugs for the treatment of these conditions in humans. A 2000 study found that animal models concorded (coincided on true positives and false negatives) with human toxicity in 71% of cases, with 63% for nonrodents alone and 43% for rodents alone.
In 1987, Davidson et al. suggested that selection of an animal model for research be based on nine considerations. These include 1) appropriateness as an analog, 2) transferability of information, 3) genetic uniformity of organisms, where applicable, 4) background knowledge of biological properties, 5) cost and availability, 6) generalizability of the results, 7) ease of and adaptability to experimental manipulation, 8) ecological consequences, and 9) ethical implications.
Animal models can be classified as homologous, isomorphic or predictive. Animal models can also be more broadly classified into four categories: 1) experimental, 2) spontaneous, 3) negative, 4) orphan.
Experimental models are most common. These refer to models of disease that resemble human conditions in phenotype or response to treatment but are induced artificially in the laboratory. Some examples include:
The use of metrazol (pentylenetetrazol) as an animal model of epilepsy
Induction of mechanical brain injury as an animal model of post-traumatic epilepsy
Injection of the neurotoxin 6-hydroxydopamine to dopaminergic parts of the basal ganglia as an animal model of Parkinson's disease.
Immunisation with an auto-antigen to induce an immune response to model autoimmune diseases such as Experimental autoimmune encephalomyelitis
Occlusion of the middle cerebral artery as an animal model of ischemic stroke
Injection of blood in the basal ganglia of mice as a model for hemorrhagic stroke
Sepsis and septic shock induction by impairing the integrity of barrier tissues, administering live pathogens or toxins
Infecting animals with pathogens to reproduce human infectious diseases
Injecting animals with agonists or antagonists of various neurotransmitters to reproduce human mental disorders
Using ionizing radiation to cause tumors
Using gene transfer to cause tumors
Implanting animals with tumors to test and develop treatments using ionizing radiation
Genetically selected (such as in diabetic mice also known as NOD mice)
Various animal models for screening of drugs for the treatment of glaucoma
The use of the ovariectomized rat in osteoporosis research
Use of Plasmodium yoelii as a model of human malaria
Spontaneous models refer to diseases that are analogous to human conditions that occur naturally in the animal being studied. These models are rare, but informative. Negative models essentially refer to control animals, which are useful for validating an experimental result. Orphan models refer to diseases for which there is no human analog and occur exclusively in the species studied.
The increase in knowledge of the genomes of non-human primates and other mammals that are genetically close to humans is allowing the production of genetically engineered animal tissues, organs and even animal species which express human diseases, providing a more robust model of human diseases in an animal model.
Animal models observed in the sciences of psychology and sociology are often termed animal models of behavior. It is difficult to build an animal model that perfectly reproduces the symptoms of depression in patients. Depression, as other mental disorders, consists of endophenotypes that can be reproduced independently and evaluated in animals. An ideal animal model offers an opportunity to understand molecular, genetic and epigenetic factors that may lead to depression. By using animal models, the underlying molecular alterations and the causal relationship between genetic or environmental alterations and depression can be examined, which would afford a better insight into pathology of depression. In addition, animal models of depression are indispensable for identifying novel therapies for depression.
== Important model organisms ==
Model organisms are drawn from all three domains of life, as well as viruses. The most widely studied prokaryotic model organism is Escherichia coli (E. coli), which has been intensively investigated for over 60 years. It is a common, gram-negative gut bacterium which can be grown and cultured easily and inexpensively in a laboratory setting. It is the most widely used organism in molecular genetics, and is an important species in the fields of biotechnology and microbiology, where it has served as the host organism for the majority of work with recombinant DNA.
Simple model eukaryotes include baker's yeast (Saccharomyces cerevisiae) and fission yeast (Schizosaccharomyces pombe), both of which share many characters with higher cells, including those of humans. For instance, many cell division genes that are critical for the development of cancer have been discovered in yeast. Chlamydomonas reinhardtii, a unicellular green alga with well-studied genetics, is used to study photosynthesis and motility. C. reinhardtii has many known and mapped mutants and expressed sequence tags, and there are advanced methods for genetic transformation and selection of genes. Dictyostelium discoideum is used in molecular biology and genetics, and is studied as an example of cell communication, differentiation, and programmed cell death.
Among invertebrates, the fruit fly Drosophila melanogaster is famous as the subject of genetics experiments by Thomas Hunt Morgan and others. They are easily raised in the lab, with rapid generations, high fecundity, few chromosomes, and easily induced observable mutations. The nematode Caenorhabditis elegans is used for understanding the genetic control of development and physiology. It was first proposed as a model for neuronal development by Sydney Brenner in 1963, and has been extensively used in many different contexts since then. C. elegans was the first multicellular organism whose genome was completely sequenced, and as of 2012, the only organism to have its connectome (neuronal "wiring diagram") completed.
Arabidopsis thaliana is currently the most popular model plant. Its small stature and short generation time facilitates rapid genetic studies, and many phenotypic and biochemical mutants have been mapped. A. thaliana was the first plant to have its genome sequenced.
Among vertebrates, guinea pigs (Cavia porcellus) were used by Robert Koch and other early bacteriologists as a host for bacterial infections, becoming a byword for "laboratory animal", but are less commonly used today. The classic model vertebrate is currently the mouse (Mus musculus). Many inbred strains exist, as well as lines selected for particular traits, often of medical interest, e.g. body size, obesity, muscularity, and voluntary wheel-running behavior.
The rat (Rattus norvegicus) is particularly useful as a toxicology model, and as a neurological model and source of primary cell cultures, owing to the larger size of organs and suborganellar structures relative to the mouse, while eggs and embryos from Xenopus tropicalis and Xenopus laevis (African clawed frog) are used in developmental biology, cell biology, toxicology, and neuroscience. Likewise, the zebrafish (Danio rerio) has a nearly transparent body during early development, which provides unique visual access to the animal's internal anatomy during this time period. Zebrafish are used to study development, toxicology and toxicopathology, specific gene function and roles of signaling pathways.
Other important model organisms and some of their uses include: T4 phage (viral infection), Tetrahymena thermophila (intracellular processes), maize (transposons), hydras (regeneration and morphogenesis), cats (neurophysiology), chickens (development), dogs (respiratory and cardiovascular systems), Nothobranchius furzeri (aging), non-human primates such as the rhesus macaque and chimpanzee (hepatitis, HIV, Parkinson's disease, cognition, and vaccines), and ferrets (SARS-CoV-2)
=== Selected model organisms ===
The organisms below have become model organisms because they facilitate the study of certain characters or because of their genetic accessibility. For example, E. coli was one of the first organisms for which genetic techniques such as transformation or genetic manipulation has been developed.
The genomes of all model species have been sequenced, including their mitochondrial/chloroplast genomes. Model organism databases exist to provide researchers with a portal from which to download sequences (DNA, RNA, or protein) or to access functional information on specific genes, for example the sub-cellular localization of the gene product or its physiological role.
== Limitations ==
Many animal models serving as test subjects in biomedical research, such as rats and mice, may be selectively sedentary, obese and glucose intolerant. This may confound their use to model human metabolic processes and diseases as these can be affected by dietary energy intake and exercise. Similarly, there are differences between the immune systems of model organisms and humans that lead to significantly altered responses to stimuli, although the underlying principles of genome function may be the same. The impoverished environments inside standard laboratory cages deny research animals of the mental and physical challenges are necessary for healthy emotional development. Without day-to-day variety, risks and rewards, and complex environments, some have argued that animal models are irrelevant models of human experience.
Mice differ from humans in several immune properties: mice are more resistant to some toxins than humans; have a lower total neutrophil fraction in the blood, a lower neutrophil enzymatic capacity, lower activity of the complement system, and a different set of pentraxins involved in the inflammatory process; and lack genes for important components of the immune system, such as IL-8, IL-37, TLR10, ICAM-3, etc. Laboratory mice reared in specific-pathogen-free (SPF) conditions usually have a rather immature immune system with a deficit of memory T cells. These mice may have limited diversity of the microbiota, which directly affects the immune system and the development of pathological conditions. Moreover, persistent virus infections (for example, herpesviruses) are activated in humans, but not in SPF mice, with septic complications and may change the resistance to bacterial coinfections. "Dirty" mice are possibly better suitable for mimicking human pathologies. In addition, inbred mouse strains are used in the overwhelming majority of studies, while the human population is heterogeneous, pointing to the importance of studies in interstrain hybrid, outbred, and nonlinear mice.
=== Unintended bias ===
Some studies suggests that inadequate published data in animal testing may result in irreproducible research, with missing details about how experiments are done omitted from published papers or differences in testing that may introduce bias. Examples of hidden bias include a 2014 study from McGill University in Montreal, Canada which suggests that mice handled by men rather than women showed higher stress levels. Another study in 2016 suggested that gut microbiomes in mice may have an impact upon scientific research.
=== Alternatives ===
Ethical concerns, as well as the cost, maintenance and relative inefficiency of animal research has encouraged development of alternative methods for the study of disease. Cell culture, or in vitro studies, provide an alternative that preserves the physiology of the living cell, but does not require the sacrifice of an animal for mechanistic studies. Human, inducible pluripotent stem cells can also elucidate new mechanisms for understanding cancer and cell regeneration. Imaging studies (such as MRI or PET scans) enable non-invasive study of human subjects. Recent advances in genetics and genomics can identify disease-associated genes, which can be targeted for therapies.
Many biomedical researchers argue that there is no substitute for a living organism when studying complex interactions in disease pathology or treatments.
== Ethics ==
Debate about the ethical use of animals in research dates at least as far back as 1822 when the British Parliament under pressure from British and Indian intellectuals enacted the first law for animal protection preventing cruelty to cattle. This was followed by the Cruelty to Animals Act 1835 and the Cruelty to Animals Act 1849, which criminalized ill-treating, over-driving, and torturing animals. In 1876, under pressure from the National Anti-Vivisection Society, the Cruelty to Animals Act 1849 was amended to include regulations governing the use of animals in research. This new act stipulated that 1) experiments must be proven absolutely necessary for instruction, or to save or prolong human life; 2) animals must be properly anesthetized; and 3) animals must be killed as soon as the experiment is over. Today, these three principles are central to the laws and guidelines governing the use of animals and research. In the U.S., the Animal Welfare Act of 1970 (see also Laboratory Animal Welfare Act) set standards for animal use and care in research. This law is enforced by APHIS's Animal Care program.
In academic settings in which NIH funding is used for animal research, institutions are governed by the NIH Office of Laboratory Animal Welfare (OLAW). At each site, OLAW guidelines and standards are upheld by a local review board called the Institutional Animal Care and Use Committee (IACUC). All laboratory experiments involving living animals are reviewed and approved by this committee. In addition to proving the potential for benefit to human health, minimization of pain and distress, and timely and humane euthanasia, experimenters must justify their protocols based on the principles of Replacement, Reduction and Refinement.
"Replacement" refers to efforts to engage alternatives to animal use. This includes the use of computer models, non-living tissues and cells, and replacement of "higher-order" animals (primates and mammals) with "lower" order animals (e.g. cold-blooded animals, invertebrates) wherever possible.
"Reduction" refers to efforts to minimize number of animals used during the course of an experiment, as well as prevention of unnecessary replication of previous experiments. To satisfy this requirement, mathematical calculations of statistical power are employed to determine the minimum number of animals that can be used to get a statistically significant experimental result.
"Refinement" refers to efforts to make experimental design as painless and efficient as possible in order to minimize the suffering of each animal subject.
== See also ==
== References ==
== Further reading ==
Marx, Vivien (June 2014). "Models: stretching the skills of cell lines and mice". Nature Methods. 11 (6): 617–620. doi:10.1038/nmeth.2966. PMID 24874573.
Goldstein, Bob; King, Nicole (November 2016). "The Future of Cell Biology: Emerging Model Organisms". Trends in Cell Biology. 26 (11): 818–824. doi:10.1016/j.tcb.2016.08.005. PMC 5077642. PMID 27639630.
Lloyd, Kent; Franklin, Craig; Lutz, Cat; Magnuson, Terry (June 2015). "Reproducibility: Use mouse biobanks or lose them". Nature. 522 (7555): 151–153. Bibcode:2015Natur.522..151L. doi:10.1038/522151a. PMC 4636083. PMID 26062496.
== External links ==
Wellcome Trust description of model organisms
National Institutes of Health Comparative Medicine Program Vertebrate Models
NIH Using Model Organisms to Study Human Disease
National Institutes of Health Model Organism Sharing Policy
Why are Animals Used in NIH Research
Disease Animal Models – BSRC Alexander Fleming
Emice – National Cancer Institute
Knock Out Mouse Project – KOMP
Mouse Biology Program
Mutant Mouse Resource & Research Centers, National Institutes of Health, supported Mouse Repository
Rat Resource & Research Center – National Institutes of Health, supported Rat Repository
NIH Model Organism Research Reproducibility and Rigor | Wikipedia/Animal_models |
Hybrid intelligent system denotes a software system which employs, in parallel, a combination of methods and techniques from artificial intelligence subfields, such as:
Neuro-symbolic systems
Neuro-fuzzy systems
Hybrid connectionist-symbolic models
Fuzzy expert systems
Connectionist expert systems
Evolutionary neural networks
Genetic fuzzy systems
Rough fuzzy hybridization
Reinforcement learning with fuzzy, neural, or evolutionary methods as well as symbolic reasoning methods.
From the cognitive science perspective, every natural intelligent system is hybrid because it performs mental operations on both the symbolic and subsymbolic levels. For the past few years, there has been an increasing discussion of the importance of A.I. Systems Integration. Based on notions that there have already been created simple and specific AI systems (such as systems for computer vision, speech synthesis, etc., or software that employs some of the models mentioned above) and now is the time for integration to create broad AI systems. Proponents of this approach are researchers such as Marvin Minsky, Ron Sun, Aaron Sloman, Angelo Dalli and Michael A. Arbib.
An example hybrid is a hierarchical control system in which the lowest, reactive layers are sub-symbolic. The higher layers, having relaxed time constraints, are capable of reasoning from an abstract world model and performing planning.
Intelligent systems usually rely on hybrid reasoning processes, which include induction, deduction, abduction and reasoning by analogy.
== See also ==
AI alignment
AI effect
Applications of artificial intelligence
Artificial intelligence systems integration
Intelligent control
Lists
List of emerging technologies
Outline of artificial intelligence
== References ==
R. Sun & L. Bookman, (eds.), Computational Architectures Integrating Neural and Symbolic Processes. Kluwer Academic Publishers, Needham, MA. 1994. http://www.cogsci.rpi.edu/~rsun/book2-ann.html Archived 2009-05-05 at the Wayback Machine
S. Wermter and R. Sun, (eds.) Hybrid Neural Systems. Springer-Verlag, Heidelberg. 2000. http://www.cogsci.rpi.edu/~rsun/book4-ann.html Archived 2009-09-24 at the Wayback Machine
R. Sun and F. Alexandre, (eds.) Connectionist-Symbolic Integration. Lawrence Erlbaum Associates, Mahwah, NJ. 1997.
Ibaraki, S. Hybrid Intelligence interview with Angelo Dalli in IEEE Technology and Management Society. 2024.
Albus, J. S., Bostelman, R., Chang, T., Hong, T., Shackleford, W., and Shneier, M. Learning in a Hierarchical Control System: 4D/RCS in the DARPA LAGR Program NIST, 2006
A.S. d'Avila Garcez, Luis C. Lamb & Dov M. Gabbay. Neural-Symbolic Cognitive Reasoning. Cognitive Technologies, Springer (2009). ISBN 978-3-540-73245-7.
International Journal of Hybrid Intelligent Systems
http://www.iospress.nl/html/14485869.php Archived 2005-12-11 at the Wayback Machine
International Conference on Hybrid Intelligent Systems http://his.hybridsystem.com/
HIS'01: http://www.softcomputing.net/his01/
HIS'02: https://web.archive.org/web/20060209160923/http://tamarugo.cec.uchile.cl/~his02/
HIS'03: http://www.softcomputing.net/his03/
HIS'04: https://web.archive.org/web/20060303051902/http://www.cs.nmt.edu/~his04/
HIS'05: https://web.archive.org/web/20051223013031/http://www.ica.ele.puc-rio.br/his05/
HIS'06 https://web.archive.org/web/20110510025133/http://his-ncei06.kedri.info/
HIS'7 September 17–19, 2007, Kaiserslautern, Germany, http://www.eit.uni-kl.de/koenig/HIS07_Web/his07main.html
hybrid systems resources: http://www.cogsci.rpi.edu/~rsun/hybrid-resource.html Archived 2009-09-25 at the Wayback Machine | Wikipedia/Hybrid_intelligent_systems |
Bayesian cognitive science, also known as computational cognitive science, is an approach to cognitive science concerned with the rational analysis of cognition through the use of Bayesian inference and cognitive modeling. The term "computational" refers to the computational level of analysis as put forth by David Marr.
This work often consists of testing the hypothesis that cognitive systems behave like rational Bayesian agents in particular types of tasks. Past work has applied this idea to categorization, language, motor control, sequence learning, reinforcement learning and theory of mind.
At other times, Bayesian rationality is assumed, and the goal is to infer the knowledge that agents have, and the mental representations that they use.
It is important to contrast this with the ordinary use of Bayesian inference in cognitive science, which is independent of rational modeling (see e.g. Michael Lee's work).
== See also ==
Active inference
Bayesian approaches to brain function
Bayesian programming
Rational analysis
== References ==
== Further reading ==
Bayesian Theory of Mind : modeling human reasoning about beliefs, desires, goals, and social relations Chris L. Baker, (2006)
Optimal Predictions in Everyday Cognition T. L. Griffiths, and J. B. Tenenbaum (2006), Psychological Science 17(9), 767-773
Rational models of cognition M.Oaksford, & N. Chater, (Eds.), (1998), Oxford University Press | Wikipedia/Bayesian_cognitive_science |
Prototype theory is a theory of categorization in cognitive science, particularly in psychology and cognitive linguistics, in which there is a graded degree of belonging to a conceptual category, and some members are more central than others. It emerged in 1971 with the work of psychologist Eleanor Rosch, and it has been described as a "Copernican Revolution" in the theory of categorization for its departure from the traditional Aristotelian categories. It has been criticized by those that still endorse the traditional theory of categories, like linguist Eugenio Coseriu and other proponents of the structural semantics paradigm.
In this prototype theory, any given concept in any given language has a real world example that best represents this concept. For example: when asked to give an example of the concept furniture, a couch is more frequently cited than, say, a wardrobe. Prototype theory has also been applied in linguistics, as part of the mapping from phonological structure to semantics.
In formulating prototype theory, Rosch drew in part from previous insights in particular the formulation of a category model based on family resemblance by Wittgenstein (1953), and by Roger Brown's How shall a thing be called? (1958).
== Overview and terminology ==
The term prototype, as defined in psychologist Eleanor Rosch's study "Natural Categories", was initially defined as denoting a stimulus, which takes a salient position in the formation of a category, due to the fact that it is the first stimulus to be associated with that category. Rosch later defined it as the most central member of a category.
Rosch and others developed prototype theory as a response to, and radical departure from, the classical theory of concepts, which defines concepts by necessary and sufficient conditions. Necessary conditions refers to the set of features every instance of a concept must present, and sufficient conditions are those that no other entity possesses. Rather than defining concepts by features, the prototype theory defines categories based on either a specific artifact of that category or by a set of entities within the category that represent a prototypical member. The prototype of a category can be understood in lay terms by the object or member of a class most often associated with that class. The prototype is the center of the class, with all other members moving progressively further from the prototype, which leads to the gradation of categories. Every member of the class is not equally central in human cognition. As in the example of furniture above, couch is more central than wardrobe. Contrary to the classical view, prototypes and gradations lead to an understanding of category membership not as an all-or-nothing approach, but as more of a web of interlocking categories which overlap.
Further development of prototype theory by psychologist James Hampton, and others replaced the notion of prototypes being the most typical exemplar, with the proposal that a prototype is a bundle of correlated features. These features may or may not be true of all members of the class (necessary or defining features), but they will all be associated with being a typical member or the class. By this means, two aspects of concept structure can be explained. Some exemplars are more typical of a category than others, because they are a better fit to the concept prototype, having more of the features. Importantly, Hampton's prototype model explains the vagueness that can occur at the boundary of conceptual categories. While some may think of pictures, telephones or cookers as atypical furniture, others will say they are not furniture at all. Membership of a category can be a matter of degree, and the same features that give rise to typicality structure are also responsible for graded degrees of category membership.
In Cognitive linguistics it has been argued that linguistic categories also have a prototype structure, like categories of common words in a language.
== Categories ==
=== Basic level categories ===
The other notion related to prototypes is that of a basic level in cognitive categorization. Basic categories are relatively homogeneous in terms of sensory-motor affordances — a chair is associated with bending of one's knees, a fruit with picking it up and putting it in your mouth, etc. At the subordinate level (e.g. [dentist's chairs], [kitchen chairs] etc.) few significant features can be added to that of the basic level; whereas at the superordinate level, these conceptual similarities are hard to pinpoint. A picture of a chair is easy to draw (or visualize), but drawing furniture would be more difficult.
Psychologists Eleanor Rosch, Carolyn Mervis and colleagues defined the basic level as that level that has the highest degree of cue validity and category validity. Thus, a category like [animal] may have a prototypical member, but no cognitive visual representation. On the other hand, basic categories in [animal], i.e. [dog], [bird], [fish], are full of informational content and can easily be categorized in terms of Gestalt and semantic features. Basic level categories tend to have the same parts and recognizable images.
Clearly semantic models based on attribute-value pairs fail to identify privileged levels in the hierarchy. Functionally, it is thought that basic level categories are a decomposition of the world into maximally informative categories. Thus, they
maximize the number of attributes shared by members of the category, and
minimize the number of attributes shared with other categories
However, the notion of Basic-ness as a Level can be problematic. Linguistically, types of bird (swallow, robin, gull) are basic level - they have mono-morphemic nouns, which fall under the superordinate BIRD, and have subordinates expressed by noun phrases (herring gull, male robin). Yet in psychological terms, bird behaves as a basic level term. At the same time, atypical birds such as ostrich and penguin are themselves basic level terms, having very distinct outlines and not sharing obvious parts with other birds.
More problems arise when the notion of a prototype is applied to lexical categories other than the noun. Verbs, for example, seem to defy a clear prototype: [to run] is hard to split up in more or less central members.
In her 1975 paper, Rosch asked 200 American college students to rate, on a scale of 1 to 7, whether they regarded certain items as good examples of the category furniture. These items ranged from chair and sofa, ranked number 1, to a love seat (number 10), to a lamp (number 31), all the way to a telephone, ranked number 60.
While one may differ from this list in terms of cultural specifics, the point is that such a graded categorization is likely to be present in all cultures. Further evidence that some members of a category are more privileged than others came from experiments involving:
1. Response Times: in which queries involving prototypical members (e.g. is a robin a bird) elicited faster response times than for non-prototypical members.
2. Priming: When primed with the higher-level (superordinate) category, subjects were faster in identifying if two words are the same. Thus, after flashing furniture, the equivalence of chair-chair is detected more rapidly than stove-stove.
3. Exemplars: When asked to name a few exemplars, the more prototypical items came up more frequently.
Subsequent to Rosch's work, prototype effects have been investigated widely in areas such as colour cognition, and also for more abstract notions: subjects may be asked, e.g. "to what degree is this narrative an instance of telling a lie?". Similar work has been done on actions (verbs like look, kill, speak, walk [Pulman:83]), adjectives like "tall", etc.
Another aspect in which Prototype Theory departs from traditional Aristotelian categorization is that there do not appear to be natural kind categories (bird, dog) vs. artifacts (toys, vehicles).
A common comparison is the use of prototype or the use of exemplars in category classification. Medin, Altom, and Murphy found that using a mixture of prototype and exemplar information, participants were more accurately able to judge categories. Participants who were presented with prototype values classified based on similarity to stored prototypes and stored exemplars, whereas participants who only had experience with exemplar only relied on the similarity to stored exemplars. Smith and Minda looked at the use of prototypes and exemplars in dot-pattern category learning. They found that participants used more prototypes than they used exemplars, with the prototypes being the center of the category, and exemplars surrounding it.
== Distance between concepts ==
The notion of prototypes is related to Wittgenstein's (later) discomfort with the traditional notion of category. This influential theory has resulted in a view of semantic components more as possible rather than necessary contributors to the meaning of texts. His discussion on the category game is particularly incisive:Consider for example the proceedings that we call 'games'. I mean board games, card games, ball games, Olympic games, and so on. What is common to them all? Don't say, "There must be something common, or they would not be called 'games'"--but look and see whether there is anything common to all. For if you look at them you will not see something common to all, but similarities, relationships, and a whole series of them at that. To repeat: don't think, but look! Look for example at board games, with their multifarious relationships. Now pass to card games; here you find many correspondences with the first group, but many common features drop out, and others appear. When we pass next to ball games, much that is common is retained, but much is lost. Are they all 'amusing'? Compare chess with noughts and crosses. Or is there always winning and losing, or competition between players? Think of patience. In ball games there is winning and losing; but when a child throws his ball at the wall and catches it again, this feature has disappeared. Look at the parts played by skill and luck; and at the difference between skill in chess and skill in tennis. Think now of games like ring-a-ring-a-roses; here is the element of amusement, but how many other characteristic features have disappeared! And we can go through the many, many other groups of games in the same way; can see how similarities crop up and disappear. And the result of this examination is: we see a complicated network of similarities overlapping and criss-crossing: sometimes overall similarities, sometimes similarities of detail.
Wittgenstein's theory of family resemblance describes the phenomenon when people group concepts based on a series of overlapping features, rather than by one feature which exists throughout all members of the category. For example, basketball and baseball share the use of a ball, and baseball and chess share the feature of a winner, etc., rather than one defining feature of "games". Therefore, there is a distance between focal, or prototypical members of the category, and those that continue outwards from them, linked by shared features.
Peter Gärdenfors has elaborated a possible partial explanation of prototype theory in terms of multi-dimensional feature spaces called conceptual spaces, where a category is defined in terms of a conceptual distance. More central members of a category are "between" the peripheral members. He postulates that most natural categories exhibit a convexity in conceptual space, in that if x and y are elements of a category, and if z is between x and y, then z is also likely to belong to the category.
== Combining categories ==
Within language we find instances of combined categories, such as tall man or small elephant. Combining categories was a problem for extensional semantics, where the semantics of a word such as red is to be defined as the set of objects having this property. This does not apply as well to modifiers such as small; a small mouse is very different from a small elephant.
These combinations pose a lesser problem in terms of prototype theory. In situations involving adjectives (e.g. tall), one encounters the question of whether or not the prototype of [tall] is a 6 foot tall man, or a 400-foot skyscraper. The solution emerges by contextualizing the notion of prototype in terms of the object being modified. This extends even more radically in compounds such as red wine or red hair which are hardly red in the prototypical sense, but the red indicates merely a shift from the prototypical colour of wine or hair respectively. The addition of red shifts the prototype from the one of hair to that of red hair. The prototype is changed by additional specific information, and combines features from the prototype of red and wine.
== Dynamic structure and distance ==
Mikulincer, Mario & Paz, Dov & Kedem, Perry focused on the dynamic nature of prototypes and how represented semantic categories actually changes due to emotional states. The 4 part study assessed the relationships between situational stress and trait anxiety and the way people organize the hierarchical level at which semantic stimuli are categorized, the way people categorize natural objects, the narrowing of the breadth of categories and the proneness to use less inclusive levels of categorization instead of more inclusive ones.
== Critique ==
Prototype theory has been criticized by those that still endorse the classic theory of categories, like linguist Eugenio Coseriu and other proponents of the structural semantics paradigm.
=== Exemplar theory ===
Douglas L. Medin and Marguerite M. Schaffer showed by experiment that a context theory of classification which derives concepts purely from exemplars (cf. exemplar theory) worked better than a class of theories that included prototype theory.
=== Graded categorization ===
Linguists, including Stephen Laurence writing with Eric Margolis, have suggested problems with the prototype theory. In their 1999 paper, they raise several issues. One of which is that prototype theory does not intrinsically guarantee graded categorization. When subjects were asked to rank how well certain members exemplify the category, they rated some members above others. For example, robins were seen as being "birdier" than ostriches, but when asked whether these categories are "all-or-nothing" or have fuzzier boundaries, the subjects stated that they were defined, "all-or-nothing" categories. Laurence and Margolis concluded that "prototype structure has no implication for whether subjects represent a category as being graded" (p. 33).
=== Compound concepts ===
Daniel Osherson and Edward Smith raised the issue of pet fish for which the prototype might be a guppy kept in a bowl in someone's house. The prototype for pet might be a dog or cat, and the prototype for fish might be trout or salmon. However, the features of these prototypes do not present in the prototype for pet fish, therefore this prototype must be generated from something other than its constituent parts.
James Hampton found that prototypes for conjunctive concepts such as pet fish are produced by a compositional function operating on the features of each concept. Initially all features of each concept are added to the prototype of the conjunction. There is then a consistency check - for example pets are warm and cuddly but fish cannot be. Fish are often eaten for dinner, but pets are never. Hence the conjunctive prototype fails to inherit features of either concept that are incompatible with the other concept. A final stage in the process looks for knowledge of the class in long term memory, and if the class is familiar may add extra features - a process called "extensional feedback". The model was tested by showing how apparently logical syntactic conjunctions or disjunctions, such as "A sport which is also a game" or "Vehicles that are not Machines", or "Fruits or Vegetables" fail to conform to Boolean set logic. Chess is considered to be a sport which is a game, but is not considered to be a sport. Mushrooms are considered to be either a fruit or a vegetable, but when asked separately very few people consider them to be a vegetable and no-one considers them to be a fruit.
Antonio Lieto and Gian Luca Pozzato have proposed a typicality-based compositional logic (TCL) that is able to account for both complex human-like concept combinations (like the PET-FISH problem) and conceptual blending. Their framework shows how concepts expressed as prototypes can account for the phenomenon of prototypical compositionality in concept combination.
== See also ==
Composite photography – British eugenist, polymath, and behavioural geneticist (1822–1911)
Composite portrait – compositing of images such as faces to produce an Ideal typePages displaying wikidata descriptions as a fallback
Exemplar theory – Psychological categorization proposal
Family resemblance – Philosophical idea popularized by Ludwig Wittgenstein
Folksonomy – Classification based on users' tags
Frame semantics – Linguistic theory
Intuitive statistics – cognitive phenomenon where organisms use data to make generalizations and predictions about the worldPages displaying wikidata descriptions as a fallback
Platonic ideal – Philosophical theory attributed to PlatoPages displaying short descriptions of redirect targets
Semantic feature-comparison model
Similarity (philosophy) – Relation of resemblance between objects
== Footnotes ==
== References == | Wikipedia/Prototype_Theory |
Visual object recognition refers to the ability to identify the objects in view based on visual input. One important signature of visual object recognition is "object invariance", or the ability to identify objects across changes in the detailed context in which objects are viewed, including changes in illumination, object pose, and background context.
== Basic stages of object recognition ==
Neuropsychological evidence affirms that there are four specific stages identified in the process of object recognition. These stages are:
Stage 1 Processing of basic object components, such as color, depth, and form.
Stage 2 These basic components are then grouped on the basis of similarity, providing information on distinct edges to the visual form. Subsequently, figure-ground segregation is able to take place.
Stage 3 The visual representation is matched with structural descriptions in memory.
Stage 4 Semantic attributes are applied to the visual representation, providing meaning, and thereby recognition.
Within these stages, there are more specific processes that take place to complete the different processing components. In addition, other existing models have proposed integrative hierarchies (top-down and bottom-up), as well as parallel processing, as opposed to this general bottom-up hierarchy.
== Hierarchical recognition processing ==
Visual recognition processing is typically viewed as a bottom-up hierarchy in which information is processed sequentially with increasing complexities. During this process, lower-level cortical processors, such as the primary visual cortex, are at the bottom of the hierarchy. Higher-level cortical processors, such as the inferotemporal cortex (IT), are at the top, where visual recognition is facilitated. A highly recognized bottom-up hierarchical theory is James DiCarlo's Untangling description whereby each stage of the hierarchically arranged ventral visual pathway performs operations to gradually transform object representations into an easily extractable format. In contrast, an increasingly popular recognition processing theory, is that of top-down processing. One model, proposed by Moshe Bar (2003), describes a "shortcut" method in which early visual inputs are sent, partially analyzed, from the early visual cortex to the prefrontal cortex (PFC). Possible interpretations of the crude visual input is generated in the PFC and then sent to the inferotemporal cortex (IT) subsequently activating relevant object representations which are then incorporated into the slower, bottom-up process. This "shortcut" is meant to minimize the number of object representations required for matching thereby facilitating object recognition. Lesion studies have supported this proposal with findings of slower response times for individuals with PFC lesions, suggesting use of only the bottom-up processing.
== Object constancy and theories of object recognition ==
A significant aspect of object recognition is that of object constancy: the ability to recognize an object across varying viewing conditions. These varying conditions include object orientation, lighting, and object variability (size, color, and other within-category differences). For the visual system to achieve object constancy, it must be able to extract a commonality in the object description across different viewpoints and the retinal descriptions.[9] Participants who did categorization and recognition tasks while undergoing a functional magnetic found as increased blood flow indicating activation in specific regions of the brain. The categorization task consisted of participants placing objects from canonical or unusual views as either indoor or outdoor objects. The recognition task occurs by presenting the participants with images that they had viewed previously. Half of these images were in the same orientation as previously shown, while the other half were presented in the opposing viewpoint. The brain regions implicated in mental rotation, such as the ventral and dorsal visual pathways and the prefrontal cortex, showed the greatest increase in blood flow during these tasks, demonstrating that they are critical for the ability to view objects from multiple angles. Several theories have been generated to provide insight on how object constancy may be achieved for the purpose of object recognition including, viewpoint-invariant, viewpoint-dependent and multiple views theories.
=== Viewpoint-invariant theories ===
Viewpoint-invariant theories suggest that object recognition is based on structural information, such as individual parts, allowing for recognition to take place regardless of the object's viewpoint. Accordingly, recognition is possible from any viewpoint as individual parts of an object can be rotated to fit any particular view.[10] This form of analytical recognition requires little memory as only structural parts need to be encoded, which can produce multiple object representations through the interrelations of these parts and mental rotation.[10] Participants in a study were presented with one encoding view from each of 24 preselected objects, as well as five filler images. Objects were then represented in the central visual field at either the same orientation or a different orientation than the original image. Then participants were asked to name if the same or different depth- orientation views of these objects presented. The same procedure was then executed when presenting the images to the left or right visual field. Viewpoint-dependent priming was observed when test views were presented directly to the right hemisphere, but not when test views were presented directly to the left hemisphere. The results support the model that objects are stored in a manner that is viewpoint dependent because the results did not depend on whether the same or a different set of parts could be recovered from the different-orientation views.
==== 3-D model representation ====
This model, proposed by Marr and Nishihara (1978), states that object recognition is achieved by matching 3-D model representations obtained from the visual object with 3-D model representations stored in memory as vertical shape precepts. Through the use of computer programs and algorithms, Yi Yungfeng (2009) was able to demonstrate the ability for the human brain to mentally construct 3D images using only the 2D images that appear on the retina. Their model also demonstrates a high degree of shape constancy conserved between 2D images, which allow the 3D image to be recognized. The 3-D model representations obtained from the object are formed by first identifying the concavities of the object, which separate the stimulus into individual parts. Recent research suggests that an area of the brain, known as the caudal intraparietal area (CIP), is responsible for storing the slant and tilt of a plan surface that allow for concavity recognition. Rosenburg et al. implanted monkeys with a scleral search coil for monitoring eye position while simultaneously recording single neuron activation from neurons within the CIP. During the experiment, monkeys sat 30 cm away from an LCD screen that displayed the visual stimuli. Binocular disparity cues were displayed on the screen by rendering stimuli as green-red anaglyphs and the slant-tilt curves ranged from 0 to 330. A single trial consisted of a fixation point and then the presentation of a stimulus for 1 second. Neuron activation were then recorded using the surgically inserted micro electrodes. These single neuron activation for specific concavities of objects lead to the discovery that each axis of an individual part of an object containing concavity are found in memory stores. Identifying the principal axis of the object assists in the normalization process via mental rotation that is required because only the canonical description of the object is stored in memory. Recognition is acquired when the observed object viewpoint is mentally rotated to match the stored canonical description.
==== Recognition by components ====
An extension of Marr and Nishihara's model, the recognition-by-components theory, proposed by Biederman (1987), proposes that the visual information gained from an object is divided into simple geometric components, such as blocks and cylinders, also known as "geons" (geometric ions), and are then matched with the most similar object representation that is stored in memory to provide the object's identification (see Figure 1).
=== Viewpoint-dependent theories ===
Viewpoint-dependent theories suggest that object recognition is affected by the viewpoint at which it is seen, implying that objects seen in novel viewpoints reduce the accuracy and speed of object identification. This theory of recognition is based on a more holistic system rather than by parts, suggesting that objects are stored in memory with multiple viewpoints and angles. This form of recognition requires a lot of memory as each viewpoint must be stored. Accuracy of recognition also depends on how familiar the observed viewpoint of the object is.
=== Multiple views theory ===
This theory proposes that object recognition lies on a viewpoint continuum where each viewpoint is recruited for different types of recognition. At one extreme of this continuum, viewpoint-dependent mechanisms are used for within-category discriminations, while at the other extreme, viewpoint-invariant mechanisms are used for the categorization of objects.
== Neural substrates ==
=== The dorsal and ventral stream ===
The visual processing of objects in the brain can be divided into two processing pathways: the dorsal stream (how/where), which extends from the visual cortex to the parietal lobes, and ventral stream (what), which extends from the visual cortex to the inferotemporal cortex (IT). The existence of these two separate visual processing pathways was first proposed by Ungerleider and Mishkin (1982) who, based on their lesion studies, suggested that the dorsal stream is involved in the processing of visual spatial information, such as object localization (where), and the ventral stream is involved in the processing of visual object identification information (what). Since this initial proposal, it has been alternatively suggested that the dorsal pathway should be known as the 'How' pathway as the visual spatial information processed here provides us with information about how to interact with objects, For the purpose of object recognition, the neural focus is on the ventral stream.
=== Functional specialization in the ventral stream ===
Within the ventral stream, various regions of proposed functional specialization have been observed in functional imaging studies. The brain regions most consistently found to display functional specialization are the fusiform face area (FFA), which shows increased activation for faces when compared with objects, the parahippocampal place area (PPA) for scenes vs. objects, the extrastriate body area (EBA) for body parts vs. objects, MT+/V5 for moving stimuli vs. static stimuli, and the Lateral Occipital Complex (LOC) for discernible shapes vs. scrambled stimuli. (See also: Neural processing for individual categories of objects)
==== Structural processing: the lateral occipital complex ====
The lateral occipital complex (LOC) has been found to be particularly important for object recognition at the perceptual structural level. In an event-related [fMRI-en] study that looked at the adaptation of neurons activated in visual processing of objects, it was discovered that the similarity of an object's shape is necessary for subsequent adaptation in the LOC, but specific object features such as edges and contours are not. This suggests that activation in the LOC represents higher-level object shape information and not simple object features. In a related [fMRI-en] study, the activation of the LOC, which occurred regardless of the presented object's visual cues such as motion, texture, or luminance contrasts, suggests that the different low-level visual cues used to define an object converge in "object-related areas" to assist in the perception and recognition process. None of the mentioned higher-level object shape information seems to provide any [semantic-en] information about the object as the LOC shows a neuronal response to varying forms including non-familiar, abstract objects.
Further experiments have proposed that the LOC consists of a hierarchical system for shape selectivity indicating greater selective activation in the posterior regions for fragments of objects whereas the [anterior-en] regions show greater activation for full or partial objects. This is consistent with previous research that suggests a hierarchical representation in the ventral temporal cortex where primary feature processing occurs in the posterior regions and the integration of these features into a whole and meaningful object occurs in the [anterior-en] regions.
==== Semantic Processing ====
Semantic associations allow for faster object recognition. When an object has previously been associated with some sort of semantic meaning, people are more prone to correctly identify the object. Research has shown that semantic associations allow for a much quicker recognition of an object, even when the object is being viewed at varying angles. When objects are viewed at increasingly deviated angles from the traditional plane of view, objects that held learned semantic associations had lower response times compared to objects that did not hold any learned semantic associations. Thus, when object recognition becomes increasingly difficult, semantic associations allow recognition to be much easier. Similarly, a subject can be primed to recognize an object by observing an action that is simply related to the target object. This shows that objects have a set of sensory, motor and semantic associations that allow a person to correctly recognize an object. This supports the claim that the brain utilizes multiple parts when trying to accurately identify an object.
Through information provided from [neuropsychological-en] patients, dissociation of recognition processing have been identified between structural and [semantic-en] processing as structural, colour, and associative information can be selectively impaired. In one PET study, areas found to be involved in associative semantic processing include the left anterior superior/middle temporal gyrus and the left temporal pole comparative to structural and colour information, as well as the right temporal pole comparative to colour decision tasks only. These results indicate that stored perceptual knowledge and semantic knowledge involve separate cortical regions in object recognition as well as indicating that there are hemispheric differences in the temporal regions.
Research has also provided evidence which indicates that visual semantic information converges in the fusiform gyri of the inferotemporal lobes. In a study that compared the semantic knowledge of category versus attributes, it was found that they play separate roles in how they contribute to recognition. For categorical comparisons, the lateral regions of the fusiform gyrus were activated by living objects, in comparison to nonliving objects which activated the medial regions. For attribute comparisons, it was found that the right fusiform gyrus was activated by global form, in comparison to local details which activated the left fusiform gyrus. These results suggest that the type of object category determines which region of the fusiform gyrus is activated for processing semantic recognition, whereas the attributes of an object determines the activation in either the left or right fusiform gyrus depending on whether global form or local detail is processed.
In addition, it has been proposed that activation in [anterior-en] regions of the fusiform gyri indicate successful recognition. However, levels of activation have been found to depend on the semantic relevance of the object. The term semantic relevance here refers to "a measure of the contribution of semantic features to the core meaning of a concept." Results showed that objects with high semantic relevance, such as artefacts, created an increase in activation compared to objects with low semantic relevance, such as natural objects. This is due to the proposed increased difficulty to distinguish between natural objects as they have very similar structural properties which makes them harder to identify in comparison to artefacts. Therefore, the easier the object is to identify, the more likely it will be successfully recognized.
Another condition that affects successful object recognition performance is that of contextual facilitation. It is thought that during tasks of object recognition, an object is accompanied by a "context frame", which offers semantic information about the object's typical context. It has been found that when an object is out of context, object recognition performance is hindered with slower response times and greater inaccuracies in comparison to recognition tasks when an object was in an appropriate context. Based on results from a study using [fMRI-en], it has been proposed that there is a "context network" in the brain for contextually associated objects with activity largely found in the Parahippocampal cortex (PHC) and the Retrosplenial Complex (RSC). Within the PHC, activity in the Parahippocampal Place Area (PPA), has been found to be preferential to scenes rather than objects; however, it has been suggested that activity in the PHC for solitary objects in tasks of contextual facilitation may be due to subsequent thought of the spatial scene in which the object is contextually represented. Further experimenting found that activation was found for both non-spatial and spatial contexts in the PHC, although activation from non-spatial contexts was limited to the [anterior-en] PHC and the posterior PHC for spatial contexts.
== Recognition memory ==
When someone sees an object, they know what the object is because they've seen it on a past occasion; this is recognition memory. Not only do abnormalities to the ventral (what) stream of the visual pathway affect our ability to recognize an object but also the way in which an object is presented to us. One notable characteristic of visual recognition memory is its remarkable capacity: even after seeing thousands of images on single trials, humans perform at high accuracy in subsequent memory tests and they remember considerable detail about the images that they have seen
=== Context ===
Context allows for a much greater accuracy in object recognition. When an identifiable object is blurred, the accuracy of recognition is much greater when the object is placed in a familiar context. In addition to this, even an unfamiliar context allows for more accurate object recognition compared to the object being shown in isolation. This can be attributed to the fact that objects are typically seen in some setting rather than no setting at all. When the setting the object is in is familiar to the viewer, it becomes much easier to determine what the object is. Though context is not required to correctly recognize, it is part of the association that one makes with a certain object.
Context becomes especially important when recognizing faces or emotions. When facial emotions are presented without any context, the ability to which someone is able to accurately describe the emotion being shown is significantly lower than when context is given. This phenomenon remains true across all age groups and cultures, signifying that context is essential in accurately identifying facial emotion for all individuals.
=== Familiarity ===
Familiarity is a mechanism that is context-free in the sense that what one recognizes just feels familiar without spending time trying to find in what context one knows the object. The ventro-lateral region of the frontal lobe is involved in memory encoding during incidental learning and then later maintaining and retrieving semantic memories.
Familiarity can induce perceptual processes different from those of unfamiliar objects which means that our perception of a finite number of familiar objects is unique. Deviations from typical viewpoints and contexts can affect the efficiency for which an object is recognized most effectively. It was found that not only are familiar objects recognized more efficiently when viewed from a familiar viewpoint opposed to an unfamiliar one, but also this principle applies to novel objects. This deduces to the thought that representations of objects in
our brain are organized in more of a familiar fashion of the objects observed in the environment. Recognition is not only largely driven by object shape and/or views but also by dynamic information. Familiarity can benefit the perception of dynamic point-light displays, moving objects, the sex of faces, and face recognition.
==== Recollection ====
Recollection shares many similarities with familiarity; however, it is context-dependent, requiring specific information from the inquired incident.
== Impairments ==
Loss of object recognition is called visual object agnosia. There are two broad categories of visual object agnosia: apperceptive and associative. When object agnosia occurs from a lesion in the dominant hemisphere, there is often a profound associated language disturbance, including loss of word meaning.
=== Effects of lesions in the ventral stream ===
Object recognition is a complex task and involves several different areas of the brain – not just one. If one area is damaged then object recognition can be impaired. The main area for object recognition takes place in the temporal lobe. For example, it was found that lesions to the perirhinal cortex in rats causes impairments in object recognition especially with an increase in feature ambiguity. Neonatal aspiration lesions of the amygdaloid complex in monkeys appear to have resulted in a greater object memory loss than early hippocampal lesions. However, in adult monkeys, the object memory impairment is better accounted for by damage to the perirhinal and entorhinal cortex than by damage to the amygdaloid nuclei. Combined amygdalohippocampal (A + H) lesions in rats impaired performance on an object recognition task when the retention intervals were increased beyond 0s and when test stimuli were repeated within a session. Damage to the [amygdala-en] or [hippocampus-en] does not affect object recognition, whereas A + H damage produces clear deficits. In an object recognition task, the level of discrimination was significantly lower in the electrolytic lesions of globus pallidus (part of the basal ganglia) in rats compared to the Substantia- Innominata/Ventral Pallidum which was in turn worse compared to Control and Medial Septum/Vertical Diagonal Band of Broca groups; however, only globus pallidus did not discriminate between new and familiar objects. These lesions damage the ventral (what) pathway of the visual processing of objects in the brain.
==== Visual agnosias ====
Agnosia is a rare occurrence and can be the result of a stroke, dementia, head injury, brain infection, or hereditary.
Apperceptive agnosia is a deficit in object perception creating an inability to understand the significance of objects.
Similarly, associative visual agnosia is the inability to understand the significance of objects; however, this time the deficit is in semantic memory. Both of these agnosias can affect the pathway to object recognition, like Marr's Theory of Vision. More specifically unlike apperceptive agnosia, associative agnosic patients are more successful at drawing, copying, and matching tasks; however, these patients demonstrate that they can perceive but not recognize.
Integrative agnosia (a subtype of associative agnosia) is the inability to integrate separate parts to form a whole image. With these types of agnosias there is damage to the ventral (what) stream of the visual processing pathway.
Object orientation agnosia is the inability to extract the orientation of an object despite adequate object recognition. With this type of agnosia there is damage to the dorsal (where) stream of the visual processing pathway.
This can affect object recognition in terms of familiarity and even more so in unfamiliar objects and viewpoints.
A difficulty in recognizing faces can be explained by prosopagnosia. Someone with prosopagnosia cannot identify the face but is still able to perceive age, gender, and emotional expression. The brain region that specifies in facial recognition is the fusiform face area. Prosopagnosia can also be divided into apperceptive and associative subtypes. Recognition of individual chairs, cars, animals can also be impaired; therefore, these object share similar perceptual features with the face that are recognized in the fusiform face area.
=== Alzheimer's disease ===
The distinction between category and attribute in semantic representation may inform our ability to assess semantic function in aging and disease states affecting semantic memory, such as Alzheimer's disease (AD). Because of semantic memory deficits, persons with Alzheimer's disease have difficulties recognizing objects as the semantic memory is known to be used to retrieve information for naming and categorizing objects. In fact, it is highly debated whether the semantic memory deficit in AD reflects the loss of semantic knowledge for particular categories and concepts or the loss of knowledge of perceptual features and attributes.
== See also ==
Face perception
Haptic perception
Neural processing for individual categories of objects
Perceptual constancy
Visual perception
Visual system
Outline of object recognition
== References == | Wikipedia/Cognitive_neuroscience_of_visual_object_recognition |
Embodied cognitive science is an interdisciplinary field of research, the aim of which is to explain the mechanisms underlying intelligent behavior. It comprises three main methodologies: the modeling of psychological and biological systems in a holistic manner that considers the mind and body as a single entity; the formation of a common set of general principles of intelligent behavior; and the experimental use of robotic agents in controlled environments.
== Contributors ==
Embodied cognitive science borrows heavily from embodied philosophy and the related research fields of cognitive science, psychology, neuroscience and artificial intelligence. Contributors to the field include:
From the perspective of neuroscience, Gerald Edelman of the Neurosciences Institute at La Jolla, Francisco Varela of CNRS in France, and J. A. Scott Kelso of Florida Atlantic University
From the perspective of psychology, Lawrence Barsalou, Michael Turvey, Vittorio Guidano and Eleanor Rosch
From the perspective of linguistics, Gilles Fauconnier, George Lakoff, Mark Johnson, Leonard Talmy and Mark Turner
From the perspective of language acquisition, Eric Lenneberg and Philip Rubin at Haskins Laboratories
From the perspective of anthropology, Edwin Hutchins, Bradd Shore, James Wertsch and Merlin Donald.
From the perspective of autonomous agent design, early work is sometimes attributed to Rodney Brooks or Valentino Braitenberg
From the perspective of artificial intelligence, Understanding Intelligence by Rolf Pfeifer and Christian Scheier or How the Body Shapes the Way We Think, by Rolf Pfeifer and Josh C. Bongard
From the perspective of philosophy, Andy Clark, Dan Zahavi, Shaun Gallagher, and Evan Thompson
In 1950, Alan Turing proposed that a machine may need a human-like body to think and speak:
It can also be maintained that it is best to provide the machine with the best sense organs that money can buy, and then teach it to understand and speak English. That process could follow the normal teaching of a child. Things would be pointed out and named, etc. Again, I do not know what the right answer is, but I think both approaches should be tried.
== Traditional cognitive theory ==
Embodied cognitive science is an alternative theory to cognition in which it minimizes appeals to computational theory of mind in favor of greater emphasis on how an organism's body determines how and what it thinks. Traditional cognitive theory is based mainly around symbol manipulation, in which certain inputs are fed into a processing unit that produces an output. These inputs follow certain rules of syntax, from which the processing unit finds semantic meaning. Thus, an appropriate output is produced. For example, a human's sensory organs are its input devices, and the stimuli obtained from the external environment are fed into the nervous system which serves as the processing unit. From here, the nervous system is able to read the sensory information because it follows a syntactic structure, thus an output is created. This output then creates bodily motions and brings forth behavior and cognition. Of particular note is that cognition is sealed away in the brain, meaning that mental cognition is cut off from the external world and is only possible by the input of sensory information.
== The embodied cognitive approach ==
Embodied cognitive science differs from the traditionalist approach in that it denies the input-output system. This is chiefly due to the problems presented by the Homunculus argument, which concluded that semantic meaning could not be derived from symbols without some kind of inner interpretation. If some little man in a person's head interpreted incoming symbols, then who would interpret the little man's inputs? Because of the specter of an infinite regress, the traditionalist model began to seem less plausible. Thus, embodied cognitive science aims to avoid this problem by defining cognition in three ways.: 340
=== Physical attributes of the body ===
The first aspect of embodied cognition examines the role of the physical body, particularly how its properties affect its ability to think. This part attempts to overcome the symbol manipulation component that is a feature of the traditionalist model. Depth perception, for instance, can be better explained under the embodied approach due to the sheer complexity of the action. Depth perception requires that the brain detect the disparate retinal images obtained by the distance of the two eyes. In addition, body and head cues complicate this further. When the head is turned in a given direction, objects in the foreground will appear to move against objects in the background. From this, it is said that some kind of visual processing is occurring without the need of any kind of symbol manipulation. This is because the objects appearing to move the foreground are simply appearing to move. This observation concludes then that depth can be perceived with no intermediate symbol manipulation necessary.
A more poignant example exists through examining auditory perception. Generally speaking the greater the distance between the ears, the greater the possible auditory acuity. Also relevant is the amount of density in between the ears, for the strength of the frequency wave alters as it passes through a given medium. The brain's auditory system takes these factors into account as it process information, but again without any need for a symbolic manipulation system. This is because the distance between the ears for example does not need symbols to represent it. The distance itself creates the necessary opportunity for greater auditory acuity. The amount of density between the ears is similar, in that it is the actual amount itself that simply forms the opportunity for frequency alteration. Thus under consideration of the physical properties of the body, a symbolic system is unnecessary and an unhelpful metaphor.
=== The body's role in the cognitive process ===
The second aspect draws heavily from George Lakoff's and Mark Johnson's work on concepts. They argued that humans use metaphors whenever possible to better explain their external world. Humans also have a basic stock of concepts in which other concepts can be derived from. These basic concepts include spatial orientations such as up, down, front, and back. Humans can understand what these concepts mean because they can directly experience them from their own bodies. For example, because human movement revolves around standing erect and moving the body in an up-down motion, humans innately have these concepts of up and down. Lakoff and Johnson contend this is similar with other spatial orientations such as front and back too. As mentioned earlier, these basic stocks of spatial concepts are the basis in which other concepts are constructed. Happy and sad for instance are seen now as being up or down respectively. When someone says they are feeling down, what they are really saying is that they feel sad for example. Thus the point here is that true understanding of these concepts is contingent on whether one can have an understanding of the human body. So the argument goes that if one lacked a human body, they could not possibly know what up or down could mean, or how it could relate to emotional states.
[I]magine a spherical being living outside of any gravitational field, with no knowledge or imagination of any other kind of experience. What could UP possibly mean to such a being?: 342
While this does not mean that such beings would be incapable of expressing emotions in other words, it does mean that they would express emotions differently from humans. Human concepts of happiness and sadness would be different because human would have different bodies. So then an organism's body directly affects how it can think, because it uses metaphors related to its body as the basis of concepts.
=== Interaction of local environment ===
A third component of the embodied approach looks at how agents use their immediate environment in cognitive processing. Meaning, the local environment is seen as an actual extension of the body's cognitive process. The example of a personal digital assistant (PDA) is used to better imagine this. Echoing functionalism (philosophy of mind), this point claims that mental states are individuated by their role in a much larger system. So under this premise, the information on a PDA is similar to the information stored in the brain. So then if one thinks information in the brain constitutes mental states, then it must follow that information in the PDA is a cognitive state too. Consider also the role of pen and paper in a complex multiplication problem. The pen and paper are so involved in the cognitive process of solving the problem that it seems ridiculous to say they are somehow different from the process, in very much the same way the PDA is used for information like the brain. Another example examines how humans control and manipulate their environment so that cognitive tasks can be better performed. Leaving one's car keys in a familiar place so they aren't missed for instance, or using landmarks to navigate in an unfamiliar city. Thus, humans incorporate aspects of their environment to aid in their cognitive functioning.
== Examples of the value of embodied approach ==
The value of the embodiment approach in the context of cognitive science is perhaps best explained by Andy Clark.: 345–351 He makes the claim that the brain alone should not be the single focus for the scientific study of cognition
It is increasingly clear that, in a wide variety of cases, the individual brain should not be the sole locus of cognitive scientific interest. Cognition is not a phenomenon that can be successfully studied while marginalizing the roles of body, world and action.: 350
The following examples used by Clark will better illustrate how embodied thinking is becoming apparent in scientific thinking.
=== Bluefin tuna ===
Thunnus, or tuna, long baffled conventional biologists with its incredible abilities to accelerate quickly and attain great speeds. A biological examination of the tuna shows that it should not be capable of such feats. However, an answer can be found when taking the tuna's embodied state into account. The bluefin tuna is able to take advantage of and exploit its local environment by finding naturally occurring currents to increase its speed. The tuna also uses its own physical body for this end as well, by utilizing its tailfin to create the necessary vortices and pressure so it can accelerate and maintain high speeds. Thus, the bluefin tuna is actively using its local environment for its own ends through the attributes of its physical body.
=== Robots ===
Clark uses the example of the hopping robot constructed by Raibert and Hodgins to demonstrate further the value of the embodiment paradigm. These robots were essentially vertical cylinders with a single hopping foot. The challenge of managing the robot's behavior can be daunting because in addition to the intricacies of the program itself, there were also the mechanical matters regarding how the foot ought to be constructed so that it could hop. An embodied approach makes it easier to see that in order for this robot to function, it must be able to exploit its system to the fullest. That is, the robot's systems should be seen as having dynamic characteristics as opposed to the traditional view that it is merely a command center that just executes actions.
=== Vision ===
Clark distinguishes between two kinds of vision, animate and pure vision. Pure vision is an idea that is typically associated with classical artificial intelligence, in which vision is used to create a rich world model so that thought and reason can be used to fully explore the inner model. In other words, pure vision passively creates the external perceivable world so that the faculties of reason can be better used introspectively. Animate vision, by contrast, sees vision as the means by which real-time action can commence. Animate vision is then more of a vehicle by which visual information is obtained so that actions can be undertaken. Clark points to animate vision as an example of embodiment, because it uses both biological and local environment cues to create an active intelligent process. Consider the Clark's example of going to the drugstore to buy some Kodak film. In one's mind, one is familiar with the Kodak logo and its trademark gold color. Thus, one uses incoming visual stimuli to navigate around the drugstore until one finds the film. Therefore, vision should not be seen as a passive system but rather an active retrieval device that intelligently uses sensory information and local environmental cues to perform specific real-world actions.
=== Affordance ===
Inspired by the work of the American psychologist James J. Gibson, this next example emphasizes the importance of action-relevant sensory information, bodily movement, and local environment cues. These three concepts are unified by the concept of affordances, which are possibilities of action provided by the physical world to a given agent. These are in turn determined by the agent's physical body, capacities, and the overall action-related properties of the local environment as well. Clark uses the example of an outfielder in baseball to better illustrate the concept of affordance. Traditional computational models would claim that an outfielder attempting to catch a fly-ball can be calculated by variables such as the running speed of the outfielder and the arc of the baseball. However, Gibson's work shows that a simpler method is possible. The outfielder can catch the ball so long as they adjust their running speed so that the ball continually moves in a straight line in their field of vision. Note that this strategy uses various affordances that are contingent upon the success of the outfielder, including their physical body composition, the environment of the baseball field, and the sensory information obtained by the outfielder.
Clark points out here that the latter strategy of catching the ball as opposed to the former has significant implications for perception. The affordance approach proves to be non-linear because it relies upon spontaneous real-time adjustments. On the contrary, the former method of computing the arc of the ball is linear as it follows a sequence of perception, calculation and performing action. Thus, the affordance approach challenges the traditional view of perception by arguing against the notion that computation and introspection are necessary. Instead, it ought to be replaced with the idea that perception constitutes a continuous equilibrium of action adjustment between the agent and the world. Ultimately Clark does not expressly claim this is certain but he does observe the affordance approach can explain adaptive response satisfactorily.: 346 This is because they utilize environmental cues made possible by perceptual information that is actively used in the real-time by the agent.
== General principles of intelligent behavior ==
In the formation of general principles of intelligent behavior, Pfeifer intended to be contrary to older principles given in traditional artificial intelligence. The most dramatic difference is that the principles are applicable only to situated robotic agents in the real world, a domain where traditional artificial intelligence showed the least promise.
Principle of cheap design and redundancy: Pfeifer realized that implicit assumptions made by engineers often substantially influence a control architecture's complexity.: 436 This insight is reflected in discussions of the scalability problem in robotics. The internal processing needed for some bad architectures can grow out of proportion to new tasks needed of an agent.
One of the primary reasons for scalability problems is that the amount of programming and knowledge engineering that the robot designers have to perform grows very rapidly with the complexity of the robot's tasks. There is mounting evidence that pre-programming cannot be the solution to the scalability problem ... The problem is that programmers introduce too many hidden assumptions in the robot's code.
The proposed solutions are to have the agent exploit the inherent physics of its environment, to exploit the constraints of its niche, and to have agent morphology based on parsimony and the principle of Redundancy. Redundancy reflects the desire for the error-correction of signals afforded by duplicating like channels. Additionally, it reflects the desire to exploit the associations between sensory modalities. (See redundant modalities). In terms of design, this implies that redundancy should be introduced with respect not only to one sensory modality but to several.: 448 It has been suggested that the fusion and transfer of knowledge between modalities can be the basis of reducing the size of the sense data taken from the real world. This again addresses the scalability problem.
Principle of parallel, loosely-coupled processes: An alternative to hierarchical methods of knowledge and action selection. This design principle differs most importantly from the Sense-Think-Act cycle of traditional AI. Since it does not involve this famous cycle, it is not affected by the frame problem.
Principle of sensory-motor coordination: Ideally, internal mechanisms in an agent should give rise to things like memory and choice-making in an emergent fashion, rather than being prescriptively programmed from the beginning. These kinds of things are allowed to emerge as the agent interacts with the environment. The motto is, build fewer assumptions into the agent's controller now, so that learning can be more robust and idiosyncratic in the future.
Principle of ecological balance: This is more a theory than a principle, but its implications are widespread. Its claim is that the internal processing of an agent cannot be made more complex unless there is a corresponding increase in complexity of the motors, limbs, and sensors of the agent. In other words, the extra complexity added to the brain of a simple robot will not create any discernible change in its behavior. The robot's morphology must already contain the complexity in itself to allow enough "breathing room" for more internal processing to develop.
Value principle: This was the architecture developed in the Darwin III robot of Gerald Edelman. It relies heavily on connectionism.
== Critical responses ==
=== Traditionalist response to local environment claim ===
A traditionalist may argue that objects may be used to aid in cognitive processes, but this does not mean they are part of a cognitive system.: 343 Eyeglasses are used to aid in the visual process, but to say they are a part of a larger system would completely redefine what is meant by a visual system. However, supporters of the embodied approach could make the case that if objects in the environment play the functional role of mental states, then the items themselves should not be counted among the mental states.
Lars Ludwig explores mind extension further outlining its role in technology. He proposes a cognitive theory of 'extended artificial memory', which represents a theoretical update and extension of the memory theories of Richard Semon.
== See also ==
== References ==
== Further reading ==
Braitenberg, Valentino (1986). Vehicles: Experiments in Synthetic Psychology. Cambridge, MA: The MIT Press. ISBN 0-262-52112-1
Brooks, Rodney A. (1999). Cambrian Intelligence: The Early History of the New AI. Cambridge, MA: The MIT Press. ISBN 0-262-52263-2
Edelman, G. Wider than the Sky (Yale University Press, 2004) ISBN 0-300-10229-1
Fowler, C., Rubin, P. E., Remez, R. E., & Turvey, M. T. (1980). Implications for speech production of a general theory of action. In B. Butterworth (Ed.), Language Production, Vol. I: Speech and Talk (pp. 373–420). New York: Academic Press. ISBN 0-12-147501-8
Lenneberg, Eric H. (1967). Biological Foundations of Language. John Wiley & Sons. ISBN 0-471-52626-6
Pfeifer, R. and Bongard J. C., How the body shapes the way we think: a new view of intelligence (The MIT Press, 2007). ISBN 0-262-16239-3
== External links ==
AI lectures from Tokyo hosted by Rolf Pfeifer
synthetic neural modelling in DARWIN IV
Society for the Simulation of Adaptive Behavior
A platform for creating Embodied Cognitive Agents | Wikipedia/Embodied_cognitive_science |
A cognitive model is a representation of one or more cognitive processes in humans or other animals for the purposes of comprehension and prediction. There are many types of cognitive models, and they can range from box-and-arrow diagrams to a set of equations to software programs that interact with the same tools that humans use to complete tasks (e.g., computer mouse and keyboard). In terms of information processing, cognitive modeling is modeling of human perception, reasoning, memory and action.
== Relationship to cognitive architectures ==
Cognitive models can be developed within or without a cognitive architecture, though the two are not always easily distinguishable. In contrast to cognitive architectures, cognitive models tend to be focused on a single cognitive phenomenon or process (e.g., list learning), how two or more processes interact (e.g., visual search and decision making), or making behavioral predictions for a specific task or tool (e.g., how instituting a new software package will affect productivity). Cognitive architectures tend to be focused on the structural properties of the modeled system, and help constrain the development of cognitive models within the architecture. Likewise, model development helps to inform limitations and shortcomings of the architecture. Some of the most popular architectures for cognitive modeling include ACT-R, Clarion, LIDA, and Soar.
== History ==
Cognitive modeling historically developed within cognitive psychology/cognitive science (including human factors), and has received contributions from the fields of machine learning and artificial intelligence among others.
== Box-and-arrow models ==
A number of key terms are used to describe the processes involved in the perception, storage, and production of speech. Typically, they are used by speech pathologists while treating a child patient. The input signal is the speech signal heard by the child, usually assumed to come from an adult speaker. The output signal is the utterance produced by the child. The unseen psychological events that occur between the arrival of an input signal and the production of speech are the focus of psycholinguistic models. Events that process the input signal are referred to as input processes, whereas events that process the production of speech are referred to as output processes. Some aspects of speech processing are thought to happen online—that is, they occur during the actual perception
or production of speech and thus require a share of the attentional resources dedicated to the speech task. Other processes, thought to happen offline, take place as part of the child's background mental processing rather than during the time dedicated to the speech task.
In this sense, online processing is sometimes defined as occurring in real-time, whereas offline processing is said to be time-free (Hewlett, 1990). In box-and-arrow psycholinguistic models, each hypothesized level of representation or processing can be represented in a diagram by a “box,” and the relationships between them by “arrows,” hence the name. Sometimes (as in the models of Smith, 1973, and Menn, 1978, described later in this paper) the arrows represent processes additional to those shown in boxes. Such models make explicit the hypothesized information-
processing activities carried out in a particular cognitive function (such as language), in a manner analogous to computer flowcharts that depict the processes and decisions carried out by a computer program. Box-and-arrow models differ widely in the number of unseen psychological processes they describe and thus in the number of boxes they contain. Some have only one or two boxes between the input and output signals (e.g., Menn, 1978; Smith, 1973), whereas others have multiple boxes representing complex relationships between a number of different information-processing events (e.g., Hewlett, 1990; Hewlett, Gibbon, & Cohen- McKenzie, 1998; Stackhouse & Wells, 1997). The most important box, however, and the source of much ongoing debate, is that representing the underlying representation (or UR). In essence, an underlying representation captures information stored in a child's mind about a word he or she knows and uses. As the following description of several models will illustrate, the nature of this information and thus the type(s) of representation present in the child's knowledge base have captured the attention of researchers for some time. (Elise Baker et al. Psycholinguistic Models of Speech Development and Their Application to Clinical Practice. Journal of Speech, Language, and Hearing Research. June 2001. 44. p 685–702.)
== Computational models ==
A computational model is a mathematical model in computational science that requires extensive computational resources to study the behavior of a complex system by computer simulation. Computational cognitive models examine cognition and cognitive functions by developing process-based computational models formulated as sets of mathematical equations or computer simulations. The system under study is often a complex nonlinear system for which simple, intuitive analytical solutions are not readily available. Rather than deriving a mathematical analytical solution to the problem, experimentation with the model is done by changing the parameters of the system in the computer, and studying the differences in the outcome of the experiments. Theories of operation of the model can be derived/deduced from these computational experiments.
Examples of common computational models are weather forecasting models, earth simulator models, flight simulator models, molecular protein folding models, and neural network models.
=== Symbolic ===
A symbolic model is expressed in characters, usually non-numeric ones, that require translation before they can be used.
=== Subsymbolic ===
A cognitive model is subsymbolic if it is made by constituent entities that are not representations in their turn, e.g., pixels, sound images as perceived by the ear, signal samples; subsymbolic units in neural networks can be considered particular cases of this category.
=== Hybrid ===
Hybrid computers are computers that exhibit features of analog computers and digital computers. The digital component normally serves as the controller and provides logical operations, while the analog component normally serves as a solver of differential equations. See more details at hybrid intelligent system.
== Dynamical systems ==
In the traditional computational approach, representations are viewed as static structures of discrete symbols. Cognition takes place by transforming static symbol structures in discrete, sequential steps. Sensory information is transformed into symbolic inputs, which produce symbolic outputs that get transformed into motor outputs. The entire system operates in an ongoing cycle.
What is missing from this traditional view is that human cognition happens continuously and in real time. Breaking down the processes into discrete time steps may not fully capture this behavior. An alternative approach is to define a system with (1) a state of the system at any given time, (2) a behavior, defined as the change over time in overall state, and (3) a state set or state space, representing the totality of overall states the system could be in. The system is distinguished by the fact that a change in any aspect of the system state depends on other aspects of the same or other system states.
A typical dynamical model is formalized by several differential equations that describe how the system's state changes over time. By doing so, the form of the space of possible trajectories and the internal and external forces that shape a specific trajectory that unfold over time, instead of the physical nature of the underlying mechanisms that manifest this dynamics, carry explanatory force. On this dynamical view, parametric inputs alter the system's intrinsic dynamics, rather than specifying an internal state that describes some external state of affairs.
=== Early dynamical systems ===
==== Associative memory ====
Early work in the application of dynamical systems to cognition can be found in the model of Hopfield networks. These networks were proposed as a model for associative memory. They represent the neural level of memory, modeling systems of around 30 neurons which can be in either an on or off state. By letting the network learn on its own, structure and computational properties naturally arise. Unlike previous models, “memories” can be formed and recalled by inputting a small portion of the entire memory. Time ordering of memories can also be encoded. The behavior of the system is modeled with vectors which can change values, representing different states of the system. This early model was a major step toward a dynamical systems view of human cognition, though many details had yet to be added and more phenomena accounted for.
==== Language acquisition ====
By taking into account the evolutionary development of the human nervous system and the similarity of the brain to other organs, Elman proposed that language and cognition should be treated as a dynamical system rather than a digital symbol processor. Neural networks of the type Elman implemented have come to be known as Elman networks. Instead of treating language as a collection of static lexical items and grammar rules that are learned and then used according to fixed rules, the dynamical systems view defines the lexicon as regions of state space within a dynamical system. Grammar is made up of attractors and repellers that constrain movement in the state space. This means that representations are sensitive to context, with mental representations viewed as trajectories through mental space instead of objects that are constructed and remain static. Elman networks were trained with simple sentences to represent grammar as a dynamical system. Once a basic grammar had been learned, the networks could then parse complex sentences by predicting which words would appear next according to the dynamical model.
==== Cognitive development ====
A classic developmental error has been investigated in the context of dynamical systems: The A-not-B error is proposed to be not a distinct error occurring at a specific age (8 to 10 months), but a feature of a dynamic learning process that is also present in older children. Children 2 years old were found to make an error similar to the A-not-B error when searching for toys hidden in a sandbox. After observing the toy being hidden in location A and repeatedly searching for it there, the 2-year-olds were shown a toy hidden in a new location B. When they looked for the toy, they searched in locations that were biased toward location A. This suggests that there is an ongoing representation of the toy's location that changes over time. The child's past behavior influences its model of locations of the sandbox, and so an account of behavior and learning must take into account how the system of the sandbox and the child's past actions is changing over time.
==== Locomotion ====
One proposed mechanism of a dynamical system comes from analysis of continuous-time recurrent neural networks (CTRNNs). By focusing on the output of the neural networks rather than their states and examining fully interconnected networks, three-neuron central pattern generator (CPG) can be used to represent systems such as leg movements during walking. This CPG contains three motor neurons to control the foot, backward swing, and forward swing effectors of the leg. Outputs of the network represent whether the foot is up or down and how much force is being applied to generate torque in the leg joint. One feature of this pattern is that neuron outputs are either off or on most of the time. Another feature is that the states are quasi-stable, meaning that they will eventually transition to other states. A simple pattern generator circuit like this is proposed to be a building block for a dynamical system. Sets of neurons that simultaneously transition from one quasi-stable state to another are defined as a dynamic module. These modules can in theory be combined to create larger circuits that comprise a complete dynamical system. However, the details of how this combination could occur are not fully worked out.
=== Modern dynamical systems ===
==== Behavioral dynamics ====
Modern formalizations of dynamical systems applied to the study of cognition vary. One such formalization, referred to as “behavioral dynamics”, treats the agent and the environment as a pair of coupled dynamical systems based on classical dynamical systems theory. In this formalization, the information from the environment informs the agent's behavior and the agent's actions modify the environment. In the specific case of perception-action cycles, the coupling of the environment and the agent is formalized by two functions. The first transforms the representation of the agents action into specific patterns of muscle activation that in turn produce forces in the environment. The second function transforms the information from the environment (i.e., patterns of stimulation at the agent's receptors that reflect the environment's current state) into a representation that is useful for controlling the agents actions. Other similar dynamical systems have been proposed (although not developed into a formal framework) in which the agent's nervous systems, the agent's body, and the environment are coupled together
===== Adaptive behaviors =====
Behavioral dynamics have been applied to locomotive behavior. Modeling locomotion with behavioral dynamics demonstrates that adaptive behaviors could arise from the interactions of an agent and the environment. According to this framework, adaptive behaviors can be captured by two levels of analysis. At the first level of perception and action, an agent and an environment can be conceptualized as a pair of dynamical systems coupled together by the forces the agent applies to the environment and by the structured information provided by the environment. Thus, behavioral dynamics emerge from the agent-environment interaction. At the second level of time evolution, behavior can be expressed as a dynamical system represented as a vector field. In this vector field, attractors reflect stable behavioral solutions, where as bifurcations reflect changes in behavior. In contrast to previous work on central pattern generators, this framework suggests that stable behavioral patterns are an emergent, self-organizing property of the agent-environment system rather than determined by the structure of either the agent or the environment.
==== Open dynamical systems ====
In an extension of classical dynamical systems theory, rather than coupling the environment's and the agent's dynamical systems to each other, an “open dynamical system” defines a “total system”, an “agent system”, and a mechanism to relate these two systems. The total system is a dynamical system that models an agent in an environment, whereas the agent system is a dynamical system that models an agent's intrinsic dynamics (i.e., the agent's dynamics in the absence of an environment). Importantly, the relation mechanism does not couple the two systems together, but rather continuously modifies the total system into the decoupled agent's total system. By distinguishing between total and agent systems, it is possible to investigate an agent's behavior when it is isolated from the environment and when it is embedded within an environment. This formalization can be seen as a generalization from the classical formalization, whereby the agent system can be viewed as the agent system in an open dynamical system, and the agent coupled to the environment and the environment can be viewed as the total system in an open dynamical system.
===== Embodied cognition =====
In the context of dynamical systems and embodied cognition, representations can be conceptualized as indicators or mediators. In the indicator view, internal states carry information about the existence of an object in the environment, where the state of a system during exposure to an object is the representation of that object. In the mediator view, internal states carry information about the environment which is used by the system in obtaining its goals. In this more complex account, the states of the system carries information that mediates between the information the agent takes in from the environment, and the force exerted on the environment by the agents behavior. The application of open dynamical systems have been discussed for four types of classical embodied cognition examples:
Instances where the environment and agent must work together to achieve a goal, referred to as "intimacy". A classic example of intimacy is the behavior of simple agents working to achieve a goal (e.g., insects traversing the environment). The successful completion of the goal relies fully on the coupling of the agent to the environment.
Instances where the use of external artifacts improves the performance of tasks relative to performance without these artifacts. The process is referred to as "offloading". A classic example of offloading is the behavior of Scrabble players; people are able to create more words when playing Scrabble if they have the tiles in front of them and are allowed to physically manipulate their arrangement. In this example, the Scrabble tiles allow the agent to offload working memory demands on to the tiles themselves.
Instances where a functionally equivalent external artifact replaces functions that are normally performed internally by the agent, which is a special case of offloading. One famous example is that of human (specifically the agents Otto and Inga) navigation in a complex environment with or without assistance of an artifact.
Instances where there is not a single agent. The individual agent is part of larger system that contains multiple agents and multiple artifacts. One famous example, formulated by Ed Hutchins in his book Cognition in the Wild, is that of navigating a naval ship.
The interpretations of these examples rely on the following logic: (1) the total system captures embodiment; (2) one or more agent systems capture the intrinsic dynamics of individual agents; (3) the complete behavior of an agent can be understood as a change to the agent's intrinsic dynamics in relation to its situation in the environment; and (4) the paths of an open dynamical system can be interpreted as representational processes. These embodied cognition examples show the importance of studying the emergent dynamics of an agent-environment systems, as well as the intrinsic dynamics of agent systems. Rather than being at odds with traditional cognitive science approaches, dynamical systems are a natural extension of these methods and should be studied in parallel rather than in competition.
== See also ==
Computational cognition
Computational models of language acquisition
Computational-representational understanding of mind
MindModeling@Home
Memory-prediction framework
Space mapping
== References ==
== External links ==
Cognitive modeling at CMU
Cognitive modeling at RPI (HCI)
Cognitive modeling at RPI (CLARION)
Cognitive modeling at the University of Memphis (LIDA)
Cognitive modeling at UMich | Wikipedia/Cognitive_model |
Structure-mapping theory is a theory of analogical reasoning, developed by Dedre Gentner, and for which she was awarded the 2016 David E. Rumelhart Prize for Contributions to the Theoretical Foundations of Human Cognition.
== Distinguishing analogy from other comparisons ==
Structure-mapping theory aims to improve upon previous theories of analogy, by distinguishing analogy from literal similarity. Previous theories, like Amos Tversky's contrast theory, assumed that an analogy is stronger, the more attributes the base and target have in common. Instead, structure-mapping theory recognizes that there can be differences between base and target domains which make no difference to the strength of the analogy. For example, we can see a battery as being like a reservoir despite them being different in shape, size, color and substance.
Structure-mapping theory respond by arguing that it is not object attributes which are mapped in an analogy. Instead the theory contends that an analogy alerts the hearer to a similarity in the relationships between objects in a domain. The distinction is made in terms of the arity of predicates - attributes are predicates with one argument, while relationships are predicates which take two or more arguments. So the proposition "x is large" asserts an attribute, while "x revolves around y" asserts a relationship. (Higher order predicates assert relationships between propositions)
=== Analogy vs literal similarity ===
By distinguishing attributes and relationships, we can distinguish literal similarities from analogies.
For example:
The X12 star system in the Andromeda nebula is like the Solar System. - This is a literal similarity, because the intention is to map both relationships (e.g. between planets and the Sun) and attributes (e.g. the size and temperature of the Sun)
The hydrogen atom is like the Solar System. (Rutherford, 1906) - This is an analogy, because only relational predicates, like relative motion and size, are to be mapped between domains.
=== Analogy vs general laws ===
Analogies can also be distinguished from general laws
The hydrogen atom is a central force system. - This is a general law, in the sense that the base domain is an abstract domain of relationships, and actually includes no object attributes. Compare this to an analogy, where the base domain includes object attributes, which are excluded from the comparison.
=== Analogy vs. chronology ===
The distinction in the role of objects, attributes and relationships in the comparison also allows us to characterize a chronology as a comparison in which objects are compared (remain relatively constant), but relationships are not (i.e. are expected to differ).
=== Summary table ===
Gentner provides the following table to summarize the different types of domain comparison above:
== Systematicity principle ==
"Part of our understanding about analogy is that it conveys a system of connected knowledge, not a mere assortment of independent facts. Such a system can be represented by an interconnected predicate structure in which higher-order predicates enforce connections among lower-order predicates. reflect this tacit preference for coherence in analogy, I propose the systematicity principle: A predicate that belongs to a mappable system of mutually interconnecting relationships is more likely to be imported into the target than is an isolated predicate." (Gentner 1983, p162-163; emphasis added)
The systematicity principle helps to explain why, when comparing the atom to the Solar System, we do not try to map the relative temperature of Sun and the Earth onto the nucleus-electron system. In short, the temperature has no strong connection to the other object relationships - such as distance, attractive force, relative mass, and relative motion (who revolves around who) - which are mapped. What these other relationships share is a strong interdependence - reversing the mass relationship reverses the relative motion relationship, and changing the distance changes the attractive force, and so on.
== Structure mapping theory ==
Structure mapping, originally proposed by Dedre Gentner, is a theory in psychology that describes the psychological processes involved in reasoning through and learning from analogies. More specifically, this theory aims to describe how familiar knowledge, or knowledge about a base domain, can be used to inform an individual's understanding of a less familiar idea, or a target domain. According to this theory, individuals view their knowledge of domains as interconnected structures. In other words, a domain is viewed as consisting of objects, their properties, and the relationships that characterize the interactions between them. The process of analogy then involves:
Recognising similar structures between the base and target domains.
Finding deeper similarities by mapping other relationships of a base domain to the target domain.
Checking those findings against existing knowledge of the target domain.
In general, it has been found that people prefer analogies where the two systems correspond highly with each other (e.g. have similar relationships across the domains as opposed to just having similar objects across domains) when these people try to compare and contrast the systems. This is also known as the systematicity principle.
An example that has been used to illustrate structure mapping theory comes from Gentner and Gentner (1983) and uses the base domain of flowing water and the target domain of electricity. In a system of flowing water, the water is carried through pipes and the rate of water flow is determined by the pressure of the water towers or hills. This relationship corresponds to that of electricity flowing through a circuit. In a circuit, the electricity is carried through wires and the current, or rate of flow of electricity, is determined by the voltage, or electrical pressure. Given the similarity in structure, or structural alignment, between these domains, structure mapping theory would predict that relationships from one of these domains would be inferred in the other via analogy.
== Factors in reasoning ==
=== Language ===
Language can support analogical reasoning when relational labels are provided to increase clarity. For example, children struggle when they are asked to identify the relational structure between sets of boxes (e.g., Set 1: a small, medium, and large box. Set 2: a medium, large, and extra large box). Children will tend to map the medium box in Set 1 (where it is intermediate in size) to the medium box in Set 2 (where it is smallest in size), and the same happens with the large box in both sets. However, they fail to recognise that they should map the smallest box in Set 1 to the smallest box in Set 2, and so on. Children improve in their ability to identify this relationship when they have given relational labels, such as 'baby', 'mommy', and 'daddy'(or, in the box example, the words smallest, middle and largest).
While language may support analogical reasoning, it may not be necessary. Research has found that apes, who have limited language abilities, are also able to reason relationally, but this only occurs when base and target are highly aligned.
=== Clarity ===
How similar the objects being mapped to each other affects analogical reasoning. When objects in the base domains correspond to highly similar ones in target domains, there it is said to be very clear, which aids analogical processes. Being very clear helps a lot when using analogy to support problem-solving. For example, if students are asked to calculate how many golf balls each golfer will need at a tournament, they will then be able to apply this solution to future problems when the objects are highly similar (e.g. reasoning about how many tennis balls each player will need).
=== Processing capacities ===
In order to engage in analogical processes, an individual needs time to work through the processes of alignment, inference, and evaluation. If not given adequate time to engage in analogical reasoning, then one is more likely to fixate on lower level object correspondences between the two systems, as opposed identifying potentially more informative higher-order relationships that are analogous. Similar effects also occur if one's working memory is under a high cognitive load at the time (e.g., the person is trying to reason through an analogy while also keeping a word in the mind).
==== Structural alignment ====
Structural alignment is one process involved in the larger structure mapping theory. When people establish structural alignment between two domains that are being compared, they attempt to identify as many similarities between the systems as possible and maintain a one-to-one correspondence between elements (i.e., objects, properties, and relationships). In the flowing water and electricity analogy, a one-to-one correspondence is illustrated by water pipes mapping on to wires but not corresponding with any other elements in the circuit. Furthermore, structural alignment is also characterized by parallel connectivity. If there is a one-to-one correspondence between relationships across two systems (e.g., the rate of water flow through a pipe increases with pressure similarly to how the current in an electrical circuit increases with voltage), then the relevant objects and properties must also correspond (e.g. the rate of flow of water corresponds to electrical current and water pressure corresponds to voltage) and vice versa.
==== Inference ====
Analogical inference is the second process involved in the theory of structure mapping. After one finds out that the domains have a one-to-one correspondence (meaning each term in the first domain represents a similar term in the second) one can use this fact to make a conclusion about the second domain. During this process an individual draws inferences about the target domain by projecting information from the base domain to said target domain. The following example can be used to illustrate this process, where 1 represents information about a base domain, 2 represents correspondences between the base and target domain, and 3 represents an inference about the target domain:
In plumbing systems, narrow pipes lead to a decrease in rate of flow of water.
Narrow pipes correspond to resistors in an electrical circuit and water corresponds to electricity.
In electrical circuits, resistors lead to a decrease in the rate of flow of electricity.
==== Evaluation ====
Evaluation is a third process involved in the theory of structure mapping and happens after individual align structures and propose inferences about the target domain. During evaluation, they judge whether the analogy is relevant and plausible. This process has been described as solving the selection problem in analogy, or explaining how individuals choose which inferences to map from the base to target domain as analogies would be fruitless if all possible inferences were made. An analogy can be evaluated by two factors:
Factual correctness. When evaluating an inference in terms of correctness, individuals compare the inference to their existing knowledge to determine whether the inference is true or false. In the case where they cannot determine the correctness, then they may consider the adaptability of the inference, or how easily the knowledge is modified when translating it from the base to target domain.
Goal When evaluating an analogy, the inferences that provide insight have to be relevant to the situation at hand. For example, when individuals attempt to solve a problem, the inference should provide insight that moves them towards a workable solution or generate new, potentially helpful knowledge.
==== Capability development ====
Research suggests children are capable of using comparisons in order to learn abstract patterns, but this sometimes requires prompting from another. To provide support for this claim, researchers taught 3- and 4-year-olds a simple relationship by showing them a series of pictures. Each picture had 3 of the same animal and was labeled as a “toma” for the child. Some of these children were prompted to compare the different ‘tomas’ while others were not. After seeing the pictures and some having been prompted to compare, the children were tested on whether or not they had learned the abstract pattern (i.e., a ‘toma’ is a triad of matching animals). Children were shown two images and asked “Which is the ‘toma’?”. The first was a relational match and displayed a triad of matching animals they had not seen before, while the second image was an object match and displayed a triad of non-matching animals that the child had seen while learning about the relationship. The children who had been prompted to compare the tomas while learning were more likely to have learned the pattern and choose the relational match when being tested.
Children do not always need prompting to make comparisons in order to learn abstract relationships. Eventually, children undergo a relational shift, after which they begin seeing similar relations across different situations and instead of merely looking at matching objects. This is critical in their cognitive development as continuing to focus attention on specific objects would reduce children's ability to learn abstract patterns and reason analogically. Interestingly, some researchers have proposed that children's basic cognitive abilities (i.e., working memory and inhibitory control) do not drive this relational shift. Instead, it is driven by their relational knowledge, such as having labels for the objects that make the relationships more explicit (see previous section). However, there is not enough evidence to determine whether the relational shift is actually because basic cognitive abilities become better or relational knowledge becomes deeper.
Additionally, research has identified several factors that may increase the likelihood that a child may spontaneously engage in comparison and learn an abstract relationship, without the need for prompts. Comparison is more likely when the objects to be compared are close together in space and/or time are highly similar (although not so similar that they are matching objects, which interfere with identifying relationships), or share common labels.
== Notes ==
== See also ==
Structure mapping engine | Wikipedia/Structure-mapping_theory |
Magnetic therapy is a pseudoscientific alternative medicine practice involving the weak static magnetic field produced by a permanent magnet which is placed on the body. It is similar to the alternative medicine practice of electromagnetic therapy, which uses a magnetic field generated by an electrically powered device. Magnet therapy products may include wristbands, jewelry, blankets, and wraps that have magnets incorporated into them.
Practitioners claim that subjecting certain parts of the body to weak electric or magnetic fields has beneficial health effects. These physical and biological claims are unproven and no effects on health or healing have been established. Although hemoglobin, the blood protein that carries oxygen, is weakly diamagnetic (when oxygenated) or paramagnetic (when deoxygenated), the magnets used in magnetic therapy are many orders of magnitude too weak to have any measurable effect on blood flow.
This is not to be confused with transcranial magnetic stimulation, a scientifically valid form of therapy, or with pulsed electromagnetic field therapy.
== Methods of application ==
Magnet therapy involves applying the weak magnetic field of permanent magnets to the body, for purported health benefits. Different effects are assigned to different orientations of the magnet.
Products include magnetic bracelets and jewelry; magnetic straps for wrists, ankles, knees, and back; shoe insoles; mattresses; magnetic blankets (blankets with magnets woven into the material); magnetic creams; magnetic supplements; plasters/patches and water that has been "magnetized". These products generally use neodymium and ferrite magnets and the application is usually performed by the patient.
It is similar to the alternative medicine practice of electromagnetic therapy, which uses the weak electric or magnetic fields as well, but generated by electrically powered devices.
== Suggested mechanisms of action ==
Perhaps the most common suggested mechanism is that magnets might improve blood flow in underlying tissues. The field surrounding magnet therapy devices is far too weak and falls off with distance far too quickly to appreciably affect hemoglobin, other blood components, muscle tissue, bones, blood vessels, or organs. A 1991 study on humans of static field strengths up to 1 T found no effect on local blood flow. Tissue oxygenation is similarly unaffected. Some practitioners claim that the magnets can restore the body's hypothetical "electromagnetic energy balance", but no such balance is medically recognized. Even in the magnetic fields used in magnetic resonance imaging, which are many times stronger, none of the claimed effects are observed. If the body were meaningfully affected by the weak magnets used in magnet therapy, MRI would be impractical.
== Efficacy ==
Several studies have been conducted in recent years to investigate what role, if any, static magnetic fields may play in health and healing. Unbiased studies of magnetic therapy are problematic, since magnetisation can be easily detected, for instance, by the attraction forces on ferrous (iron-containing) objects; because of this, effective blinding of studies (where neither patients nor assessors know who is receiving treatment versus placebo) is difficult. Incomplete or insufficient blinding tends to exaggerate treatment effects, particularly where any such effects are small. Health claims regarding longevity and cancer treatment are implausible and unsupported by any research. More mundane health claims, most commonly about anecdotal pain relief, also lack any credible proposed mechanism and clinical research is not promising.
The American Cancer Society states that "available scientific evidence does not support these claims". According to the National Center for Complementary and Integrative Health, studies of magnetic jewelry have not shown demonstrable effects on pain, nerve function, cell growth or blood flow.
A 2008 systematic review of magnet therapy for all indications found insufficient evidence to determine whether magnet therapy is effective for pain relief, as did 2012 reviews focused on osteoarthritis and rheumatoid arthritis. These reviews found that the data was either inconclusive or did not support a significant effect of magnet therapy. They also raised concerns about allocation concealment, small sample sizes, inadequate blinding, and heterogeneity of results, some of which may have biased results.
== Safety ==
These devices are generally considered safe in themselves, though there can be significant financial and opportunity costs to magnet therapy, especially when treatment or diagnosis are avoided or delayed. Use is not recommended with pacemakers, insulin pumps, and other devices that may be negatively affected by magnetic fields.
== Reception ==
The worldwide magnet therapy industry totals sales of over a billion dollars per year, including $300 million per year in the United States alone.
A 2002 U.S. National Science Foundation report on public attitudes and understanding of science noted that magnet therapy is "not at all scientific." A number of vendors make unsupported claims about magnet therapy by using pseudoscientific and new-age language. Such claims are unsupported by the results of scientific and clinical studies.
=== Legal regulations ===
Marketing of any therapy as effective treatment for any condition is heavily restricted by law in many jurisdictions unless all such claims are scientifically validated. In the United States, for example, U.S. Food and Drug Administration regulations prohibit marketing any magnet therapy product using medical claims, as such claims are unfounded.
== See also ==
== References ==
== External links ==
Magnetic Therapy: Can magnets alleviate pain? by Cecil Adams — The Straight Dope
Magnetic Therapy: Plausible Attraction? by James D. Livingston — Skeptical Inquirer
Magnet therapy in the Skeptic's Dictionary by Robert Todd Carroll
Magnet therapy — editorial in the British Medical Journal
Magnet Therapy: A Skeptical View by Stephen Barrett — Quackwatch | Wikipedia/Magnet_therapy |
Blood irradiation therapy is an alternative medical procedure in which the blood is exposed to low-level light (often laser light) for therapeutic reasons. The practice was originally developed in the United States, but most recent research on it has been conducted in Germany (by UV lamps) and in Russia (in all variants). Low-level laser therapy has been tested for a wide range of conditions, but rigorous double-blinded studies have not yet been performed. Furthermore, it has been claimed that ultraviolet irradiation of blood kills bacteria by DNA damage and also activation of the immune system. Blood irradiation therapy is highly controversial, and has fallen from mainstream use since its heyday in the 1940s and 1950s.
Blood irradiation therapy can be administered in three ways: extracorporeally, transcutaneously, and intravenously. The extracorporeal (outside the body) method removes blood from the body and irradiates it in a special cuvette (tube). This method is used for the ultraviolet (UV) blood irradiation (UVBI) by UV lamps. In the transcutaneous method, the radiation goes through the skin, by placing a device on the outside of the skin. In the intravenous method, a device is inserted into a large blood vessel. The laser light is monochromatic.
It is not related to the practice of gamma irradiation of blood in transfusion medicine.
== History ==
In 1928, Dr. Emmet Knott and a medical student named Lester Edblom received a United States patent for a "Means for Treating Blood-Stream Infection" that incorporated a rudimentary ultraviolet bulb, vacuum extraction system and a cuvette. The "Knott Hemo-Irradiator" was used from the 1930s through the 1950s on patients with multiple infectious diseases.
George P Miley at the Hahnemann Hospital in Philadelphia, Pennsylvania, published a series of articles on the use of the procedure in the treatment of thrombophlebitis, staphylococcal sepsis, peritonitis, botulism, poliomyelitis, non-healing wounds, and asthma.
One of the best known and most comprehensive set of studies was published in 1947 by Dr. George Miley and Dr. Jens A Christensen (from the Blood Irradiation Clinic of the Hahnemann Medical College and Hospital of Philadelphia, Pennsylvania). The authors studied 445 cases of acute pyogenic infections and 74 cases of virus and virus-like infections. Findings included the following: sulfonamide-resistant and penicillin-resistant infections have responded to the treatment. Further finding included: "We have observed that toxemias due to various virus and virus-like infections subside rapidly …” Some of the more impressive results included cases involving septic infection, 57 out of 57 cases recovered. In treating peritonitis, 16 out of 18 patients recovered. With puerperal sepsis, 14 out of 14 patients recovered. With thrombophlebitis, 34 out of 34 recovered. The authors emphasized the need to follow the protocol set for by Knott. Of importance, this protocol included the use of a chamber or cuvette with a flat quartz surface.
Henry A Barrett at the Willard Parker Hospital in New York City, in 1940 reported on 110 cases including a number of infections. Twenty-nine different conditions were described as responding including the following: infectious arthritis, septic abortion, osteoarthritis, tuberculosis glands, chronic blepharitis, mastoiditis, uveitis, furunculosis, chronic paranasal sinusitis, acne vulgaris, and secondary anemia.
This procedure fell out of favor in the late 1950s, at a time when antibiotics and the polio vaccine were becoming widely used. Since then it has been sidelined as a type of alternative and complementary medicine.
The U.S. Food and Drug Administration (FDA) has approved one type of this treatment for T cell lymphoma. This particular process was developed by a team at Yale, led by Richard Edelson who developed a photopheresis machine. This machine separates the white and red blood cells. The white cells are then routed into a blood chamber, where those cells are subjected to UV light from the UVA part of the spectrum. This process uses a photosensitizing agent which enhances the effectiveness of the light. Observational evidence suggests that photopheresis might be effective in the treatment of graft-versus-host disease, though controlled trials are needed to support this use.
The American Cancer Society lists blood irradiation therapy as one of many types of ineffective cancer treatment fraudulently sold by alternative cancer treatment clinics in Mexico.
== Types ==
=== Intravenous laser blood irradiation ===
Intravenous or intravascular laser blood irradiation (ILBI) involves the in-vivo illumination of the blood by feeding low level laser light generated by a 1–3 mW helium–neon laser at a wavelength of 632.8 nanometers (nm) into a vascular channel, usually a vein in the forearm, under the assumption that any therapeutic effect will be circulated through the circulatory system. Most often wavelengths of 365, 405, 525 and 635 nm and power of 2.3 mW are used. The technique is widely used at present in Russia, less in Asia, and not extensively in other parts of the world. It is shown that ILBI improves blood flow and its transport activities, therefore, tissue tropism, has a positive effect on the immune system and cell metabolism. This issue is subject to skepticism.
=== Transcutaneous laser blood irradiation ===
Transcutaneous therapy applies laser light on unbroken skin in areas with large numbers of blood vessels (such as the forearm). Because of the skin acting as a barrier to the blood, absorbing low level laser energy, the power of the laser is often boosted to compensate.
The problem can be solved by using pulsed matrix laser light sources.
=== Extracorporeal irradiation ===
Extracorporeal irradiation is used only for ultraviolet blood irradiation, that involves drawing blood out through a vein and irradiating it outside of the body.
Though promoted as a treatment for cancer, a 1952 review in the Journal of the American Medical Association and another review by the American Cancer Society in 1970 concluded the treatment was ineffective.
== See also ==
Caesium-137
Light therapy
Photodynamic therapy
Photopheresis
== References == | Wikipedia/Blood_irradiation_therapy |
Cranial electrotherapy stimulation (CES) is a form of neurostimulation that delivers a small, pulsed, alternating current via electrodes on the head. CES is used with the intention of treating a variety of conditions such as anxiety, depression and insomnia. CES has been suggested as a possible treatment for headaches, fibromyalgia, smoking cessation, and opiate withdrawal, but there is little evidence of effectiveness for many of these conditions and the evidence for use in acute depression is not sufficient to justify it.
== Medical uses ==
A 2014 Cochrane review found insufficient evidence to determine whether or not CES with alternating current is safe and effective for treating depression. The FDA came to the same conclusion in December 2019.
A 2018 systematic review found that evidence is insufficient that CES has clinically important effects on fibromyalgia, headache, neuromusculoskeletal pain, degenerative joint pain, depression, or insomnia; low-strength evidence suggests modest benefit in patients with anxiety and depression.
== Description ==
Electrodes are placed on the earlobes, maxilla-occipital junction, mastoid processes or temples.
Despite the long history of CES, its underlying principles and mechanisms are still not clear.
CES stimulation of 1 mA (milliampere) has shown to reach the thalamic area at a radius of 13.30 mm. CES has shown to induce changes in the electroencephalogram, increasing alpha relative power and decreasing relative power in delta and beta frequencies.
CES has also shown to reach cortical and subcortical areas of the brain, in electromagnetic tomography and functional MRI studies. CES treatments have been found to induce changes in neurohormones and neurotransmitters that have been implicated in psychiatric disorders: substantial increases in beta endorphins, adrenocorticotrophic hormone, and serotonin; moderate increases in melatonin and norepinephrine, modest or unquantified increases in cholinesterase, gamma-aminobutyric acid, and dehydroepiandrosterone, and moderate reductions in cortisol.
== History ==
Low intensity electrical stimulation is believed to have originated in the studies of galvanic currents in humans and animals as conducted by Giovanni Aldini, Alessandro Volta and others in the 18th century. Aldini had experimented with galvanic head current as early as 1794 (upon himself) and reported the successful treatment of patients with melancholia using direct low-intensity currents in 1804.
CES was initially studied for insomnia and called electrosleep therapy; it is also known as cranial-electro stimulation and transcranial electrotherapy.
Due to the rise of pharmaceutical treatments for depression, anxiety and insomnia, such as Prozac in the 1980s and Ambien in the 1990s, CES was not a well-known treatment for doctors and patients. During the mid-2000s, the combination of pharmaceutical brands becoming generic and Internet advertising caused CES devices to gain popularity. In 2011, the devices received media attention from the Wall Street Journal.
== Regulation ==
In the United States, CES technology is classified by the Food and Drug Administration (FDA) as a Class III medical device and must be dispensed by or on the order of a licensed healthcare practitioner, i.e., a physician, psychiatrist, nurse practitioner, psychologist, physician assistant, or occupational therapist who has an appropriate electrotherapy license, dependent upon state regulations. The United States requires a prescription for CES devices from a licensed healthcare practitioner. The FDA says that there are 11 CES devices cleared for marketing in the United States.
In June 2014, the FDA announced that it "has determined that there is sufficient information to establish special controls, and that these special controls, together with general controls, will provide a reasonable assurance of safety and effectiveness for CES devices. In this action, FDA is withdrawing the proposed rule and proposed order to call for PMAs [premarket approvals] for CES devices. FDA plans to issue a proposed order in the future for the reclassification of the CES device into class II."
In December 2019, the FDA announced that there is no valid evidence for CES as a treatment for depression, and request new trials to be made. "FDA concluded that the four studies published after January 1, 2016, through November 1, 2019, did not contribute sufficient information in the form of valid scientific evidence to demonstrate that the subjects met the criteria for any recognized depressive disorder, as defined in DSM-5"
== See also ==
Electroconvulsive therapy
Fisher Wallace Laboratories, markets a CES device
Neuromodulation
Neurostimulation
Neurotechnology
Transcranial direct-current stimulation
Transcranial magnetic stimulation
== References == | Wikipedia/Cranial_electrotherapy_stimulation |
Cytoluminescent Therapy is a proposed cancer treatment as a form of Photodynamic Therapy (PDT) and Neurotherapy characterized by a photosensitiser that is supposedly eliminated from normal tissue but selectively accumulated in neoplastic and dysplastic tissue. This is followed by whole body irradiation with light of the specific wave length which activates the photosensitiser. The result is supposed to be selective damage or elimination of tumor cells while normal tissues are unharmed. However, tests as of 2003 did not show any positive clinical effects in a group of 48 patients treated in this way.
The original providers of CLT in Killaloe, Ireland, are no longer performing the treatment. Much of their claims of effectiveness were based upon anecdotal reports, not research. In fact, the wavelength of light used to active the chlorophyll-derived photosensitizer used in CLT is incapable of penetrating tissue more than several millimeters. The FDA-approved therapy PDT uses red light (wavelength approximately 600-700 nm) and penetrates human tissue up to 2 centimeters. No wavelength can fully penetrate the human body, as the purveyors of CLT claimed.
== References ==
== External links ==
SAGE citation | Wikipedia/Cytoluminescent_therapy |
Cognitive skills are skills of the mind, as opposed to other types of skills such as motor skills, social skills or life skills. Some examples of cognitive skills are literacy, self-reflection, logical reasoning, abstract thinking, critical thinking, introspection and mental arithmetic. Cognitive skills vary in processing complexity, and can range from more fundamental processes such as perception and various memory functions, to more sophisticated processes such as decision making, problem solving and metacognition.
== Specialisation of functions ==
Cognitive science has provided theories of how the brain works, and these have been of great interest to researchers who work in the empirical fields of brain science. A fundamental question is whether cognitive functions, for example visual processing and language, are autonomous modules, or to what extent the functions depend on each other. Research evidence points towards a middle position, and it is now generally accepted that there is a degree of modularity in aspects of brain organisation. In other words, cognitive skills or functions are specialised, but they also overlap or interact with each other. Deductive reasoning, on the other hand, has been shown to be related to either visual or linguistic processing, depending on the task; although there are also aspects that differ from them. All in all, research evidence does not provide strong support for classical models of cognitive psychology.
== Cognitive functioning ==
Cognitive functioning refers to a person's ability to process thoughts. It is defined as "the ability of an individual to perform the various mental activities most closely associated with learning and problem-solving. Examples include the verbal, spatial, psychomotor, and processing-speed ability." Cognition mainly refers to things like memory, speech, and the ability to learn new information. The brain is usually capable of learning new skills in the aforementioned areas, typically in early childhood, and of developing personal thoughts and beliefs about the world. Old age and disease may affect cognitive functioning, causing memory loss and trouble thinking of the right words while speaking or writing ("drawing a blank"). Multiple sclerosis (MS), for example, can eventually cause memory loss, an inability to grasp new concepts or information, and depleted verbal fluency.
Humans generally have a high capacity for cognitive functioning once born, so almost every person is capable of learning or remembering. Intelligence is tested with IQ tests and others, although these have issues with accuracy and completeness. In such tests, patients may be asked a series of questions, or to perform tasks, with each measuring a cognitive skill, such as level of consciousness, memory, awareness, problem-solving, motor skills, analytical abilities, or other similar concepts. Early childhood is when the brain is most malleable to orientate to tasks that are relevant in the person's environment.
Exercise, even at light intensity, significantly improves general cognition across all populations, with the largest cognitive gains seen from shorter interventions (1–3 months), light to moderate intensity activity.
== See also ==
Adaptive behavior
Adaptive functioning
Intelligence Quotient (IQ)
Cognition
Cognitive Abilities Test
Jungian cognitive functions
== Notes ==
== References ==
[1] NCME - Glossary of Important Assessment and Measurement Terms [cognitive ability] | Wikipedia/Cognitive_function |
Pulsed electromagnetic field therapy (PEMFT, or PEMF therapy), also known as low field magnetic stimulation (LFMS) is the use of electromagnetic fields in an attempt to heal non-union fractures and depression. By 2007, the FDA had cleared several such stimulation devices.
In 2013, the U.S. Food and Drug Administration (FDA) warned a manufacturer for promoting the device for unapproved uses such as cerebral palsy and spinal cord injury.
== Efficacy ==
While PEMF therapy is claimed to offer some benefits in the treatment of fractures, the evidence is inconclusive and is insufficient to inform current clinical practice.
== History ==
Prior to 2000, in parallel with the PEMF research being done in Western Europe, the United States, and Japan, a great deal of scientific work was being done in scientific isolation behind the Iron Curtain, as summarized in a detailed technical report, showing scientific evidence for promising benefits from the use of PEMF for a very wide range of applications including peripheral vascular disease, lung disease, gastrointestinal disease, neurological disease, rheumatic disease, pediatrics, dermatology, surgery, gynecology, oral medicine, otorhinolaryngology, ophthalmology, immunity, inflammation, reproduction, and tumors, based on over 200 referenced scientific papers involving both human and animal studies.
Veterinarians were the first health professionals to use PEMF therapy, usually to attempt to heal broken legs in racehorses.
In 2004, a pulsed electromagnetic field system was approved by the FDA as an adjunct to cervical fusion surgery in patients at high risk for non-fusion. On 8/9 September 2020 the FDA recommended to shift PEMF medical devices from the Class 3 category to a Class 2 status. PEMF devices that have been FDA cleared are able to make health claims that require a doctor's prescription for use.
Although claims that electricity might aid bone healing were reported as early as 1841, it was not until the mid-1950s that scientists seriously studied the subject. During the 1970s, Bassett and his team introduced a new approach which attempted to treat delayed fractures; a technique that employed a very specific biphasic low frequency signal to be applied for non-union/delayed fractures. The use of electrical stimulation in the lumbosacral region was first attempted by Alan Dwyer of Australia.
== Wellness devices ==
The original PEMF devices consisted of a Helmholtz coil which generated a magnetic field. The patient's body was placed inside the magnetic field to deliver treatment. Today, the majority of PEMF wellness devices resemble a typical yoga mat in dimensions but are slightly thicker to house several flat spiral coils to produce an even electromagnetic field. A frequency generator is then used to energize the coils to create a pulsed electromagnetic field. A wide variety of professional and consumer PEMF devices are sold and marketed as FDA registered wellness devices. The majority are manufactured in Germany, Austria and Switzerland and are imported into North America as electric massagers or full body electric yoga mats. They are either placed on a massage table for clinical use or directly on the floor in the home to practice simple yoga postures. The companies that sell and manufacture them as "general wellness products" are not permitted to make medical claims of effectiveness in treating disease.
== See also ==
Neuromodulation
Neurostimulation
Neurotechnology
Neurotherapy
Radionics
Pulsed radiofrequency#Therapeutic uses
Transcranial magnetic stimulation
== References == | Wikipedia/Pulsed_electromagnetic_field_therapy |
Heart rate is the frequency of the heartbeat measured by the number of contractions of the heart per minute (beats per minute, or bpm). The heart rate varies according to the body's physical needs, including the need to absorb oxygen and excrete carbon dioxide. It is also modulated by numerous factors, including (but not limited to) genetics, physical fitness, stress or psychological status, diet, drugs, hormonal status, environment, and disease/illness, as well as the interaction between these factors. It is usually equal or close to the pulse rate measured at any peripheral point.
The American Heart Association states the normal resting adult human heart rate is 60–100 bpm. An ultra-trained athlete would have a resting heart rate of 37–38 bpm. Tachycardia is a high heart rate, defined as above 100 bpm at rest. Bradycardia is a low heart rate, defined as below 60 bpm at rest. When a human sleeps, a heartbeat with rates around 40–50 bpm is common and considered normal. When the heart is not beating in a regular pattern, this is referred to as an arrhythmia. Abnormalities of heart rate sometimes indicate disease.
== Physiology ==
While heart rhythm is regulated entirely by the sinoatrial node under normal conditions, heart rate is regulated by sympathetic and parasympathetic input to the sinoatrial node. The accelerans nerve provides sympathetic input to the heart by releasing norepinephrine onto the cells of the sinoatrial node (SA node), and the vagus nerve provides parasympathetic input to the heart by releasing acetylcholine onto sinoatrial node cells. Therefore, stimulation of the accelerans nerve increases heart rate, while stimulation of the vagus nerve decreases it.
As water and blood are incompressible fluids, one of the physiological ways to deliver more blood to an organ is to increase heart rate. Normal resting heart rates range from 60 to 100 bpm. Bradycardia is defined as a resting heart rate below 60 bpm. However, heart rates from 50 to 60 bpm are common among healthy people and do not necessarily require special attention. Tachycardia is defined as a resting heart rate above 100 bpm, though persistent rest rates between 80 and 100 bpm, mainly if they are present during sleep, may be signs of hyperthyroidism or anemia (see below).
Central nervous system stimulants such as substituted amphetamines increase heart rate.
Central nervous system depressants or sedatives decrease the heart rate (apart from some particularly strange ones with equally strange effects, such as ketamine which can cause – amongst many other things – stimulant-like effects such as tachycardia).
There are many ways in which the heart rate speeds up or slows down. Most involve stimulant-like endorphins and hormones being released in the brain, some of which are those that are 'forced'/'enticed' out by the ingestion and processing of drugs such as cocaine or atropine.
This section discusses target heart rates for healthy persons, which would be inappropriately high for most persons with coronary artery disease.
=== Influences from the central nervous system ===
==== Cardiovascular centres ====
The heart rate is rhythmically generated by the sinoatrial node. It is also influenced by central factors through sympathetic and parasympathetic nerves. Nervous influence over the heart rate is centralized within the two paired cardiovascular centres of the medulla oblongata. The cardioaccelerator regions stimulate activity via sympathetic stimulation of the cardioaccelerator nerves, and the cardioinhibitory centers decrease heart activity via parasympathetic stimulation as one component of the vagus nerve. During rest, both centers provide slight stimulation to the heart, contributing to autonomic tone. This is a similar concept to tone in skeletal muscles. Normally, vagal stimulation predominates as, left unregulated, the SA node would initiate a sinus rhythm of approximately 100 bpm.
Both sympathetic and parasympathetic stimuli flow through the paired cardiac plexus near the base of the heart. The cardioaccelerator center also sends additional fibers, forming the cardiac nerves via sympathetic ganglia (the cervical ganglia plus superior thoracic ganglia T1–T4) to both the SA and AV nodes, plus additional fibers to the atria and ventricles. The ventricles are more richly innervated by sympathetic fibers than parasympathetic fibers. Sympathetic stimulation causes the release of the neurotransmitter norepinephrine (also known as noradrenaline) at the neuromuscular junction of the cardiac nerves. This shortens the repolarization period, thus speeding the rate of depolarization and contraction, which results in an increased heartrate. It opens chemical or ligand-gated sodium and calcium ion channels, allowing an influx of positively charged ions.
Norepinephrine binds to the beta–1 receptor. High blood pressure medications are used to block these receptors and so reduce the heart rate.
Parasympathetic stimulation originates from the cardioinhibitory region of the brain with impulses traveling via the vagus nerve (cranial nerve X). The vagus nerve sends branches to both the SA and AV nodes, and to portions of both the atria and ventricles. Parasympathetic stimulation releases the neurotransmitter acetylcholine (ACh) at the neuromuscular junction. ACh slows HR by opening chemical- or ligand-gated potassium ion channels to slow the rate of spontaneous depolarization, which extends repolarization and increases the time before the next spontaneous depolarization occurs. Without any nervous stimulation, the SA node would establish a sinus rhythm of approximately 100 bpm. Since resting rates are considerably less than this, it becomes evident that parasympathetic stimulation normally slows HR. This is similar to an individual driving a car with one foot on the brake pedal. To speed up, one need merely remove one's foot from the brake and let the engine increase speed. In the case of the heart, decreasing parasympathetic stimulation decreases the release of ACh, which allows HR to increase up to approximately 100 bpm. Any increases beyond this rate would require sympathetic stimulation.
==== Input to the cardiovascular centres ====
The cardiovascular centre receive input from a series of visceral receptors with impulses traveling through visceral sensory fibers within the vagus and sympathetic nerves via the cardiac plexus. Among these receptors are various proprioreceptors, baroreceptors, and chemoreceptors, plus stimuli from the limbic system which normally enable the precise regulation of heart function, via cardiac reflexes. Increased physical activity results in increased rates of firing by various proprioreceptors located in muscles, joint capsules, and tendons. The cardiovascular centres monitor these increased rates of firing, suppressing parasympathetic stimulation or increasing sympathetic stimulation as needed in order to increase blood flow.
Similarly, baroreceptors are stretch receptors located in the aortic sinus, carotid bodies, the venae cavae, and other locations, including pulmonary vessels and the right side of the heart itself. Rates of firing from the baroreceptors represent blood pressure, level of physical activity, and the relative distribution of blood. The cardiac centers monitor baroreceptor firing to maintain cardiac homeostasis, a mechanism called the baroreceptor reflex. With increased pressure and stretch, the rate of baroreceptor firing increases, and the cardiac centers decrease sympathetic stimulation and increase parasympathetic stimulation. As pressure and stretch decrease, the rate of baroreceptor firing decreases, and the cardiac centers increase sympathetic stimulation and decrease parasympathetic stimulation.
There is a similar reflex, called the atrial reflex or Bainbridge reflex, associated with varying rates of blood flow to the atria. Increased venous return stretches the walls of the atria where specialized baroreceptors are located. However, as the atrial baroreceptors increase their rate of firing and as they stretch due to the increased blood pressure, the cardiac center responds by increasing sympathetic stimulation and inhibiting parasympathetic stimulation to increase HR. The opposite is also true.
Increased metabolic byproducts associated with increased activity, such as carbon dioxide, hydrogen ions, and lactic acid, plus falling oxygen levels, are detected by a suite of chemoreceptors innervated by the glossopharyngeal and vagus nerves. These chemoreceptors provide feedback to the cardiovascular centers about the need for increased or decreased blood flow, based on the relative levels of these substances.
The limbic system can also significantly impact HR related to emotional state. During periods of stress, it is not unusual to identify higher than normal HRs, often accompanied by a surge in the stress hormone cortisol. Individuals experiencing extreme anxiety may manifest panic attacks with symptoms that resemble those of heart attacks. These events are typically transient and treatable. Meditation techniques have been developed to ease anxiety and have been shown to lower HR effectively. Doing simple deep and slow breathing exercises with one's eyes closed can also significantly reduce this anxiety and HR.
=== Factors influencing heart rate ===
Using a combination of autorhythmicity and innervation, the cardiovascular center is able to provide relatively precise control over the heart rate, but other factors can impact on this. These include hormones, notably epinephrine, norepinephrine, and thyroid hormones; levels of various ions including calcium, potassium, and sodium; body temperature; hypoxia; and pH balance.
==== Epinephrine and norepinephrine ====
The catecholamines, epinephrine and norepinephrine, secreted by the adrenal medulla form one component of the extended fight-or-flight mechanism. The other component is sympathetic stimulation. Epinephrine and norepinephrine have similar effects: binding to the beta-1 adrenergic receptors, and opening sodium and calcium ion chemical- or ligand-gated channels. The rate of depolarization is increased by this additional influx of positively charged ions, so the threshold is reached more quickly and the period of repolarization is shortened. However, massive releases of these hormones coupled with sympathetic stimulation may actually lead to arrhythmias. There is no parasympathetic stimulation to the adrenal medulla.
==== Thyroid hormones ====
In general, increased levels of the thyroid hormones (thyroxine(T4) and triiodothyronine (T3)), increase the heart rate; excessive levels can trigger tachycardia. The impact of thyroid hormones is typically of a much longer duration than that of the catecholamines. The physiologically active form of triiodothyronine, has been shown to directly enter cardiomyocytes and alter activity at the level of the genome. It also impacts the beta-adrenergic response similar to epinephrine and norepinephrine.
==== Calcium ====
Calcium ion levels have a great impact on heart rate and myocardial contractility: increased calcium levels cause an increase in both. High levels of calcium ions result in hypercalcemia and excessive levels can induce cardiac arrest. Drugs known as calcium channel blockers slow HR by binding to these channels and blocking or slowing the inward movement of calcium ions.
==== Caffeine and nicotine ====
Caffeine and nicotine are both stimulants of the nervous system and of the cardiac centres causing an increased heart rate. Caffeine works by increasing the rates of depolarization at the SA node, whereas nicotine stimulates the activity of the sympathetic neurons that deliver impulses to the heart.
==== Effects of stress ====
Both surprise and stress induce physiological response: elevate heart rate substantially. In a study conducted on 8 female and male student actors ages 18 to 25, their reaction to an unforeseen occurrence (the cause of stress) during a performance was observed in terms of heart rate. In the data collected, there was a noticeable trend between the location of actors (onstage and offstage) and their elevation in heart rate in response to stress; the actors present offstage reacted to the stressor immediately, demonstrated by their immediate elevation in heart rate the minute the unexpected event occurred, but the actors present onstage at the time of the stressor reacted in the following 5 minute period (demonstrated by their increasingly elevated heart rate). This trend regarding stress and heart rate is supported by previous studies; negative emotion/stimulus has a prolonged effect on heart rate in individuals who are directly impacted.
In regard to the characters present onstage, a reduced startle response has been associated with a passive defense, and the diminished initial heart rate response has been predicted to have a greater tendency to dissociation. Current evidence suggests that heart rate variability can be used as an accurate measure of psychological stress and may be used for an objective measurement of psychological stress.
==== Factors decreasing heart rate ====
The heart rate can be slowed by altered sodium and potassium levels, hypoxia, acidosis, alkalosis, and hypothermia. The relationship between electrolytes and HR is complex, but maintaining electrolyte balance is critical to the normal wave of depolarization. Of the two ions, potassium has the greater clinical significance. Initially, both hyponatremia (low sodium levels) and hypernatremia (high sodium levels) may lead to tachycardia. Severely high hypernatremia may lead to fibrillation, which may cause cardiac output to cease. Severe hyponatremia leads to both bradycardia and other arrhythmias. Hypokalemia (low potassium levels) also leads to arrhythmias, whereas hyperkalemia (high potassium levels) causes the heart to become weak and flaccid, and ultimately to fail.
Heart muscle relies exclusively on aerobic metabolism for energy. Severe myocardial infarction (commonly called a heart attack) can lead to a decreasing heart rate, since metabolic reactions fueling heart contraction are restricted.
Acidosis is a condition in which excess hydrogen ions are present, and the patient's blood expresses a low pH value. Alkalosis is a condition in which there are too few hydrogen ions, and the patient's blood has an elevated pH. Normal blood pH falls in the range of 7.35–7.45, so a number lower than this range represents acidosis and a higher number represents alkalosis. Enzymes, being the regulators or catalysts of virtually all biochemical reactions – are sensitive to pH and will change shape slightly with values outside their normal range. These variations in pH and accompanying slight physical changes to the active site on the enzyme decrease the rate of formation of the enzyme-substrate complex, subsequently decreasing the rate of many enzymatic reactions, which can have complex effects on HR. Severe changes in pH will lead to denaturation of the enzyme.
The last variable is body temperature. Elevated body temperature is called hyperthermia, and suppressed body temperature is called hypothermia. Slight hyperthermia results in increasing HR and strength of contraction. Hypothermia slows the rate and strength of heart contractions. This distinct slowing of the heart is one component of the larger diving reflex that diverts blood to essential organs while submerged. If sufficiently chilled, the heart will stop beating, a technique that may be employed during open heart surgery. In this case, the patient's blood is normally diverted to an artificial heart-lung machine to maintain the body's blood supply and gas exchange until the surgery is complete, and sinus rhythm can be restored. Excessive hyperthermia and hypothermia will both result in death, as enzymes drive the body systems to cease normal function, beginning with the central nervous system.
==== Physiological control over heart rate ====
A study shows that bottlenose dolphins can learn – apparently via instrumental conditioning – to rapidly and selectively slow down their heart rate during diving for conserving oxygen depending on external signals. In humans regulating heart rate by methods such as listening to music, meditation or a vagal maneuver takes longer and only lowers the rate to a much smaller extent.
== In different circumstances ==
Heart rate is not a stable value and it increases or decreases in response to the body's need in a way to maintain an equilibrium (basal metabolic rate) between requirement and delivery of oxygen and nutrients. The normal SA node firing rate is affected by autonomic nervous system activity: sympathetic stimulation increases and parasympathetic stimulation decreases the firing rate.
=== Resting heart rate ===
Normal pulse rates at rest, in beats per minute (BPM):
The basal or resting heart rate (HRrest) is defined as the heart rate when a person is awake, in a neutrally temperate environment, and has not been subject to any recent exertion or stimulation, such as stress or surprise. The normal resting heart rate is based on the at-rest firing rate of the heart's sinoatrial node, where the faster pacemaker cells driving the self-generated rhythmic firing and responsible for the heart's autorhythmicity are located.
In one 1993 study, 98% of cardiologists suggested that as a desirable target range, 50 to 90 beats per minute is more appropriate than 60 to 100. The available evidence indicates that the normal range for resting heart rate is 50–90 beats per minute (bpm). In a study of over 35,000 American men and women over age 40 during the 1999–2008 period, 71 bpm was the average for men, and 73 bpm was the average for women.
Resting heart rate is often correlated with mortality. In the Copenhagen City Heart Study a heart rate of 65 bpm rather than 80 bpm was associated with 4.6 years longer life expectancy in men and 3.6 years in women. Other studies have shown all-cause mortality is increased by 1.22 (hazard ratio) when heart rate exceeds 90 beats per minute. ECG of 46,129 individuals with low risk for cardiovascular disease revealed that 96% had resting heart rates ranging from 48 to 98 beats per minute. The mortality rate of patients with myocardial infarction increased from 15% to 41% if their admission heart rate was greater than 90 beats per minute. For endurance athletes at the elite level, it is not unusual to have a resting heart rate between 33 and 50 bpm.
=== Maximum heart rate ===
The maximum heart rate (HRmax) is the age-related highest number of beats per minute of the heart when reaching a point of exhaustion without severe problems through exercise stress.
In general it is loosely estimated as 220 minus one's age.
It generally decreases with age. Since HRmax varies by individual, the most accurate way of measuring any single person's HRmax is via a cardiac stress test. In this test, a person is subjected to controlled physiologic stress (generally by treadmill or bicycle ergometer) while being monitored by an electrocardiogram (ECG). The intensity of exercise is periodically increased until certain changes in heart function are detected on the ECG monitor, at which point the subject is directed to stop. Typical duration of the test ranges ten to twenty minutes. Adults who are beginning a new exercise regimen are often advised to perform this test only in the presence of medical staff due to risks associated with high heart rates.
The theoretical maximum heart rate of a human is 300 bpm; however, there have been multiple cases where this theoretical upper limit has been exceeded. The fastest human ventricular conduction rate recorded to this day is a conducted tachyarrhythmia with ventricular rate of 600 beats per minute, which is comparable to the heart rate of a mouse.
For general purposes, a number of formulas are used to estimate HRmax. However, these predictive formulas have been criticized as inaccurate because they only produce generalized population-averages and may deviate significantly from the actual value. (See § Limitations.)
==== Haskell & Fox (1970) ====
Notwithstanding later research, the most widely cited formula for HRmax is still:
HRmax = 220 − age
Although attributed to various sources, it is widely thought to have been devised in 1970 by Dr. William Haskell and Dr. Samuel Fox. They did not develop this formula from original research, but rather by plotting data from approximately 11 references consisting of published research or unpublished scientific compilations. It gained widespread use through being used by Polar Electro in its heart rate monitors, which Dr. Haskell has "laughed about", as the formula "was never supposed to be an absolute guide to rule people's training."
While this formula is commonly used (and easy to remember and calculate), research has consistently found that it is subject to bias, particularly in older adults. Compared to the age-specific average HRmax, the Haskell and Fox formula overestimates HRmax in young adults, agrees with it at age 40, and underestimates HRmax in older adults. For example, in one study, the average HRmax at age 76 was about 10bpm higher than the Haskell and Fox equation. Consequently, the formula cannot be recommended for use in exercise physiology and related fields.
==== Other formulas ====
HRmax is strongly correlated to age, and most formulas are solely based on this. Studies have been mixed on the effect of gender, with some finding that gender is statistically significant, although small when considering overall equation error, while others finding negligible effect. The inclusion of physical activity status, maximal oxygen uptake, smoking, body mass index, body weight, or resting heart rate did not significantly improve accuracy. Nonlinear models are slightly more accurate predictors of average age-specific HRmax, particularly above 60 years of age, but are harder to apply, and provide statistically negligible improvement over linear models. The Wingate formula is the most recent, had the largest data set, and performed best on a fresh data set when compared with other formulas, although it had only a small amount of data for ages 60 and older so those estimates should be viewed with caution. In addition, most formulas are developed for adults and are not applicable to children and adolescents.
==== Limitations ====
Maximum heart rates vary significantly between individuals. Age explains only about half of HRmax variance. For a given age, the standard deviation of HRmax from the age-specific population mean is about 12bpm, and a 95% interval for the prediction error is about 24bpm. For example, Dr. Fritz Hagerman observed that the maximum heart rates of men in their 20s on Olympic rowing teams vary from 160 to 220. Such a variation would equate to an age range of -16 to 68 using the Wingate formula. The formulas are quite accurate at predicting the average heart rate of a group of similarly-aged individuals, but relatively poor for a given individual.
Robergs and Landwehr opine that for VO2 max, prediction errors in HRmax need to be less than ±3 bpm. No current formula meets this accuracy. For prescribing exercise training heart rate ranges, the errors in the more accurate formulas may be acceptable, but again it is likely that, for a significant fraction of the population, current equations used to estimate HRmax are not accurate enough. Froelicher and Myers describe maximum heart formulas as "largely useless". Measurement via a maximal test is preferable whenever possible, which can be as accurate as ±2bpm.
=== Heart rate reserve ===
Heart rate reserve (HRreserve) is the difference between a person's measured or predicted maximum heart rate and resting heart rate. Some methods of measurement of exercise intensity measure percentage of heart rate reserve. Additionally, as a person increases their cardiovascular fitness, their HRrest will drop, and the heart rate reserve will increase. Percentage of HRreserve is statistically indistinguishable from percentage of VO2 reserve.
HRreserve = HRmax − HRrest
This is often used to gauge exercise intensity (first used in 1957 by Karvonen).
Karvonen's study findings have been questioned, due to the following:
The study did not use VO2 data to develop the equation.
Only six subjects were used.
Karvonen incorrectly reported that the percentages of HRreserve and VO2 max correspond to each other, but newer evidence shows that it correlated much better with VO2 reserve as described above.
=== Target heart rate ===
For healthy people, the Target Heart Rate (THR) or Training Heart Rate Range (THRR) is a desired range of heart rate reached during aerobic exercise which enables one's heart and lungs to receive the most benefit from a workout. This theoretical range varies based mostly on age; however, a person's physical condition, sex, and previous training also are used in the calculation.
==== By percent, Fox–Haskell-based ====
The THR can be calculated as a range of 65–85% intensity, with intensity defined simply as percentage of HRmax. However, it is crucial to derive an accurate HRmax to ensure these calculations are meaningful.
Example for someone with a HRmax of 180 (age 40, estimating HRmax As 220 − age):
65% Intensity: (220 − (age = 40)) × 0.65 → 117 bpm
85% Intensity: (220 − (age = 40)) × 0.85 → 154 bpm
==== Karvonen method ====
The Karvonen method factors in resting heart rate (HRrest) to calculate target heart rate (THR), using a range of 50–85% intensity:
THR = ((HRmax − HRrest) × % intensity) + HRrest
Equivalently,
THR = (HRreserve × % intensity) + HRrest
Example for someone with a HRmax of 180 and a HRrest of 70 (and therefore a HRreserve of 110):
50% Intensity: ((180 − 70) × 0.50) + 70 = 125 bpm
85% Intensity: ((180 − 70) × 0.85) + 70 = 163 bpm
==== Zoladz method ====
An alternative to the Karvonen method is the Zoladz method, which is used to test an athlete's capabilities at specific heart rates. These are not intended to be used as exercise zones, although they are often used as such. The Zoladz test zones are derived by subtracting values from HRmax:
THR = HRmax − Adjuster ± 5 bpm
Zone 1 Adjuster = 50 bpm
Zone 2 Adjuster = 40 bpm
Zone 3 Adjuster = 30 bpm
Zone 4 Adjuster = 20 bpm
Zone 5 Adjuster = 10 bpm
Example for someone with a HRmax of 180:
Zone 1 (easy exercise): 180 − 50 ± 5 → 125 − 135 bpm
Zone 4 (tough exercise): 180 − 20 ± 5 → 155 − 165 bpm
=== Heart rate recovery ===
Heart rate recovery (HRR) is the reduction in heart rate at peak exercise and the rate as measured after a cool-down period of fixed duration. A greater reduction in heart rate after exercise during the reference period is associated with a higher level of cardiac fitness.
Heart rates assessed during treadmill stress test that do not drop by more than 12 bpm one minute after stopping exercise (if cool-down period after exercise) or by more than 18 bpm one minute after stopping exercise (if no cool-down period and supine position as soon as possible) are associated with an increased risk of death. People with an abnormal HRR defined as a decrease of 42 beats per minutes or less at two minutes post-exercise had a mortality rate 2.5 times greater than patients with a normal recovery. Another study reported a four-fold increase in mortality in subjects with an abnormal HRR defined as ≤12 bpm reduction one minute after the cessation of exercise. A study reported that a HRR of ≤22 bpm after two minutes "best identified high-risk patients". They also found that while HRR had significant prognostic value it had no diagnostic value.
=== Heart rate prediction ===
Heart rate prediction using machine learning has gained significant attention in health monitoring and sports performance research. Namazi et.al., 2025 study evaluated various models including Long Short-Term Memory (LSTM), Physics-Informed Neural Networks (PINNs), and 1D Convolutional Neural Networks (1D CNNs), using physiological data such as heart rate (HR), breathing rate (BR), and RR intervals collected from wearable sensors during sports activities. The study introduced a hybrid approach combining Singular Spectrum Analysis (SSA) with these models to enhance predictive performance. Among the tested models, the SSA-LSTM method yielded the lowest prediction error, particularly when multivariate inputs (HR + BR + RR) were used. These findings support the use of AI-driven, multivariate prediction models for real-time cardiovascular monitoring in athletic and healthcare settings.
=== Development ===
The human heart beats more than 2.8 billion times in an average lifetime.
The heartbeat of a human embryo begins at approximately 21 days after conception, or five weeks after the last normal menstrual period (LMP), which is the date normally used to date pregnancy in the medical community. The electrical depolarizations that trigger cardiac myocytes to contract arise spontaneously within the myocyte itself. The heartbeat is initiated in the pacemaker regions and spreads to the rest of the heart through a conduction pathway. Pacemaker cells develop in the primitive atrium and the sinus venosus to form the sinoatrial node and the atrioventricular node respectively. Conductive cells develop the bundle of His and carry the depolarization into the lower heart.
The human heart begins beating at a rate near the mother's, about 75–80 beats per minute (bpm). The embryonic heart rate then accelerates linearly for the first month of beating, peaking at 165–185 bpm during the early 7th week, (early 9th week after the LMP). This acceleration is approximately 3.3 bpm per day, or about 10 bpm every three days, an increase of 100 bpm in the first month.
After peaking at about 9.2 weeks after the LMP, it decelerates to about 150 bpm (+/-25 bpm) during the 15th week after the LMP. After the 15th week the deceleration slows reaching an average rate of about 145 (+/-25 bpm) bpm at term. The regression formula which describes this acceleration before the embryo reaches 25 mm in crown-rump length or 9.2 LMP weeks is:
A
g
e
i
n
d
a
y
s
=
E
H
R
(
0.3
)
+
6
{\displaystyle \mathrm {Age\ in\ days} =\ \mathrm {EHR} (0.3)+6}
== Clinical significance ==
=== Manual measurement ===
Heart rate is measured by finding the pulse of the heart. This pulse rate can be found at any point on the body where the artery's pulsation is transmitted to the surface by pressuring it with the index and middle fingers; often it is compressed against an underlying structure like bone. The thumb should not be used for measuring another person's heart rate, as its strong pulse may interfere with the correct perception of the target pulse.
The radial artery is the easiest to use to check the heart rate. However, in emergency situations the most reliable arteries to measure heart rate are carotid arteries. This is important mainly in patients with atrial fibrillation, in whom heart beats are irregular and stroke volume is largely different from one beat to another. In those beats following a shorter diastolic interval left ventricle does not fill properly, stroke volume is lower and pulse wave is not strong enough to be detected by palpation on a distal artery like the radial artery. It can be detected, however, by doppler.
Possible points for measuring the heart rate are:
The ventral aspect of the wrist on the side of the thumb (radial artery).
The ulnar artery.
The inside of the elbow, or under the biceps muscle (brachial artery).
The groin (femoral artery).
Behind the medial malleolus on the feet (posterior tibial artery).
Middle of dorsum of the foot (dorsalis pedis).
Behind the knee (popliteal artery).
Over the abdomen (abdominal aorta).
The chest (apex of the heart), which can be felt with one's hand or fingers. It is also possible to auscultate the heart using a stethoscope.
In the neck, lateral of the larynx (carotid artery)
The temple (superficial temporal artery).
The lateral edge of the mandible (facial artery).
The side of the head near the ear (posterior auricular artery).
=== Electronic measurement ===
A more precise method of determining heart rate involves the use of an electrocardiograph, or ECG (also abbreviated EKG). An ECG generates a pattern based on electrical activity of the heart, which closely follows heart function. Continuous ECG monitoring is routinely done in many clinical settings, especially in critical care medicine. On the ECG, instantaneous heart rate is calculated using the R wave-to-R wave (RR) interval and multiplying/dividing in order to derive heart rate in heartbeats/min. Multiple methods exist:
HR = 1000 · 60/(RR interval in milliseconds)
HR = 60/(RR interval in seconds)
HR = 300/number of "large" squares between successive R waves.
HR= 1,500 number of large blocks
Heart rate monitors allow measurements to be taken continuously and can be used during exercise when manual measurement would be difficult or impossible (such as when the hands are being used). Various commercial heart rate monitors are also available. Some monitors, used during sport, consist of a chest strap with electrodes. The signal is transmitted to a wrist receiver for display.
Alternative methods of measurement include seismocardiography.
=== Optical measurements ===
Pulse oximetry of the finger and laser Doppler imaging of the eye fundus are often used in the clinics. Those techniques can assess the heart rate by measuring the delay between pulses.
=== Tachycardia ===
Tachycardia is a resting heart rate more than 100 beats per minute. This number can vary as smaller people and children have faster heart rates than average adults.
Physiological conditions where tachycardia occurs:
Pregnancy
Emotional conditions such as anxiety or stress.
Exercise
Pathological conditions where tachycardia occurs:
Sepsis
Fever
Anemia
Hypoxia
Hyperthyroidism
Hypersecretion of catecholamines
Cardiomyopathy
Valvular heart diseases
Acute Radiation Syndrome
Dehydration
Metabolic myopathies (At rest, tachycardia is commonly seen in fatty acid oxidation disorders. An inappropriate rapid heart rate response to exercise is seen in muscle glycogenoses and mitochondrial myopathies, where the tachycardia is faster than would be expected during exercise).
=== Bradycardia ===
Bradycardia was defined as a heart rate less than 60 beats per minute when textbooks asserted that the normal range for heart rates was 60–100 bpm. The normal range has since been revised in textbooks to 50–90 bpm for a human at total rest. Setting a lower threshold for bradycardia prevents misclassification of fit individuals as having a pathologic heart rate. The normal heart rate number can vary as children and adolescents tend to have faster heart rates than average adults. Bradycardia may be associated with medical conditions such as hypothyroidism, heart disease, or inflammatory disease. At rest, although tachycardia is more commonly seen in fatty acid oxidation disorders, more rarely acute bradycardia can occur.
Trained athletes tend to have slow resting heart rates, and resting bradycardia in athletes should not be considered abnormal if the individual has no symptoms associated with it. For example, Miguel Indurain, a Spanish cyclist and five time Tour de France winner, had a resting heart rate of 28 beats per minute, one of the lowest ever recorded in a healthy human. Daniel Green achieved the world record for the slowest heartbeat in a healthy human with a heart rate of just 26 bpm in 2014.
=== Arrhythmia ===
Arrhythmias are abnormalities of the heart rate and rhythm (sometimes felt as palpitations). They can be divided into two broad categories: fast and slow heart rates. Some cause few or minimal symptoms. Others produce more serious symptoms of lightheadedness, dizziness and fainting.
=== Hypertension ===
Elevated heart rate is a powerful predictor of morbidity and mortality in patients with hypertension. Atherosclerosis and dysautonomia are major contributors to the pathogenesis.
=== Correlation with cardiovascular mortality risk ===
A number of investigations indicate that faster resting heart rate has emerged as a new risk factor for mortality in homeothermic mammals, particularly cardiovascular mortality in human beings. High heart rate is associated with endothelial dysfunction and increased atheromatous plaque formation leading to atherosclerosis. Faster heart rate may accompany increased production of inflammation molecules and increased production of reactive oxygen species in cardiovascular system, in addition to increased mechanical stress to the heart. There is a correlation between increased resting rate and cardiovascular risk. This is not seen to be "using an allotment of heart beats" but rather an increased risk to the system from the increased rate.
An Australian-led international study of patients with cardiovascular disease has shown that heart beat rate is a key indicator for the risk of heart attack. The study, published in The Lancet (September 2008) studied 11,000 people, across 33 countries, who were being treated for heart problems. Those patients whose heart rate was above 70 beats per minute had significantly higher incidence of heart attacks, hospital admissions and the need for surgery. Higher heart rate is thought to be correlated with an increase in heart attack and about a 46 percent increase in hospitalizations for non-fatal or fatal heart attack.
Other studies have shown that a high resting heart rate is associated with an increase in cardiovascular and all-cause mortality in the general population and in patients with chronic diseases. A faster resting heart rate is associated with shorter life expectancy and is considered a strong risk factor for heart disease and heart failure, independent of level of physical fitness. Specifically, a resting heart rate above 65 beats per minute has been shown to have a strong independent effect on premature mortality; every 10 beats per minute increase in resting heart rate has been shown to be associated with a 10–20% increase in risk of death. In one study, men with no evidence of heart disease and a resting heart rate of more than 90 beats per minute had a five times higher risk of sudden cardiac death. Similarly, another study found that men with resting heart rates of over 90 beats per minute had an almost two-fold increase in risk for cardiovascular disease mortality; in women it was associated with a three-fold increase. In patients having heart rates of 70 beats/minute or above, each additional beat/minute was associated with increased rate of cardiovascular death and heart failure hospitalization.
Given these data, heart rate should be considered in the assessment of cardiovascular risk, even in apparently healthy individuals. Heart rate has many advantages as a clinical parameter: It is inexpensive and quick to measure and is easily understandable. Although the accepted limits of heart rate are between 60 and 100 beats per minute, this was based for convenience on the scale of the squares on electrocardiogram paper; a better definition of normal sinus heart rate may be between 50 and 90 beats per minute.
Standard textbooks of physiology and medicine mention that heart rate (HR) is readily calculated from the ECG as follows: HR = 1000*60/RR interval in milliseconds, HR = 60/RR interval in seconds, or HR = 300/number of large squares between successive R waves. In each case, the authors are actually referring to instantaneous HR, which is the number of times the heart would beat if successive RR intervals were constant.
Lifestyle and pharmacological regimens may be beneficial to those with high resting heart rates. Exercise is one possible measure to take when an individual's heart rate is higher than 80 beats per minute. Diet has also been found to be beneficial in lowering resting heart rate: In studies of resting heart rate and risk of death and cardiac complications on patients with type 2 diabetes, legumes were found to lower resting heart rate. This is thought to occur because in addition to the direct beneficial effects of legumes, they also displace animal proteins in the diet, which are higher in saturated fat and cholesterol. Another nutrient is omega-3 long chain polyunsaturated fatty acids (omega-3 fatty acid or LC-PUFA). In a meta-analysis with a total of 51 randomized controlled trials (RCTs) involving 3,000 participants, the supplement mildly but significantly reduced heart rate (-2.23 bpm; 95% CI: -3.07, -1.40 bpm). When docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were compared, modest heart rate reduction was observed in trials that supplemented with DHA (-2.47 bpm; 95% CI: -3.47, -1.46 bpm), but not in those received EPA.
A very slow heart rate (bradycardia) may be associated with heart block. It may also arise from autonomous nervous system impairment.
== See also ==
Heart rate monitor
Cardiac cycle
Electrocardiography
Sinus rhythm
Second wind (heart rate is measured during 12 Minute Walk Test)
Bainbridge reflex
== Notes ==
== References ==
This article incorporates text from the CC BY book: OpenStax College, Anatomy & Physiology. OpenStax CNX. 30 July 2014.
== Bibliography ==
== External links ==
Online Heart Beats Per Minute Calculator Tap along with your heart rate
An application (open-source) for contactless real time heart rate measurements by means of an ordinary web cam | Wikipedia/Heart_rate |
Ultraviolet light therapy or ultraviolet phototherapy is a treatment for psoriasis, atopic skin disorder, vitiligo and other skin diseases.
== Mechanism of action ==
Ultraviolet light exerts its therapeutic effects largely by modulating cutaneous immune responses and inducing apoptosis of pathogenic cells, thereby reducing inflammation in a variety of photoresponsive skin disorders.
== Treatment modalities ==
There are two main treatments: UVB that is the most common, and PUVA.
Despite the advent of biologic drugs, narrow-band UVB remains an important option for moderate-to-severe inflammatory dermatoses and was the most cost-effective therapy for psoriasis in a 2023 analysis.
=== UVB phototherapy ===
There are four UVB types of lamps: Fluorescent Broad-Band UVB that emit 280–330 nanometres, Fluorescent Narrow-Band that emit 312 nanometres, Excimer that emit 308 nanometres and LED that emit 290–300 nanometres.
=== PUVA phototherapy ===
PUVA means UVA + psoralen. It consists of irradiation of the skin with the UVA ultraviolet light, from a fluorescent bulb or LED lamps.
Clinical protocols sometimes augment PUVA with interferon-α, a strategy that can improve complete-response rates while allowing lower cumulative UVA doses. PUVA therapy delivers deeper-penetrating UVA after oral administration of 8-methoxypsoralen, and is therefore often selected for thicker or more recalcitrant plaques, whereas narrow-band UVB (311–312 nm) is preferred for superficial lesions because of its shallow penetration.
== Equipment and usage ==
Tanning beds are used both in dermatology practices for the treatment of cosmetic skin conditions (such as psoriasis, acne, eczema and vitiligo) and in indoor tanning salons for cosmetic tanning.
Typical treatment regimens involve short exposure to UVB rays 3 to 5 times a week at a hospital or clinic, and repeated sessions may be required before results are noticeable. Almost all of the conditions that respond to UVB light are chronic problems, so continuous treatment is required to keep those problems in check. Home UVB systems are common solutions for those whose conditions respond to treatment. Home systems permit patients to treat themselves every other day (the ideal treatment regimen for most) without the frequent, costly trips to the office/clinic and back, mainly when the area is small, and the price of the lamp is low.
== Safety and side effects ==
A 2024 multi-centre study reported higher incidences of squamous cell carcinoma, basal cell carcinoma and melanoma among patients treated with narrow-band UVB, highlighting the need for long-term dermatological surveillance.
Side-effects may include itching and redness of the skin due to UVB exposure, and possibly sunburn, if patients do not minimize exposure to natural UV rays during treatment days. Cataracts can frequently develop if the eyes are not protected from UV light exposure. To date, there is no link between an increase in a patient's risk of skin cancer and the proper use of narrow-band UVB phototherapy. "Proper use" is generally defined as reaching the "Sub-Erythemic Dose" (S.E.D.), the maximum amount of UVB your skin can receive without burning. Certain fungal growths under the toenail can be treated using a specific wavelength of UV delivered from a high-power LED (light-emitting diode) and can be safer than traditional systemic drugs.
== See also ==
Indoor tanning
Light therapy
== References == | Wikipedia/Ultraviolet_light_therapy |
Low-level laser therapy (LLLT), cold laser therapy or photobiomodulation (PBM) is a medical treatment approach that applies low-level (low-power) lasers or light-emitting diodes (LEDs) to the surface of the body. Whereas high-power lasers are used in laser medicine to cut or destroy tissue, it is claimed that application of low-power lasers stimulates healing, relieves pain, and enhances cell function. Described sometimes as Low-level Red-light Therapy (LLRL), has effects that appear to be limited to a specified set of wavelengths. The effectiveness of red light therapy for treating various conditions is still under investigation. Repeated low level red light therapy may be effective for controlling myopia in children. Several such devices are cleared by the United States Food and Drug Administration (FDA), and low level red light therapy is being tested for treating a range of medical problems including rheumatoid arthritis and oral mucositis.
== Mechanism ==
Research is ongoing about the mechanism of LLLT. The effects of LLLT appear to be limited to a specified set of wavelengths of laser, and administering LLLT below the dose range does not appear to be effective. Photochemical reactions are well known in biological research, and LLLT make use of the first law in photochemistry (Grotthuss-Draper law): light must be absorbed by a chemical substance in order for a photochemical reaction to take place. In LLLT that chemical substance is represented by the respiratory enzyme cytochrome c oxidase which is involved in the electron transport chain in mitochondria, which is the generally accepted theory.
== Medical uses ==
Various LLLT devices have been promoted for use in treatment of several musculoskeletal conditions including carpal tunnel syndrome (CTS), fibromyalgia, osteoarthritis, and rheumatoid arthritis. They have also been promoted for temporomandibular joint disorders, wound healing, smoking cessation, and tuberculosis. LLLT appears to be effective for preventing oral mucositis in recipients of a stem cell transplant with chemotherapy. In other areas, evidence for LLLT remains conflicted. Some studies suggest that LLLT may be modestly effective in relieving short-term pain for rheumatoid arthritis, osteoarthritis, chronic low back pain, acute and chronic neck pain, tendinopathy, and chronic joint disorders. The evidence for LLLT being useful in dentistry, and in the treatment of wound healing is unclear.
Concerns have been raised in the literature about brain stimulation techniques that rely upon low-level (low-power) lasers and light-emitting diodes (LEDs). The transcranial photobiomodulation or transcranial low level light therapy is limited in neuromodulation due to several reasons:
An excessive dose of radiation can be harmful. Therefore, at adequate doses of light there may be stimulation of growth, but at high doses excessive singlet oxygen may be produced and its chemical action may be harmful to cells.
Regarding LED light therapy, this neurostimulation method based on the light-emitting diodes stimulation cannot pass through the skin, only laser can penetrate deeper tissues and stimulate brain areas accordingly. The penetration depth of white light and LED light into the skin increases with increasing wavelength from the UV to the visible light range, and then decreases again in the IR range depending on the selected optical properties. This depth further increases if the thickness of the stratum corneum decreases. Broadband polychromatic light (white light) and LED radiation can only penetrate 0.0017 mm to 5 mm of tissue. For example, research shows that at wavelengths of 450 nm and 650 nm only 1% of the light reaches approximately 1.6 mm and very little reaches 5 mm. Only laser radiation can propagate into deeper tissues.
Since the action spectrum for tissue regeneration and repair consist of more than one wavelength, laser and LED light sources may offer some disadvantages, destroying healthy cells. We still lack knowledge of mental processes at the cellular level. The link between neuronal activity and mental processes is still an intriguing research question and a problem in treatment targeting. Therefore, no one can be sure whether the laser beam only reaches the neuronal structures in the brain that need treatment. An undetermined dose of radiation and the target of radiation can destroy healthy cells during the treatment procedure.
There is not enough information from clinical trials to compare the effectiveness of different types of devices or device parameters (wavelengths, power output, session time, area of actuation).
=== Veterinary use ===
Veterinary clinics use cold laser devices to treat a wide variety of ailments, from arthritis to wounds, on dogs and cats. Very little research has been done on the effects of this treatment on animals. Brennen McKenzie, president of the Evidence-Based Veterinary Medicine Association, has stated that "research into cold laser in dogs and cats is sparse and generally low quality. Most studies are small and have minimal or uncertain controls for bias and error". While allowing that some studies show promising results, he reports that others do not. While believing that there is enough evidence to warrant further study, he concludes that there is not enough evidence to support routine clinical use of cold laser in animals.
== Contraindications ==
Based on the results of a systematic review, there is no evidence to suggest that people with cancer or people who are at risk of getting cancer should avoid photobiomodulation.
== Side effects ==
There are some reports of mild pain or skin irritation after red light therapy. The long term effects on the skin or on the hair are not known. Eye protection is suggested for some devices. For skin applications, different wavelengths of light may result in different 'biological effects' depending on the person's skin type, race, and ethnicity. Clinical guideline suggest that a dermatologist is consulted before undergoing treatment.
For safety, if a person chooses to use red light therapy, a device that has been approved for use on humans by the country the person lives in is recommended. For example, in the US, it is suggested to only use devices approved by the FDA for dermatologic application.
== Society and culture ==
=== History ===
Faroese physician Niels Finsen is believed to be the father of modern light therapy. He used red light to treat smallpox lesions. He received the Nobel Prize in Physiology or Medicine in 1903. Scientific evidence for some of his treatments is lacking, and later eradication of smallpox and development of antibiotics for tuberculosis rendered light therapy obsolete for these diseases.
Hungarian physician and surgeon Endre Mester (1903–1984) is credited with the discovery of the biological effects of low power lasers, which occurred a few years after the 1960 invention of the ruby laser and the 1961 invention of the helium–neon (HeNe) laser. Mester accidentally discovered that low-level ruby laser light could regrow hair during an attempt to replicate an experiment that showed that such lasers could reduce tumors in mice. The laser he was using was faulty and was not as powerful as he thought. It failed to affect the tumors, but he noticed that in the places where he had shaved the mice in order to do the experiments, the hair grew back more quickly on the treated mice than on those among the control group. He published those results in 1967. He went on to show that low level HeNe light could accelerate wound healing in mice.
By the 1970s, he was applying low level laser light to treat people with skin ulcers. In 1974, he founded the Laser Research Center at the Semmelweis Medical University in Budapest, and continued working there for the remainder of his life. His sons carried on his work and brought it to the United States. By 1987, companies selling lasers were claiming that they could treat pain, accelerate healing of sports injuries, and treat arthritis, but there was little evidence for this at that time. Mester originally called this approach "laser biostimulation'", but it soon became known as “low-level laser therapy" and with the adaptation of light emitting diodes by those studying this approach, it became known as "low-level light therapy", and to resolve confusion around the exact meaning of "low level", the term "photobiomodulation" arose.
=== Names ===
The following terms are accepted as alternatives of low level light therapy term: LLLT, laser biostimulation, laser phototherapy, low-level laser therapy, low-power laser irradiation, low-power laser therapy, and photobiomodulation therapy. The term photobiomodulation therapy is considered the preferred term by industry professionals. However LLLT has been marketed and researched under a number of other terms, including red light therapy, low-power laser therapy (LPLT), soft laser therapy, low-intensity laser therapy, low-energy laser therapy, cold laser therapy, bio-stimulation laser therapy, photo-biotherapy, therapeutic laser, and monochromatic infrared light energy (MIRE) therapy. More specific applications sometimes have their own terms, for example when administered to acupuncture points, the procedure is called laser acupuncture. When applied to the head, LLLT may be known as transcranial photobiomodulation, transcranial near-infrared laser therapy (NILT), or transcranial low level light therapy.
=== Government action ===
The FDA filed a complaint for injunction in 2014, alleging that company QLaser PMA were marketing their devices as being able to treat “over 200 different diseases and disorders,” including cancer, cardiac arrest, deafness, diabetes, HIV/AIDS, macular degeneration, and venereal disease. This case resulted in a permanent injunction against the manufacture, marketing, sale, and distribution of those devices in 2015.
In 2017, the owner of QLaser, Robert Lytle, and two of QLaser's distributors were charged with a criminal conspiracy to commit fraud. Lytle pleaded guilty to one count of conspiracy to introduce misbranded medical devices into interstate commerce with the intent to defraud and mislead, and one count of criminal contempt in January 2018. Lytle was sentenced to serve 12 years in prison and made an initial restitution payment of $637,000. Lytle's conspirators were sentenced to 24 months and 15 months, respectively.
=== Reimbursement ===
Blue Cross Blue Shield Association and Aetna provide coverage for the prevention of oral mucositis, but not any other reason. The Centers for Medicare and Medicaid Services does not provide coverage for LLLT. Cigna lists LLLT as "experimental, investigational, or unproven for any indication" and provides literature review summaries for a number of conditions.
== Research ==
=== Musculoskeletal ===
Evidence does not support a benefit in delayed-onset muscle soreness. It may be useful for muscle pain and injuries. A 2008 Cochrane Library review concluded that LLLT has insufficient evidence for treatment of nonspecific low back pain, a finding echoed in a 2010 review of chronic low back pain. A 2015 review found benefit in nonspecific chronic low-back pain. LLLT may be useful in the treatment of both acute and chronic neck pain. In 2013, however, a systematic review and meta-analysis of LLLT for neck pain indicated that the benefit was not of significant importance and that the evidence had a high risk of bias. In a study testing the efficacy of low-level laser therapy treating plantar fasciitis found that LLLT significantly reduces pain in lower extremity tendinopathy and plantar fasciitis in the short and medium terms. The same study also stated that while comparing the effect of LLLT to that of therapeutic ultrasound in persons with patellar tendinopathy, and they found a statistically significant effect in favour of LLLT, both on pain reduction and function.
There are tentative data that LLLT is useful in the short-term treatment of pain caused by rheumatoid arthritis, and possibly chronic joint disorders. Research that compared the effects of LLLT against other treatments, sham treatments, or no treatment at all, and randomized adult patients with rheumatoid arthritis to receive it were considered. These outcomes included pain, functional capacity, adverse events, inflammation, disease activity, range of motion, stiffness in the morning, muscle strength, and quality of life. The findings indicate that the differences between utilizing a sham and an infrared laser may be negligible or nonexistent in terms of pain, stiffness in the morning, grip strength, functional ability, inflammation, range of motion, disease activity, and side events. It was also discovered that the data about the effects of laser acupuncture against reflexology in terms of functional ability, quality of life, and inflammation is quite hazy, and about the effects of red laser versus sham in terms of pain, morning stiffness, and side events. The usefulness of red laser, laser acupuncture, and reflexology in the treatment of RA patients is not well enough demonstrated. A 2019 systematic review and meta-analysis found evidence for pain reduction in osteoarthritis. While it does not appear to improve pain in temporomandibular disorders, it may improve function.
There is tentative evidence of benefit in tendinopathy. A 2014 review found benefit in shoulder tendinopathy. A 2014 Cochrane review found tentative evidence that it may help in frozen shoulders.
=== Mouth ===
Similarly, the use of lasers to treat chronic periodontitis and to speed healing of infections around dental implants is suggested, but there is insufficient evidence to indicate a use superior to traditional practices. There is tentative evidence for dentin hypersensitivity. It does not appear to be useful for orthodontic pain LLLT might be useful for wisdom tooth extraction (complications).
=== Hair loss ===
LLLT has been studied as a treatment for hair loss; a review in 2012 found little evidence to support the use of lasers to treat hair loss. A 2014 review found tentative evidence for benefit for lasers, while another 2014 review concluded that the results were mixed, had a high risk of bias, and that its effectiveness was unclear. A 2015 review found tentative evidence of benefit. Additionally, a 2017 review of clinical trials found 10 of 11 trials reviewed "demonstrated significant improvement of androgenic alopecia in comparison to baseline or controls when treated with LLLT."
LLLT is shown to increase hair density and growth in both genders. The types of devices (hat, comb, helmet) and duration did not alter the effectiveness, with more emphasis to be placed on lasers compared to LEDs. Ultraviolet and infrared light are more effective for alopecia areata, while red light and infrared light is more effective for androgenetic alopecia.
Medical reviews suggest that LLLT is as effective or potentially more than other non invasive and traditional therapies such as minoxidil and finasteride but further studies such as RCTs, long term follow up studies, and larger double blinded trials need to be conducted to confirm the initial findings.
=== Brain injuries ===
LLLT has been studied for traumatic brain injury (TBI) and stroke among other conditions. When applied to the head it is known as transcranial photobiomodulation or transcranial low level light therapy.
=== Cancer treatment side effects ===
LLLT has been studied as a way to reduce pain and swelling in breast-cancer related lymphedema. The 2015 systematic review & meta-analysis by Smoot, Chiavola-Larson, et al found “Moderate-strength evidence supports LLLT in the management of [breast cancer related lymphoedema], with […] reductions in volume and pain immediately after conclusion of LLLT treatments. Greater reductions in volume [of lymph nodes or surrounding tissues] were found with the use of LLLT than in treatments without it.”
=== Stem cells ===
An ongoing area of research is the application of LLLT for increasing cell proliferation, including stem cells.
=== Wound healing ===
Low level laser therapy has been studied as a potential treatment for chronic wounds, and higher-power lasers have sometimes been successfully used to close acute wounds as an alternative to stitching. However, as of 2012 and due to inconsistent results and the low quality of extant research, reviews in the scientific literature have not supported its widespread application.
== See also ==
Blood irradiation therapy – Alternative medical procedure
Light therapy – Therapy involving intentional exposure to sunlight
Neurotechnology
Neurotherapy
Photomedicine – interdisciplinary field examining the effects of light on human healthPages displaying wikidata descriptions as a fallback
Photorejuvenation – Skin treatment
== References == | Wikipedia/Low-level_laser_therapy |
Stereotactic surgery is a minimally invasive form of surgical intervention that makes use of a three-dimensional coordinate system to locate small targets inside the body and to perform on them some action such as ablation, biopsy, lesion, injection, stimulation, implantation, radiosurgery (SRS), etc.
In theory, any organ system inside the body can be subjected to stereotactic surgery. However, difficulties in setting up a reliable frame of reference (such as bone landmarks, which bear a constant spatial relation to soft tissues) mean that its applications have been, traditionally and until recently, limited to brain surgery. Besides the brain, biopsy and surgery of the breast are done routinely to locate, sample (biopsy), and remove tissue. Plain X-ray images (radiographic mammography), computed tomography, and magnetic resonance imaging can be used to guide the procedure.
Another accepted form of "stereotactic" is "stereotaxic". The word roots are stereo-, a prefix derived from the Greek word στερεός (stereos, "solid"), and -taxis (a suffix of Neo-Latin and ISV, derived from Greek taxis, "arrangement", "order", from tassein, "to arrange").
== Uses ==
The surgery is used to treat various brain cancers, benign, and functional disorders of the brain. This is sometimes combined with whole brain radiotherapy, and a 2021 systematic review found this combination led to the greatest improvement of survival for those with single brain metastasis.
Amongst the malignant brain disorders are: brain metastasis and glioblastoma. The benign brain disorders are: meningioma, cerebral arteriovenous malformation, vestibular schwannoma, and pituitary adenoma. Functional disorders are: trigeminal neuralgia, Parkinson's disease, and epilepsy.
== Procedure ==
Stereotactic surgery works on the basis of three main components:
A stereotactic planning system, including atlas, multimodality image matching tools, coordinates calculator, etc.
A stereotactic device or apparatus
A stereotactic localization and placement procedure
Modern stereotactic planning systems are computer based. The stereotactic atlas is a series of cross sections of anatomical structure (for example, a human brain), depicted in reference to a two-coordinate frame. Thus, each brain structure can be easily assigned a range of three coordinate numbers, which will be used for positioning the stereotactic device. In most atlases, the three dimensions are: latero-lateral (x), dorso-ventral (y) and rostro-caudal (z).
The stereotactic apparatus uses a set of three coordinates (x, y and z) in an orthogonal frame of reference (cartesian coordinates), or, alternatively, a cylindrical coordinates system, also with three coordinates: angle, depth and antero-posterior (or axial) location. The mechanical device has head-holding clamps and bars which puts the head in a fixed position in reference to the coordinate system (the so-called zero or origin). In small laboratory animals, these are usually bone landmarks which are known to bear a constant spatial relation to soft tissue. For example, brain atlases often use the external auditory meatus, the inferior orbital ridges, the median point of the maxilla between the incisive teeth. or the bregma (confluence of sutures of frontal and parietal bones), as such landmarks. In humans, the reference points, as described above, are intracerebral structures which are clearly discernible in a radiograph or tomograph. In newborn human babies, the "soft spot" where the coronal and sagittal sutures meet (known as the fontanelle) becomes the bregma when this gap closes.
Guide bars in the x, y and z directions (or alternatively, in the polar coordinate holder), fitted with high precision vernier scales allow the neurosurgeon to position the point of a probe (an electrode, a cannula, etc.) inside the brain, at the calculated coordinates for the desired structure, through a small trephined hole in the skull.
Currently, a number of manufacturers produce stereotactic devices fitted for neurosurgery in humans, for both brain and spine procedures, as well as for animal experimentation.
=== Types frame systems ===
Simple orthogonal system: The probe is directed perpendicular to a square base unit fixed to the skull. These provide three degrees of freedom by means of a carriage that moved orthogonally along the base plate or along a bar attached parallel to the base plate of the instrument. Attached to the carriage was a second track that extended across the head frame perpendicularly.
Burr hole mounted system: This provides a limited range of possible intracranial target points with a fixed entry point. They provided two angular degrees of freedom and a depth adjustment. The surgeon could place the burr hole over nonessential brain tissue and utilize the instrument to direct the probe to the target point from the fixed entry point at the burr hole.
Arc-quadrant systems: Probes are directed perpendicular to the tangent of an arc (which rotates about the vertical axis) and a quadrant (which rotates about the horizontal axis). The probe, directed to a depth equal to the radius of the sphere defined by the arc-quadrant, will always arrive at the center or focal point of that sphere.
Arc-phantom systems: An aiming bow attaches to the head ring, which is fixed to the patient's skull, and can be transferred to a similar ring that contains a simulated target. In this system, the phantom target is moved on the simulator to 3D coordinates. After adjusting the probe holder on the aiming bow so that the probe touches the desired target on the phantom, the transferable aiming bow is moved from the phantom base ring to the base ring on the patient. The probe is then lowered to the determined depth in order to reach the target point deep in the patient's brain.
== Treatment ==
=== Stereotactic radiosurgery ===
Stereotactic radiosurgery utilizes externally generated ionizing radiation to inactivate or eradicate defined targets in the head or spine without the need to make an incision. This concept requires steep dose gradients to reduce injury to adjacent normal tissue while maintaining treatment efficacy in the target. As a consequence of this definition, the overall treatment accuracy should match the treatment planning margins of 1–2 mm or better. To use this paradigm optimally and treat patients with the highest possible accuracy and precision, all errors, from image acquisition over treatment planning to mechanical aspects of the delivery of treatment and intra-fraction motion concerns, must be systematically optimized. To assure quality of patient care the procedure involves a multidisciplinary team consisting of a radiation oncologist, medical physicist, and radiation therapist. Dedicated, commercially available stereotactic radiosurgery programs are provided by the irrespective Gamma Knife, CyberKnife, and Novalis Radiosurgery devices.
Stereotactic radiosurgery provides an efficient, safe, and minimal invasive treatment alternative for patients diagnosed with malignant, benign and functional indications in the brain and spine, including but not limited to both primary and secondary tumors. Stereotactic radiosurgery is a well-described management option for most metastases, meningiomas, schwannomas, pituitary adenomas, arteriovenous malformations, and trigeminal neuralgia, among others.
Irrespective of the similarities between the concepts of stereotactic radiosurgery and fractionated radiotherapy and although both treatment modalities are reported to have identical outcomes for certain indications, the intent of both approaches is fundamentally different. The aim of stereotactic radiosurgery is to destroy target tissue while preserving adjacent normal tissue, where fractionated radiotherapy relies on a different sensitivity of the target and the surrounding normal tissue to the total accumulated radiation dose. Historically, the field of fractionated radiotherapy evolved from the original concept of stereotactic radiosurgery following discovery of the principles of radiobiology: repair, reassortment, repopulation, and reoxygenation. Today, both treatment techniques are complementary as tumors that may be resistant to fractionated radiotherapy may respond well to radiosurgery and tumors that are too large or too close to critical organs for safe radiosurgery may be suitable candidates for fractionated radiotherapy.
A second, more recent evolution extrapolates the original concept of stereotactic radiosurgery to extra-cranial targets, most notably in the lung, liver, pancreas, and prostate. This treatment approach, entitled stereotactic body radiotherapy or SBRT, is challenged by various types of motion. On top of patient immobilization challenges and the associated patient motion, extra-cranial lesions move with respect to the patient's position due to respiration, bladder and rectum filling. Like stereotactic radiosurgery, the intent of stereotactic body radiotherapy is to eradicate a defined extra-cranial target. However, target motion requires larger treatment margins around the target to compensate for the positioning uncertainty. This in turn implies more normal tissue exposed to high doses, which could result in negative treatment side effects. As a consequence, stereotactic body radiotherapy is mostly delivered in a limited number of fractions, thereby blending the concept of stereotactic radiosurgery with the therapeutic benefits of fractionated radiotherapy. To monitor and correct target motion for accurate and precise patient positioning prior and during treatment, advanced image-guided technologies are commercially available and included in the radiosurgery programs offered by the CyberKnife and Novalis communities.
=== Parkinson's disease ===
Functional neurosurgery comprises treatment of several disorders such as Parkinson's disease, hyperkinesia, disorder of muscle tone, intractable pain, convulsive disorders and psychological phenomena. Treatment for these phenomena was believed to be located in the superficial parts of the CNS and PNS. Most of the interventions made for treatment consisted of cortical extirpation.
To alleviate extra pyramidal disorders, pioneer Russell Meyers dissected or transected the head of the caudate nucleus in 1939, and part of the putamen and globus pallidus.
Attempts to abolish intractable pain were made with success by transection of the spinothalamic tract at spinal medullary level and further proximally, even at mesencephalic levels.
In 1939-1941 Putnam and Oliver tried to improve Parkinsonism and hyperkinesias by trying a series of modifications of the lateral and antero-lateral cordotomies. Additionally, other scientists like Schurman, Walker, and Guiot made significant contributions to functional neurosurgery. In 1953, Cooper discovered by chance that ligation of the anterior chorioidal artery resulted in improvement of Parkinson's disease. Similarly, when Grood was performing an operation in a patient with Parkinson's, he accidentally lesioned the thalamus. This caused the patient's tremors to stop. From then on, thalamic lesions became the target point with more satisfactory results.
More recent clinical applications can be seen in surgeries used to treat Parkinson's disease, such as Pallidotomy or Thalamotomy (lesioning procedures), or Deep Brain Stimulation (DBS). During DBS, an electrode is placed into the thalamus, the pallidum of the subthalmamic nucleus, parts of brain that are involved in motor control, and are affected by Parkinson's disease. The electrode is connected to a small battery operated stimulator that is placed under the collarbone, where a wire runs beneath the skin to connect it to the electrode in the brain. The stimulator produces electrical impulses that affect the nerve cells around the electrode and should help alleviate tremors or symptoms that are associated with the affected area.
In Thalamotomy, a needle electrode is placed into the thalamus, and the patient must cooperate with tasks assigned to find the affected area- after this area of the thalamus is located, a small high frequency current is applied to the electrode and this destroys a small part of the thalamus. Approximately 90% of patients experience instantaneous tremor relief.
In Pallidotomy, an almost identical procedure to thalamotomy, a small part of the pallidum is destroyed and 80% of patients see improvement in rigidity and hypokinesia and a tremor relief or improvement comes weeks after the procedure.
== History ==
The stereotactic method was first published in 1908 by two British scientists, Victor Horsley, a physician and neurosurgeon, and Robert H. Clarke, a physiologist, and was built by Swift & Son; the two scientists stopped collaborating after the 1908 publication. The Horsley–Clarke apparatus used a Cartesian (three-orthogonal axis) system. That device is in the Science Museum, London; a copy was brought to the US by Ernest Sachs and is in the Department of Neurosurgery at UCLA. Clarke used the original to do research that led to publications of primate and cat brain atlases. There is no evidence it was ever used in a human surgery.: 12 The first stereotactic device designed for the human brain appears to have been an adaptation of the Horseley–Clarke frame built at Aubrey T. Mussen's behest by a London workshop in 1918, but it received little attention and does not appear to have been used on people. It was a frame made of brass.: 12
The first stereotactic device used in humans was used by Martin Kirschner, for a method to treat trigeminal neuralgia by inserting an electrode into the trigeminal nerve and ablating it. He published this in 1933.: 13 : 420
In 1947 and 1949, two neurosurgeons working at Temple University in Philadelphia, Ernest A. Spiegel (who had fled Austria when the Nazis took over) and Henry T. Wycis, published their work on a device similar to the Horsley–Clarke apparatus in using a cartesian system; it was attached to the patient's head with a plaster cast instead of screws. Their device was the first to be used for brain surgery; they used it for psychosurgery. They also created the first atlas of the human brain, and used intracranial reference points, generated by using medical images acquired with contrast agents.: 13 : 72
The work of Spiegel and Wycis sparked enormous interest and research.: 13 In Paris, Jean Talairach collaborated with Marcel David, Henri Hacaen, and Julian de Ajuriaguerra on a stereotactic device, publishing their first work in 1949 and eventually developing the Talairach coordinates.: 13 : 93 In Japan, Hirotaro Narabayashi was doing similar work.
In 1949, Lars Leksell published a device that used polar coordinates instead of cartesian, and two years later he published work where he used his device to target a beam of radiation into a brain.: 13 : 91 Leksell's radiosurgery system is also used by the Gamma Knife device, and by other neurosurgeons, using linear accelerators, proton beam therapy and neutron capture therapy. Lars Leksell went on to commercialize his inventions by founding Elekta in 1972.
In 1979, Russell A. Brown proposed a device, now known as the N-localizer, that enables guidance of stereotactic surgery using tomographic images that are obtained via medical imaging technologies such as X-ray computed tomography (CT), magnetic resonance imaging (MRI), or positron emission tomography (PET). The N-localizer comprises a diagonal rod that spans two vertical rods to form an N-shape that allows tomographic images to be mapped to physical space. This device became almost universally adopted by the 1980s and is included in the Brown-Roberts-Wells (BRW), Kelly-Goerss, Leksell, Cosman-Roberts-Wells (CRW), Micromar-ETM03B, FiMe-BlueFrame, Macom, and Adeor-Zeppelin stereotactic frames and in the Gamma Knife radiosurgery system. An alternative to the N-localizer is the Sturm-Pastyr localizer that is included in the Riechert-Mundinger and Zamorano-Dujovny stereotactic frames.
Other localization methods also exist that do not make use of tomographic images produced by CT, MRI, or PET, but instead conventional radiographs.
The stereotactic method has continued to evolve, and at present employs an elaborate mixture of image-guided surgery that uses computed tomography, magnetic resonance imaging and stereotactic localization.
== History in Latin America ==
In 1970, in the city of Buenos Aires, Argentina, Aparatos Especiales company, produced the first Stereotactic System in Latin America. Antonio Martos Calvo, together with Jorge Candia and Jorge Olivetti through the request of neurosurgeon Jorge Schvarc (1942-2019), developed an equipment based on the principle of Hitchcock Stereotactic System. The patient was seated in an adapted chair with two telescopic arms attached at it base, which fixed the stereotactic frame preventing the patient’s movement.
A double radiopaque ruler attached to the side of the frame made it possible to obtain the antero-posterior and latero-lateral X-ray images without the need of moving the radiopaque ruler. The thermal coagulation lesion was performed using tungsten monopole electrodes of 1,5mm of diameter (without temperature control) with a 3mm active tip, utilizing an electrical bipolar coagulator. The lesion size was previously determined by testing the electrode in egg albumin. Coagulation size was the result of the electrical coagulator power regulation and the application time of the radiofrequency. The first surgery performed with this system was a Trigeminal Nucleotractothomy. Jorge Schvarcz performed more than 700 functional surgeries until 1994 when, due to health problems he stopped exercising his profession. But the equipment developed kept improving on a neurosurgery history.
This was the beginning of the developing of technology to produce stereotactic devices in Latin America. This was the beginning of the first stereotactic manufacturer of Latin America – The Brazilian Micromar.
== Research ==
Stereotactic surgery is sometimes used to aid in several different types of animal research studies. Specifically, it is used to target specific sites of the brain and directly introduce pharmacological agents to the brain which otherwise may not be able to cross the blood–brain barrier. In rodents, the main applications of stereotactic surgery are to introduce fluids directly to the brain or to implant cannulae and microdialysis probes. Site specific central microinjections are used when rodents do not need to be awake and behaving or when the substance to be injected has a long duration of action. For protocols in which rodents’ behaviors must be assessed soon after injection, stereotactic surgery can be used to implant a cannula through which the animal can be injected after recovery from the surgery. These protocols take longer than site-specific central injections in anesthetized mice because they require the construction of cannulae, wire plugs, and injection needles, but induce less stress in the animals because they allow for a recovery period for the healing of trauma induced to the brain before injection. Surgery can also be used for microdialysis protocols to implant and tether the dialysis probe and guide cannula.
== See also ==
== References ==
== Further reading ==
Armando Alaminos Bouza, "Imaging, Stereotactic Space and Targeting in Functional Neurosurgery", Functional Neurosurgery, First Edition, Publisher: Alaúde Editorial LTDA, Editor: Arthur Cukiert, pp. 67–79, (2014), ISBN 978-85-7881-248-5
Philip L. Gildenberg, "Stereotactic Surgery: Present and Past", Stereotactic Neurosurgery (Editor: M. Peter Heilbrun). Baltimore: Williams and Wilkins (1988)
Patrick J. Kelly, "Introduction and Historical Aspects", Tumor Stereotaxis, Philadelphia: W. B. Saunders Company (1991)
Robert Levy, A Short History of Stereotactic Surgery Archived 2017-05-13 at the Wayback Machine, Cyber Museum of Neurosurgery.
William Regine; Lawrence Chin (2008). Principles of Stereotactic Surgery. Berlin: Springer. ISBN 978-0-387-71069-3.
Steel, G. Gordon (2002). Basic clinical radiobiology (3rd ed.). London: Hodder Arnold. ISBN 978-0340807835.
Tasker RR, Organ LW, Hawrylyshyn P (1976). "Sensory organization of the human thalamus". Applied Neurophysiology. 39 (3–4): 139–53. doi:10.1159/000102487. PMID 801856.
Tasker RR, Hawrylyshyn P, Rowe IH, Organ LW (1977). "Computerized Graphic Display of Results of Subcortical Stimulation During Stereotactic Surgery". Advances in Stereotactic and Functional Neurosurgery 2. Acta Neurochirurgica Supplementum. Vol. 24. pp. 85–98. doi:10.1007/978-3-7091-8482-0_14. ISBN 978-3-211-81422-2. PMID 335811.
van Manen, Jaap (1967). Stereotactic Methods and their Applications in Disorders of the Motor System. Springfield, IL: Royal Van Gorcum.
Zapata, A.; Chefer, V.I.; Shippenberg, T.S. (2009). "Microdialysis in Rodents". Current Protocols in Neuroscience. 47: 7.2.1–7.2.29. doi:10.1002/0471142301.ns0702s47. PMC 2945307. PMID 19340813. | Wikipedia/Stereotactic_surgery |
Functional electrical stimulation (FES) is a technique that uses low-energy electrical pulses to artificially generate body movements in individuals who have been paralyzed due to injury to the central nervous system. More specifically, FES can be used to generate muscle contraction in otherwise paralyzed limbs to produce functions such as grasping, walking, bladder voiding and standing. This technology was originally used to develop neuroprostheses that were implemented to permanently substitute impaired functions in individuals with spinal cord injury (SCI), head injury, stroke and other neurological disorders. In other words, a person would use the device each time he or she wanted to generate a desired function. FES is sometimes also referred to as neuromuscular electrical stimulation (NMES).
FES technology has been used to deliver therapies to retrain voluntary motor functions such as grasping, reaching and walking. In this embodiment, FES is used as a short-term therapy, the objective of which is restoration of voluntary function and not lifelong dependence on the FES device, hence the name functional electrical stimulation therapy, FES therapy (FET or FEST). In other words, the FEST is used as a short-term intervention to help an individual's central nervous system re-learn how to execute impaired functions, instead of making them dependent on neuroprostheses for the rest of their life. Initial Phase II clinical trials conducted with FEST for reaching and grasping, and walking were carried out at KITE, the research arm of the Toronto Rehabilitation Institute.
== Principles ==
Neurons are electrically active cells. In neurons, information is coded and transmitted as a series of electrical impulses called action potentials, which represent a brief change in cell electric potential of approximately 80–90 mV. Nerve signals are frequency modulated; i.e. the number of action potentials that occur in a unit of time is proportional to the intensity of the transmitted signal. Typical action potential frequency is between 4 and 12 Hz. An electrical stimulation can artificially elicit this action potential by changing the electric potential across a nerve cell membrane (this also includes the nerve axon) by inducing electrical charge in the immediate vicinity of the outer membrane of the cell.
FES devices take advantage of this property to electrically activate nerve cells, which then may go on to activate muscles or other nerves. However, special care must be taken in designing safe FES devices, as electric current through tissue can lead to adverse effects such as decrease in excitability or cell death. This may be due to thermal damage, electroporation of the cell membrane, toxic products from electrochemical reactions at the electrode surface, or over-excitation of the targeted neurons or muscles. Typically FES is concerned with stimulation of neurons and nerves. In some applications, FES can be used to directly stimulate muscles, if their peripheral nerves have been severed or damaged (i.e., denervated muscles). However, the majority of the FES systems used today stimulate the nerves or the points where the junction occurs between the nerve and the muscle. The stimulated nerve bundle includes motor nerves (efferent nerves—descending nerves from the central nervous system to muscles) and sensory nerves (afferent nerves—ascending nerves from sensory organs to the central nervous system).
The electrical charge can stimulate both motor and sensory nerves. In some applications, the nerves are stimulated to generate localized muscle activity, i.e., the stimulation is aimed at generating direct muscle contraction. In other applications, stimulation is used to activate simple or complex reflexes. In other words, the afferent nerves are stimulated to evoke a reflex, which is typically expressed as a coordinated contraction of one or more muscles in response to the sensory nerve stimulation.
When a nerve is stimulated, i.e., when sufficient electrical charge is provided to a nerve cell, a localized depolarization of the cell wall occurs resulting in an action potential that propagates toward both ends of the axon. Typically, one "wave" of action potentials will propagate along the axon towards the muscle (orthodromic propagation) and concurrently, as the other "wave" of action potentials will propagate towards the cell body in the central nervous system (antidromic propagation). While the direction of propagation in case of the antidromic stimulation and the sensory nerve stimulation is the same, i.e., towards the central nervous system, their end effects are very different. The antidromic stimulus has been considered an irrelevant side effect of FES. However, in recent years a hypothesis has been presented suggesting the potential role of the antidromic stimulation in neurorehabilitation. Typically, FES is concerned with orthodromic stimulation and uses it to generate coordinated muscle contractions.
In the case where sensory nerves are stimulated, the reflex arcs are triggered by the stimulation on sensory nerve axons at specific peripheral sites. One example of such a reflex is the flexor withdrawal reflex. The flexor withdrawal reflex occurs naturally when a sudden, painful sensation is applied to the sole of the foot. It results in flexion of the hip, knee and ankle of the affected leg, and extension of the contralateral leg in order to get the foot away from the painful stimulus as quickly as possible. The sensory nerve stimulation can be used to generate desired motor tasks, such as evoking flexor withdrawal reflex to facilitate walking in individuals following stroke, or they can be used to alter reflexes or the function of the central nervous system. In the later case, the electrical stimulation is commonly described by the term neuromodulation.
Nerves can be stimulated using either surface (transcutaneous) or subcutaneous (percutaneous or implanted) electrodes. The surface electrodes are placed on the skin surface above the nerve or muscle that needs to be "activated". They are noninvasive, easy to apply, and generally inexpensive. Until recently the common belief in the FES field has been that due to the electrode-skin contact impedance, skin and tissue impedance, and current dispersion during stimulation, much higher-intensity pulses are required to stimulate nerves using surface stimulation electrodes as compared to the subcutaneous electrodes.
(This statement is correct for all commercially available stimulators except MyndMove stimulator (developed my Milos R. Popovic), which has implemented a new stimulation pulse that allows the stimulator to generate muscle contractions without causing discomfort during stimulation, which is a common problem with commercially available transcutaneous electrical stimulation systems, based on US Patents 8,880,178 (2014), 9,440,077 (2016), and 9,592,380 (2016) and related foreign patents.)
A major limitation of the transcutaneous electrical stimulation is that some nerves, for example those innervating the hip flexors, are too profound to be stimulated using surface electrodes. This limitation can be partly addressed by using arrays of electrodes, which can use several electrical contacts to increase selectivity.
Subcutaneous electrodes can be divided into percutaneous and implanted electrodes. The percutaneous electrodes consist of thin wires inserted through the skin and into muscular tissue close to the targeted nerve. These electrodes typically remain in place for a short period of time and are only considered for short-term FES interventions. However, it is worth mentioning that some groups, such as Cleveland FES Center, have been able to safely use percutaneous electrodes with individual patients for months and years at a time. One of the drawbacks of using the percutaneous electrodes is that they are prone to infection and special care has to be taken to prevent such events.
The other class of subcutaneous electrodes is implanted electrodes. These are permanently implanted in the consumer's body and remain in the body for the remainder of the consumer's life. Compared to surface stimulation electrodes, implanted and percutaneous electrodes potentially have higher stimulation selectivity, which is a desired characteristics of FES systems. To achieve higher selectivity while applying lower stimulation amplitudes, it is recommended that both cathode and anode are in the vicinity of the nerve that is stimulated. The drawbacks of the implanted electrodes are they require an invasive surgical procedure to install, and, as is the case with every surgical intervention, there exists a possibility of infection following implantation.
Typical stimulation protocols used in clinical FES involves trains of electric pulses. Biphasic, charged balanced pulses are employed as they improve the safety of electrical stimulation and minimize some of the adverse effects. Pulse duration, pulse amplitude and pulse frequency are the key parameters that are regulated by the FES devices. The FES devices can be current or voltage regulated. Current regulated FES systems always deliver the same charge to the tissue regardless of the skin/tissue resistance. Because of that, the current regulated FES systems do not require frequent adjustments of the stimulation intensity. The voltage regulated devices may require more frequent adjustments of the stimulation intensity as the charge that they deliver changes as the skin/tissue resistance changes. The properties of the stimulation pulse trains and how many channels are used during stimulation define how complex and sophisticated FES-induced function is. The system can be as simple such as FES systems for muscle strengthening or they can be complex such as FES systems used to deliver simultaneous reaching and grasping, or bipedal locomotion.
Note: This paragraph was developed in part using material from the following reference. For more information on FES please consult that and other references provided in the paragraph.
== History ==
Electrical stimulation had been utilized as far back as ancient Egypt, when it was believed that placing torpedo fish in a pool of water with a human was therapeutic. FES – which involves stimulating the target organ during a functional movement (e.g., walking, reaching for an item) – was initially referred to as functional electrotherapy by Liberson. It was not until 1967 that the term functional electrical stimulation was coined by Moe and Post, and used in a patent entitled, "Electrical stimulation of muscle deprived of nervous control with a view of providing muscular contraction and producing a functionally useful moment". Offner's patent described a system used to treat foot drop.
The first commercially available FES devices treated foot drop by stimulating the peroneal nerve during gait. In this case, a switch, located in the heel end of a user's shoe, would activate a stimulator worn by the user.
== Common applications ==
=== Spinal cord injury ===
Injuries to the spinal cord interfere with electrical signals between the brain and the muscles, resulting in paralysis below the level of injury. Restoration of limb function as well as regulation of organ function are the main application of FES, although FES is also used for treatment of pain, pressure, sore prevention, etc. Some examples of FES applications involve the use of neuroprostheses that allow the people with paraplegia to walk, stand, restore hand grasp function in people with quadriplegia, or restore bowel and bladder function. High intensity FES of the quadriceps muscles allows patients with complete lower motor neuron lesion to increase their muscle mass, muscle fiber diameter, improve ultrastructural organization of contractile material, increase of force output during electrical stimulation and perform FES assisted stand-up exercises. Regeneration associated genes (RAG) expression, responsible for axonal outgrowth and survival, is promoted with administration of FES.
==== Walking in spinal cord injury ====
Kralj and his colleagues described a technique for paraplegic gait using surface stimulation, which remains the most popular method in use today. Electrodes are placed over the quadriceps muscles and peroneal nerves bilaterally. The user controls the neuroprosthesis with two pushbuttons attached to the left and right handles of a walking frame, or on canes or crutches. When the neuroprosthesis is turned on, both quadriceps muscles are stimulated to provide a standing posture.
Kralj's approach was extended by Graupe et al. into a digital FES system that employs the power of digital signal processing to result in the Parastep FES system, based on US Patents 5,014,705 (1991), 5,016,636 (1991), 5,070,873 (1991), 5,081,989 (1992), 5,092,329 (1992) and related foreign patents. The Parastep system became the first FES system for standing and walking to receive the US FDA approval (FDA, PMA P900038, 1994) and become commercially available.
The Parastep's digital design allows a considerable reduction in rate of patient-fatigue by drastically reducing of stimulation pulse-width (100–140 microseconds) and pulse-rate (12–24 per sec.), to result, in walking times of 20–60 minutes and average walking distances of 450 meters per walk, for adequately trained thoracic-level complete paraplegics patients who complete training that includes daily treadmill sessions, with some patients exceeding one mile per walk. Also, Parestep-based walking was reported to result in several medical and psychological benefits, including restoration of near-normal blood flow to lower extremities and holding of bone density decline.
Walking performance with the Parastep system greatly depends on rigorous upper body conditioning-training and on a completing 3–5 months of a daily one–two-hour training program which includes 30 of more minutes of treadmill training.
An alternative approach to the above techniques is the FES system for walking developed using the Compex Motion neuroprosthesis, by Popovic et al. The Compex Motion neuroprosthesis for walking is an eight to sixteen channel surface FES system used to restore voluntary walking in stroke and spinal cord injury individuals. This system does not apply peroneal nerve stimulation to enable locomotion. Instead, it activates all relevant lower limb muscles in a sequence similar to the one that brain uses to enable locomotion. The hybrid assistive systems (HAS) and the RGO walking neuroprostheses are devices that also apply active and passive braces, respectively. The braces were introduced to provide additional stability during standing and walking. A major limitation of neuroprostheses for walking that are based on surface stimulation is that the hip flexors cannot be stimulated directly. Therefore, hip flexion during walking must come from voluntary effort, which is often absent in paraplegia, or from the flexor withdrawal reflex. Implanted systems have the advantage of being able to stimulate the hip flexors, and therefore, to provide better muscle selectivity and potentially better gait patterns. Hybrid systems with exoskeleton have been also proposed to solve this problem. These technologies have been found to be successful and promising, but at the present time these FES systems are mostly used for exercise purposes and seldom as an alternative to wheelchair mobility.
=== Stroke and upper limb recovery ===
Peripheral nerves have a regeneration rate of ~1mm per day. With nerve injury often requiring a large distance of restoration, down-regulation of regenerative mechanisms over time limits nerve proliferation. In the acute stage of stroke recovery, the use of cyclic electrical stimulation has been seen to increase the isometric strength of wrist extensors. In order to increase strength of wrist extensors, there must be a degree of motor function at the wrist spared following the stroke and have significant hemiplegia. Patients who will elicit benefits of cyclic electrical stimulation of the wrist extensors must be highly motivated to follow through with treatment. After 8 weeks of electrical stimulation, an increase in grip strength can be apparent. Many scales, which assess the level of disability of the upper extremities following a stroke, use grip strength as a common item. Therefore, increasing strength of wrist extensors will decrease the level of upper extremity disability.
Patients with hemiplegia following a stroke commonly experience shoulder pain and subluxation; both of which will interfere with the rehabilitation process. Functional electrical stimulation has been found to be effective for the management of pain and reduction of shoulder subluxation, as well as accelerating the degree and rate of motor recovery. Furthermore, the benefits of FES are maintained over time; research has demonstrated that the benefits are maintained for at least 24 months.
A systematic review was done to assess three types of functional electronic stimulation (FES) used in post stroke upper limb rehab and compare them to patients that did not use any FES. The types focused on were manual FES, BCI-FES, and EMG-FES. Studies showed that when comparing clinical scores in post stroke patients who used FES versus patients that did not, the patients that used FES had more functional benefits. The scores suggested that FES decreases spasticity of wrist flexors as compared to non-FES and motor outcomes showed improved recovery in upper extremities, specifically when using the BCI-FES system. In the end the study showed that it is difficult to say which specific FES system is best. Many research studies showed that closed-loop FES, or BCI/EMG, are more beneficial than open-loop FES, or manual, for motor recovery. Among closed-loop FES, which system is more effective (either BCI-FES or EMG-FES) remains unspecified, because as of right now no randomized controlled clinical trial has been conducted to directly compare the two and their benefits when in the context of neurorehabilitation. An open-loop FES has been widely used clinically for many years when treating post stroke patients, whereas closed-loop FES is typically applied in the laboratory setting as a research protocol (especially BCI-FES).
=== Drop foot ===
Drop foot is a common symptom in hemiplegia, characterized by a lack of dorsiflexion during the swing phase of gait, resulting in short, shuffling strides. It has been shown that FES can be used to effectively compensate for the drop foot during the swing phase of the gait. At the moment just before the heel off phase of gait occurs, the stimulator delivers a stimulus to the common peroneal nerve, which results in contraction of the muscles responsible for dorsiflexion. There are currently a number of drop foot stimulators that use surface and implanted FES technologies. Drop foot stimulators have been used successfully with various patient populations, such as stroke, spinal cord injury and multiple sclerosis.
The term "orthotic effect" can be used to describe the immediate improvement in function observed when the individual switches on their FES device compared to unassisted walking. This improvement disappears as soon as the person switches off their FES device. In contrast, a "training" or "therapeutic effect" is used to describe a long term improvement or restoration of function following a period of using the device which is still present even when the device is switched off. A further complication to measuring an orthotic effect and any long term training or therapeutic effects is the presence of a so-called "temporary carry over effect". Liberson et al., 1961 was the first to observe that some stroke patients appeared to benefit from a temporary improvement in function and were able to dorsiflex their foot for up to an hour after the electrical stimulation had been turned off. It has been hypothesised that this temporary improvement in function may be linked to a long term training or therapeutic effect.
=== Stroke ===
Hemiparetic stroke patients, who are impacted by the denervation, muscular atrophy, and spasticity, typically experience an abnormal gait pattern due to muscular weakness and the incapacity to voluntary contract certain ankle and hip muscles at the appropriate walking phase. Liberson et al. (1961) were the first to pioneer FES in stroke patients. More recently, there have been a number of studies that have been conducted in this area. A systematic review conducted in 2012 on the use of FES in chronic stroke included seven randomized controlled trials with a total of 231 participants. The review found a small treatment effect for using FES for the 6-minute walking test.
=== Multiple sclerosis ===
FES has also been found to be useful for treating foot drop in people with multiple sclerosis. The first use was reported in 1977 by Carnstam et al., who found that it was possible to generate strength increases through using peroneal stimulation. A more recent study examined the use of FES compared to an exercise group and found that although there was an orthotic effect for the FES group, no training effect in walking speed was found. Further qualitative analysis including all participants from the same study found improvements in activities of daily living and a reduced number of falls for those using FES compared with exercise. A further small scale (n=32) longitudinal observational study has found evidence for a significant training effect through using FES.
With NMES treatment there were measurable gains in ambulatory function.
However, a further large observational study (n=187) was supportive of previous findings and found a significant improvement in orthotic effect for walking speed.
=== Cerebral palsy ===
FES has been found to be useful for treating the symptoms of cerebral palsy. A recent randomised controlled trial (n=32) found significant orthotic and training effects for children with unilateral spastic cerebral palsy. Improvements were found in gastrocnemius spasticity, community mobility and balance skills. A recent comprehensive literature review of the area of using electrical stimulation and FES to treat children with disabilities mostly included studies on children with cerebral palsy. The reviewers summarised the evidence as the treatment having the potential to improve a number of different areas including muscle mass and strength, spasticity, passive range of motion, upper extremity function, walking speed, positioning of the foot and ankle kinematics. The review further concludes that adverse events were rare and the technology is safe and well tolerated by this population. The applications of FES for children with cerebral palsy are similar to those for adults. Some common applications of FES devices include stimulation of muscles whilst mobilizing to strengthen muscle activity, to reduce muscle spasticity, to facilitate initiation of muscle activity, or to provide a memory of movement.
=== National Institute for Health and Care Excellence Guidelines (NICE) (UK) ===
NICE have issued full guidelines on the treatment of drop foot of central neurological origin (IPG278). NICE have stated that "current evidence on the safety and efficacy (in terms of improving gait) of functional electrical stimulation (FES) for drop foot of central neurological origin appears adequate to support the use of this procedure provided that normal arrangements are in place for clinical governance, consent and audit".
== In popular culture ==
Mark Coggins' novel No Hard Feelings (2015) features a female protagonist with a spinal cord injury who regains mobility via advanced FES technology developed by a fictional biomedical startup.
== See also ==
Electrical muscle stimulation
Electrotherapy
Cleveland FES Center
Shannon Criteria
== References ==
== Further reading ==
Chudler, Eric H. "Neuroscience For Kids - Cells of the Nervous System." UW Faculty Web Server. Eric H. Chudler, 1 June 2011. Web. 7 June 2011.<http://faculty.washington.edu/chudler/cells.html>.
Cooper E.B., Scherder E.J.A., Cooper J.B (2005) "Electrical treatment of reduced consciousness: experience with coma and Alzheimer's disease," Neuropsyh Rehab (UK).Vol. 15,389-405.
Cooper E.B, Cooper J.B. (2003). "Electrical treatment of coma via the median nerve". In Y. Katayama (ed.). Neurosurgical Re-Engineering of the Damaged Brain and Spinal Cord. Acta Neurochirurgica Supplements. Vol. 87. pp. 7–10. doi:10.1007/978-3-7091-6081-7_2. ISBN 978-3-7091-7223-0. PMID 14518514.
"FEScenter.org » Cleveland FES Center." FEScenter.org » Home. Cleveland VA Medical Center, Case Western Reserve University, MetroHealth Medical Center, 3 June 2011. Web. 8 June 2011. <http://fescenter.org/index.php?option=com_content>
Graupe D (2002). "An overview of the state of the art of noninvasive FES for independent ambulation by thoracic level paraplegics". Neurological Research. 24 (5): 431–442. doi:10.1179/016164102101200302. PMID 12117311. S2CID 29537770.
Graupe D, Cerrel-Bazo H, Kern H, Carraro U (2008). "Walking Performance, Medical Outcomes and Patient Training in FES of Innervated Muscles for Ambulation by Thoracic-Level Complete Paraplegics". Neurol. Res. 31 (2): 123–130. doi:10.1179/174313208X281136. PMID 18397602. S2CID 34621751.
Johnston, Laurance. "FES." Human Spinal Cord Injury: New & Emerging Therapies. Institute of Spinal Cord Injury, Iceland. Web. 7 June 2011. Web site.
Lichy A., Libin A., Ljunberg I., Groach L., (2007) " Preserving bone health after acute spinal cord injury: Differential responses to a neuromuscular electrical stimulation intervention", Proc. 12th Annual Conf. of the International FES Soc., Philadelphia, PA, Session 2, Paper 205.
Liu Yi-Liang, Ling Qi-Dan, Kang En-Tang, Neoh Koon-Gee, Liaw Der-Jang, Wang Kun-Li, Liou Wun-Tai, Zhu Chun-Xiang, Siu-Hung Chan Daniel (2009). "Volatile Electrical Switching in a Functional Polyimide Containing Electron-donor and -acceptor Moieties". Journal of Applied Physics. 105 (4): 1–9. Bibcode:2009JAP...105d4501L. doi:10.1063/1.3077286.{{cite journal}}: CS1 maint: multiple names: authors list (link)
Nolte, John, and John Sundsten. The Human Brain: an Introduction to Its Functional Anatomy. 5th ed. St. Louis: Mosby, 2002.
Rosenzweig, Mark R., Arnold L. Leiman, and S. Marc. Breedlove. Biological Psychology. Sunderland: Sinauer Associates, 2003.
Wilkenfeld Ari J., Audu Musa L., Triolo Ronald J. (2006). "Feasibility of Functional Electrical Stimulation for Control of Seated Posture after Spinal Cord Injury: A Simulation Study". The Journal of Rehabilitation Research and Development. 43 (2): 139–43. doi:10.1682/jrrd.2005.06.0101. PMID 16847781.{{cite journal}}: CS1 maint: multiple names: authors list (link)
Yuan Wang, Ming Zhang, Rana Netra, Hai Liu, Chen-wang Jin, Shao-hui Ma (2010). "A Functional Magnetic Resonance Imaging Study of Human Brain in Pain-related Areas Induced by Electrical Stimulation with Different Intensities". Neurology India. 58 (6): 922–27. doi:10.4103/0028-3886.73748. PMID 21150060.{{cite journal}}: CS1 maint: multiple names: authors list (link)
== External links ==
History of Functional Electrical Stimulation, 1998
Back From the Dead, Wired Magazine
Functional electrical stimulation (FES) factsheet | Wikipedia/Functional_electrical_stimulation |
Photothermal therapy (PTT) refers to efforts to use electromagnetic radiation (most often in infrared wavelengths) for the treatment of various medical conditions, including cancer. This neurotherapy is an extension of photodynamic therapy, in which a photosensitizer is excited with specific band light. This activation brings the sensitizer to an excited state where it then releases vibrational energy (heat), which is what kills the targeted cells.
Unlike photodynamic therapy, photothermal therapy does not require oxygen to interact with the target cells or tissues. Current studies also show that photothermal therapy is able to use longer wavelength light, which is less energetic and therefore less harmful to other cells and tissues.
== Nanoscale materials ==
Most materials of interest currently being investigated for photothermal therapy are on the nanoscale. One of the key reasons behind this is the enhanced permeability and retention effect observed with particles in a certain size range (typically 20–300 nm). Molecules in this range have been observed to preferentially accumulate in tumor tissue. When a tumor forms, it requires new blood vessels in order to fuel its growth; these new blood vessels in/near tumors have different properties as compared to regular blood vessels, such as poor lymphatic drainage and a disorganized, leaky vasculature. These factors lead to a significantly higher concentration of certain particles in a tumor as compared to the rest of the body.
=== Gold NanoRods (AuNR) ===
Huang et al. investigated the feasibility of using gold nanorods for both cancer cell imaging as well as photothermal therapy. The authors conjugated antibodies (anti-EGFR monoclonal antibodies) to the surface of gold nanorods, allowing the gold nanorods to bind specifically to certain malignant cancer cells (HSC and HOC malignant cells). After incubating the cells with the gold nanorods, an 800 nm Ti:sapphire laser was used to irradiate the cells at varying powers. The authors reported successful destruction of the malignant cancer cells, while nonmalignant cells were unharmed.
When AuNRs are exposed to NIR light, the oscillating electromagnetic field of the light causes the free electrons of the AuNR to collectively coherently oscillate. Changing the size and shape of AuNRs changes the wavelength that gets absorbed. A desired wavelength would be between 700-1000 nm because biological tissue is optically transparent at these wavelengths. While all AuNP are sensitive to change in their shape and size, Au nanorods properties are extremely sensitive to any change in any of their dimensions regarding their length and width or their aspect ratio. When light is shone on a metal NP, the NP forms a dipole oscillation along the direction of the electric field. When the oscillation reaches its maximum, this frequency is called the surface plasmon resonance (SPR). AuNR have two SPR spectrum bands: one in the NIR region caused by its longitudinal oscillation which tends to be stronger with a longer wavelength and one in the visible region caused by the transverse electronic oscillation which tends to be weaker with a shorter wavelength. The SPR characteristics account for the increase in light absorption for the particle. As the AuNR aspect ratio increases, the absorption wavelength is redshifted and light scattering efficiency is increased. The electrons excited by the NIR lose energy quickly after absorption via electron-electron collisions, and as these electrons relax back down, the energy is released as a phonon that then heats the environment of the AuNP which in cancer treatments would be the cancerous cells. This process is observed when a laser has a continuous wave onto the AuNP. Pulsed laser light beams generally results in the AuNP melting or ablation of the particle. Continuous wave lasers take minutes rather than a single pulse time for a pulsed laser, continues wave lasers are able to heat larger areas at once.
=== Gold Nanoshells ===
Gold nanoshells, coated silica nanoparticles with a thin layer of gold. have been conjugated to antibodies (anti-HER2 or anti-IgG) via PEG linkers. After incubation of SKBr3 cancer cells with the gold nanoshells, an 820 nm laser was used to irradiate the cells. Only the cells incubated with the gold nanoshells conjugated with the specific antibody (anti-HER2) were damaged by the laser. Another category of gold nanoshells are gold layer on liposomes, as soft template. In this case, drug can also be encapsulated inside and/or in bilayer and the release can be triggered by laser light.
=== thermo Nano-Architectures (tNAs) ===
The failure of clinical translation of nanoparticles-mediated PTT is mainly ascribed to concerns about their persistence in the body. Indeed, the optical response of anisotropic nanomaterials can be tuned in the NIR region by increasing their size to up to 150 nm. On the other hand, body excretion of non-biodegradable noble metals nanomaterials above 10 nm occurs through the hepatobiliary route in a slow and inefficient manner. A common approach to avoid metal persistence is to reduce the nanoparticles size below the threshold for renal clearance, i.e. ultrasmall nanoparticles (USNPs), meanwhile the maximum light-to-heat transduction is for < 5 nm nanoparticles. On the other hand, the surface plasmon of excretable gold USNPs is in the UV/visible region (far from the first biological windows), severely limiting their potential application in PTT.
Excretion of metals has been combined with NIR-triggered PTT by employing ultrasmall-in-nano architectures composed by metal USNPs embedded in biodegradable silica nanocapsules. tNAs are the first reported NIR-absorbing plasmonic ultrasmall-in-nano platforms that jointly combine: i) photothermal conversion efficacy suitable for hyperthermia, ii) multiple photothermal sequences and iii) renal excretion of the building blocks after the therapeutic action. Nowadays, tNAs therapeutic effect has been assessed on valuable 3D models of human pancreatic adenocarcinoma.
=== Graphene and graphene oxide ===
Graphene is viable for photothermal therapy. An 808 nm laser at a power density of 2 W/cm2 was used to irradiate the tumor sites on mice for 5 minutes. As noted by the authors, the power densities of lasers used to heat gold nanorods range from 2 to 4 W/cm2. Thus, these nanoscale graphene sheets require a laser power on the lower end of the range used with gold nanoparticles to photothermally ablate tumors.
In 2012, Yang et al. incorporated the promising results regarding nanoscale reduced graphene oxide reported by Robinson et al. into another in vivo mice study.< The therapeutic treatment used in this study involved the use of nanoscale reduced graphene oxide sheets, nearly identical to the ones used by Robinson et al. (but without any active targeting sequences attached). Nanoscale reduced graphene oxide sheets were successfully irradiated in order to completely destroy the targeted tumors. Most notably, the required power density of the 808 nm laser was reduced to 0.15 W/cm2, an order of magnitude lower than previously required power densities. This study demonstrates the higher efficacy of nanoscale reduced graphene oxide sheets as compared to both nanoscale graphene sheets and gold nanorods.
=== Conjugated polymers (CPs) ===
PTT utilizes photothermal transduction agents (PTAs) which can transform light energy to heat through photothermal effect to raise the temperature of tumor area and thus cause the ablation of tumor cells. Specifically, ideal PTAs should have high photothermal conversion efficiency (PCE), excellent optical stability and biocompatibility, and strong light adsorption in the near-infrared (NIR) region (650-1350 nm) due to the deep-tissue penetration and minimal absorption of NIR light in the biological tissues. PTAs mainly include inorganic materials and organic materials. Inorganic PTAs, such as noble metal materials, carbon-based nanomaterials, and other 2D materials, have high PCE and excellent photostability, but they are not biodegradable and thus have potential long-term toxicity in vivo. Organic PTAs including small molecule dyes and conjugated polymers (CPs) have good biocompatibility and biodegradability, but poor photostability. Among them, small molecule dyes, such as cyanine, porphyrin, phthalocyanine, are limited in the field of cancer treatment because of their susceptibility to photobleaching and poor tumor enrichment ability. Conjugated polymers with large π−π conjugated skeleton and a high electron delocalization structure show potential for PTT due to their strong NIR absorption, excellent photostability, low cytotoxicity, outstanding PCE, good dispersibility in aqueous medium, increased accumulation at tumor site, and long blood circulation time. Moreover, conjugated polymers can be easily combined with other imaging agents and drugs to construct multifunctional nanomaterials for selective and synergistic cancer therapy.
The CPs used for tumor PTT mainly include polyaniline (PANI), polypyrrole (PPy), polythiophene (PTh), polydopamine (PDA), donor−acceptor (D-A) conjugated polymers, and poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS).
==== Photothermal conversion mechanism ====
The nonradiative process for heat generation of organic PTAs is different from that of inorganic PTAs such as metals and semiconductors which is related with surface plasmon resonance. As shown in the figure, conjugated polymers are first activated to the excited state (S1) under light irradiation and then excited state (S1) decays back to the ground state (S0) via three processes: (I) emitting a photon (fluorescence), (II) intersystem crossing, and (III) nonradiative relaxation (heat generation). Because these three pathways of the S1 decaying back to the S0 are usually competitive in photosensitive materials, light emitting and intersystem crossing must be efficiently reduced in order to increase the heat generation and improve the photothermal conversion efficiency. For conjugated polymers, on the one hand, their unique structures lead to closed stacking of the molecular sensitizers with highly frequent intermolecular collisions which can efficiently quench the fluorescence and intersystem crossing, and thus enhance the yield of nonradiative relaxation. On the other hand, compared with monomeric phototherapeutic molecules, conjugated polymers possess higher stability in vivo against disassembly and photobleaching, longer blood circulation time, and more accumulation at tumor site due to the enhanced permeability and retention (EPR) effect. Therefore, conjugated polymers have high photothermal conversion efficiency and a large amount of heat generation. One of the most widely used equations to calculate photothermal conversion efficiency (η) of organic PTAs is as follows:
η = (hAΔΤmax-Qs)/I(1-10-Aλ)
where h is the heat transfer coefficient, A is the container surface area, ΔΤmax means the maximum temperature change in the solution, Aλ means the light absorbance, I is the laser power density, and Qs is the heat associated with the light absorbance of the solvent.
Furthermore, various efficient methods, especially donor-acceptor (D-A) strategy, have been designed to enhance the photothermal conversion efficiency and heat generation of conjugated polymers. The D-A assembly system in the conjugated polymers contributes to strong intermolecular electron transfer from the donor to the acceptor, thus bringing efficient fluorescence and intersystem crossing quenching, and improved heat generation. In addition, the HOMO-LUMO gap of the D−A conjugated polymers can be easily tuned through changing the selection of electron donor (ED) and electron acceptor (EA) moieties, and thus D−A structured polymers with extremely low band gap can be developed to improve the NIR absorption and photothermal conversion efficiency of CPs.
==== Polyaniline (PANI) ====
Polyaniline (PANI) is one of the earliest types of conjugated polymers reported for tumor PTT.
==== Polypyrrole (PPy) ====
Polypyrrole (PPy) is suited for PTT applications because of its strong NIR absorbance, large PCE, stability, and biocompatibility. In vivo experiments show that tumors treated with PPy NPs could be effectively eliminated under the irradiation of an 808 nm laser (1 W cm−2, 5 min). PPy nanosheets exhibit promising photothermal ablation ability toward cancer cells in the NIR II window for deep-tissue PTT.
PPy nanoparticles and its derivative nanomaterials can also be combined with imaging contrast agents and diverse drugs to construct multifunctional theranostic applications in imaging-guided PTT and synergistic treatment, including fluorescent imaging, magnetic resonance imaging (MRI), photoacoustic imaging (PA), computed tomography (CT), photodynamic therapy (PDT), chemotherapy, etc. For example, PPy has been used to encapsulate ultrasmall iron oxide nanoparticles (IONPs) and finally develop IONP@PPy NPs for in vivo MR and PA imaging-guided PTT. Polypyrrole (I-PPy) nanocomposites have been investigated for CT imaging-guided tumor PTT.
==== Polythiophene (PTh) ====
Polythiophene (PTh) and its derivatives-based polymers are also one kind of conjugated polymers for PTT. Polythiophene-based polymers usually exhibit excellent photostability, large light-harvesting ability, easy synthesis, and facile functionalization with different substituents.
Conjugated copolymer (C3) with promising photothermal properties can be prepared by linking 2-N,N′-bis(2-(ethyl)hexyl)-perylene-3,4,9,10-tetra-carboxylic acid bis-imide to a thienylvinylene oligomer. C3 was coprecipitated with PEG-PCL and indocyanine green (ICG) to obtain PEG-PCL-C3-ICG nanoparticles for fluorescence-guided photothermal/photodynamic therapy against oral squamous cell carcinoma (OSCC). A biodegradable PLGA-PEGylated DPPV (poly{2,2′-[(2,5-bis(2-hexyldecyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]-pyrrole-1,4-diyl)-dithiophene]-5,5′-diyl-alt-vinylene) conjugated polymer for PA-guided PTT with PCE 71% (@ 808 nm, 0.3 W cm−2). The vinylene bonds in the main chain improves the biodegradability, biocompatibility and photothermal conversion efficiency of CPs.
==== Polydopamine (PDA) ====
Dopamine is one of neurotransmitters in the body which helps cells send impulses. Polydopamine (PDA) is obtained through the self-aggregation of dopamine to form a melanin-like substance under mild alkaline conditions. PDA has strong NIR absorption, good photothermal stability, excellent biocompatibility and biodegradability, and high photothermal conversion efficiency. Furthermore, with π conjugated structure and different active groups, PDA can be easily combined with various materials to achieve multifunction, such as fluorescence imaging, MRI, CT, PA, targeted therapy etc. In view of this, PDA and its composite nanomaterials have a broad application prospect in the biomedical field.
Dopamine-melanin colloidal nanospheres is an efficient near-infrared photothermal therapeutic agent for in vivo cancer therapy. PDA can also be modified on the surface of other PTAs, such as gold nanorods, carbon-based materials, to enhance the photothermal stability and efficiency in vivo. For example, PDA-modified spiky gold nanoparticles (SGNP@PDAs) have been investigated for chemo-photothermal therapy.
==== Donor−Acceptor (D−A) CPs ====
Donor−acceptor (D−A) conjugated polymers have been investigated for the medicinal purposes. Nano-PCPDTBT CPs have two moieties: 2-ethylhexyl cyclopentadithiophene and 2,1,3-benzothiadiazole. When the PCPDTBT nanoparticle solution (0.115 mg/mL) was exposed to an 808 nm NIR laser (0.6 W/cm2), the temperature could be increased by more than 30 °C. Wang et al. designed four NIR-absorbing D-A structured conjugated polymer dots (Pdots) containing diketopyrrolo-pyrrole (DPP) and thiophene units as effective photothermal materials with the PCE up to 65% for in vivo cancer therapy. Zhang et al. constructed PBIBDF-BT D-A CPs by using isoindigo derivative (BIBDF) and bithiophene (BT) as EA and ED respectively. PBIBDF-BT was further modified with poly(ethylene glycol)-block-poly(hexyl ethylene phosphate) (mPEG-b-PHEP) to obtain PBIBDF-BT@NP PPE with PCE of 46.7% and high stability in physiological environment. Yang’s group designed PBTPBF-BT CPs, in which the bis(5-oxothieno[3,2-b]pyrrole-6-ylidene)-benzodifurandione (BTPBF) and the 3,3′-didodecyl-2,2′-bithiophene (BT) units acting as EA and ED respectively. The D-A CPs have a maximum absorption peak at 1107 nm and a relative high photothermal conversion efficiency (66.4%). Pu et al. synthesized PC70BM-PCPDTBT D-A CPs via nanoprecipitation of EA (6,6)-phenyl-C71-butyric acid methyl ester (PC70BM) and ED PCPDTBT (SPs) for PA-guided PTT. Wang et al. developed D-A CPs TBDOPV-DT containing thiophene-fused benzodifurandione-based oligo(p-phenylenevinylene) (TBDOPV) as EA unit and 2,2′-bithio-phene (DT) as ED unit. TBDOPV-DT CPs have a strong absorption at 1093 nm and achieve highly efficient NIR-II photothermal conversion.
==== PEDOT:PSS ====
Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) is often used in organic electronics and have strong NIR absorption. In 2012, Liu’s group first reported PEGylated PEDOT:PSS polymeric nanoparticle (PEDOT:PSS-PEG) for near-infrared photothermal therapy of cancer. PEDOT:PSS-PEG nanoparticles have high stability in vivo and long blood circulation half-life of 21.4 ± 3.1 h. The PTT in animals showed no appreciable side effects for the tested dose and an excellent therapeutic efficacy under the 808 nm laser irradiation. Kang et al. synthesized magneto-conjugated polymer core−shell MNP@PEDOT:PSS nanoparticles for multimodal imaging-guided PTT. Furthermore, PEDOT:PSS NPs can not only serve as PTAs but also as a drug carrier to load various types of drugs, such as SN38, chemotherapy drugs DOX and photodynamic agent chlorin e6 (Ce6), thus achieving synergistic cancer therapy.
== See also ==
Photomedicine
Light Therapy
Hyperthermia therapy
Experimental cancer treatment
== References ==
== Further reading == | Wikipedia/Photothermal_therapy |
PUVA (psoralen and UVA) is an ultraviolet light therapy treatment for skin diseases: vitiligo, eczema, psoriasis, graft-versus-host disease, mycosis fungoides, large plaque parapsoriasis, and cutaneous T-cell lymphoma, using the sensitizing effects of the drug psoralen.: 686 The psoralen is applied or taken orally to sensitize the skin, then the skin is exposed to UVA.
Photodynamic therapy is the general use of nontoxic light-sensitive compounds that are exposed selectively to light, whereupon they become toxic to targeted malignant and other diseased cells. Still, PUVA therapy is often classified as a separate technique from photodynamic therapy.
== Procedure ==
Psoralens are materials that make the skin more sensitive to UV light. They are photosensitizing agents found in plants naturally and manufactured synthetically. Psoralens are taken as pills (systemically) or can be applied directly to the skin, by soaking the skin in a solution that contains the psoralens. They allow UVA energy to be effective at lower doses. When combined with exposure to the UVA in PUVA, psoralens are highly effective at clearing psoriasis and vitiligo. In the case of vitiligo, they work by increasing the sensitivity of melanocytes, the cells that manufacture skin color, to UVA light. Melanocytes have sensors that detect UV light and trigger the manufacture of brown skin color. This color protects the body from the harmful effects of UV light. It can also be connected to the skin's immune response.
LED PUVA lamps give much more intense light compared to fluorescent type lamps. This reduces the treatment time, makes the treatment more effective, and enables the use of a weaker psoralen.
The physician and physiotherapists can choose a starting dose of UV based on the patient's skin type. The UV dose will be increased in every treatment until the skin starts to respond, normally when it becomes a little bit pink.
Normally the UVA dose is increased slowly, starting from 10 seconds and increased by 10 seconds a day, until the skin becomes a little bit pink. When the skin is little bit pink the time should be steady.
To reduce the number of treatments, some clinics test the skin before the treatments, by exposing a small area of the patient's skin to UVA, after ingestion of psoralen. The dose of UVA that produces redness 12 hours later, called the minimum phototoxic dose (MPD), or minimal erythema dose (MED) becomes the starting dose for treatment.
=== Comparison with narrowband UVB therapy ===
At least for vitiligo, narrowband ultraviolet B (UVB) nanometer phototherapy is now used more commonly than PUVA since it does not require the use of the psoralen and is easier to use with larger involved areas. As with PUVA, treatment is carried out twice per week in a clinic or every day at home, and there is no need to use psoralen.
Narrowband UVB therapy is less effective for the legs and hands, compared to the face and neck. To the hands and legs PUVA may be more effective. The reason can be because UVA penetrates deeper in the skin, and the melanocytes in the skin of the hands and legs are positioned deeper in the skin. Narrowband UVB 311 nanometer is blocked by the topmost skin layer, and UVA 365 nanometer reaches the melanocytes that are in the bottom skin layer.
Melanin is a dark pigment of the skin and the melanocytes produce it. The melanocytes produce melanin when their receptors detect UV light. The purpose of the melanin is to block UV light so that it will not cause damage to the body cells under the skin.
== Side effects and complications ==
For small spots of vitiligo, it is possible to use psoralen as drops, applied only on the spots. This method does not have side effects since the amount is very low.
For larger area, the psoralen is taken as a pill, and the amount is high (10 mg); some patients experience nausea and itching after ingesting the psoralen compound. For these patients PUVA bath therapy may be a good option.
Long term use of PUVA therapy with a pill has been associated with higher rates of skin cancer.
The most significant complication of PUVA therapy for psoriasis is squamous cell skin cancer. Two carcinogenic components of the therapy include the nonionizing radiation of UVA light as well as the psoralen intercalation with DNA. Both processes negatively contribute to genome instability.
== History ==
In Egypt around 2000 BC, the juice of Ammi majus was rubbed on patches of vitiligo after which patients were encouraged to lie in the sun. In the 13th century, vitiligo was treated with a tincture of honey and the powdered seeds of a plant called "aatrillal", which was abundant in the Nile Valley. The plant has since been identified as A. majus, which contains significant amounts of both bergapten and methoxsalen, two psoralen derivatives well known for their photosensitizing effects.
In the 1890s Niels Ryberg Finsen of Copenhagen developed a bulky phototherapy machine to treat skin diseases using UV light. In 1900, the French electrical engineer Gustave Trouvé miniaturized Finsen's machine with a series of portable light radiators to heal skin diseases such as lupus and epithelioma. Such machines have only been available in a chemically synthesized form since the 1970s.
In the 1940s, Abdel Monem El Mofty from Cairo University Medical School used crystalline methoxsalen (8-methoxypsoralen, also called xanthotoxin) followed by sunlight exposure to treat vitiligo. This began the development of modern PUVA therapy for the treatment of vitiligo, psoriasis, and other diseases of the skin.
== See also ==
Goeckerman therapy
PUVA lentigines
== References ==
== External links ==
Phototherapy Course, New Zealand Dermatological Society
PUVA Therapy Description at Oxsoralen-Ultra Indications
Light Therapy for Dermatologic Conditions at Blue Cross and Blue Shield Association of North Carolina | Wikipedia/PUVA_therapy |
Electroconvulsive therapy (ECT) is a psychiatric treatment that causes a generalized seizure by passing electrical current through the brain. ECT is often used as an intervention for mental disorders when other treatments are inadequate. Conditions responsive to ECT include major depressive disorder, mania, and catatonia.
The general physical risks of ECT are similar to those of brief general anesthesia.: 259 Immediately following treatment, the most common adverse effects are confusion and transient memory loss. Among treatments for severely depressed pregnant women, ECT is one of the least harmful to the fetus.
The usual course of ECT involves multiple administrations, typically given two or three times per week until the patient no longer has symptoms. ECT is administered under anesthesia with a muscle relaxant. ECT can differ in its application in three ways: electrode placement, treatment frequency, and the electrical waveform of the stimulus. Differences in these parameters affect symptom remission and adverse side effects.
Placement can be bilateral, where the electric current is passed from one side of the brain to the other, or unilateral, in which the current is solely passed across one hemisphere of the brain. High-dose unilateral ECT has some cognitive advantages compared to moderate-dose bilateral ECT while showing no difference in antidepressant efficacy.
== History ==
As early as the 16th century, agents to induce seizures were used to treat psychiatric conditions. In 1785, the therapeutic use of seizure induction was documented in the London Medical and Surgical Journal. As to its earliest antecedents one doctor claims 1744 as the dawn of electricity's therapeutic use, as documented in the first issue of Electricity and Medicine. Treatment and cure of hysterical blindness was documented eleven years later. Benjamin Franklin wrote that an electrostatic machine cured "a woman of hysterical fits." By 1801, James Lind as well as Giovanni Aldini had used galvanism to treat patients with various mental disorders. G.B.C. Duchenne, the mid-19th century "Father of Electrotherapy", said its use was integral to a neurological practice.
In the second half of the 19th century, such efforts were frequent enough in British asylums as to make it notable.
Convulsive therapy was introduced in 1934 by Hungarian neuropsychiatrist Ladislas J. Meduna who, believing mistakenly that schizophrenia and epilepsy were antagonistic disorders, induced seizures first with camphor and then metrazol (cardiazol). Meduna is thought to be the father of convulsive therapy.
In 1937, the first international meeting on schizophrenia and convulsive therapy was held in Switzerland by the Swiss psychiatrist Max Müller. The proceedings were published in the American Journal of Psychiatry and, within three years, cardiazol convulsive therapy was being used worldwide.
The ECT procedure was first conducted in 1938 by Italian neuro-psychiatrist Ugo Cerletti and rapidly replaced less safe and effective forms of biological treatments in use at the time. Cerletti, who had been using electric shocks to produce seizures in animal experiments, and his assistant Lucio Bini at Sapienza University of Rome developed the idea of using electricity as a substitute for metrazol in convulsive therapy and, in 1938, experimented for the first time on a person affected by delusions.
It was believed early on that inducing convulsions aided in helping those with severe schizophrenia but later found to be most useful with affective disorders such as depression. Cerletti had noted a shock to the head produced convulsions in dogs. The idea to use electroshock on humans came to Cerletti when he saw how pigs were given an electric shock before being butchered to put them in an anesthetized state. Cerletti and Bini practiced until they felt they had the right parameters needed to have a successful human trial. Once they started trials on patients, they found that after 10–20 treatments the results were significant. Patients had much improved.
A positive side effect to the treatment was retrograde amnesia. It was because of this side effect that patients could not remember the treatments and had no ill feelings toward it.
ECT soon replaced metrazol therapy all over the world because it was cheaper, less frightening and more convenient. Cerletti and Bini were nominated for a Nobel Prize but did not receive one. By 1940, the procedure was introduced to both England and the US. In Germany and Austria, it was promoted by Friedrich Meggendorfer. Through the 1940s and 1950s, the use of ECT became widespread. At the time the ECT device was patented and commercialized abroad, the two Italian inventors had competitive tensions that damaged their relationship. In the 1960s, despite a climate of condemnation, the original Cerletti-Bini ECT apparatus prototype was contended by scientific museums between Italy and the US. The ECT apparatus prototype is now owned and displayed by the Sapienza Museum of the History of Medicine in Rome.
In the early 1940s, in an attempt to reduce the memory disturbance and confusion associated with treatment, two modifications were introduced: the use of unilateral electrode placement and the replacement of sinusoidal current with brief pulse. It took many years for brief-pulse equipment to be widely adopted.
In the 1940s and early 1950s, ECT was usually given in an "unmodified" form, without muscle relaxants, and the seizure resulted in a full-scale convulsion. A rare but serious complication of unmodified ECT was fracture or dislocation of the long bones. In the 1940s, psychiatrists began to experiment with curare, the muscle-paralysing South American poison, in order to modify the convulsions. The introduction of suxamethonium (succinylcholine), a safer synthetic alternative to curare, in 1951 led to the more widespread use of "modified" ECT. A short-acting anesthetic was usually given in addition to the muscle relaxant in order to spare patients the terrifying feeling of suffocation that can be experienced with muscle relaxants.
The steady growth of antidepressant use along with negative depictions of ECT in the mass media led to a marked decline in the use of ECT during the 1950s to the 1970s. The Surgeon General stated there were problems with electroshock therapy in the initial years before anesthesia was routinely given, and that "these now-antiquated practices contributed to the negative portrayal of ECT in the popular media." The New York Times described the public's negative perception of ECT as being caused mainly by one movie: "For Big Nurse in One Flew Over the Cuckoo's Nest, it was a tool of terror, and, in the public mind, shock therapy has retained the tarnished image given it by Ken Kesey's novel: dangerous, inhumane and overused".
In 1976, Dr. Blatchley demonstrated the effectiveness of his constant current, brief pulse device ECT. This device eventually largely replaced earlier devices because of the reduction in cognitive side effects, although as of 2012 some ECT clinics still were using sine-wave devices.
The 1970s saw the publication of the first American Psychiatric Association (APA) task force report on electroconvulsive therapy (to be followed by further reports in 1990 and 2001). The report endorsed the use of ECT in the treatment of depression. The decade also saw criticism of ECT. Specifically, critics pointed to shortcomings such as noted side effects, the procedure being used as a form of abuse, and uneven application of ECT. The use of ECT declined until the 1980s, "when use began to increase amid growing awareness of its benefits and cost-effectiveness for treating severe depression". In 1985, the National Institute of Mental Health and National Institutes of Health convened a consensus development conference on ECT and concluded that, while ECT was the most controversial treatment in psychiatry and had significant side-effects, it had been shown to be effective for a narrow range of severe psychiatric disorders.
Because of the backlash noted previously, national institutions reviewed past practices and set new standards. In 1978, the American Psychiatric Association released its first task force report in which new standards for consent were introduced and the use of unilateral electrode placement was recommended. The 1985 NIMH Consensus Conference confirmed the therapeutic role of ECT in certain circumstances. The American Psychiatric Association released its second task force report in 1990 where specific details on the delivery, education, and training of ECT were documented. Finally, in 2001 the American Psychiatric Association released its latest task force report. This report emphasizes the importance of informed consent, and the expanded role that the procedure has in modern medicine. By 2017, ECT was routinely covered by insurance companies for providing the "biggest bang for the buck" for otherwise intractable cases of severe mental illness, was receiving favorable media coverage, and was being provided in regional medical centers.
Though ECT use declined with the advent of modern antidepressants, there has been a resurgence of ECT with new modern technologies and techniques. Modern shock voltage is given for a shorter duration of 0.5 milliseconds where conventional brief pulse is 1.5 milliseconds.
In a review from 2022 of neuroimaging studies based on a global data collaboration, ECT was suggested to work via a temporary disruption of neural circuits followed by augmented neuroplasticity and rewiring.
== Modern use ==
ECT is used, where possible, with informed consent in treatment-resistant major depressive disorder, bipolar depression, treatment-resistant catatonia, prolonged or severe mania, and in conditions where "there is a need for rapid, definitive response because of the severity of a psychiatric or medical condition (e.g., when illness is characterized by suicidality, psychosis, stupor, marked psychomotor retardation, depressive delusions or hallucinations, or life-threatening physical exhaustion associated with mania)." It has also been used to treat autism in adults with an intellectual disability, yet findings from a systematic review found this an unestablished intervention.
=== Major depressive disorder ===
For major depressive disorder, despite a Canadian guideline and some experts arguing for using ECT as a first line treatment, ECT is generally used only when one or other treatments have failed, or in emergencies, such as imminent suicide. ECT has also been used in selected cases of depression occurring in the setting of multiple sclerosis, Parkinson's disease, Huntington's chorea, developmental delay, brain arteriovenous malformations, and hydrocephalus.
==== Efficacy ====
A meta-analysis on the effectiveness of ECT in unipolar and bipolar depression indicated that although patients with unipolar depression and bipolar depression responded to other medical treatments very differently, both groups responded equally well to ECT. Overall remission rate for patients given a round of ECT treatment was 50.9% for those with unipolar depression and 53.2% for those with bipolar depression. Most severely depressed patients respond to ECT.
In 2004, a meta-analysis found in terms of efficacy, "a significant superiority of ECT in all comparisons: ECT versus simulated ECT, ECT versus placebo, ECT versus antidepressants in general, ECT versus tricyclics and ECT versus monoamine oxidase inhibitors."
In 2003, the UK ECT Review Group published a systematic review and meta-analysis comparing ECT to placebo and antidepressant drugs. This meta-analysis demonstrated a large effect size (high efficacy relative to the mean in terms of the standard deviation) for ECT versus placebo, and versus antidepressant drugs.
Compared with repetitive transcranial magnetic stimulation (rTMS) for people with treatment-resistant major depressive disorder, ECT relieves depression as shown by reducing the score on the Hamilton Rating Scale for Depression by about 15 points, while rTMS reduced it by 9 points.
Other estimates regarding the response rate in treatment resistant depression vary between 60–80%, with a remission rate of 50–60%. In addition to reducing symptoms of depression and inducing relapse, ECT has also been shown to reduce the risk of suicide, improve functional outcomes and quality of life as well as reduce the risk of re-hospitalization. Efficacy does not depend on depression subtype. With regards to treatment resistant schizophrenia, the response rate is 40–70%.
==== Follow-up ====
There is little agreement on the most appropriate follow-up to ECT for people with major depressive disorder. The initial course of ECT is then transitioned to maintenance ECT, pharmacotherapy or both. When ECT is stopped abruptly, without a bridge to maintenance ECT or medications (usually antidepressants and Lithium), it is associated with a relapse rate of 84%. There is no defined schedule for maintenance ECT, however it is usually started weekly with intervals extended permissibly with the goal of maintaining remission. When ECT is followed by treatment with antidepressants, about 50% of people relapsed by 12 months following successful initial treatment with ECT, with about 37% relapsing within the first 6 months. About twice as many relapsed with no antidepressants. Most of the evidence for continuation therapy is with tricyclic antidepressants; evidence for relapse prevention with newer antidepressants is lacking. Adjunct maintenance ECT paired with cognitive behavioral therapy has also been shown to reduce relapse rates. Maintenance ECT may safely continue indefinitely, with no set maximum treatment interval established.
Lithium has also been found to reduce the risk of relapse, especially in younger patients.
=== Catatonia ===
ECT is generally a second-line treatment for people with catatonia who do not respond to other treatments, but is a first-line treatment for severe or life-threatening catatonia. There is a plethora of evidence for its efficacy, notwithstanding a lack of randomised controlled trials, such that "the excellent efficacy of ECT in catatonia is generally acknowledged". For people with autism spectrum disorders who have catatonia, there is little published evidence about the efficacy of ECT.
=== Mania ===
ECT is used to treat people who have severe or prolonged mania; NICE recommends it only in life-threatening situations or when other treatments have failed and as a second-line treatment for bipolar mania.
=== Schizophrenia ===
ECT is widely used worldwide in the treatment of schizophrenia. However, in North America and Western Europe it is invariably used only in treatment resistant schizophrenia when symptoms show little response to antipsychotics; there is comprehensive research evidence for such practice. It is useful in the case of severe exacerbations of catatonic schizophrenia, whether excited or stuporous. There are also case reports of ECT improving persistent psychotic symptoms associated with stimulant-induced psychosis.
== Effects and adverse effects ==
Aside from effects on the brain, the general risk for adverse effects stemming from ECT are similar to those of brief general anesthesia; a Surgeon General of the United States's report stated that there are "no absolute health contraindications" to its use.: 259 Immediately following treatment, the most common adverse effects are confusion and memory loss. Some patients experience muscle soreness after ECT. Other common adverse effects of ECT include headache, jaw soreness, nausea, vomiting, and fatigue. These side effects are transient and respond to treatment. There is evidence and rationale to support giving low doses of benzodiazepines or lower doses of general anesthetics, which induce sedation but not unconsciousness, to patients to reduce the likelihood of adverse effects of ECT.
While there are no absolute contraindications for ECT, there is an increased risk for patients who have unstable or severe cardiovascular conditions or aneurysms; who have recently had a stroke; who have increased intracranial pressure (for instance, due to a solid brain tumor); who have severe pulmonary conditions; or who are generally at high risk for adverse effects from anesthesia.: 30
In adolescents, ECT is highly efficient for several psychiatric disorders, with few and relatively benign adverse effects.
=== Risk of death ===
A meta-analysis from 2017 found that the death rate of ECT was around 2.1 per 100,000 procedures. A review from 2011 reported an estimated ECT mortality rate of fewer than one death per 73,440 treatments.
=== Cognitive impairment ===
Cognitive impairment sometimes occurs after ECT. The American Psychiatric Association (APA) report in 2001 acknowledged: "In some patients the recovery from retrograde amnesia will be incomplete, and evidence has shown that ECT can result in persistent or permanent memory loss". It is the purported effects of ECT on long-term memory that give rise to much of the concern surrounding its use. However, the methods used to measure memory loss are non-specific, and their application to people with depressive disorders, who have cognitive deficits related to depression, including problems with memory, may further limit their utility.
The acute effects of ECT can include amnesia, both retrograde (for events occurring before the treatment) and anterograde (for events occurring after the treatment). Memory loss and confusion are more pronounced with bilateral electrode placement rather than unilateral and with outdated sine-wave rather than brief-pulse currents. Using either constant or pulsing electrical impulses also varied the memory loss results in patients. Patients who received pulsing electrical impulses, as opposed to a steady flow, seemed to incur less memory loss. The vast majority of modern treatments use brief pulse currents. A greater number of treatments and higher electrical charges (stimulus charges) have also been associated with a greater risk of memory impairment.
Retrograde amnesia is most marked for events occurring in the weeks or months before treatment. Anterograde memory loss usually resolves 2–4 weeks after treatment, whereas retrograde amnesia (which develops gradually after repeated treatments in the initial course) usually takes weeks to months to resolve; amnesia rarely persists for more than 1 year. Retrograde amnesia after ECT usually affects autobiographical memory rather than semantic memory. One published review summarizing the results of questionnaires about subjective memory loss found that between 29% and 55% of respondents believed they experienced long-lasting or permanent memory changes. In 2000, American psychiatrist Sarah Lisanby and colleagues found that bilateral ECT left patients with more persistently impaired memory of public events as compared to right unilateral ECT. However, bilateral ECT may be more efficacious than unilateral in the treatment of mood disorders.
ECT has not been found to increase the risk of dementia or cause structural brain damage.
=== Effects on brain structure ===
Considerable controversy exists over the effects of ECT on brain tissue, although a number of mental health associations—including the APA—have concluded that there is no evidence that ECT causes structural brain damage. A 1999 report by the US Surgeon General states: "The fears that ECT causes gross structural brain pathology have not been supported by decades of methodologically sound research in both humans and animals."
Many expert proponents of ECT maintain that the procedure is safe and does not cause brain damage. Dr. Charles Kellner, a prominent ECT researcher and former chief editor of the Journal of ECT, stated in a 2007 interview that, "There are a number of well-designed studies that show ECT does not cause brain damage and numerous reports of patients who have received a large number of treatments over their lifetime and have suffered no significant problems due to ECT." Kellner cites a study purporting to show an absence of cognitive impairment in eight subjects after more than 100 lifetime ECT treatments. Kellner stated, "Rather than cause brain damage, there is evidence that ECT may reverse some of the damaging effects of serious psychiatric illness." Two meta-analyses find that ECT is associated with brain matter growth.
=== Effects in pregnancy ===
If steps are taken to decrease potential risks, ECT is generally considered relatively safe during all trimesters of pregnancy, particularly when compared to pharmacological treatments. Suggested preparation for ECT during pregnancy includes a pelvic examination, discontinuation of nonessential anticholinergic medication, uterine tocodynamometry, intravenous hydration, and administration of a nonparticulate antacid. During ECT, elevation of the pregnant woman's right hip, external fetal cardiac monitoring, intubation, and avoidance of excessive hyperventilation are recommended. In many instances of active mood disorder during pregnancy, the risks of untreated symptoms may outweigh the risks of ECT. Modifications in technique can minimize potential complications of ECT during pregnancy. The use of ECT during pregnancy requires a thorough evaluation of the patient's capacity for informed consent.
=== Effects on the heart ===
ECT can cause a lack of blood flow and oxygen to the heart, heart arrhythmia, and "persistent asystole". A 2019 systematic review and meta-analysis of 82 studies found that the rate of major adverse cardiac events with ECT was 1 in 39 patients or about 1 in 200 to 500 procedures. The risk of death with ECT however is low. If death does occur, cardiovascular complications are considered as causal in about 30% of individuals.
== Procedure ==
The placement of electrodes, as well as the dose and duration of the stimulation is determined on a per-patient basis.: 1881
In unilateral ECT, both electrodes are placed on the same side of the patient's head. Unilateral ECT may be used first to minimize side effects such as memory loss.
In bilateral ECT, the two electrodes are placed on opposite sides of the head. Usually bitemporal placement is used, whereby the electrodes are placed on the temples. Uncommonly bifrontal placement is used; this involves positioning the electrodes on the patient's forehead, roughly above each eye.
Unilateral ECT is thought to cause fewer cognitive effects than bilateral treatment, but is less effective unless administered at higher doses.: 1881 Most patients in the US and almost all in the UK receive bilateral ECT.
The electrodes deliver an electrical stimulus. The stimulus levels recommended for ECT are in excess of an individual's seizure threshold: about one and a half times seizure threshold for bilateral ECT and up to 12 times for unilateral ECT.: 1881 Below these levels treatment may not be effective in spite of a seizure, while doses massively above threshold level, especially with bilateral ECT, expose patients to the risk of more severe cognitive impairment without additional therapeutic gains. Seizure threshold is determined by trial and error ("dose titration"). Some psychiatrists use dose titration, some still use "fixed dose" (that is, all patients are given the same dose) and others compromise by roughly estimating a patient's threshold according to age and sex. Older men tend to have higher thresholds than younger women, but it is not a hard and fast rule, and other factors, for example drugs, affect seizure threshold.
Immediately prior to treatment, a patient is given a short-acting anesthetic such as methohexital, propofol, etomidate, or thiopental, a muscle relaxant such as suxamethonium (succinylcholine), and occasionally atropine to inhibit salivation.: 1882 Studies have shown that adding ketamine, an NMDA receptor antagonist, to the anesthesia regimen produced greater decreases in depression scores when compared to propofol, methohexital, and thiopental alone. In a minority of countries such as Japan, India, and Nigeria, ECT may be used without anesthesia. The Union Health Ministry of India recommended a ban on ECT without anesthesia in India's Mental Health Care Bill of 2010 and the Mental Health Care Bill of 2013. The practice was abolished in Turkey's largest psychiatric hospital in 2008.
The patient's EEG, ECG, and blood oxygen levels are monitored during treatment.: 1882
ECT is usually administered three times a week, on alternate days, over a course of two to four weeks.: 1882–1883
=== Neuroimaging prior to ECT ===
Neuroimaging prior to ECT may be useful for detecting intracranial pressure or mass given that patients respond less when one of these conditions exist. Nonetheless, it is not indicated due to high cost and low prevalence of these conditions in patients needing ECT.
=== Concurrent pharmacotherapy ===
Whether psychiatric medications are terminated prior to treatment or maintained, varies.: 1885 However, drugs that are known to cause toxicity in combination with ECT, such as lithium, are discontinued, and benzodiazepines, which increase the seizure threshold, are either discontinued, a benzodiazepine antagonist is administered at each ECT session, or the ECT treatment is adjusted accordingly.: 1875, 1879
A 2009 RCT provides some evidence indicating that concurrent use of some antidepressant improves ECT efficacy.
=== Course ===
ECT is usually done from 6 to 12 times in 2 to 4 weeks but can sometimes exceed 12 rounds. It is also recommended to not do ECT more than 3 times per week. Evidence suggest that ECTs for depression may be stopped if there is no improvement during the first six sessions.
=== Treatment team ===
In the US, the medical team performing the procedure typically consists of a psychiatrist, an anesthetist, an ECT treatment nurse or qualified assistant, and one or more recovery nurses.: 109 Medical trainees may assist, but only under the direct supervision of credentialed attending physicians and staff.: 110
=== Devices ===
Most modern ECT devices deliver a brief-pulse current, which is thought to cause fewer cognitive effects than the sine-wave currents which were originally used in ECT. A small minority of psychiatrists in the US still use sine-wave stimuli.As of March 2025 Sine-wave is no longer used in the UK or Ireland.
Typically, the electrical stimulus used in ECT is about 800 milliamps and has up to several hundred watts, and the current flows for between one and six seconds.
Typically, 70 to 120 volts are applied externally to the patient's head, resulting in approximately 800 milliamperes of direct current passing between the electrodes, for a duration of 100 milliseconds to 6 seconds, either from temple to temple (bilateral ECT) or from front to back of one side of the head (unilateral ECT). However, only about 1% of the electrical current crosses the bony skull into the brain because skull impedance is about 100 times higher than skin impedance.
In the US, ECT devices are manufactured by two companies, Somatics, which is owned by psychiatrists Richard Abrams and Conrad Swartz, and Mecta. In the UK, the market for ECT devices was long monopolized by Ectron Ltd, which was set up by psychiatrist Robert Russell.
== Mechanism of action ==
Despite decades of research, the exact mechanism of action of ECT remains elusive. A review from 2022 of neuroimaging studies based on a global data collaboration, resulted in a model of temporary disruption of neural circuits followed by augmented neuroplasticity and rewiring. Other brain changes observed after ECT include increased gray matter volume in the frontolimbic areas including the hippocampus and amygdala, increased white matter tracts in the frontal and temporal lobes, increased monoamine neurotransmitters and increased neurogenesis in the dentate gyrus. Changes in sleep architecture due to the induced seizures have also been hypothesized as a mechanism of action.
== Use ==
As of 2001, it was estimated that about one million people received ECT annually.
There is wide variation in ECT use between different countries, different hospitals, and different psychiatrists. International practice varies considerably from widespread use of the therapy in many Western countries to a small minority of countries that do not use ECT at all, such as Slovenia and Luxembourg.
About 70 percent of ECT patients are women. This may be because women are more likely to be diagnosed with depression. Older and more affluent patients are also more likely to receive ECT. The use of ECT is not as common in ethnic minorities.
In Sweden, which has a complete register of all ECT treatments in the country, in 2013 the rate of persons treated in that year per 100,000 inhabitants was 41. Almost the same rate had already been present in 1975 with 42 patients per 100,000 inhabitants.
=== United States ===
ECT became popular in the US in the 1940s. At the time, psychiatric hospitals were overrun with patients whom doctors were desperate to treat and cure. Whereas lobotomies would reduce a patient to a more manageable submissive state, ECT helped to improve mood in those with severe depression. A survey of psychiatric practice in the late 1980s found that an estimated 100,000 people received ECT annually, with wide variation between metropolitan statistical areas.
Accurate statistics about the frequency, context and circumstances of ECT in the US are difficult to obtain because only a few states have reporting laws that require the treating facility to supply state authorities with this information. In 13 of the 50 states, the practice of ECT is regulated by law.
In the mid-1990s in Texas, ECT was used in about one third of psychiatric facilities and given to about 1,650 people annually.
Usage of ECT has since declined slightly; in 2000–01 ECT was given to about 1,500 people aged from 16 to 97 (in Texas it is illegal to give ECT to anyone under sixteen). ECT is more commonly used in private psychiatric hospitals than in public hospitals, and minority patients are underrepresented in the ECT statistics.
In the United States, ECT is usually given three times a week; in the United Kingdom, it is usually given twice a week. Occasionally it is given on a daily basis. A course usually consists of 6–12 treatments, but may be more or fewer. Following a course of ECT some patients may be given continuation or maintenance ECT with further treatments at weekly, fortnightly or monthly intervals. A few psychiatrists in the US use multiple-monitored ECT (MMECT), where patients receive more than one treatment per anesthetic. Electroconvulsive therapy is not a required subject in US medical schools and not a required skill in psychiatric residency training. Privileging for ECT practice at institutions is a local option: no national certification standards are established, and no ECT-specific continuing training experiences are required of ECT practitioners.
=== United Kingdom ===
In the UK in 1980, an estimated 50,000 people received ECT annually, with use declining steadily since then to about 12,000 per annum in 2002. It is still used in nearly all psychiatric hospitals, with a survey of ECT use from 2002 finding that 71 percent of patients were women and 46 percent were over 65 years of age. Eighty-one percent had a diagnosis of mood disorder; schizophrenia was the next most common diagnosis. Sixteen percent were treated without their consent. In 2003, the National Institute for Health and Care Excellence, a government body which was set up to standardize treatment throughout the National Health Service in England and Wales, issued guidance on the use of ECT. Its use was recommended "only to achieve rapid and short-term improvement of severe symptoms after an adequate trial of treatment options has proven ineffective and/or when the condition is considered to be potentially life-threatening in individuals with severe depressive illness, catatonia or a prolonged manic episode".
The guidance received a mixed reception. It was welcomed by an editorial in the British Medical Journal but the Royal College of Psychiatrists launched an unsuccessful appeal. The NICE guidance, as the British Medical Journal editorial points out, is only a policy statement and psychiatrists may deviate from it if they see fit. Adherence to standards has not been universal in the past. A survey of ECT use in 1980 found that more than half of ECT clinics failed to meet minimum standards set by the Royal College of Psychiatrists, with a later survey in 1998 finding that minimum standards were largely adhered to, but that two-thirds of clinics still fell short of current guidelines, particularly in the training and supervision of junior doctors involved in the procedure. A voluntary accreditation scheme, ECTAS, was set up in 2004 by the Royal College, and as of 2017 the vast majority of ECT clinics in England, Wales, Northern Ireland and the Republic of Ireland have signed up.
The Mental Health Act 2007 allows people to be treated against their will. This law has extra protections regarding ECT. A patient capable of making the decision can decline the treatment, and in that case treatment cannot be given unless it will save that patient's life or is immediately necessary to prevent deterioration of the patient's condition. A patient may not be capable of making the decision (they "lack capacity"), and in that situation ECT can be given if it is appropriate and also if there are no advance directives that prevent the use of ECT.
=== China ===
ECT was introduced in China in the early 1950s and while it was originally practiced without anesthesia, as of 2012 almost all procedures were conducted with it. As of 2012, there are approximately 400 ECT machines in China, and 150,000 ECT treatments are performed each year. Chinese national practice guidelines recommend ECT for the treatment of schizophrenia, depressive disorders, and bipolar disorder and in the Chinese literature, ECT is an effective treatment for schizophrenia and mood disorders.
Although the Chinese government stopped classifying homosexuality as an illness in 2001, electroconvulsive therapy is still used by some establishments as a form of "conversion therapy". Alleged Internet addiction (or general unruliness) in adolescents is also known to have been treated with ECT, sometimes without anesthesia, most notably by Yang Yongxin. The practice was banned in 2009 after a news story featuring Yang was published.
== Society and culture ==
=== Controversy ===
Surveys of public opinion, the testimony of former patients, legal restrictions on the use of ECT and disputes as to the efficacy, ethics and adverse effects of ECT within the psychiatric and wider medical community indicate that the use of ECT remains controversial. This is reflected in the January 2011 vote by the FDA's Neurological Devices Advisory Panel to recommend that FDA maintain ECT devices in the Class III device category for high risk devices, except for patients with catatonia, major depressive disorder, and bipolar disorder. This may result in the manufacturers of such devices having to do controlled trials on their safety and efficacy for the first time. In justifying their position, panelists referred to the memory loss associated with ECT and the lack of long-term data.
=== Legal status ===
==== Informed consent ====
The World Health Organization (2005) advises that ECT should be used only with the informed consent of the patient (or their guardian if their incapacity to consent has been established).
In the US, this doctrine places a legal obligation on a doctor to make a patient aware of the reason for treatment, the risks and benefits of a proposed treatment, the risks and benefits of alternative treatment, and the risks and benefits of receiving no treatment. The patient is then given the opportunity to accept or reject the treatment. The form states how many treatments are recommended and also makes the patient aware that consent may be revoked and treatment discontinued at any time during a course of ECT. The US Surgeon General's Report on Mental Health states that patients should be warned that the benefits of ECT are short-lived without active continuation treatment in the form of drugs or further ECT, and that there may be some risk of permanent, severe memory loss after ECT. The report advises psychiatrists to involve patients in discussion, possibly with the aid of leaflets or videos, both before and during a course of ECT.
According to the US Surgeon General, involuntary treatment is uncommon in the US and is typically used only in cases of great extremity, and only when all other treatment options have been exhausted. The use of ECT is believed to be a potentially life-saving treatment.
In one of the few jurisdictions where recent statistics on ECT usage are available, a national audit of ECT by the Scottish ECT Accreditation Network indicated that 77% of patients who received the treatment in 2008 were capable of giving informed consent.
In the UK, in order for consent to be valid it requires an explanation in "broad terms" of the nature of the procedure and its likely effects. One review from 2005 found that only about half of patients felt they were given sufficient information about ECT and its adverse effects and another survey found that about fifty percent of psychiatrists and nurses agreed with them.
A 2005 study published in the British Journal of Psychiatry described patients' perspectives on the adequacy of informed consent before ECT. The study found that "About half (45–55%) of patients reported they were given an adequate explanation of ECT, implying a similar percentage felt they were not." The authors also stated:
Approximately a third did not feel they had freely consented to ECT even when they had signed a consent form. The proportion who feel they did not freely choose the treatment has actually increased over time. The same themes arise whether the patient had received treatment a year ago or 30 years ago. Neither current nor proposed safeguards for patients are sufficient to ensure informed consent with respect to ECT, at least in England and Wales.
==== Involuntary ECT ====
Procedures for involuntary ECT vary from country to country depending on local mental health laws.
===== United States =====
In most states in the US, a judicial order following a formal hearing is needed before a patient can be forced to undergo involuntary ECT. However, ECT can also be involuntarily administered in situations with less immediate danger. Suicidal intent is a common justification for its involuntary use, especially when other treatments are ineffective.
In 2007, a psychiatric patient in the Creedmoor Psychiatric Center in New York, given the pseudonym of Simone D., won a court ruling which set aside a two-year-old court order to give her electroshock treatment against her will.
===== United Kingdom =====
Until 2007 in England and Wales, the Mental Health Act 1983 allowed the use of ECT on detained patients whether or not they had capacity to consent to it. However, following amendments which took effect in 2007, ECT may not generally be given to a patient who has capacity and refuses it, irrespective of his or her detention under the Act. In fact, even if a patient is deemed to lack capacity, if they made a valid advance decision refusing ECT then they should not be given it; and even if they do not have an advance decision, the psychiatrist must obtain an independent second opinion (which is also the case if the patient is under age of consent). However, there is an exception regardless of consent and capacity; under Section 62 of the Act, if the treating psychiatrist says the need for treatment is urgent they may start a course of ECT without authorization. From 2003 to 2005, about 2,000 people a year in England and Wales were treated without their consent under the Mental Health Act. Concerns have been raised by the official regulator that psychiatrists are too readily assuming that patients have the capacity to consent to their treatments, and that there is a worrying lack of independent advocacy. In Scotland, the Mental Health (Care and Treatment) (Scotland) Act 2003 also gives patients with capacity the right to refuse ECT.
==== Regulation ====
In the US, ECT devices came into existence prior to medical devices being regulated by the Food and Drug Administration. In 1976, the Medical Device Regulation Act required the FDA to retrospectively review already existing devices, classify them, and determine whether clinical trials were needed to prove efficacy and safety. The FDA initially classified the devices used to administer ECT as Class III medical devices. In 2014, the American Psychiatric Association petitioned the FDA to reclassify ECT devices from Class III (high-risk) to Class II (medium-risk). A similar reclassification proposal in 2010 did not pass. In 2018, the FDA re-classified ECT devices as Class II devices when used to treat catatonia or a severe major depressive episode associated with major depressive disorder or bipolar disorder.
==== By country ====
===== Australia =====
In Western Australia, ECT has been heavily restricted since 2014, after a bill passed with bipartisan support introducing restrictions on ECT, which were welcomed by mental health experts. Children under 14 are prohibited from receiving ECT, while those aged 14 to 18 must have informed consent approval from the Mental Health Tribunal. The law imposes a $15,000 fine on anyone who performs ECT on a child under the age of 14.
Similarly, ECT is also banned on children under the age of 12 in the Australian Capital Territory (ACT).
===== United States =====
Many mental health facilities offer ECT for specific diagnoses, such as chronic depression, mania, catatonia and schizophrenia. However, ECT is often only used as a treatment of last resort. To be considered for ECT, often testing such as an EKG and lab tests are required, in addition to a physical and neurological exam. Certain medications and conditions, such as cardiac conditions or hypertension, may disqualify a patient from ECT. Patients should give proper informed consent before ECT is performed. In the United States, ECT is performed under general anesthesia. Both trained health professionals with experience in ECT administration as well as a specifically trained and certified anesthesiologist should administer the procedure and anesthesia respectively.
=== Public perception ===
A questionnaire survey of 379 members of the general public in Australia indicated that more than 60% of respondents had some knowledge about the main aspects of ECT. Participants were generally opposed to the use of ECT on depressed individuals with psychosocial issues, on children, and on involuntary patients. Public perceptions of ECT were found to be mainly negative. A sample of the general public, medical students, and psychiatry trainees in the United Kingdom found that the psychiatry trainees were more knowledgeable and had more favorable opinions of ECT than did the other groups. More members of the general public believed that ECT was used for control or punishment purposes than medical students or psychiatry trainees.
=== Famous cases ===
Ernest Hemingway, an American author, died by suicide in 1961 half a year after ECT treatment at the Mayo Clinic in 1960. He is reported to have said to his biographer, "Well, what is the sense of ruining my head and erasing my memory, which is my capital, and putting me out of business? It was a brilliant cure but we lost the patient." However, the same biographer (Hotchner, 1966) and also a second biographer (Lynn, 1987) emphasized - according to a review from 2008 - "that Hemingway’s serious mental illness and plans for suicide significantly predated his ECT treatments."
Robert Pirsig had a nervous breakdown and spent time in and out of psychiatric hospitals between 1961 and 1963. He was diagnosed with paranoid schizophrenia and clinical depression as a result of an evaluation conducted by psychoanalysts, and was treated with electroconvulsive therapy on numerous occasions, a treatment he discusses in his novel, Zen and the Art of Motorcycle Maintenance.
Thomas Eagleton, United States Senator from Missouri, was dropped from the Democratic ticket in the 1972 United States Presidential Election as the party's vice presidential candidate after it was revealed that he had received electroshock treatment in the past for depression. Presidential nominee George McGovern replaced him with Sargent Shriver, and later went on to lose by a landslide to Richard Nixon.
American surgeon and award-winning author Sherwin B. Nuland is another notable person who has undergone ECT. In his 40s, his depression became so severe that he had to be institutionalized. After exhausting all treatment options, a young resident assigned to his case suggested ECT, which was successful.
Author David Foster Wallace also received ECT for many years, beginning as a teenager, before his suicide at age 46.
New Zealand author Janet Frame experienced both insulin coma therapy and ECT (but without the use of anesthesia or muscle relaxants). She wrote about this in her autobiography, An Angel at My Table (1984), which was later adapted into a film (1990).
American actor Carrie Fisher wrote about her experience with memory loss after ECT treatments in her memoir Wishful Drinking.
Lou Reed had ECT as a teenager to "cure" his homosexuality. He later claimed it had induced multiple personality disorder, and resulted in his hatred of psychiatrists. After Reed's death, his sister denied the ECT treatments were intended to suppress his "homosexual urges", asserting that their parents were not homophobic but had been told by his doctors that ECT was necessary to treat Reed's mental and behavioral issues.
On October 31, 2024, a Chinese transgender woman was approved by Changli county people’s court in Qinhuangdao to receive 60,000 yuan (£6,552) in compensation from a hospital that gave her electroshock conversion treatment against her will. This was the first time any transgender person in China won a legal challenge against the use of electroshock conversion treatment.
=== Fictional examples ===
Electroconvulsive therapy has been depicted in fiction, including fictional works partly based on true experiences. These include Sylvia Plath's semi-autobiographical novel, The Bell Jar, Ken Loach's film Family Life, and Ken Kesey's novel One Flew Over the Cuckoo's Nest; Kesey's novel is a direct product of his time working the graveyard shift as an orderly at a mental health facility in Menlo Park, California.
Two analyses of large numbers of films using ECT scenes found that almost all presented fictional settings that were unrelated to real treatment routines and were apparently aimed at stigmatizing ECT as a tool of repression and of mind and behavior control - having effects of memory-erosion, pain and damage.
The song “The Mind Electric” by Miracle Musical is typically interpreted as depicting someone undergoing ECT.
In the television series "Mr Bates vs The Post Office", which is based on true events, the character of Saman Kaur receives ECT following a deep depression and attempted suicide.
== See also ==
Neurostimulation
Neurotherapy
Psychosurgery
Magnetic seizure therapy
== References ==
== External links ==
Position Statement on Electroconvulsive Therapy (ECT) 2015 – from the American Psychiatric Association.
ECT – information from mental health charity The Royal College of Psychiatrists | Wikipedia/Electroconvulsive_therapy |
Light therapy, also called phototherapy or bright light therapy is the exposure to direct sunlight or artificial light at controlled wavelengths in order to treat a variety of medical disorders, including seasonal affective disorder (SAD), circadian rhythm sleep-wake disorders, cancers, neonatal jaundice, and skin wound infections. Treating skin conditions such as neurodermatitis, psoriasis, acne vulgaris, and eczema with ultraviolet light is called ultraviolet light therapy.
== Medical uses ==
=== Nutrient deficiency ===
==== Vitamin D deficiency ====
Exposure to UV-B light at wavelengths of 290-300 nanometers enables the body to produce vitamin D3 to treat vitamin D3 deficiency.
=== Skin conditions ===
Light therapy treatments for the skin usually involve exposure to ultraviolet light. The exposures can be to a small area of the skin or over the whole body surface, as in a tanning bed. The most common treatment is with narrowband UVB, which has a wavelength of approximately 311–313 nanometers. Full body phototherapy can be delivered at a doctor's office or at home using a large high-power UVB booth. Tanning beds, however, generate mostly UVA light, and only 4% to 10% of tanning-bed light is in the UVB spectrum.
==== Acne vulgaris ====
As of 2012 evidence for light therapy and lasers in the treatment of acne vulgaris was not sufficient to recommend them. There is moderate evidence for the efficacy of blue and blue-red light therapies in treating mild acne, but most studies are of low quality. While light therapy appears to provide short-term benefit, there is a lack of long-term outcome data or data in those with severe acne.
==== Atopic dermatitis ====
Light therapy is considered one of the best monotherapy treatments for atopic dermatitis (AD) when applied to patients who have not responded to traditional topical treatments. The therapy offers a wide range of options: UVA1 for acute AD, NB-UVB for chronic AD, and balneophototherapy have proven their efficacy. Patients tolerate the therapy safely but, as in any therapy, there are potential adverse effects and care must be taken in its application, particularly to children. According to a study involving 21 adults with severe atopic dermatitis, narrowband UVB phototherapy administered three times per week for 12 weeks reduced atopic dermatitis severity scores by 68%. In this open study, 15 patients still experienced long-term benefits six months later.
==== Cancer ====
According to the American Cancer Society, there is some evidence that ultraviolet light therapy may be effective in helping treat certain kinds of skin cancer, and ultraviolet blood irradiation therapy is established for this application. However, alternative uses of light for cancer treatment – light box therapy and colored light therapy – are not supported by evidence. Photodynamic therapy (often with red light) is used to treat certain superficial non-melanoma skin cancers.
==== Psoriasis ====
For psoriasis, UVB phototherapy has been shown to be effective. A feature of psoriasis is localized inflammation mediated by the immune system. Ultraviolet radiation is known to suppress the immune system and reduce inflammatory responses. Light therapy for skin conditions like psoriasis usually use 313 nanometer UVB though it may use UVA (315–400 nm wavelength) or a broader spectrum UVB (280–315 nm wavelength). UVA combined with psoralen, a drug taken orally, is known as PUVA treatment. In UVB phototherapy the exposure time is very short, seconds to minutes depending on intensity of lamps and the person's skin pigment and sensitivity.
==== Vitiligo ====
About 1% of the human population has vitiligo which causes painless distinct light-colored patches of the skin on the face, hands, and legs. Phototherapy is an effective treatment because it forces skin cells to manufacture melanin to protect the body from UV damage. Prescribed treatment is generally 3 times a week in a clinic or daily at home. About 1 month usually results in re-pigmentation in the face and neck, and 2–4 months in the hands and legs. Narrowband UVB is more suitable to the face and neck and PUVA is more effective at the hands and legs.
==== Other skin conditions ====
Some types of phototherapy may be effective in the treatment of polymorphous light eruption, cutaneous T-cell lymphoma and lichen planus. Narrowband UVB between 311 and 313 nanometers is the most common treatment.
=== Retinal conditions ===
There is preliminary evidence that light therapy is an effective treatment for diabetic retinopathy and diabetic macular oedema.
=== Mood and sleep related ===
==== Seasonal affective disorder ====
The effectiveness of light therapy for treating seasonal affective disorder (SAD) may be linked to reduced sunlight exposure in the winter months. Light resets the body's internal clock. Studies show that light therapy helps reduce the debilitating depressive symptoms of SAD, such as excessive sleepiness and fatigue, with results lasting for at least 1 month. Light therapy is preferred over antidepressants in the treatment of SAD because it is a relatively safe and easy therapy with minimal side effects. Two methods of light therapy, bright light and dawn simulation, have similar success rates in the treatment of SAD.
It is possible that response to light therapy for SAD could be season dependent. Morning therapy has provided the best results because light in the early morning aids in regulating the circadian rhythm. People affected by SAD often have low energy, tend to eat more carbohydrates and sleep longer, but symptoms can vary between people.
A Cochrane review conducted in 2019 states the evidence that light therapy's effectiveness as a treatment for the prevention of seasonal affective disorder is limited, although the risk of adverse effects are minimal. Therefore, the decision to use light therapy should be based on a person's preference of treatment.
==== Non-seasonal depression ====
Light therapy has also been suggested in the treatment of non-seasonal depression and other psychiatric mood disturbances, including major depressive disorder, bipolar disorder and postpartum depression. A meta-analysis by the Cochrane Collaboration concluded that "for patients suffering from non-seasonal depression, light therapy offers modest though promising antidepressive efficacy." A 2008 systematic review concluded that "overall, bright light therapy is an excellent candidate for inclusion into the therapeutic inventory available for the treatment of nonseasonal depression today, as adjuvant therapy to antidepressant medication, or eventually as stand-alone treatment for specific subgroups of depressed patients." A 2015 review found that supporting evidence for light therapy was limited due to serious methodological flaws.
A 2016 meta-analysis showed that bright light therapy appeared to be efficacious, particularly when administered for 2–5 weeks' duration and as monotherapy.
==== Chronic circadian rhythm sleep disorders (CRSD) ====
In the management of circadian rhythm disorders such as delayed sleep phase disorder (DSPD), the timing of light exposure is critical. Light exposure administered to the eyes before or after the nadir of the core body temperature rhythm can affect the phase response curve. Use upon awakening may also be effective for non-24-hour sleep–wake disorder. Some users have reported success with lights that turn on shortly before awakening (dawn simulation). Evening use is recommended for people with advanced sleep phase disorder. Some, but not all, totally blind people whose retinae are intact, may benefit from light therapy.
==== Circadian rhythm sleep disorders and jet lag ====
Source:
===== Situational CRSD =====
Light therapy has been tested for individuals with shift work sleep disorder and for jet lag.
===== Sleep disorder in Parkinson's disease =====
Light therapy has been trialed in treating sleep disorders experienced by patients with Parkinson's disease.
===== Sleep disorder in Alzheimer's disease =====
Studies have shown that daytime and evening light therapy for nursing home patients with Alzheimer's disease, who often struggle with agitation and fragmented wake/rest cycles effectively led to more consolidated sleep and an increase in circadian rhythm stability.
=== Neonatal jaundice (Postnatal Jaundice) ===
Light therapy is used to treat cases of neonatal jaundice. Bilirubin, a yellow pigment normally formed in the liver during the breakdown of old red blood cells, cannot always be effectively cleared by a neonate's liver causing neonatal jaundice. Accumulation of excess bilirubin can cause central nervous system damage, and so this buildup of bilirubin must be treated. Phototherapy uses the energy from light to isomerize the bilirubin and consequently transform it into compounds that the newborn can excrete via urine and stools. Bilirubin is most successful absorbing light in the blue region of the visible light spectrum, which falls between 460 and 490 nm. Therefore, light therapy technologies that utilize these blue wavelengths are the most successful at isomerizing bilirubin.
== Techniques ==
=== Photodynamic therapy ===
Photodynamic therapy (PDT) is a form of phototherapy using nontoxic light-sensitive compounds (photosensitizers) that are exposed selectively to light at a controlled wavelength, laser intensity, and irradiation time, whereupon they generate toxic reactive oxygen species (ROS) that target malignant and other diseased cells. Oxygen is thus required for activity, lowering efficacy in highly developed tumors and other hypoxic environments. Selective apoptosis of diseased cells is difficult due to the radical nature of ROS, but may be controlled for through membrane potential and other cell-type specific properties' effects on permeability or through photoimmunotherapy. In developing any phototherapeutic agent, the phototoxicity of the treatment wavelength should be considered.
==== Photodynamic cancer therapy ====
Various cancer treatments utilizing PDT have been approved by the FDA. Treatments are available for actinic keratosis (blue light with aminolevulinic acid), cutaneous T-cell lymphoma, Barrett esophagus, basal cell skin cancer, esophageal cancer, non-small cell lung cancer, and squamous cell skin cancer (Stage 0). Photosensitizing agents clinically-approved or undergoing clinical trials for the treatment of cancers include Photofrin, Temoporfin, Motexafin lutetium, Palladium bacteriopheophorbide, Purlytin, and Talaporfin. Verteporfin is approved to treat eye conditions such as macular degeneration, myopia, and ocular histoplasmosis. Third-generation photosensitizers are currently in development, but none are yet approved for clinical trials.
==== Antimicrobial photodynamic therapy ====
PDT may also be utilized to treat multidrug-resistant skin, wound, or other superficial infections. This is known as antimicrobial photodynamic therapy (aPDT) or photodynamic inactivation (PDI). aPDT has been observed to be effective against both gram-positive and gram-negative bacteria such as Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Mycobacterium. aPDT has shown lowered efficacy on some other bacterial species, such as Klebsiella pneumoniae and Acinetobacter baumannii. This is likely due to factors such as cell wall thickness and membrane potential. Many studies utilizing aPDT focus on the application of the photosensitizer through leakage from a hydrogel, which has been found to increase wound healing speed of skin infections through the upregulation of vascular endothelial growth factor (VEGF) and hypoxia inducible factor (HIF). This controlled leakage allows for prolonged but limited generation of ROS, lowering the impact on human cell viability due to ROS cytotoxicity. It is unlikely for drug resistance to photosensitizers to form due to the nontoxic nature of the photosensitizer itself as well as the ROS generation mechanism of action, which cannot be prevented outside of hypoxic environments. Certain dental infections (peri-implantitis, periodontitis) are more difficult to treat with PDT as opposed to photothermal therapy due to the requirement of oxygen, though a significant response is still observed.
Increased antimicrobial activity and wound healing speeds are typically observed when PDT is combined with photothermal therapy in photodynamic/photothermal combination therapy.
=== Photothermal Therapy ===
Photothermal therapy (PTT) is a form of phototherapy that uses non-toxic compounds called photothermal agents (PTA) that, when irradiated at a certain wavelength of light, converts the light energy directly to heat energy. The photothermal conversion efficiency determines the amount of light converted to heat, which can dictate the necessary irradiation time and/or laser intensity for treatments. Typically PTT treatments use wavelengths in the near-infrared (NIR) spectra, which can be further divided into NIR-I (760-900 nm), NIR-II (900-1880 nm), and NIR-III (2080-2340 nm) windows. Wavelengths in these regions are typically less phototoxic than UV or high-energy visible light. In addition, NIR-II wavelengths have been observed to show deeper penetration than NIR-I wavelengths, allowing for treatment of deeper wounds, infections, and cancers. Important considerations for the development of a PTA include photothermal conversion efficiency, phototoxicity, laser intensity, irradiation time, and the temperature at which human cell viability is impaired (around 46-60 °C). Currently, the only FDA-approved photothermal agent is indocyanine green which is active against both tumor and bacterial cells.
PTT is less selective than photodynamic therapy (PDT, see above) due to its heat-based mechanism of action, but also less likely to promote drug resistance than most, if not all, currently developed treatments. In addition, PTT can be used in hypoxic environments and on deeper wounds, infections, and tumors than PDT due to the higher wavelength of light. Due to PTT activity in hypoxic environments, it may be also used on more developed tumors than PDT. Low-temperature PTT (≤ 45 °C) for treatment of infections is also a possibility when combined with an antibiotic compound due to heat's proportionality with membrane permeability - a hotter environment causes heightened membrane permeability, which thus allows the drug into the cell. This would reduce/eliminate the impact on human cell viability, and aiding in antibiotic accumulation within the target cell may assist in restoring activity in antibiotics that pathogens had developed resistance to.
PTT is typically seen to have improved antimicrobial and wound healing activity when combined with an additional mechanism of action through PDT or added antibiotic compounds in the application.
=== Light boxes ===
The production of the hormone melatonin, a sleep regulator, is inhibited by light and permitted by darkness as registered by photosensitive ganglion cells in the retina. To some degree, the reverse is true for serotonin, which has been linked to mood disorders. Hence, for the purpose of manipulating melatonin levels or timing, light boxes providing very specific types of artificial illumination to the retina of the eye are effective.
Light therapy uses either a light box which emits up to 10,000 lux of light at a specified distance, much brighter than a customary lamp, or a lower intensity of specific wavelengths of light from the blue (460 nm) to the green (525 nm) areas of the visible spectrum. A 1995 study showed that green light therapy at doses of 350 lux produces melatonin suppression and phase shifts equivalent to 10,000 lux white light therapy, but another study published in May 2010 suggests that the blue light often used for SAD treatment should perhaps be replaced by green or white illumination, because of a possible involvement of the cones in melatonin suppression.
== Risks and complications ==
=== Ultraviolet ===
Ultraviolet light causes progressive damage to human skin and erythema even from small doses. This is mediated by genetic damage, collagen damage, as well as destruction of vitamin A and vitamin C in the skin and free radical generation. Ultraviolet light is also known to be a factor in formation of cataracts. Ultraviolet radiation exposure is strongly linked to incidence of skin cancer.
=== Visible light ===
Optical radiation of any kind with enough intensity can cause damage to the eyes and skin including photoconjunctivitis and photokeratitis. Researchers have questioned whether limiting blue light exposure could reduce the risk of age-related macular degeneration. According to the American Academy of Ophthalmology, there is no scientific evidence showing that exposure to blue light emitting devices result in eye damage. According to Harriet Hall, blue light exposure is reported to suppress the production of melatonin, which affects our body's circadian rhythm and can decrease sleep quality. It is reported that, in reproductive-age females, bright light therapy may activate the production of reproductive hormones, such as luteinizing hormone, follicle-stimulating hormone, and estradiol
Modern phototherapy lamps used in the treatment of seasonal affective disorder and sleep disorders either filter out or do not emit ultraviolet light and are considered safe and effective for the intended purpose, as long as photosensitizing drugs are not being taken at the same time and in the absence of any existing eye conditions. Light therapy is a mood altering treatment, and just as with drug treatments, there is a possibility of triggering a manic state from a depressive state, causing anxiety and other side effects. While these side effects are usually controllable, it is recommended that patients undertake light therapy under the supervision of an experienced clinician, rather than attempting to self-medicate.
Contraindications to light therapy for seasonal affective disorder include conditions that might render the eyes more vulnerable to phototoxicity, tendency toward mania, photosensitive skin conditions, or use of a photosensitizing herb (such as St. John's wort) or medication. Patients with porphyria should avoid most forms of light therapy. Patients on certain drugs such as methotrexate or chloroquine should use caution with light therapy as there is a chance that these drugs could cause porphyria.
Side effects of light therapy for sleep phase disorders include jumpiness or jitteriness, headache, eye irritation and nausea. Some non-depressive physical complaints, such as poor vision and skin rash or irritation, may improve with light therapy.
== History ==
Many ancient cultures practiced various forms of heliotherapy, including people of Ancient Greece, Ancient Egypt, and Ancient Rome. The Inca, Assyrian and early Germanic peoples also worshipped the sun as a health bringing deity. Indian medical literature dating to 1500 BCE describes a treatment combining herbs with natural sunlight to treat non-pigmented skin areas. Buddhist literature from about 200 CE and 10th-century Chinese documents make similar references.
The Faroese physician Niels Finsen is believed to be the father of modern phototherapy. He developed the first artificial light source for this purpose. Finsen used short wavelength light to treat lupus vulgaris, a skin infection caused by Mycobacterium tuberculosis. He thought that the beneficial effect was due to ultraviolet light killing the bacteria, but recent studies showed that his lens and filter system did not allow such short wavelengths to pass through, leading instead to the conclusion that light of approximately 400 nanometers generated reactive oxygen that would kill the bacteria. Finsen also used red light to treat smallpox lesions. He received the Nobel Prize in Physiology or Medicine in 1903. Scientific evidence for some of his treatments is lacking, and later eradication of smallpox and development of antibiotics for tuberculosis rendered light therapy obsolete for these diseases. In the early 20th-century light therapy was promoted by Auguste Rollier and John Harvey Kellogg. In 1924, Caleb Saleeby founded The Sunlight League.
From the late nineteenth century until the early 1930s, light therapy was considered an effective and mainstream medical therapy in the UK for conditions such as varicose ulcer, 'sickly children' and a wide range of other conditions. Controlled trials by the medical scientist Dora Colebrook, supported by the Medical Research Council, indicated that light therapy was not effective for such a wide range of conditions.
== Controversy ==
Red light therapy involves exposure to low levels of red light or near-infrared light, typically through lamps or masks. It is promoted for various skin-related benefits, including improved appearance and reduced signed of aging. However, there is currently insufficient scientific evidence to support many of these claims. There has been some indication that it may reduce inflammation associated with conditions such as acne or rosacea, but evidence supporting its anti-aging effects remain limited. Most existing research has focused on in-office treatments, while at-home devices are generally less powerful and precise, which may lead to inconsistent results. It is generally considered safe, however if misused red light therapy could cause eye or skin damage.
== See also ==
Blood irradiation therapy
Chromotherapy
Crib A'Glow
Free-running sleep
Low level laser therapy
Neuromodulation
Neurostimulation
Neurotechnology
Photodynamic therapy
Sun tanning
UV-B lamps
== References ==
== External links ==
Media related to Phototherapy at Wikimedia Commons
Our Friend, the Sun: Images of Light Therapeutics from the Osler Library Collection, c. 1901–1944. Digital exhibition by the Osler Library of the History of Medicine, McGill University | Wikipedia/Light_therapy |
Cognitive skills are skills of the mind, as opposed to other types of skills such as motor skills, social skills or life skills. Some examples of cognitive skills are literacy, self-reflection, logical reasoning, abstract thinking, critical thinking, introspection and mental arithmetic. Cognitive skills vary in processing complexity, and can range from more fundamental processes such as perception and various memory functions, to more sophisticated processes such as decision making, problem solving and metacognition.
== Specialisation of functions ==
Cognitive science has provided theories of how the brain works, and these have been of great interest to researchers who work in the empirical fields of brain science. A fundamental question is whether cognitive functions, for example visual processing and language, are autonomous modules, or to what extent the functions depend on each other. Research evidence points towards a middle position, and it is now generally accepted that there is a degree of modularity in aspects of brain organisation. In other words, cognitive skills or functions are specialised, but they also overlap or interact with each other. Deductive reasoning, on the other hand, has been shown to be related to either visual or linguistic processing, depending on the task; although there are also aspects that differ from them. All in all, research evidence does not provide strong support for classical models of cognitive psychology.
== Cognitive functioning ==
Cognitive functioning refers to a person's ability to process thoughts. It is defined as "the ability of an individual to perform the various mental activities most closely associated with learning and problem-solving. Examples include the verbal, spatial, psychomotor, and processing-speed ability." Cognition mainly refers to things like memory, speech, and the ability to learn new information. The brain is usually capable of learning new skills in the aforementioned areas, typically in early childhood, and of developing personal thoughts and beliefs about the world. Old age and disease may affect cognitive functioning, causing memory loss and trouble thinking of the right words while speaking or writing ("drawing a blank"). Multiple sclerosis (MS), for example, can eventually cause memory loss, an inability to grasp new concepts or information, and depleted verbal fluency.
Humans generally have a high capacity for cognitive functioning once born, so almost every person is capable of learning or remembering. Intelligence is tested with IQ tests and others, although these have issues with accuracy and completeness. In such tests, patients may be asked a series of questions, or to perform tasks, with each measuring a cognitive skill, such as level of consciousness, memory, awareness, problem-solving, motor skills, analytical abilities, or other similar concepts. Early childhood is when the brain is most malleable to orientate to tasks that are relevant in the person's environment.
Exercise, even at light intensity, significantly improves general cognition across all populations, with the largest cognitive gains seen from shorter interventions (1–3 months), light to moderate intensity activity.
== See also ==
Adaptive behavior
Adaptive functioning
Intelligence Quotient (IQ)
Cognition
Cognitive Abilities Test
Jungian cognitive functions
== Notes ==
== References ==
[1] NCME - Glossary of Important Assessment and Measurement Terms [cognitive ability] | Wikipedia/Cognitive_functions |
Psycho Surgery is the second studio album by the American Christian metal band Tourniquet. It was originally released on Intense Records and Metal Blade Records in 1991. A remastered version was released on Pathogenic Records in 2001 as Psychosurgery and includes revised artwork, an expanded album booklet, and bonus tracks that include live versions of songs featuring then-lead vocalist Luke Easter as well as demos; the title was changed since co-founder and drummer Ted Kirkpatrick always felt that it should have been just one. Retroactive Records released a Collector's Edition remaster on June 26, 2020, retaining the original album title and including an extended booklet as well as different bonus tracks. Considered by critics to be Tourniquet's most balanced of the band's first three albums, Heaven's Metal fanzine ranked Psycho Surgery Christian metal's second-best album of all time (after Vengeance Rising's 1988 debut album Human Sacrifice).
== Recording history ==
Produced by Metal Blade Records' Bill Metoyer, Tourniquet recorded Psycho Surgery at Mixing Lab A & B studio in Garden Grove, California. Guitarist Erik Mendez and the bassist Victor Macias joined Tourniquet for this album, forming the quintet known as Tourniquet's classic line-up. After the release of Stop the Bleeding in 1990, the band caught Metal Blade Records' attention. Metal Blade Records released Psycho Surgery to the secular market, leaving the Christian market to original label Intense Records. The album cover is a reference to Romans 12:2.
Psycho Surgery represented a more modern, experimental, and technical thrash-metal style, leaving behind the previous album's speed metal elements and incorporating classical music-influenced guitar riffs, complex tempo changes, and virtuosic guitar solos. One reviewer described the album as "Slayer plays Beethoven in a slightly rearranged way." Vocalist Guy Ritter also abandoned his King Diamond-like high-pitched falsetto in favor of a more melodic baritone register.
The album's crisp production creates a somewhat clinical and sterile atmosphere that serves to undergird the album's medical themes. Using his pharmaceutical background, drummer Ted Kirkpatrick infused the lyrics with medical terminology to serve as metaphors for particular social issues such as heretical sects ("A Dog's Breakfast") which also included a jab at three teachers in the Word of Faith Movement (Kenneth Copeland, Benny Hinn, and Kenneth Hagin), discrimination of the developmentally delayed ("Broken Chromosomes"), and parental neglect ("Dysfunctional Domicile"). The song "Stereotaxic Atrocities," a sequel to the previous album's "Ark of Suffering," features a brief reprise of the original's signature guitar riff and criticizes laboratory testing of animals. A re-recorded version of "Stereotaxic Atrocities" appeared on the album Onward to Freedom in 2014 and featured Marty Friedman of Megadeth on guitar and Luke Easter on vocals, with an instrumental version later appearing on Onward to Freedom: Voiceless in 2016.
Taking advantage of rap metal's new popularity, the album's popular song "Spineless" featured the vocal and sampling contributions of Christian hip-hop group Preachers in Disguise (P.I.D.). Although Kirkpatrick wrote most of the song's lyrics prior to entering the studio, P.I.D.'s Fred "Doug Tray" Lynch and Barry "G" Hogan crafted their own lyrical contributions on the spot. The fast-moving instrumental "Viento Borrascoso (Devastating Wind)" features Kirkpatrick's virtuosic drumming. The album's final song, "Officium Defunctorum," is a doom metal piece written by guitarist/vocalist Gary Lenaire that addresses Jesus Christ's crucifixion.
== Reception ==
Metal Blade Records' wide distribution of Psycho Surgery increased Tourniquet's exposure and popularity. Following the album's release, the songs "Psycho Surgery," "Spineless," and "Viento Borrascoso" all achieved number-one positions on several charts, and readers of HM Magazine voted Psycho Surgery their "Favorite Album of the Year" in 1991. In 1992, Psycho Surgery also achieved two GMA Dove Award nominations in the categories Metal Album of the Year and Metal Recorded Song of the Year ("Psycho Surgery"). Critics consider the album a display of talented musicianship, intelligent lyrics, and originality. In August 2010, HM Magazine ranked Psycho Surgery #18 on its list of Top 100 Christian Rock Albums of All Time and the #2 album on its list of Top 100 Christian Metal Albums of All Time. In an interview with Noisecreep about the list, HM Magazine editor Doug Van Pelt explained that Psycho Surgery "found this band playing as a five-member band for the first time and they really bent creativity in metal in new directions that have still not been matched. Nobody has ever sounded like this band. I mean, Between the Buried and Me and maybe System of a Down are the closest in stretching creative boundaries. You almost had to pull out a medical dictionary to understand their [Tourniquet's] lyrics. Standout song would have to be the epic 'Broken Chromosomes,' which is a touching song about mistreated kids that are mentally handicapped. Chilling song."
== Track listing ==
== Personnel ==
== References == | Wikipedia/Psycho_Surgery |
Psychic surgery is a medical fraud in which practitioners create the illusion of performing surgery with their bare hands and use sleight of hand, fake blood, and animal parts to convince the patient that diseased lesions have been removed and that the incision has spontaneously healed. The technique may fool the general public, but it can be observed by experienced stage magicians, who use the same sleight of hand techniques for entertainment.
The US Federal Trade Commission described psychic surgery as a "total hoax". It has also been described as fraud, fakery, deceitful, irrational, charlatanry, and quackery. Even supporters have been forced to admit that sleight-of-hand tricks were "widely used" and that charlatans were common and miracles unlikely. Psychic surgery may cause needless death by keeping the ill away from life-saving medical care. Medical professionals and skeptics classify it as sleight of hand and any positive results as a placebo effect.
Psychic surgery first appeared in the spiritualist communities of the Philippines and Brazil in the middle of the 20th century; it has taken different paths in those two countries.
== Procedure ==
Although psychic surgery varies by region and practitioner, it usually follows some common lines. Without the use of a surgical instrument, a practitioner will press the tips of their fingers against the patient's skin in the area to be treated. The practitioner's hands appear to penetrate into the patient's body painlessly and blood seems to flow. The practitioner will then show organic matter or foreign objects apparently removed from the patient's body, clean the area, and then end the procedure with the patient's skin showing no wounds or scars.
Most cases do not involve actual surgery although some practitioners make real incisions. The lack of pain upon incision has been attributed to a type of hypnosis.
In regions of the world where belief in evil spirits is prevalent, practitioners will sometimes exhibit objects, such as glass, saying that the foreign bodies were placed in the patient's body by evil spirits.
== History ==
Accounts of psychic surgery started to appear in the spiritualist communities of the Philippines and Brazil in the mid-1900s. The 16th-century explorer Álvar Núñez Cabeza de Vaca records an account, related to him by Native Americans, of a bearded figure known as "Mala Cosa" (Evil Thing), who would take hold of a person, cut into their abdomen with a flint knife, and remove a portion of their entrails, which he would then burn in a fire. When he was done the incision would close spontaneously.
=== Philippines ===
In the Philippines, the procedure was first noticed in the 1940s, when performed routinely by Eleuterio Terte. Terte and his pupil Tony Agpaoa, who was apparently associated with the Union Espiritista Christiana de Filipinas (The Christian Spiritist Union of the Philippines), trained others in this procedure.
In 1959, the procedure came to the attention of the U.S. public after the publication of Into the Strange Unknown by Ron Ormond and Ormond McGill. The authors called the practice "fourth dimensional surgery", and wrote "[we] still don’t know what to think; but we have motion pictures to show it wasn’t the work of any normal magician, and could very well be just what the Filipinos said it was — a miracle of God performed by a fourth dimensional surgeon."
In "...1973, a group of medical doctors, scientists, and parapsychologists visited the Philippine Islands to study a phenomenon that was causing increased furor amongst health professionals ... Filipino psychic surgeons, also known as spiritual/magnetic healers."
Alex Orbito, who became well known in the United States through his association with actress Shirley MacLaine was a practitioner of the procedure. On June 14, 2005, Orbito was arrested by Canadian authorities and indicted for fraud. On January 20, 2006, the charges were dropped as it then seemed unlikely that Orbito would be convicted.
Psychic surgery made U.S. tabloid headlines in March 1984 when entertainer Andy Kaufman, diagnosed with large cell carcinoma (a rare lung cancer), traveled to the Philippines for a six-week course of psychic surgery. Practitioner Jun Labo claimed to have removed large cancerous tumors and Kaufman declared he believed this cancer had been removed. Kaufman died from renal failure as consequence of a metastatic lung cancer, on May 16, 1984.
=== Brazil ===
The origins of the practice in Brazil are obscure, but by the late 1950s "spiritual healers" were practicing in the country. Many of them were associated with Kardecist spiritism, a major spiritualistic movement in Brazil, and claimed to be performing their operations merely as channels for spirits of deceased medical doctors.
A known Brazilian psychic healer who routinely practiced psychic surgery was Zé Arigó, who claimed to be channeling a (fictional) medical doctor named Dr. Fritz. Unlike most other psychic healers, who work bare-handed, Arigó used a non-surgical blade. Other psychic healers who claimed to channel Dr. Fritz were Edson Queiroz and Rubens Farias Jr. Later, one João de Faria, also known as João de Deus, became popular while he operated in Abadiânia, state of Goiás. Faria has since been arrested and found guilty of the rapes of several women. Dozens of similar accusations are awaiting trial.
According to the descriptions of Yoshiaki Omura, Brazilian psychic surgery appears to be different from that practiced in the Philippines. Omura calls attention to the fact that practitioners in Brazil use techniques resembling qigong, shiatsu massage, and chiropractic manipulation. Some patients are also injected with a brown liquid, and alleged minor surgery was performed in about 20% of the cases observed. While Arigó performed his procedures using kitchen knives in improvised settings, Omura reports that the clamping of blood vessels and the closing of the surgical wounds were performed by licensed surgeons or licensed nurses.
=== North America ===
In the 1970s a specific form of surgery known as psychic dentistry emerged in America. Willard Fuller was the most well known proponent. It was alleged that Fuller could cause dental fillings to appear spontaneously, change silver into golden fillings, straighten crooked teeth or produce new teeth. However, magicians and skeptics have found these claims to be unsupported by solid evidence. One dentist examined some patients of Fuller. In one case miraculous gold fillings turned out to be tobacco stains. In another case a female patient who reported a miraculous new silver filling admitted she had forgotten that the filling was already there.
== Medical and legal criticism ==
In 1975, the Federal Trade Commission declared that "'psychic surgery' is nothing but a total hoax". Judge Daniel H. Hanscom, when granting the FTC an injunction against travel agencies promoting psychic surgery tours, declared: "Psychic surgery is pure and unmitigated fakery. The 'surgical operations' of psychic surgeons ... with their bare hands are simply phony."
In 1975 the FTC stated:
It has been found that "psychic surgery" is pure fakery. The body is not opened, no "surgery" is performed with the bare hands or with anything else, and nothing is removed from the body. The entire "operation" is an egregious fraud perpetrated by sleight-of-hand and similar tricks and devices.
In 1990, the American Cancer Society stated that it "found no evidence that 'psychic surgery' results in objective benefit in the treatment of any medical condition," and strongly urged individuals who are ill not to seek treatment by psychic surgery.
The British Columbia Cancer Agency "strongly urges individuals who are ill not to seek treatment by psychic surgeon".
While not directly hazardous to the patient, the belief in the alleged benefits of psychic surgery may carry considerable risk for individuals with diagnosed medical conditions, as they may delay or forgo conventional medical help, sometimes with fatal consequences.
== Replication by stage magicians ==
Stage magician James Randi said psychic surgery is a sleight of hand confidence trick. He said that in personal observations of the procedure, and in movies showing the procedures, he could spot sleight-of-hand moves that are evident to experienced stage magicians, but might deceive a casual observer. Randi replicated the appearance of psychic surgery himself through the use of sleight-of-hand. Professional magician Milbourne Christopher also investigated psychic surgeons at work, and observed sleight of hand. On his A&E show Mindfreak in the episode "Sucker", illusionist Criss Angel performed "Psychic Surgery", showing first-hand how it may be done (fake blood, plastic bags and chicken livers were used).
Randi said the healer would slightly roll or pinch the skin over the area to be treated. When his flattened hand reaches under the roll of skin, it looks and feels as if the practitioner is actually entering into the patient's body. The healer would have prepared in advance small pellets or bags of animal entrails which would be palmed in his hand or hidden beneath the table within easy reach. This organic matter would simulate the "diseased" tissue that the healer would claim to be removing. If the healer wants to simulate bleeding, he might squeeze a bladder of animal blood or an impregnated sponge. If done properly, this procedure may deceive patients and observers. Some "psychic surgery" procedures do not rely solely on the "sleight of hand" described, as at least one Brazilian "surgeon" also cuts his victims' skin with an unsterilized scalpel to heighten the illusion.
== Accusations of fraud ==
The physician William Nolen investigated psychic surgery and his book Healing: A Doctor in Search of a Miracle (1974) uncovered many cases of fraud. Tony Agpaoa, a famous psychic surgeon, was detected several times using trickery.
John Taylor has written there is no real case for psychic surgery as the explanation of fraud is highly likely in all the operations. The practitioners use sleight of hand techniques to produce blood or blood-like fluids, animal tissue or substitutes, and/or various foreign objects from folds of skin of the patient as part of a confidence trick for financial benefit.
Science writer Terence Hines has written:
The "operation" starts as the hand appears to enter the patient’s belly. This is accomplished by creating an impression in the belly by pushing down and flexing the fingers slowly into a fist—the fingers thus appear to be moving into the belly, but are really simply hidden behind the hand. The blood that further disguises the true movement of the fingers and adds drama to the proceedings can come from two sources. One is a fake thumb, worn over the real thumb and filled with a red liquid. Such a fake thumb is a common magician’s implement. Blood can also be passed to the surgeon in red balloons hidden in cotton the psychic surgeon is using, the cotton and its hidden contents being passed to him by an "assistant". The bits of "tumor" can also be passed to the psychic surgeon this way, or hidden in the false thumb... the "tumor" material turns out to be chicken intestines or similar animal remains. The blood is either animal blood or red dye.
Two "psychic surgeons" provided testimony in a Federal Trade Commission trial that, to their knowledge, the organic matter supposedly removed from the patients usually consists of animal tissue and clotted blood.
== In popular culture ==
In the 1989 film Penn & Teller Get Killed, comedic magicians Penn and Teller demonstrate how to perform the illusion of psychic surgery.
A 1989 episode of Unsolved Mysteries featured a police officer whose mother claimed to have been cured by psychic surgery, only to die shortly thereafter; her autopsy revealed several tumors. The policeman described himself going undercover to feign illness and pretended to desire psychic surgery, having the feeling of the practitioner using sleight of hand to supposedly dig into his tissue, as well as suspecting that the "cysts" and "tumors" being removed from his body were actually ready-made chicken parts.
"Milagro", a sixth-season episode from The X-Files, features a killer accused of using psychic surgery on his victims, killing them in the process.
In the BBC TV series Full Circle with Michael Palin, Michael Palin witnesses two separate instances of psychic surgery in the Baguio district of the Philippines. On raising his suspicion with the medic that it seemed a sleight of hand to him, the medic told him he was a westerner and could only understand the surgery if he had a third eye. Palin assists another medic in a surgery and was told that no contamination happens in this procedure because of the use of garlic.
In the 1993 novel by Ana Castillo, So Far from God, Filipino Dr. Tolentino performs psychic surgery on La Loca after diagnosing her with HIV.
In the 1998 Christmas Special of the BBC1 series Jonathan Creek, entitled "Black Canary", the husband of the illusionist known as Black Canary undergoes psychic surgery at the start of the episode and this form of surgery forms a plot device throughout the special.
In the 1999 movie Man on the Moon, based on the life of Andy Kaufman, Kaufman (Jim Carrey) receives psychic surgery and notices the "sleight of hand," laughing at the irony. He is next seen dead, with his funeral being conducted.
In the TV series Angel, Season 1 episode "I Fall to Pieces (Angel)" features a doctor who practices psychic surgery.
In the TV show Criss Angel Mindfreak, Season 2 Episode "Sucker", Criss explains psychic surgery as a deception.
In the television show 1000 Ways to Die, a con artist was using this to scam poor country people, only to lead to his death when he used it on a leper from whom he caught the disease.
In the 2012 movie Red Lights Simon Silver, an alleged psychic, performs a psychic surgery on stage.
In a deleted scene from the 2016 movie Deadpool, Wade Wilson (Ryan Reynolds) visits a psychic surgery clinic in an attempt to cure his cancer, but upon realizing the clinic is scamming innocent clients into spending their life savings on simple sleight of hand, he attacks and murders the head surgeon in front of the staff.
== See also ==
Alternative cancer treatments
Faith healing
Gray's Anatomy (film)
Health fraud
List of topics characterized as pseudoscience
Psychic
Psychokinesis
== References ==
== Further reading ==
Gordon, Henry. (1988). Extrasensory Deception: ESP, Psychics, Shirley MacLaine, Ghosts, UFOs. Macmillan of Canada. ISBN 0-7715-9539-5
Nolen, William. (1974). Healing: A Doctor in Search of a Miracle. New York: Random House. ISBN 0-394-49095-9
Randi, James. (1982). Flim-Flam! Psychics, ESP, Unicorns, and Other Delusions. Prometheus Books. ISBN 0-87975-198-3
Taylor, John. (1980). Science and the Supernatural: An Investigation of Paranormal Phenomena Including Psychic Healing, Clairvoyance, Telepathy, and Precognition by a Distinguished Physicist and Mathematician. Temple Smith. ISBN 0-85117-191-5
== External links ==
James Randi debunks "psychic surgery"
Turkish Television Brian Brushwood debunks psychic surgery
Unconventional therapies - Psychic Surgery — overview by the British Columbia Cancer Agency
Psychic "surgery" — definition in the Skeptic's Dictionary
Abstract
"Psychic Surgery" (1990) Ca. Cancer J. Clin. 40(3) 184-8 [1] [2] Terte/Agpaoa origins; exposed by Milbourne Christopher and Robert Gurtler.
"Sideshows of Science", David Perlman, San Francisco Chronicle, January 8, 2001. Reference to "psychic underground"
'Psychic surgeon' a heel, not a healer, police say Globe and Mail story on Orbito's 2005 arrest in Toronto | Wikipedia/Psychic_surgery |
Involuntary treatment or mandatory treatment refers to medical treatment undertaken without the consent of the person being treated. Involuntary treatment is permitted by law in some countries when overseen by the judiciary through court orders; other countries defer directly to the medical opinions of doctors.
Some countries have general legislation allowing for any treatment deemed necessary if an individual is unable to consent to a treatment due to lack of capacity, other legislation may specifically deal with involuntary psychiatric treatment of individuals who have been diagnosed with a mental disorder. Psychiatric treatment normally happens in a psychiatric hospital after some form of involuntary commitment, though individuals may be compelled to undergo treatment outside of hospitals via outpatient commitment.
The diagnosis of mental disorders can be carried out by some form clinical practitioner, or in some cases law enforcement or others, to be a danger to themselves or to others is permitted in some jurisdictions, while other jurisdictions have more recently allowed for forced treatment for persons deemed to be "gravely disabled" or asserted to be at risk of psychological deterioration.
A patient may be detained because they are diagnosed with a psychiatric disorder or infectious disease.
== History ==
In the early 20th century, many countries passed laws allowing the compulsory sterilization of some women. In the US more than half the states passed laws allowing the forced sterilization of people with certain illnesses or criminals as well as sterilization based on race. Forcible sterilization took place in the United States until at least 1981, more than 64 thousand people were forcibly sterilized. Denmark sterilized 60 thousand people between 1935 and 1976. During Nazi rule in Germany as part of their eugenics program about 600 thousand people were compulsorily sterilized.
Involuntary euthanasia was carried out in Nazi Germany for those who had certain psychiatric disorders or learning disabilities as part of the Aktion T4 program. This program was run by Karl Brandt, a medical doctor, and Philipp Bouhler.: 185 Victims were murdered together in gas chambers and this program was a prototype for the extermination camps such as Auschwitz where the Holocaust took place. As part of Action 14f13, physicians involved in the euthanasia program visited concentration camps where they looked at documentation provided by SS camp doctors and approved the murder of camp inmates on the grounds of race, behavior and ability to work using the euthanasia program's facilities.: 192
Throughout the latter half of the 20th century, homosexual men in the UK were given the choice between chemical castration with female sex hormones or prison including, notably, Alan Turing.
Until 2004, every European state required that transgender people must be sterilized or provably infertile to have their preferred gender formally recognized.: 7 This practice continued in Sweden until 2012 and Denmark until 2014. Japan currently requires transgender people to be sterilized and have their ovaries removed to be recognized as a different gender.
=== Ethics and the law ===
The Hippocratic Corpus, an ancient Greek text discussing medical ethics, advises that physicians conceal most information from patients to give the patients the best care.: 61 The 1767 English case Slater vs Baker and Stapleton found against two doctors who had refractured a patient's leg without consent.: 116 Thomas Percival was a British physician who published a book called Medical Ethics in 1803, which makes no mention of soliciting for the consent of patients or respecting their decisions.: 68 Percival said that patients have a right to truth, but when the physician could provide better treatment by lying or withholding information, he advised that the physician do as he thought best.: 68 Benjamin Rush, an 18th-century United States physician, in a lecture entitled "On the duties of patients to their physicians", stated that patients should be strictly obedient to the physician's orders; this was representative of much of his writings.: 65
The US Canterbury v. Spence case established the principle of informed consent in US law. Earlier legal cases had created the underpinnings for informed consent, but his judgment gave a detailed and thought-through discourse on the matter. The judgment cites cases going back to 1914 as precedent for informed consent.: 56
=== Infectious disease ===
In response to the bubonic plague, some city states restricted movement of people into them using cordon sanitaires, and separated those were suspected of being infected into makeshift camps.: 254 Merchant sailors were made to isolate in lazarettos, hospitals for infectious diseases.: 255 England created quarantine regulations in 1663 to confine ships suspected of being infected with the plague.: 255 In response to cholera outbreaks in the 1830s, some European cities people with symptoms were forced into lazarettos.: 256 An 1853 law in the United Kingdom made vaccination compulsory with those refusing to comply receiving fines. People with symptoms of tuberculosis have been detained in New York from 1902.: 237 During the Spanish flu pandemic western cities implemented social distancing and closed schools, churches, theatres and restricted public gatherings.: 257 During the COVID-19 pandemic many countries implemented lockdowns restricting movement, enforcing working from home and social distancing.
=== Mental health ===
In 1789, during the French Revolution, the French government issued a directive for the management of the insane. This directive ordered that the insane be incarcerated and treated.: 84 Bethlem Royal Hospital is a mental hospital in the United Kingdom, which started exclusively treating mental illness in 1377. In 1818, Urban Metcalf, a patient at Bethlam, published a book describing his experience there. He described physical restraint of patients who were attached to walls. This followed a report by the government in 1815 describing conditions in asylums in the UK.: 85
=== Political use ===
Psychiatric diagnoses have been used for political purposes.: 65 Psychiatry can be used to bypass standard legal procedures and political incarceration. The use of hospitals instead of jails prevents those detainend from receiving legal aid, makes indefinite incarceration possible, discredits the individuals and their ideas.: 29 During the Nazi era and the Soviet rule religious and political dissenters were labeled as "mentally ill" and subjected to inhumane "treatments". From the 1960s to 1986, abuse of psychiatry for political and ideological purposes was reported to be systematic in the Soviet Union, and occasional in Eastern European countries such as Romania, Hungary, Czechoslovakia and Yugoslavia.: 66
== Legislative distinctions ==
Legislation may allow for involuntary of a particular disease or class of diseases such as mental disorders.: 263 Some countries have legislation to involuntarily detain or examine those suspected to have tuberculosis, or treat them if infected.: 610 Some countries have general legislation allowing for any treatment deemed necessary if an individual is unable to consent to a treatment due to lack of capacity.: 108
Those treated for mental health disorders are committed before involuntary treatment. Those under community treatment orders (also known as outpatient commitment in some countries) may be ordered to take medication, and if they fail to may be committed and treated involuntarily.: 16
In some countries, involuntary treatment for mental health is not used to treat a symptom that is present, but rather to reduce the risk of symptoms returning through the use prophylactic psychotropic medication. This is achieved through the use of outpatient commitment where a patient may be detained in hospital if they fail to take the medication doctors have prescribed them.: 16
== Forms ==
Chemical restraint, such as forcible injection with the antipsychotic haloperidol or benzodiazepine sedative midazolam, may be used to sedate a patient who is agitated.: 624 : 152 In some countries, antipsychotics and sedatives can be forcibly administered to those who are committed, using intramuscular depot injection. Those with anorexia nervosa may receive force-feeding.
Those with infectious diseases such as tuberculosis can be detained and isolated. Brazil, Bulgaria, Costa Rica, Croatia, Czechia, France, Hungary, Indonesia, Italy, Poland, and Russia make certain vaccinations mandatory.
In the Czech Republic, men convicted of sex offenses are in practice given the choice of long-term detention or castration.: 346 Japan requires transgender people to undergo sterilization to have their gender formally recognized.
=== Coercion in voluntary mental health treatment ===
Individuals may be forced to undergo mental health treatment which is legally "voluntary" under the threat of involuntary treatment.: 98 Many individuals who legally would be viewed as receiving mental health treatment voluntarily believe that they have no choice in the matter.
Once voluntarily within a mental health hospital, rules, process, and information asymmetry (the fact that healthcare providers know more about how the hospital functions than a patient) can be used to achieve compliance from a person in voluntary treatment. To prevent someone from leaving voluntarily, staff may use stalling tactics made possible by the fact that all doors are locked. For example, the person may be referred to a member of staff who is rarely on the ward, or made to wait until after lunch or a meeting, behaving as if a person in voluntary treatment does not have the right to leave without permission. When the person is able to talk about leaving, the staff may use vague language to imply that the person is required to stay, relying on the fact that people in voluntary treatment do not understand their legal status.
Szmukler and Appelbaum constructed a hierarchy of types of coercion in mental health care, ranging from persuasion to interpersonal leverage, inducements, threats and compulsory treatment. Here persuasion refers to argument through reason. Forms of coercion that do not use legal compulsion are referred to as informal coercion or leverage.: 98 Interpersonal leverage may arise from the desire to please health workers with whom a relationship has formed. Threats may revolve around a health worker helping or hindering the receipt of government benefits. Studies show that 51%, 35% and 29% of mental health patients have experienced some form of informal coercion in the US, England and Switzerland respectively.: 100
=== Non-voluntary treatment ===
In certain limited circumstance a patient may have capacity but be unable to consent to treatment at a time when a decision is necessary, in such cases surgery may be performed on a patient without consent.: 1 A patient may issue an advance healthcare directive specifying how they would like to be treated if they are unable to consent to treatment. In the UK, a healthcare worker does not need to follow an advanced directive but they will influence decisions.: 5 Alternatively, a surrogate decision-maker such as a relative, friend or healthcare professional may make decisions on a patient's behalf if a patient is unable to.: 810
=== Covert treatment ===
In some instances when a patient refuses the medication suggested by a healthcare professional healthcare workers will cause a patient to take the medication by hiding medication in their food a practice known as covert medication.
== Competent adults ==
The faith of Jehovah's Witnesses forbids blood transfusion. Courts in the United States have consistently upheld the right of competent adults to decline blood transfusion even when it would be life-saving, though there have been exceptions where the death of a patient could leave a child orphaned.: 255
In the United States, courts have ordered pregnant women to involuntarily undergo caesarean section, intrauterine transfusion, and enforced bed rest.: 188 There are cases of clinicians threatening pregnant patients with removal of child custody or withdrawal of care if they decline treatment.: 192 In the UK, courts are unable to force treatment on pregnant women who are deemed to have capacity, however as of 2016 there were no cases of a still pregnant woman being deemed to have capacity by a court.: 40
== Children ==
Parents or medical doctors may make decision about the treatment of children, a principle known as parens patriae.: 5 In the United States, doctors are responsible for providing a good standard of care for patients who are children which can lead them to make decisions at odds with the parents wishes. Parents have less autonomy to make decisions about their children's care than adult patients have over their own care.: 5 Treatment may take place even if a child or adolescent disagree with treatment, though the wishes of a child patient are taken more into account the more burdensome treatment is and the worse the prognosis.: 8
If a child does not assent to treatment they may be physically held while a procedure is carried out or anaesthesia is carried out.: 162 For some procedures, a child may be distracted to allow for treatment.: 159
In Italy, court orders have been used to give children of Jehovah's Witnesses life-saving blood transfusion that were refused by their parents.: 102
== Prevalence ==
There is a lot of variation in the rate of involuntary commitment between countries. A review in Europe in 2004 found a thirty-fold difference in the rate of psychiatric commitment between countries, with the median rate being 74 per hundred thousand people. It is estimated that 38% of people who are involuntarily committed experience another form of compulsion such as seclusion or forced medication.: 2
== Effects ==
A 2014 Cochrane systematic review found that compulsory outpatient treatment of those with severe mental health disorders "results in no significant difference in service use, social functioning or quality of life compared with standard voluntary care." A 2006 review found that as many as 48% of respondents did not agree with their treatment, though a majority of people retrospectively agreed that involuntary medication had been in their best interest.
A review in 2011 looked at people's experience of coercion in mental health care. It found common themes of feeling violated, disrespected, and not being heard, commonly conceptualized as being dehumanized through isolation. A minority of narratives from people who had been treated involuntarily talked about the necessity of treatment in retrospect. Studies suggest that coercion in mental health care has a long-lasting psychological effect on individuals leading to reduced engagement and poorer social outcomes, but that this may be reduced by clinicians' knowledge of the effects of coercion.
== Ethics ==
In medical ethics, involuntary treatment is conceptualized as a form of parens patriae whereby the state takes on the responsibilities of incompetent adults on the basis of the duty to protect and the duty of beneficence (the duty of the state to repair the random harms of nature). The duty to protect is reflected in utilitarianism and communitarianism philosophy, though psychiatrist Paul Chodoff asserted a responsibility to "chasten" this responsibility in light of the political abuse of psychiatry in the Soviet Union.: 82 This duty to protect has been criticized on the grounds that psychiatrists are not effective at predicting violence, and tend to overestimate the risk.: 89
The obligatory dangerousness criterion is a principle that has been applied to some mental health law that holds that parens patriae should only be applied if an individual is a danger to themselves or others.
Paul Ricœur distinguishes two forms of self, the idem, a short term experience of the self, and the ipse, a longer term persistent experience of the self. In mental illness, the autonomy of the ipse can be undermined by the autonomy of the idem, so involuntary mental health treatment can trade one form of autonomy for another.: 90
== Sociology ==
Medical sociology seeks to understand the social processes underlying decisions made in medicine.
Sociologist Jeremy Dixon, speaking in the context of the United Kingdom, argues that assessment and monitoring of risk is a core part of mental health practice: 126 but that this risk is often in conflict with broadly-defined goals of recovery including living a satisfying life.: 129 He argues that this focus on risk causes mental health professionals to make decisions defensively based on reputational damage if there were to be any inquiry and that multidisciplinary approaches are used for this purpose.: 134 He cites research showing how mental health professionals may seek to shift the burden of responsibility onto individuals themselves (noting different clinical decisions for those with personality disorders compared to those with psychotic disorders because they are viewed as more responsible for their behaviours), or shift responsibility onto other public health services.: 134 Risk assessments themselves are rarely shared with patients.: 135
== Proponents and detractors ==
=== Proponents ===
Supporters of involuntary treatment include organizations such as the National Alliance on Mental Illness (NAMI), the American Psychiatric Association, and the Treatment Advocacy Center.
=== Detractors ===
A number of civil and human rights activists, anti-psychiatry groups, medical and academic organizations, researchers, and members of the psychiatric survivors movement vigorously oppose involuntary treatment on human rights grounds or on grounds of effectiveness and medical appropriateness, particularly with respect to involuntary administration of mind altering substances, ECT, and psychosurgery. Some criticism has been made regarding cost, as well as of conflicts of interest with the pharmaceutical industry. Critics, such as the New York Civil Liberties Union, have denounced the strong racial and socioeconomic biases in forced treatment orders.
Special rapporteurs of the United Nations (Catalina Devandas Aguilar and Dainius Puras) consider it as an infringement of the dignity of those subjected to it, with severe consequences for their physical and mental integrity and call on concerned states to put an end to respect individual's autonomy.
Involuntary treatment is compared to torture on at least two special reports of the UN, one noting "forced psychiatric interventions, when committed against persons with psychosocial disabilities, satisfies both intent and purpose required under the article 1 of the Convention against Torture, notwithstanding claims of 'good intentions' by medical professionals." However, jurisdiction of some countries (e.g. France) requires intended harm (see: punitive psychiatry) to classify it as such and would classify involuntary treatment, rather as a degrading treatment, if recognize as it.
Amnesty International and Human Rights Watch oppose involuntary treatment.
== Laws internationally ==
=== United States ===
Mentally competent patients have a general right to refuse medical treatment.
All states in the U.S. allow for some form of involuntary treatment for mental illness or erratic behavior for short periods of time under emergency conditions, although criteria vary. Further involuntary treatment outside clear and pressing emergencies where there is asserted to be a threat to public safety usually requires a court order, and all states currently have some process in place to allow this. Since the late 1990s, a growing number of states have adopted Assisted Outpatient Commitment (AOC) laws.
Under assisted outpatient commitment, people committed involuntarily can live outside the psychiatric hospital, sometimes under strict conditions including reporting to mandatory psychiatric appointments, taking psychiatric drugs in the presence of a nursing team, and testing medication blood levels. Forty-five states presently allow for outpatient commitment.
In 1975, the U.S. Supreme Court ruled in O'Connor v. Donaldson that involuntary hospitalization and/or treatment violates an individual's civil rights. The individual must be exhibiting behavior that is a danger to themselves or others and a court order must be received for more than a short (e.g. 72-hour) detention. The treatment must take place in the least restrictive setting possible. This ruling has since been watered down through jurisprudence in some respects and strengthened in other respects. Long term "warehousing", through de-institutionalization, declined in the following years, though the number of people receiving involuntary treatment has increased more recently. The statutes vary somewhat from state to state.
In 1979, the United States Court of Appeals for the First Circuit established in Rogers v. Okin that a competent person committed to a psychiatric hospital has the right to refuse treatment in non-emergency situations. The case of Rennie v. Klein established that an involuntarily committed individual has a constitutional right to refuse psychotropic medication without a court order. Rogers v. Okin established the person's right to make treatment decisions so long as they are still presumed competent.
Additional U.S. Supreme Court decisions have added more restraints, and some expansions or effective sanctioning, to involuntary commitment and treatment. Foucha v. Louisiana established the unconstitutionality of the continued commitment of an insanity acquittee who was not suffering from a mental illness. In Jackson v. Indiana the court ruled that a person adjudicated incompetent could not be indefinitely committed. In Perry v. Louisiana the court struck down the forcible medication of a prisoner for the purposes of rendering him competent to be executed. In Riggins v. Nevada the court ruled that a defendant had the right to refuse psychiatric medication while he was on trial, given to mitigate his psychiatric symptoms. Sell v. United States imposed stringent limits on the right of a lower court to order the forcible administration of antipsychotic medication to a criminal defendant who had been determined to be incompetent to stand trial for the sole purpose of making them competent and able to be tried. In Washington v. Harper the Supreme Court upheld the involuntary medication of correctional facility inmates only under certain conditions as determined by established policy and procedures.
=== Europe ===
== See also ==
=== Related concepts ===
Coerced abstinence
Political abuse of psychiatry (also known as "political psychiatry" and as "punitive psychiatry")
Social control
Specific jurisdictions' provisions for a temporary detention order for the purpose of mental-health evaluation and possible further voluntary or involuntary commitment:
United States:
California: 5150 (involuntary psychiatric hold) and Laura's Law (providing for court-ordered outpatient treatment)
Lanterman–Petris–Short Act, codifying the conditions for and of involuntary commitment in California
Florida: Baker Act and Marchman Act
=== Notable activists ===
Giorgio Antonucci (elimination)
Thomas Szasz (elimination)
Robert Whitaker (reduction)
E. Fuller Torrey (expansion)
DJ Jaffe (expansion)
=== Advocacy organizations ===
Mental Health America (reduction/modification)
Mad in America (reduction/elimination)
PsychRights (reduction/elimination)
Anti-psychiatry, also known as the "anti-psychiatric movement" (reduction/elimination)
Citizens Commission on Human Rights (reduction/elimination; founded as a joint effort of the anti-psychiatric Church of Scientology and libertarian mental-health-rights advocate Thomas Szasz)
MindFreedom International (reduction/elimination)
Treatment Advocacy Center (expansion)
NAMI (expansion)
== Notes ==
== References ==
== External links ==
National Mental Health Consumers' Self-Help Clearinghouse | Wikipedia/Involuntary_treatment |
Insulin shock therapy or insulin coma therapy was a form of psychiatric treatment in which patients were repeatedly injected with large doses of insulin in order to produce daily comas over several weeks. It was introduced in 1927 by Austrian-American psychiatrist Manfred Sakel and used extensively in the 1940s and 1950s, mainly for schizophrenia, before falling out of favour and being replaced by neuroleptic drugs in the 1960s.
It was one of a number of physical treatments introduced into psychiatry in the first four decades of the 20th century. These included the convulsive therapies (cardiazol/metrazol therapy and electroconvulsive therapy), deep sleep therapy, and psychosurgery. Insulin coma therapy and the convulsive therapies are collectively known as the shock therapies.
== Origins ==
In 1927, Sakel, who had recently qualified as a medical doctor in Vienna and was working in a psychiatric clinic in Berlin, began to use low (sub-coma) doses of insulin to treat drug addicts and psychopaths, and when one of the patients experienced improved mental clarity after having slipped into an accidental coma, Sakel reasoned the treatment might work for mentally ill patients. Having returned to Vienna, he treated schizophrenic patients with larger doses of insulin in order to deliberately produce coma and sometimes convulsions. Sakel made his results public in 1933, and his methods were soon taken up by other psychiatrists.
Joseph Wortis, after seeing Sakel practice it in 1935, introduced it to the US. British psychiatrists from the Board of Control visited Vienna in 1935 and 1936, and by 1938, 31 hospitals in England and Wales had insulin treatment units. In 1936, Sakel moved to New York and promoted the use of insulin coma treatment in US psychiatric hospitals. By the late 1940s, the majority of psychiatric hospitals in the US were using insulin coma treatment.
== Technique ==
Insulin coma therapy was a labour-intensive treatment that required trained staff and a special unit. Patients, who were almost invariably diagnosed with schizophrenia, were selected on the basis of having a good prognosis and the physical strength to withstand an arduous treatment. There were no standard guidelines for treatment. Different hospitals and psychiatrists developed their own protocols. Typically, injections were administered six days a week for about two months.
The daily insulin dose was gradually increased to 100–150 units (1 unit = 34.7 μg) until comas were produced, at which point the dose would be levelled out. Occasionally doses of up to 450 units were used. After about 50 or 60 comas, or earlier if the psychiatrist thought that maximum benefit had been achieved, the dose of insulin was rapidly reduced before treatment was stopped. Courses of up to 2 years have been documented.
After the insulin injection patients would experience various symptoms of decreased blood glucose: flushing, pallor, perspiration, salivation, drowsiness or restlessness. Sopor and coma—if the dose was high enough—would follow. Each coma would last for up to an hour and be terminated by intravenous glucose or via naso-gastric tube. Seizures occurred before or during the coma. Many would be tossing, rolling, moaning, twitching, spasming or thrashing around.
Some psychiatrists regarded seizures as therapeutic and patients were sometimes also given electroconvulsive therapy or cardiazol/metrazol convulsive therapy during the coma, or on the day of the week when they didn't have insulin treatment. When they were not in a coma, insulin coma patients were kept together in a group and given special treatment and attention. One handbook for psychiatric nurses, written by British psychiatrist Eric Cunningham Dax, instructs nurses to take their insulin patients out walking and occupy them with games and competitions, flower-picking and map-reading, etc. Patients required continuous supervision as there was a danger of hypoglycemic aftershocks after the coma.
In "modified insulin therapy", used in the treatment of neurosis, patients were given lower (sub-coma) doses of insulin.
== Effects ==
A few psychiatrists (including Sakel) claimed success rates for insulin coma therapy of over 80% in the treatment of schizophrenia. A few others argued that it merely accelerated remission in those patients who were undergoing remission anyway. The consensus at the time was somewhere in between, claiming a success rate of about 50% in patients who had been ill for less than a year (about double the spontaneous remission rate) with no influence on relapse.
Sakel suggested the therapy worked by "causing an intensification of the tonus of the parasympathetic end of the autonomic nervous system, by blockading the nerve cell, and by strengthening the anabolic force which induces the restoration of the normal function of the nerve cell and the recovery of the patient." The shock therapies in general had developed on the erroneous premise that epilepsy and schizophrenia rarely occurred in the same patient. The premise was supported by neuropathologic studies that found a dearth of glia in the brains of schizophrenic patients and a surplus of glia in epileptic brains. These observations led the Hungarian neuropsychiatrist Ladislas Meduna to induce seizures in schizophrenic patients with injections of camphor, soon replaced by pentylenetetrazol (Metrazole). Another theory was that patients were somehow "jolted" out of their mental illness.
The hypoglycemia (pathologically low glucose levels) that resulted from insulin coma therapy made patients extremely restless, sweaty, and liable to further convulsions and "after-shocks". In addition, patients invariably emerged from the long course of treatment "grossly obese", probably due to glucose rescue-induced glycogen storage disease. The most severe risks of insulin coma therapy were death and brain damage, resulting from irreversible or prolonged coma respectively. A study at the time claimed that many of the cases of brain damage were actually therapeutic improvement because they showed "loss of tension and hostility". Mortality risk estimates varied from about 1% to 4.9%.
Respected singer-songwriter Townes Van Zandt was said to have lost much of his long-term memory from this treatment, performed on him for bipolar disorder, preceding a life of substance abuse and depression.
== Decline ==
Insulin coma therapy was used in most hospitals in the US and the UK during the 1940s and 1950s. The numbers of patients were restricted by the requirement for intensive medical and nursing supervision and the length of time it took to complete a course of treatment. For example, at one typical large British psychiatric hospital, Severalls Hospital in Essex, insulin coma treatment was given to 39 patients in 1956. In the same year, 18 patients received modified insulin treatment, while 432 patients were given electroconvulsive treatment.
In 1953, British psychiatrist Harold Bourne published a paper entitled "The insulin myth" in the Lancet, in which he argued that there was no sound basis for believing that insulin coma therapy counteracted the schizophrenic process in a specific way. If treatment worked, he said, it was because patients were chosen for their good prognosis and were given special treatment: "insulin patients tend to be an elite group sharing common privileges and perils". Prior to publishing "The insulin myth" in The Lancet, Bourne had tried to submit the article to the Journal of Mental Science; after a 12-month delay, the Journal informed Bourne they had rejected the article, telling him to "get more experience".
In 1957, when insulin coma treatment use was declining, The Lancet published the results of a randomized, controlled trial in which patients were either given insulin coma treatment or identical treatment but with unconsciousness produced by barbiturates. There was no difference in outcome between the groups and the authors concluded that, whatever the benefits of the coma regimen, insulin was not the specific therapeutic agent.
In 1958, American neuropsychiatrist Max Fink published in the Journal of the American Medical Association the results of a random controlled comparison in 60 patients treated with 50 iatrogenic insulin-induced comas or chlorpromazine in doses from 300 mg to 2000 mg/day. The results were essentially the same in relief and discharge ratings but chlorpromazine was safer with fewer side-effects, easier to administer, and better suited to long-term care.
In 1958, Bourne published a paper on increasing disillusionment in the psychiatric literature about insulin coma therapy for schizophrenia. He suggested there were several reasons it had received almost universal uncritical acceptance by reviews and textbooks for several decades despite the occasional disquieting negative finding, including that, by the 1930s when it all started, schizophrenics were considered inherently unable to engage in psychotherapy, and insulin coma therapy "provided a personal approach to the schizophrenic, suitably disguised as a physical treatment so as to slip past the prejudices of the age."
By the 1970s, insulin shock therapy had mostly fallen out of use in the United States, though was still practiced in some hospitals. Its use may have continued longer in China, India, and the Soviet Union.
== Recent writing ==
Recent articles about insulin coma treatment have attempted to explain why it was given such uncritical acceptance. In the US, Deborah Doroshow wrote that insulin coma therapy secured its foothold in psychiatry not because of scientific evidence or knowledge of any mechanism of therapeutic action, but due to the impressions it made on the minds of the medical practitioners within the local world in which it was administered and the dramatic recoveries observed in some patients. Today, she writes, those who were involved are often ashamed, recalling it as unscientific and inhumane. Administering insulin coma therapy made psychiatry seem a more legitimate medical field. Harold Bourne, who questioned the treatment at the time, said: "It meant that psychiatrists had something to do. It made them feel like real doctors instead of just institutional attendants".
One retired psychiatrist who was interviewed by Doroshow "described being won over because his patients were so sick and alternative treatments did not exist". Doroshow argues that "psychiatrists used complications to exert their practical and intellectual expertise in a hospital setting" and that collective risk-taking established "especially tight bonds among unit staff members". She finds it ironic that psychiatrists "who were willing to take large therapeutic risks were extremely careful in their handling of adverse effects". Psychiatrists interviewed by Doroshow recalled how insulin coma patients were provided with various routines and recreational and group-therapeutic activities, to a much greater extent than most psychiatric patients. Insulin coma specialists often chose patients whose problems were the most recent and who had the best prognosis; in one case discussed by Doroshow a patient had already started to show improvement before insulin coma treatment, and after the treatment denied that it had helped, but the psychiatrists nevertheless argued that it had.
=== A Beautiful Mind ===
In 1959, the 1994 Nobel Prize winner in Economics, John Nash, was diagnosed with schizophrenia and was initially treated at McLean Hospital. When he relapsed, he was admitted to Trenton Psychiatric Hospital in New Jersey. His associates at Princeton University pleaded with the hospital director to have Nash admitted to the insulin coma unit, recognizing that it was better staffed than other hospital units. He responded to treatment and was subsequently medicated with neuroleptics.
Nash's life story was presented in the film A Beautiful Mind, which accurately portrayed the seizures associated with his treatments. In a review of the Nash history, Fink ascribed the success of coma treatments to the 10% of associated seizures, noting that physicians often augmented the comas by convulsions induced by ECT. He envisioned insulin coma treatment as a weak form of convulsive therapy.
=== Other explanations ===
In the UK, psychiatrist Kingsley Jones sees the support of the Board of Control as important in persuading psychiatrists to use insulin coma therapy. The treatment then acquired the privileged status of a standard procedure, protected by professional organizational interests. He also notes that it has been suggested that the Mental Treatment Act 1930 encouraged psychiatrists to experiment with physical treatments.
British lawyer Phil Fennell notes that patients "must have been terrified" by the insulin coma therapy procedures and the effects of the massive overdoses of insulin, and were often rendered more compliant and easier to manage after a course.
Leonard Roy Frank, an American activist from the psychiatric survivors movement who underwent 50 forced insulin coma treatments combined with ECT, described the treatment as "the most devastating, painful and humiliating experience of my life", a "flat-out atrocity" glossed over by psychiatric euphemism, and a violation of basic human rights.
In 2013, French physician-and-novelist Laurent Seksik wrote an historical novel about the tragic life of Eduard Einstein: Le cas Eduard Einstein. He related the encounter between Dr Sakel and Mileva Maric, Albert Einstein's first wife (and Eduard's mother), and the way Sakel's therapy had been given to Eduard, who had schizophrenia.
== Representation in media ==
Like many new medical treatments for diseases previously considered incurable, depictions of insulin coma therapy in the media were initially favorable. In the 1940 film Dr. Kildare's Strange Case, young Kildare uses the new "insulin shock cure for schizophrenia" to bring a man back from insanity. The film dramatically shows a five-hour treatment that ends with a patient eating jelly sandwiches and reconnecting with his wife. Other films of the era began to show a more sinister approach, beginning with the 1946 film Shock, in which actor Vincent Price plays a doctor who plots to murder a patient using an overdose of insulin in order to keep the fact that he was a murderer a secret. More recent films include Frances (1982) in which actress Frances Farmer undergoes insulin coma treatment, and A Beautiful Mind, which depicted genius John Nash undergoing insulin treatment. In an episode of the medical drama House M.D., House puts himself in an insulin shock to try to make his hallucinations disappear. Sylvia Plath's The Bell Jar refers to insulin coma therapy in chapter 15. In Kelly Rimmer's book, The German Wife, the character Henry Davis undergoes insulin shock therapy to treat 'combat fatigue'. Russian novelist Eduard Limonov recounts his personal experience being put under insulin shock therapy in his 1986 novel A Young Scoundrel, scenes from which are adapted for film in the 2004 crime comedy-drama It's Russian.
== See also ==
Deep sleep therapy
Electroconvulsive therapy
Manfred Sakel
== References ==
24. "House M.D" "Under My Skin" episode 23, Season 5. Plot synopsis "House" Under My Skin (TV Episode 2009) - IMDb
== External links ==
The History of Shock Therapy in Psychiatry Archived 31 January 2023 at the Wayback Machine
Drug Treatment in Modern Psychiatry
1944 textbook extract on 'The Insulin Treatment of Schizophrenia'
Insulin Coma Therapy Archived 15 October 2002 at the Wayback Machine by the head of the insulin coma unit at the Hillside Hospital in New York from 1952 to 1958
Shock Treatment - The Killing of Susan Kelly Archived 12 October 2008 at the Wayback Machine A poem by insulin/electro shock survivor Dorothy Dundas | Wikipedia/Insulin_shock_therapy |
Constraint-induced movement therapy (CI, CIT, or CIMT) is a form of rehabilitation therapy that improves upper extremity function in stroke and other central nervous system damage patients by increasing the use of their affected upper limb. Due to its high duration of treatment, the therapy has been found to frequently be infeasible when attempts have been made to apply it to clinical situations, and both patients and treating clinicians have reported poor compliance and concerns with patient safety. In the United States, the high duration of the therapy has also made the therapy not able to get reimbursed in most clinical environments.
However, distributed or "modified" CIT protocols have enjoyed similar efficacy to CIMT, have been able to be administered in outpatient clinical environments, and have enjoyed high success rates internationally.
== Types of constraint ==
The focus of CIMT is to combine restraint of the unaffected limb and intensive use of the affected limb. Types of restraints include a sling or triangular bandage, a splint, a sling combined with a resting hand splint, a half glove, and a mitt. Determination of the type of restraint used for therapy depends on the required level of safety vs. intensity of therapy. Some restraints restrict the wearer from using their hand and wrist, though allow use of their non-involved upper extremity for protection by extension of their arm in case of loss of balance or falls. However, restraints that allow some use of the non-involved extremity will result in less intensive practice because the non-involved arm can still be used to complete tasks. Constraint typically consists of placing a mitt on the unaffected hand or a sling or splint on the unaffected arm, forcing the use of the affected limb with the goal of promoting purposeful movements when performing functional tasks. The use of the affected limb is called shaping.
== Duration and timing of "traditional" versus "modified" CI therapy programs ==
Traditionally, CIMT involves restraining the unaffected arm in patients with hemiparetic stroke or hemiparetic cerebral palsy (HCP) for 90% of waking hours while engaging the affected limb in a range of everyday activities However, given concerns with compliance (both among patients and clinicians), reimbursement, and patient safety, studies have varied on hours of restraint per day and length of therapy. More specifically, CIMT involves the person performing supervised structured tasks with the affected limb 6 hours a day for 10 days over a 14-day period, in addition to wearing the restrictive mitt or sling for 90% of waking hours.
Alternatively, modified constraint induced movement therapy protocols have been found to be equally effective as "traditional" CI therapy protocols. The most established, commonly used, and evidence based form of modified CI therapy that has been found to be effective in improving motor control asks patients to attend goal directed therapy sessions lasting a half hour per day, on 3 days/week over a 10-week period. Concurrently, patients wear a mitt on the less affected limb for 5 hours/weekday during the same 10-week period. In addition to providing more practice with the affected limb than "traditional" CI therapy over the 10-week period, the regimen is in greater accord with outpatient therapy regimens around the world, is less costly, and the efficacy has been shown to be comparable to a more intensive CI therapy schedule.
Practitioners say that stroke survivors disabled for many years have recovered the use of their limbs using CIMT. However, it has been shown that receiving CIMT early on (3–9 months post-stroke) will result in greater functional gains than receiving delayed treatment (15–21 months post-stroke), with no benefits associated with its administration acutely (< 3 months post stroke). However, modified CI therapy protocols have shown larger treatment effects when administered in the acute phase.
== Mechanism of change ==
CIMT was developed by Edward Taub of the University of Alabama at Birmingham. Taub argues that, after a stroke, the patient stops using the affected limb because they are discouraged by the difficulty. As a result, a process that Taub calls "learned non-use" sets in, furthering the deterioration. Learned non-use is a type of negative feedback. Individuals are unable to move their affected limb or the movements are inefficient and clumsy and in response to this a suppression of movement occurs. It is this process that CIMT seeks to reverse. The American Stroke Association has written that Taub's therapy is "at the forefront of a revolution" in what is regarded possible in terms of recovery for stroke survivors.
As a result of the patient engaging in repetitive exercises with the affected limb, the brain grows new neural pathways. This change in the brain is referred to as cortical reorganization or neuroplasticity. One study by Deluca et al. showed that using transcranial magnetic stimulation (TMS) that the excitable cortex of the affected cortex in adults patients with HCP doubled in size after 12 days of therapy. Recently, the possible benefits of cortical reorganization has led to studies of CIMT on children because neuroplasticity is even greater among children than adults. Particular interest is growing in CIMT for children who have cerebral palsy where one arm is more affected than the other.
As with adults, however, the plausibility of administering CIMT in pediatric models is low except in specialized, for profit, clinics, due to its intensive parameters, and it has been noted that compliance is especially low in most community-dwelling children.
== Application of constraint-induced movement therapy ==
Both CIMT and modified CIMT may be applicable to up to 20–25 percent of stroke patients, and the amount of improvement produced by either regimen appears to diminish as the initial motor ability of the patient decreases. Both CIMT and modified CI therapy has been shown to be an effective means of stroke rehabilitation regardless of the level of initial motor ability, amount of chronicity, amount of prior therapy, side of hemiparesis, or infarct location. This suggests that plasticity may work irrespective of the pathways in the damaged motor network. Although, due to the duration of this treatment, patients who have had profound upper extremity paralysis from their condition are normally not eligible for constraint-induced upper extremity training. A consistent exclusion criterion for CIMT and modified CI therapy has been the inability to perform voluntary wrist and finger extension in the involved hand. As stated above, this criterion typically limits the population eligible for this family of therapies to 20–25% of the entire stroke population.
CIAT (Constraint Induced Aphasia Therapy) is an adaptation of CIMT for people with Aphasia. It can be used for clients with either expressive or receptive aphasia. Like CIMT, treatment is intensive and usually occurs over a ten-day period for several hours per day. In CIAT, patient must use verbal communication without gestures or pointing in order communicate. The constraints are placed on the use of gestures with the aim of improving verbal communication. Also like CIMT, CIAT has been shown to not be feasible in most clinical environments due to its parameters and distributed protocols are now being investigated.
Both constraint-induced movement therapy (CIMT) and modified CI therapy coupled with intensive and varied exercise training has proven to be effective in reducing spasticity and increasing function of the hemiplegic upper extremity in chronic stroke patients.
The effects of constraint-induced movement therapy and its modified versions have been found to improve movements that not only remain stable for months after the completion of therapy, but translate well to improvements of everyday functional task.
== Limitations to implementation ==
As stated earlier, the "traditional" form of constraint-induced movement therapy (CIMT) has not been incorporated as part of standard practice for the rehabilitation of the hemiplegic upper extremity. Most notably, concerns have been cited over the reimbursement, intensity, and both patient and clinician compliance with the therapy, especially in light of equally-effective, less intense alternative forms. Concerns have also been raised over the generalizability of the results obtained from research, as selection criteria for CIMT research has excluded patients with a moderate or more severe stroke, due to balance problems, serious cognitive deficits, and global aphasia, which may reduce understanding of safety instructions and interfere with a patient's ability to communicate difficulties.
The cost of resources needed to conduct CIMT treatment protocol are high. Costs are generated due to the intensity of therapy required for CIMT, as participants typically receive up to 6 hours of one-on-one therapy at least 5 days per week for 2 weeks. CIMT can be prohibitively expensive for patients paying out-of-pocket or for publicly funded health care systems attempting to make this program available to all eligible stroke survivors.
Therapist apprehension directed at safety issues with constraint use, lack of facilities, the cost of providing one-on-one therapy sessions, and the opportunity costs associated with the therapist's inability to see and treat other patients during that time has contributed to the resistance of adopting the CIMT protocol.
The patient's ability to tolerate the intensity and duration of the therapy sessions is a limiting factor to protocol adoption. Stroke patients have commonly expressed the length of time wearing the constraint and time-consuming hours of therapy as reasons they wish not to participate.
While the CIMT protocol results in improved function in its target population, it is unknown whether the combination of constraint and therapy is necessary to achieve the outcome seen or whether the benefit is due to exposure to high-intensity, task-specific activities focused on the use of the more affected limb. Additionally, the therapy only appears to work on stroke survivors with some initial movement in their wrists and fingers; about 25% of the entire population of stroke survivors.
== See also ==
Neuroplasticity
Silver Spring Monkeys
== References == | Wikipedia/Constraint-induced_movement_therapy |
A motor controller is a device or group of devices that can coordinate in a predetermined manner the performance of an electric motor. A motor controller might include a manual or automatic means for starting and stopping the motor, selecting forward or reverse rotation, selecting and regulating the speed, regulating or limiting the torque, and protecting against overloads and electrical faults. Motor controllers may use electromechanical switching, or may use power electronics devices to regulate the speed and direction of a motor.
== Applications ==
Motor controllers are used with both DC motors (direct current) and AC motors (alternating current). A controller includes means to connect the motor's windings to the electrical power supply, and may also include overload, over-current, and oveheating protection and wiring (i.e. magnetic starter). A motor controller may also supervise the motor's field circuit, or detect conditions such as low supply voltage, incorrect polarity or incorrect phase sequence, or high motor temperature. Some motor controllers limit the inrush starting current, allowing the motor to accelerate itself and connected mechanical load more slowly than a direct connection. Motor controllers may be manual, requiring an operator to sequence a starting switch through steps to accelerate the load, or may be fully automatic, using internal timers or current sensors to accelerate the motor.
Some types of motor controllers also allow adjustment of the speed of the electric motor. For direct-current motors, the controller may adjust the voltage applied to the motor, or adjust the current flowing in the motor's field winding. Alternating current motors may have little or no speed response to adjusting terminal voltage, so controllers for alternating current instead adjust rotor circuit resistance (for wound rotor motors) or change the frequency of the AC applied to the motor for speed control using power electronic devices or electromechanical frequency changers.
The physical design and packaging of motor controllers is about as varied as that of electric motors themselves. A wall-mounted toggle switch with suitable ratings may be all that is needed for a household ventilation fan. Power tools and household appliances may have a trigger switch that only turns the motor on and off. Industrial motors may be more complex controllers connected to automation systems; a factory may have a large number of motor controllers grouped in a motor control center. Controllers for electric travelling cranes or electric vehicles may be mounted on the mobile equipment. The largest motor controllers are used with the pumping motors of pumped storage hydroelectric plants, and may carry ratings of tens of thousands of horsepower (kilowatts).
== Types of motor controller ==
Motor controllers can be manually, remotely or automatically operated. They may include only the means for starting and stopping the motor or they may include other functions.
An electric motor controller can be classified by the type of motor it is to drive, such as permanent magnet, servo, series, separately excited, and alternating current.
A motor controller is connected to a power source, such as a battery pack or power supply, and control circuitry in the form of analog or digital input signals.
=== Motor starters ===
A small motor can be started by simply connecting it to power. A larger motor requires a specialized switching unit called a motor starter or motor contactor. When energized, a direct on line (DOL) starter immediately connects the motor terminals directly to the power supply. In smaller sizes a motor starter is a manually operated switch; larger motors, or those requiring remote or automatic control, use magnetic contactors. Very large motors running on medium voltage power supplies (thousands of volts) may use power circuit breakers as switching elements.
A direct on line (DOL) or across the line starter applies the full line voltage to the motor terminals. This is the simplest type of motor starter. A DOL motor starter often contains protection devices (see below), and in some cases, condition monitoring. Smaller sizes of direct on-line starters are manually operated; larger sizes use an electromechanical contactor to switch the motor circuit. Solid-state direct on line starters also exist.
A direct on line starter can be used if the high inrush current of the motor does not cause excessive voltage drop in the supply circuit. The maximum size of a motor allowed on a direct on line starter may be limited by the supply utility for this reason. For example, a utility may require rural customers to use reduced-voltage starters for motors larger than 10 kW.
DOL starting is sometimes used to start small water pumps, compressors, fans and conveyor belts. In the case of an asynchronous motor, such as the 3-phase squirrel-cage motor, the motor will draw a high starting current until it has run up to full speed. This starting current is typically 6-7 times greater than the full load current. To reduce the inrush current, larger motors will have reduced-voltage starters or adjustable-speed drives in order to minimise voltage dips to the power supply.
A reversing starter can connect the motor for rotation in either direction. Such a starter contains two DOL circuits — one for clockwise operation and the other for counter-clockwise operation, with mechanical and electrical interlocks to prevent simultaneous closure. For three phase motors, this is achieved by swapping the wires connecting any two phases. Single phase AC motors and direct-current motors often can be reversed by swapping two wires but this is not always the case.
Motor starters other than 'DOL' connect the motor through a resistance to reduce the voltage the motor coils get on start up. The resistance for this needs to be sized to the motor - and a quick source for a good resistance to use is another coil in the motor - i.e. series/parallel. In series gives a gentler start then switched to parallel for full power running. When this is done with three phase motors, it is commonly called a star-delta (US: Y-delta) starter. Old star-delta starters were manually operated and often incorporated an ammeter so the person operating the starter could see when the motor was up to speed by the fact the current it was drawing had stopped decreasing. More modern starters have built-in timers to switch from star to delta and are set by the electrical installer of the machine. The machin's operator simply presses a green button once and the rest of the start procedure is automated.
A typical starter includes protection against overload, both electrical and mechanical, and protection against 'random' starting - if, for instance, the power has been off and has just come back on. An acronym for this type of protection is TONVR - Thermal Overload, No Volt Release. It insists that the green button is pressed to start the motor. The green button switches on a solenoid which closes a contactor (i.e. switch) to primarily power the motor. It also powers the solenoid to keep the power turned on when the green button is released. In a power failure, the contactor opens turning itself and the motor off. The only way the motor can then be started is by pressing the green button. The contactor can be quickly tripped by the starter passing a very high current due to an electrical fault downstream of it in either the wiring to the motor or within the motor. The thermal overload protection consists of a heating element on each power wire which heats a bimetallic strip. The hotter the strip, the more it deflects to the point it pushes a trip bar which disconnects power to the contactor solenoid, turning everything off. Thermal overloads come in different range ratings and this should be chosen to match the motor. Within the range, they are adjustable enabling the installer to set it correctly for the given motor.
Which type for specific applications? DOL gives a quick start so is used more commonly with generally smaller motors. It is also used on machines with an uneven load such as piston type compressors where the full power of the motor is needed to get the piston past the compression stage - the actual working stage. Star-delta is generally used with larger motors or where either the motor is under no load at starting, very little load or a consistent load. It is particularly suited to motors driving machinery with heavy flywheels - to get the flywheels up to speed before the machine is engaged and driven by the flywheel.
=== Reduced voltage starters ===
Reduced-voltage or soft starters connect the motor to the power supply through a voltage reduction device and increases the applied voltage gradually or in steps. Two or more contactors may be used to provide reduced voltage starting of a motor. By using an autotransformer or a series inductance, a lower voltage is present at the motor terminals, reducing starting torque and inrush current. Once the motor has come up to some fraction of its full-load speed, the starter switches to full voltage at the motor terminals. Since the autotransformer or series reactor only carries the heavy motor starting current for a few seconds, the devices can be much smaller compared to continuously rated equipment. The transition between reduced and full voltage may be based on elapsed time, or triggered when a current sensor shows the motor current has begun to reduce. An autotransformer starter was patented in 1908.
Larger 3 phase induction motors can have their power reduced within the motor ! The motor is started 'DOL' with full voltage supplied to the field coils of the motor outer part ('stator'). The inner part ('rotor') has a current induced into it to once again react with the magnetic field generated by the stator. By breaking the rotor into parts and electrically connecting these parts to external resistances via slip rings and brushes as well as control contactors, the magnetic power of the rotor can be varied - i.e. reduced, for starting or low power running. Although a much more complex process, it means the currents (electrical loads) being switched are significantly lower than if reducing the power to the main feed of the motor.
A third way to achieve a very smooth progressive start is to dip resistance rods into a conductive liquid (e.g. mercury) which has a layer of insulative oil on the top. As the rods are lowered the resistance is gradually reduced.
A star delta starter is another type of Reduced-voltage starter in induction motor. A star delta starter will start a motor with a star connected stator winding. When motor reaches about 80% of its full load speed, it will begin to run in a delta connected stator winding. Star Delta Starter are two types. (1) Manual Operated Star Delta Starter, (2) Automatic Star Delta.
The manual operated star delta starter mainly consists of a TPDP switch which stands for Triple Pole Double Throw switch. This switch changes stator winding from star to delta. During starting condition stator winding is connected in the form of a star. Now we shall see how a star delta starter reduces the starting current of a three-phase induction motor.
The above function achieved by using a power contactor and timer in automatic star delta starter. The automatic star delta starter is manufactured from three contactors, a timer and a thermal overload. The contactors are smaller than the single contactor used in a direct on line starter as they are controlling winding currents only. The currents through the winding are 1/root 3 (58%) of the current in the line. There are two contactors that are close during run, often referred to as the main contractor and the delta contactor. These are AC3 rated at 58% of the current rating of the motor. The third contactor is the star contactor and that only carries star current while the motor is connected in star. The current in star is one third of the current in delta, so this contactor can be AC3 rated at one third (33%) of the motor rating.
The transition from star to delta can be an open transition or a closed transition. During open transition, the motor starter momentarily disconnects from the motor and reconnects in a delta configuration. In closed transition, the transition from the star to delta configuration is achieved without disconnecting the motor. In order to achieve that, an additional three-pole contactor and three resistors are required.
=== Adjustable-speed drives ===
An adjustable-speed drive (ASD) or variable-speed drive (VSD) is an interconnected combination of equipment that provides a means of driving and adjusting the operating speed of a mechanical load. An electrical adjustable-speed drive consists of an electric motor and a speed controller or power converter plus auxiliary devices and equipment. In common usage, the term "drive" is often applied to just the controller. Most modern ASDs and VSDs can also implement soft motor starting.
=== Intelligent controllers ===
An Intelligent Motor Controller (IMC) uses a microprocessor to control power electronic devices used for motor control. IMCs monitor the load on a motor and accordingly match motor torque to motor load. This is accomplished by reducing the voltage to the AC terminals and at the same time lowering current and kvar. This can provide a measure of energy efficiency improvement for motors that run under light load for a large part of the time, resulting in less heat, noise, and vibrations
generated by the motor.
== Overload relays ==
A starter will contain protective devices for the motor. At a minimum this would include a thermal overload relay. The thermal overload is designed to open the starting circuit and thus cut the power to the motor in the event of the motor drawing too much current from the supply for an extended time. The overload relay has a normally closed contact which opens due to heat generated by excessive current flowing through the circuit. Thermal overloads have a small heating device that increases in temperature as the motor running current increases.
There are two types of thermal overload relay. In one type, a bimetallic strip located close to a heater deflects as the heater temperature rises until it mechanically causes the device to trip and open the circuit, cutting power to the motor should it become overloaded. A thermal overload will accommodate the brief high starting current of a motor while accurately protecting it from a running current overload. The heater coil and the action of the bi-metallic strip introduce a time delay that affords the motor time to start and settle into normal running current without the thermal overload tripping. Thermal overloads can be manually or automatically resettable depending on their application and have an adjuster that allows them to be accurately set to the motor run current.
A second type of thermal overload relay uses a eutectic alloy, like a solder, to retain a spring-loaded contact. When too much current passes through the heating element for too long a time, the alloy melts and the spring releases the contact, opening the control circuit and shutting down the motor. Since eutectic alloy elements are not adjustable, they are resistant to casual tampering but require changing the heater coil element to match the motor rated current.
Electronic digital overload relays containing a microprocessor may also be used, especially for high-value motors. These devices model the heating of the motor windings by monitoring the motor current. They can also include metering and communication functions.
== Loss of voltage protection ==
Starters using magnetic contactors usually derive the power supply for the contactor coil from the same source as the motor supply. An auxiliary contact from the contactor is used to maintain the contactor coil energized after the start command for the motor has been released. If a momentary loss of supply voltage occurs, the contactor will open and not close again until a new start command is given. This prevents restarting of the motor after a power failure. This connection also provides a small degree of protection against low power supply voltage and loss of a phase. However, since contactor coils will hold the circuit closed with as little as 80% of normal voltage applied to the coil, this is not a primary means of protecting motors from low voltage operation.
== Motor ride-through under voltage events ==
Some devices can be added so that during a voltage drop, the device maintains the current flow
that is sufficient for the hold-in coil to keep the contacts closed. The circuit is designed allows current for the hold-in coil for voltage sags down to 15-25% voltage.
== Timed Sequenced Schedule of the Automatic Restarts Of Multiple Motors ==
After the electrical power has been restored (typically after a time delay of 30 to 60 seconds), then the time sequences of the automatic restarts of multiple motors are set to automatically begin.
Without a time sequenced schedule, any attempt to restart many motors simultaneously could lead to partial or total site wide power failure.
== Servo controllers ==
Servo controllers are a wide category of motor control. Common features are:
precise closed loop position control
fast acceleration rates
precise speed control Servo motors may be made from several motor types, the most common being:
brushed DC motor
brushless DC motors
AC servo motors
Servo controllers use position feedback to close the control loop. This is commonly implemented with position encoders, resolvers, and Hall effect sensors to directly measure the rotor's position.
Other position feedback methods measure the back EMF in the undriven coils to infer the rotor position, or detect the Kick-Back voltage transient (spike) that is generated whenever the power to a coil is instantaneously switched off. These are therefore often called "sensorless" control methods.
A servo may be controlled using pulse-width modulation (PWM). How long the pulse remains high (typically between 1 and 2 milliseconds) determines where the motor will try to position itself. Another control method is pulse and direction.
== Stepper motor controllers ==
A stepper, or stepping, motor is a synchronous, brushless, high pole count, polyphase motor. Control is usually, but not exclusively, done open loop, i.e., the rotor position is assumed to follow a controlled rotating field. Because of this, precise positioning with steppers is simpler and cheaper than closed loop controls.
Modern stepper controllers drive the motor with much higher voltages than the motor nameplate rated voltage, and limit current through chopping. The usual setup is to have a positioning controller, known as an indexer, sending step and direction pulses to a separate higher voltage drive circuit which is responsible for commutation and current limiting.
== See also ==
Motor control center (MCC)
== References ==
"Dallas Personal Robotics Group". Brief H-Bridge Theory of Operation. Archived from the original on January 12, 2013. Retrieved July 7, 2005.
Links to manufacturers, associations, and other resources. Archived 2013-08-29 at the Wayback Machine | Wikipedia/Motor_controller |
Motor Function (stylized in all caps) is the debut EP by American singer-songwriter and rapper Binki. It was released on August 13, 2021 through Fader Label.
Motor Function was met with acclaim from music critics, who praised Binki's blending of genres and his energy on the album.
== Background and recording ==
Prior to Motor Function, Binki had been releasing singles after he shifted focus from acting pursuits toward venturing into music following his graduation from university in 2018, and subsequent move to New York City. Garnering attention from music media outlets for these singles, The Line of Best Fit's Hannah Browne wrote that Binki developed a reputation for "gritty, punkish energy" due to his "novel fusion of sophisticated pop, brattish indie, grungy rap, and the majority in between." Based in Brooklyn, Binki has cited the borough's "genre-less" approach to music, as well as the "kinetic energy" of New York's music scene as inspiration for Motor Function.
Binki's debut EP, Motor Function also drew inspiration from his quarantine stemming from the COVID-19 pandemic. The EP's intro track, "Clay Pigeon", as well as "Landline" were both recorded remotely. The first song finished for Motor Function, "Revolve" was written and recorded in one day. "Revolve" included "glitchy vocals and creeping synth." The song also layered "heavy drums and guitars interspersed with short electronic instruments."
The EP includes Binki's commentary on themes such as "vulnerability, youthful frustration, and broken relationships."
== Release and singles ==
In May 2021, Binki released the single "Clay Pigeon". "Revolve" was then released on June 30. The EP was released through Fader Label shortly thereafter, on August 13.
== Critical reception ==
Motor Function received praise from music reviewers, who noted its tracks to have an appealing raw kineticism. Margaret Farrell, writing for Flood, stated the tracks on Motor Function "are a spectrum of thrills", pointing to the "pummeling bass" on "Revolve", as well as the "grime and glamour" of "Landline". Farrell went on to say "Binki's vocals are commanding without being overbearing," noting the juxtaposition of the "rich" delivery on his singing vocals and the "harshness of his spoken-word" segments. Farrell opined that "the overall intensity of Motor Function is an electric balm in a year with much need for catharsis."
Sophie Williams of NME wrote that Motor Function is a "medley of genre-splicing anthems that ring in your ears for days afterwards," and noted that Binki's commentary on the project's themes "[tumble] out of him with audacious energy over stop-start riffs and ear-bending beats." Williams went on to rate the EP four out five stars; in her review, Williams praised the EP as "wonderfully tight and electric", stating it established Binki as "a versatile singer-songwriter, whose magnetic choruses thrive off duelling forces of freedom and anxiety." Williams called "Revolve" a "highlight" on the EP, writing that the song "upholds the EP's overarching acceptance of difficult truths as it moves into the murky territory of romantic frustration."
== Track listing ==
== References == | Wikipedia/Motor_Function |
As humans move through their environment, they must change the stiffness of their joints in order to effectively interact with their surroundings. Stiffness is the degree to a which an object resists deformation when subjected to a known force. This idea is also referred to as impedance, however, sometimes the idea of deformation under a given load is discussed under the term "compliance" which is the opposite of stiffness (defined as the amount an object deforms under a certain known load).
In order to effectively interact with their environment, humans must adjust the stiffness of their limbs. This is accomplished via the co-contraction of antagonistic muscle groups.
Humans use neural control along with the mechanical constraints of the body to adjust this stiffness as the body performs various tasks. It has been shown that humans change the stiffness of their limbs as they perform tasks such as hopping, performing accurate reaching tasks, or running on different surfaces.
While the exact method by which this neural-modulation of limb stiffness occurs is unknown, many different hypotheses have been proposed. A thorough understanding of how and why the brain controls limb stiffness could lead to improvements in many robotic technologies that attempt to mimic human movement.
== Stiffness ==
Stiffness is typically viewed as a material property describing the amount a material deforms under a given force as described by Hooke's law. This means that objects with higher stiffness are more difficult to bend or deform than objects with lower stiffnesses. This concept can be extended to the limbs and joints of biological organisms in which stiffness describes the degree to which a limb or joint deflects (or bends) under a given load. Limb stiffness can also be described as the static component of impedance. Humans change the stiffness of their limbs and joints to adapt to their environment. Limb and joint stiffness has been previously studied and can be quantified in various ways. The basic principle for calculating stiffness is dividing the deformation of a limb by the force applied to the limb, however, there are multiple methods of quantifying limb and joint stiffness with various pros and cons. When quantifying limb stiffness, one cannot simply sum the individual joint stiffnesses due to the nonlinearities of the multi-joint system.
A few of the specific methods for calculating limb stiffness can be seen below:
Vertical Stiffness (k vert) is a quantitative measure of leg stiffness that can be defined by the equations below:
K
vert
=
F
max
Δ
y
{\displaystyle K_{\text{vert}}={\frac {F_{\text{max}}}{\Delta y}}}
Where F max is the maximum vertical force and delta y is the maximum vertical displacement of the center of mass
K
vert
=
m
(
2
π
P
)
2
{\displaystyle K_{\text{vert}}=m({\frac {2\pi }{P}})^{2}}
Where m is the body mass and P is the period of vertical vibration
K
vert
=
m
ω
0
2
{\displaystyle K_{\text{vert}}=m\omega _{\text{0}}^{2}}
Where m is the mass of the body mass and ω 0 is the natural frequency of oscillation
Limb Stiffness (K_limb) is the stiffness of the entire limb and can be defined by the equations below:
K
limb
=
F
max
Δ
L
{\displaystyle K_{\text{limb}}={\frac {F_{\text{max}}}{\Delta L}}}
Where F max is the maximum applied force and ΔL is the change in length of the limb
Torsional Stiffness (K_joint) is the rotational stiffness of the joint and can be defined by the equations below:
K
joint
=
Δ
M
Δ
θ
{\displaystyle K_{\text{joint}}={\frac {\Delta M}{\Delta \theta }}}
Where ΔM is the change in joint moment and Δθ is the change in joint angle
K
joint
=
2
W
Δ
θ
{\displaystyle K_{\text{joint}}={\frac {2W}{\Delta \theta }}}
Where W is the negative mechanical work at the joint and Δθ is the change in joint angle
These different mathematical definitions of limb stiffness help to describe limb stiffness and show the methods by which such a limb characteristic can be quantified.
== Stiffness modulation ==
The human body is able to modulate its limb stiffnesses through various mechanisms with the goal of more effectively interacting with its environment. The body varies the stiffness of its limbs by three primary mechanisms: muscle cocontraction, posture selection, and through stretch reflexes.
Muscle cocontraction (similar to muscle tone) is able to vary the stiffness of a joint by the action of antagonistic muscles acting on the joint. The stronger the forces of the antagonistic muscles on the joint are, the stiffer the joint becomes. The selection of body posture also affects the stiffness of the limb. By adjusting the orientation of the limb, the inherent stiffness of the limb can be manipulated. Additionally, the stretch reflexes within a limb can affect the stiffness of the limb, however these commands are not sent from the brain.
=== Locomotion and hopping ===
As humans walk or run across different surfaces, they adjust the stiffness of their limbs to maintain similar locomotor mechanics independent of the surface. As the stiffness of a surface changes, humans adapt by changing their limb stiffness. This stiffness modulation allows for running and walking with similar mechanics regardless of the surface, therefore allowing humans to better interact and adapt with their environment. The modulation of stiffness therefore, has applications in the areas of motor control and other areas pertaining to the neural control of movement.
Studies also show that the variation of limb stiffness is important when hopping, and that different people may control this stiffness variation in different ways. One study showed that adults had more feedforward neural control, muscle reflexes, and higher relative leg stiffness than their juvenile counterparts when performing a hopping task. This indicates that the control of stiffness may vary from person to person.
=== Movement accuracy ===
The nervous system also controls limb stiffness to modulate the degree of accuracy that is required for a given task. For example, the accuracy required to grab a cup off of a table is very different from that of a surgeon performing a precise task with a scalpel. To accomplish these tasks with varying degrees of required accuracy, the nervous system adjusts limb stiffness. To accomplish very accurate tasks higher stiffness is required, however, when performing tasks where accuracy is not as imperative, lower limb stiffness is needed. In the case of accurate movements, the central nervous system is able to precisely control limb stiffness to limit movement variability. The cerebellum also plays a large role in controlling for the accuracy of movements.
This is an important concept for everyday tasks such as tool use. For example, when using a screwdriver, if limb stiffness is too low, the user will not have enough control over the screwdriver to drive a screw. Because of this, the central nervous system increases limb stiffness to allow the user to accurately maneuver the tool and perform a task.
== Neural control ==
The exact mechanism for the neural control of stiffness is unknown, but progress has been made in the field with multiple proposed models of how stiffness modulation may be accomplished by the nervous system. Limb stiffness has multiple components that must be controlled to produce the appropriate limb stiffness.
=== Combination of mechanics and neural control ===
Both the neural control and the mechanics of the limb contribute to its overall stiffness. The cocontraction of antagonistic muscles, posture of the limb, and stretch reflexes within the limb all contribute to stiffness and are affected by the nervous system.
The stiffness of a limb is dependent on its configuration or joint arrangement. For example, an arm that is slightly bent, it will deform more easily under a force directed from the hand to the shoulder than an arm that is straight. In this way, the stiffness of a limb is partially dictated by the limb's posture. This component of limb stiffness is due to the mechanics of the limb and is controlled voluntarily.
=== Voluntary vs. involuntary stiffness modulation ===
Some components of limb stiffness are under voluntary control while others are involuntary. The determining factor as to whether a component of stiffness is controlled voluntarily or involuntarily is the timescale of that particular component's method of action. For example, stiffness corrections that happen very quickly (80-100 milliseconds) are involuntary while slower stiffness corrections and adjustments are under voluntary control. Many of the voluntary stiffness adjustments are controlled by the motor cortex while involuntary adjustments can be controlled by reflex loops in the spinal cord or other parts of the brain.
Stiffness adjustments due to reflexes are involuntary and are controlled by the spinal cord while posture selection is controlled voluntarily. However, not each component of stiffness is strictly voluntary or involuntary. For example, Antagonistic muscle cocontraction can be either voluntary or involuntary. Additionally, because much of the legs' movements are controlled by the spinal cord and because of the larger neural delay associated with sending signals to the leg muscles, leg stiffness is more involuntarily controlled than arm stiffness.
=== Possible neural control models ===
Researchers have begun implementing controllers in into robots to control for stiffness. One such model adjusts for stiffness during robotic locomotion by virtually cocontracting antagonistic muscles about the robot's joints to modulate stiffness while a central pattern generator (CPG) controls the robot's locomotion.
Other models of the neural modulation of stiffness include a feedforward model of stiffness adjustment. These models of neural control support the idea that humans use a feedforward mechanism of stiffness selection in anticipation of the required stiffness needed to accomplish a given task.
Most models of the neural control of stiffness promote the idea that humans choose an optimal limb stiffness based on their environment or the task at hand. Studies postulate the humans do this in order to stabilize unstable dynamics of the environment and also to maximize the energy efficiency of a given movement. The exact method by which humans accomplish this is unknown, but impedance control has been used to give insight into how humans may choose an appropriate stiffness in different environments and as they perform different tasks. Impedance control has served as the basis for much of the work done in the area of determining how humans interact with their environment. The work of Neville Hogan has been particularly useful in this area as much of the work being done today in this area is based on his previous work.
== Applications in robotics ==
=== Neuroprosthetics and exoskeletons ===
Knowledge of human stiffness variation and stiffness selection has influenced robotic designs as researchers attempt to design robots that act more like biological systems. In order for robots to act more like biological systems, work is being done to attempt to implement stiffness modulation in robots so that they may interact more effectively with their environment.
State of the art neuroprosthetics have attempted to implements stiffness control in their robotic devices. The goal of these devices is to replace the limbs of amputees and allow the new limbs to adjust their stiffness in order to effectively interact with the environment.
Additionally, robotic exoskeletons have attempted to implement similar adjustable stiffness in their devices. These robots implement stiffness control for multiple reasons. The robots must be able to interact efficiently with the external environment but they must also be able to interact safely with their human user. Stiffness modulation and impedance control can be leveraged to accomplish both of these goals.
These devices achieve variable stiffness in various ways. Some devices use controllers and rigid servomotors to simulate variable stiffness. Other devices utilize specific flexible actuators to achieve a various levels of limb stiffness.
=== Actuation Techniques ===
These robotic devices are able to achieve variable stiffness through various mechanisms such as simulating stiffness variation through control of stiff actuators or by utilizing variable stiffness actuators. Variable stiffness actuators mimic biological organisms by changing their inherent stiffness. These variable stiffness actuators are able to control their inherent stiffness in multiple ways. Some vary their stiffness much like humans do, by varying the force contribution of antagonistic mechanical muscles. Other actuators are able to adjust their stiffness by taking advantage of the properties of deformable elements housed within the actuators.
By utilizing these variable stiffness actuation technologies, new robots have been able to more accurately replicate the motions of biological organisms and mimic their energetic efficiencies.
== See also ==
Powered exoskeleton
Neuroprosthetics
Robotics
Stiffness
Motor control
Neuroscience
Motor coordination
== References == | Wikipedia/Neural_control_of_limb_stiffness |
Motor control is the regulation of movements in organisms that possess a nervous system. Motor control includes conscious voluntary movements, subconscious muscle memory and involuntary reflexes, as well as instinctual taxes.
To control movement, the nervous system must integrate multimodal sensory information (both from the external world as well as proprioception) and elicit the necessary signals to recruit muscles to carry out a goal. This pathway spans many disciplines, including multisensory integration, signal processing, coordination, biomechanics, and cognition, and the computational challenges are often discussed under the term sensorimotor control. Successful motor control is crucial to interacting with the world to carry out goals as well as for posture, balance, and stability.
Some researchers (mostly neuroscientists studying movement, such as Daniel Wolpert and Randy Flanagan) argue that motor control is the reason brains exist at all.
== Neural control of muscle force ==
All movements, e.g. touching your nose, require motor neurons to fire action potentials that results in contraction of muscles. In humans, ~150,000 motor neurons control the contraction of ~600 muscles. To produce movements, a subset of 600 muscles must contract in a temporally precise pattern to produce the right force at the right time.
=== Motor units and force production ===
A single motor neuron and the muscle fibers it innervates are called a motor unit. For example, the rectus femoris contains approximately 1 million muscle fibers, which are controlled by around 1000 motor neurons. Activity in the motor neuron causes contraction in all of the innervated muscle fibers so that they function as a unit. Increasing action potential frequency (spike rate) in the motor neuron increases the muscle fiber contraction force, up to the maximal force. The maximal force depends on the contractile properties of the muscle fibers. Within a motor unit, all the muscle fibers are of the same type (e.g. type I (slow twitch) or Type II fibers (fast twitch)), and motor units of multiple types make up a given muscle. Motor units of a given muscle are collectively referred to as a motor pool.
The force produced in a given muscle thus depends on: 1) How many motor neurons are active, and their spike rates; 2) the contractile properties and number of muscle fibers innervated by the active neurons. To generate more force, increase the spike rates of active motor neurons and/or recruiting more and stronger motor units. In turn, how the muscle force produces limb movement depends on the limb biomechanics, e.g. where the tendon and muscle originate (which bone, and precise location) and where the muscle inserts on the bone that it moves.
=== Recruitment order ===
Motor units within a motor pool are recruited in a stereotypical order, from motor units that produce small amounts of force per spike, to those producing the largest force per spike. The gradient of motor unit force is correlated with a gradient in motor neuron soma size and motor neuron electrical excitability. This relationship was described by Elwood Henneman and is known as Henneman's size principle, a fundamental discovery of neuroscience and an organizing principle of motor control.
For tasks requiring small forces, such as continual adjustment of posture, motor units with fewer muscle fibers that are slowly-contracting, but less fatigueable, are used. As more force is required, motor units with fast twitch, fast-fatigeable muscle fibers are recruited.
High|
| _________________
Force required | /
| |
| |
| _____________|_________________
| __________|_______________________________
Low|__________|__________________________________________
↑ ↑ ↑ Time
Type I Recruit first Type II A Type IIB
== Computational issues of motor control ==
The nervous system produces movement by selecting which motor neurons are activated, and when. The finding that a recruitment order exists within a motor pool is thought to reflect a simplification of the problem: if a particular muscle should produce a particular force, then activate the motor pool along its recruitment hierarchy until that force is produced.
But then how to choose what force to produce in each muscle? The nervous system faces the following issues in solving this problem.
Redundancy. Infinite trajectories of movements can accomplish a goal (e.g. touch my nose). How is a trajectory chosen? Which trajectory is best?
Noise. Noise is defined as small fluctuations that are unrelated to a signal, which can occur in neurons and synaptic connections at any point from sensation to muscle contraction.
Delays. Motor neuron activity precedes muscle contraction, which precedes the movement. Sensory signals also reflect events that have already occurred. Such delays affect the choice of motor program.
Uncertainty. Uncertainty arises because of neural noise, but also because inferences about the state of the world may not be correct (e.g. speed of on coming ball).
Nonstationarity. Even as a movement is being executed, the state of the world changes, even through such simple effects as reactive forces on the rest of the body, causing translation of a joint while it is actuated.
Nonlinearity. The effects of neural activity and muscle contraction are highly non-linear, which the nervous system must account for when predicting the consequences of a pattern of motor neuron activity.
Much ongoing research is dedicated to investigating how the nervous system deals with these issues, both at the behavioral level, as well as how neural circuits in the brain and spinal cord represent and deal with these factors to produce the fluid movements we witness in animals.
"Optimal feedback control" is an influential theoretical framing of these computation issues.
== Model systems for motor control ==
All organisms face the computational challenges above, so neural circuits for motor control have been studied in humans, monkeys, horses, cats, mice, fish lamprey, flies, locusts, and nematodes, among many others. Mammalian model systems like mice and monkeys offer the most straightforward comparative models for human health and disease. They are widely used to study the role of higher brain regions common to vertebrates, including the cerebral cortex, thalamus, basal ganglia and deep brain medullary and reticular circuits for motor control. The genetics and neurophysiology of motor circuits in the spine have also been studied in mammalian model organisms, but protective vertebrae make it difficult to study the functional role of spinal circuits in behaving animals. Here, larval and adult fish have been useful in discovering the functional logic of the local spinal circuits that coordinate motor neuron activity. Invertebrate model organisms do not have the same brain regions as vertebrates, but their brains must solve similar computational issues and thus are thought to have brain regions homologous to those involved in motor control in the vertebrate nervous system, The organization of arthropod nervous systems into ganglia that control each leg as allowed researchers to record from neurons dedicated to moving a specific leg during behavior.
Model systems have also demonstrated the role of central pattern generators in driving rhythmic movements. A central pattern generator is a neural network that can generate rhythmic activity in the absence of an external control signal, such as a signal descending from the brain or feedback signals from sensors in the limbs (e.g. proprioceptors). Evidence suggests that real CPGs exist in several key motor control regions, such as the stomachs of arthropods or the pre-Boetzinger complex that control breathing in humans. Furthermore, as a theoretical concept, CPGs have been useful to frame the possible role of sensory feedback in motor control.
== Sensorimotor feedback ==
=== Response to stimuli ===
The process of becoming aware of a sensory stimulus and using that information to influence an action occurs in stages. Reaction time of simple tasks can be used to reveal information about these stages. Reaction time refers to the period of time between when the stimulus is presented, and the end of the response. Movement time is the time it takes to complete the movement. Some of the first reaction time experiments were carried out by Franciscus Donders, who used the difference in response times to a choice task to determine the length of time needed to process the stimuli and choose the correct response. While this approach is ultimately flawed, it gave rise to the idea that reaction time was made up of a stimulus identification, followed by a response selection, and ultimately culminates in carrying out the correct movement. Further research has provided evidence that these stages do exist, but that the response selection period of any reaction time increases as the number of available choices grows, a relationship known as Hick's law.
=== Closed loop control ===
The classical definition of a closed loop system for human movement comes from Jack A. Adams (1971). A reference of the desired output is compared to the actual output via error detection mechanisms; using feedback, the error is corrected for. Most movements that are carried out during day-to-day activity are formed using a continual process of accessing sensory information and using it to more accurately continue the motion. This type of motor control is called feedback control, as it relies on sensory feedback to control movements. Feedback control is a situated form of motor control, relying on sensory information about performance and specific sensory input from the environment in which the movement is carried out. This sensory input, while processed, does not necessarily cause conscious awareness of the action. Closed loop control: 186 is a feedback based mechanism of motor control, where any act on the environment creates some sort of change that affects future performance through feedback. Closed loop motor control is best suited to continuously controlled actions, but does not work quickly enough for ballistic actions. Ballistic actions are actions that continue to the end without thinking about it, even when they no longer are appropriate. Because feedback control relies on sensory information, it is as slow as sensory processing. These movements are subject to a speed-accuracy trade-off, because sensory processing is being used to control the movement, the faster the movement is carried out, the less accurate it becomes.
=== Open loop control ===
The classical definition from Jack A. Adams is: “An open loop system has no feedback or mechanisms for error regulation. The input events for a system exert their influence, the system effects its transformation on the input and the system has an output...... A traffic light with fixed timing snarls traffic when the load is heavy and impedes the flow when the traffic is light. The system has no compensatory capability.”
Some movements, however, occur too quickly to integrate sensory information, and instead must rely on feed forward control. Open loop control is a feed forward form of motor control, and is used to control rapid, ballistic movements that end before any sensory information can be processed. To best study this type of control, most research focuses on deafferentation studies, often involving cats or monkeys whose sensory nerves have been disconnected from their spinal cords. Monkeys who lost all sensory information from their arms resumed normal behavior after recovering from the deafferentation procedure. Most skills were relearned, but fine motor control became very difficult. It has been shown that the open loop control can be adapted to different disease conditions and can therefore be used to extract signatures of different motor disorders by varying the cost functional governing the system.
== Coordination ==
A core motor control issue is coordinating the various components of the motor system to act in unison to produce movement.
Peripheral neurons receive input from the central nervous system and innervate the muscles. In turn, muscles generate forces which actuate joints. Getting the pieces to work together is a challenging problem for the motor system and how this problem is resolved is an active area of study in motor control research.
=== Reflexes ===
In some cases the coordination of motor components is hard-wired, consisting of fixed neuromuscular pathways that are called reflexes. Reflexes are typically characterized as automatic and fixed motor responses, and they occur on a much faster time scale than what is possible for reactions that depend on perceptual processing. Reflexes play a fundamental role in stabilizing the motor system, providing almost immediate compensation for small perturbations and maintaining fixed execution patterns. Some reflex loops are routed solely through the spinal cord without receiving input from the brain, and thus do not require attention or conscious control. Others involve lower brain areas and can be influenced by prior instructions or intentions, but they remain independent of perceptual processing and online control.
The simplest reflex is the monosynaptic reflex or short-loop reflex, such as the monosynaptic stretch response. In this example, Ia afferent neurons are activated by muscle spindles when they deform due to the stretching of the muscle. In the spinal cord, these afferent neurons synapse directly onto alpha motor neurons that regulate the contraction of the same muscle. Thus, any stretching of a muscle automatically signals a reflexive contraction of that muscle, without any central control. As the name and the description implies, monosynaptic reflexes depend on a single synaptic connection between an afferent sensory neuron and efferent motor neuron. In general the actions of monosynaptic reflexes are fixed and cannot be controlled or influenced by intention or instruction. However, there is some evidence to suggest that the gain or magnitude of these reflexes can be adjusted by context and experience.
Polysynaptic reflexes or long-loop reflexes are reflex arcs which involve more than a single synaptic connection in the spinal cord. These loops may include cortical regions of the brain as well, and are thus slower than their monosynaptic counterparts due to the greater travel time. However, actions controlled by polysynaptic reflex loops are still faster than actions which require perceptual processing.: 171, 578 While the actions of short-loop reflexes are fixed, polysynaptic reflexes can often be regulated by instruction or prior experience. A common example of a long loop reflex is the asymmetrical tonic neck reflex observed in infants.
=== Synergies ===
A motor synergy is a neural organization of a multi-element system that (1) organizes sharing of a task among a set of elemental variables; and (2) ensures co-variation among elemental variables with the purpose to stabilize performance variables. The components of a synergy need not be physically connected, but instead are connected by their response to perceptual information about the particular motor task being executed. Synergies are learned, rather than being hardwired like reflexes, and are organized in a task-dependent manner; a synergy is structured for a particular action and not determined generally for the components themselves. Nikolai Bernstein famously demonstrated synergies at work in the hammering actions of professional blacksmiths. The muscles of the arm controlling the movement of the hammer are informationally linked in such a way that errors and variability in one muscle are automatically compensated for by the actions of the other muscles. These compensatory actions are reflex-like in that they occur faster than perceptual processing would seem to allow, yet they are only present in expert performance, not in novices. In the case of blacksmiths, the synergy in question is organized specifically for hammering actions and is not a general purpose organization of the muscles of the arm. Synergies have two defining characteristics in addition to being task dependent; sharing and flexibility/stability.
"Sharing" requires that the execution of a particular motor task depends on the combined actions of all the components that make up the synergy. Often, there are more components involved than are strictly needed for the particular task (see "Redundancy" below), but the control of that motor task is distributed across all components nonetheless. A simple demonstration comes from a two-finger force production task, where participants are required to generate a fixed amount of force by pushing down on two force plates with two different fingers. In this task, participants generated a particular force output by combining the contributions of independent fingers. While the force produced by any single finger can vary, this variation is constrained by the action of the other such that the desired force is always generated.
Co-variation also provides "flexibility and stability" to motor tasks. Considering again the force production task, if one finger did not produce enough force, it could be compensated for by the other. The components of a motor synergy are expected to change their action to compensate for the errors and variability in other components that could affect the outcome of the motor task. This provides flexibility because it allows for multiple motor solutions to particular tasks, and it provides motor stability by preventing errors in individual motor components from affecting the task itself.
Synergies simplify the computational difficulty of motor control. Coordinating the numerous degrees of freedom in the body is a challenging problem, both because of the tremendous complexity of the motor system, as well as the different levels at which this organization can occur (neural, muscular, kinematic, spatial, etc.). Because the components of a synergy are functionally coupled for a specific task, execution of motor tasks can be accomplished by activating the relevant synergy with a single neural signal. The need to control all of the relevant components independently is removed because organization emerges automatically as a consequence of the systematic covariation of components. Similar to how reflexes are physically connected and thus do not require control of individual components by the central nervous system, actions can be executed through synergies with minimal executive control because they are functionally connected. Beside motor synergies, the term of sensory synergies has recently been introduced. Sensory synergy are believed to play an important role in integrating the mixture of environmental inputs to provide low-dimensional information to the CNS thus guiding the recruitment of motor synergies.
Synergies are fundamental for controlling complex movements, such as the ones of the hand during grasping. Their importance has been demonstrated for both muscle control and in the kinematic domain in several studies, lately on studies including large cohorts of subjects. The relevance of synergies for hand grasps is also enforced by studies on hand grasp taxonomies, showing muscular and kinematic similarities among specific groups of grasps, leading to specific clusters of movements.
=== Motor Programs ===
While synergies represent coordination derived from peripheral interactions of motor components, motor programs are specific, pre-structured motor activation patterns that are generated and executed by a central controller (in the case of a biological organism, the brain).: 227 They represent at top-down approach to motor coordination, rather than the bottom-up approach offered by synergies. Motor programs are executed in an open-loop manner, although sensory information is most likely used to sense the current state of the organism and determine the appropriate goals. However, similar to central pattern generators, once the program has been executed, it cannot be altered online by additional sensory information.
Evidence for the existence of motor programs comes from studies of rapid movement execution and the difficulty associated with changing those movements once they have been initiated. For example, people who are asked to make fast arm swings have extreme difficulty in halting that movement when provided with a "STOP" signal after the movement has been initiated. This reversal difficulty persists even if the stop signal is presented after the initial "GO" signal but before the movement actually begins. This research suggests that once selection and execution of a motor program begins, it must run to completion before another action can be taken. This effect has been found even when the movement that is being executed by a particular motor program is prevented from occurring at all. People who attempt to execute particular movements (such as pushing with the arm), but unknowingly have the action of their body arrested before any movement can actually take place, show the same muscle activation patterns (including stabilizing and support activation that does not actually generate the movement) as when they are allowed to complete their intended action.
Although the evidence for motor programs seems persuasive, there have been several important criticisms of the theory. The first is the problem of storage. If each movement an organism could generate requires its own motor program, it would seem necessary for that organism to possess an unlimited repository of such programs and where these would be kept is not clear. Aside from the enormous memory requirements such a facility would take, no motor program storage area in the brain has yet been identified. The second problem is concerned with novelty in movement. If a specific motor program is required for any particular movement, it is not clear how one would ever produce a novel movement. At best, an individual would have to practice any new movement before executing it with any success, and at worst, would be incapable of new movements because no motor program would exist for new movements. These difficulties have led to a more nuanced notion of motor programs known as generalized motor programs.: 240–257 A generalized motor program is a program for a particular class of action, rather than a specific movement. This program is parameterized by the context of the environment and the current state of the organism.
=== Redundancy ===
An important issue for coordinating the motor system is the problem of the redundancy of motor degrees of freedom. As detailed in the "Synergies" section, many actions and movements can be executed in multiple ways because functional synergies controlling those actions are able to co-vary without changing the outcome of the action. This is possible because there are more motor components involved in the production of actions than are generally required by the physical constraints on that action. For example, the human arm has seven joints which determine the position of the hand in the world. However, only three spatial dimensions are needed to specify any location the hand could be placed in. This excess of kinematic degrees of freedom means that there are multiple arm configurations that correspond to any particular location of the hand.
Some of the earliest and most influential work on the study of motor redundancy came from the Russian physiologist Nikolai Bernstein. Bernstein's research was primarily concerned with understanding how coordination was developed for skilled actions. He observed that the redundancy of the motor system made it possible to execute actions and movements in a multitude of different ways while achieving equivalent outcomes. This equivalency in motor action means that there is no one-to-one correspondence between the desired movements and the coordination of the motor system needed to execute those movements. Any desired movement or action does not have a particular coordination of neurons, muscles, and kinematics that make it possible. This motor equivalency problem became known as the degrees of freedom problem because it is a product of having redundant degrees of freedom available in the motor system.
== Perception in motor control ==
Related, yet distinct from the issue of how the processing of sensory information affects the control of movements and actions is the question of how the perception of the world structures action. Perception is extremely important in motor control because it carries the relevant information about objects, environments and bodies which is used in organizing and executing actions and movements. What is perceived and how the subsequent information is used to organize the motor system is an ongoing area of research.
=== Model based control strategies ===
Most model based strategies of motor control rely on perceptual information, but assume that this information is not always useful, veridical or constant. Optical information is interrupted by eye blinks, motion is obstructed by objects in the environment, distortions can change the appearance of object shape. Model based and representational control strategies are those that rely on accurate internal models of the environment, constructed from a combination of perceptual information and prior knowledge, as the primary source information for planning and executing actions, even in the absence of perceptual information.
==== Inference and indirect perception ====
Many models of the perceptual system assume indirect perception, or the notion that the world that gets perceived is not identical to the actual environment. Environmental information must go through several stages before being perceived, and the transitions between these stages introduce ambiguity. What actually gets perceived is the mind's best guess about what is occurring in the environment based on previous experience. Support for this idea comes from the Ames room illusion, where a distorted room causes the viewer to see objects known to be a constant size as growing or shrinking as they move around the room. The room itself is seen as being square, or at least consisting of right angles, as all previous rooms the perceiver has encountered have had those properties. Another example of this ambiguity comes from the doctrine of specific nerve energies. The doctrine presents the finding that there are distinct nerve types for different types of sensory input, and these nerves respond in a characteristic way regardless of the method of stimulation. That is to say, the color red causes optical nerves to fire in a specific pattern that is processed by the brain as experiencing the color red. However, if that same nerve is electrically stimulated in an identical pattern, the brain could perceive the color red when no corresponding stimuli is present.
==== Forward models ====
Forward models are a predictive internal model of motor control that takes the available perceptual information, combined with a particular motor program, and tries to predict the outcome of the planned motor movement. Forward models structure action by determining how the forces, velocities, and positions of motor components affect changes in the environment and in the individual. It is proposed that forward models help with the Neural control of limb stiffness when individuals interact with their environment. Forward models are thought to use motor programs as input to predict the outcome of an action. An error signal is generated when the predictions made by a forward model do not match the actual outcome of the movement, prompting an update of an existing model and providing a mechanism for learning. These models explain why it is impossible to tickle yourself. A sensation is experienced as ticklish when it is unpredictable. However, forward models predict the outcome of your motor movements, meaning the motion is predictable, and therefore not ticklish.
Evidence for forward models comes from studies of motor adaptation. When a person's goal-directed reaching movements are perturbed by a force field, they gradually, but steadily, adapt the movement of their arm to allow them to again reach their goal. However, they do so in such a way that preserves some high level movement characteristics; bell-shaped velocity profiles, straight line translation of the hand, and smooth, continuous movements. These movement features are recovered, despite the fact that they require startlingly different arm dynamics (i.e. torques and forces). This recovery provides evidence that what is motivating movement is a particular motor plan, and the individual is using a forward model to predict how arm dynamics change the movement of the arm to achieve particular task level characteristics. Differences between the expected arm movement and the observed arm movement produces an error signal which is used as the basis for learning. Additional evidence for forward models comes from experiments which require subjects to determine the location of an effector following an unvisualized movement
==== Inverse models ====
Inverse models predict the necessary movements of motor components to achieve a desired perceptual outcome. They can also take the outcome of a motion and attempt to determine the sequence of motor commands that resulted in that state. These types of models are particularly useful for open loop control, and allow for specific types of movements, such as fixating on a stationary object while the head is moving. Complementary to forward models, inverse models attempt to estimate how to achieve a particular perceptual outcome in order to generate the appropriate motor plan. Because inverse models and forward model are so closely associated, studies of internal models are often used as evidence for the roles of both model types in action.
Motor adaptation studies, therefore, also make a case for inverse models. Motor movements seem to follow predefined "plans" that preserve certain invariant features of the movement. In the reaching task mentioned above, the persistence of bell-shaped velocity profiles and smooth, straight hand trajectories provides evidence for the existence of such plans. Movements that achieve these desired task-level outcomes are estimated by an inverse model. Adaptation therefore proceeds as a process of estimating the necessary movements with an inverse model, simulating with a forward model the outcome of those movement plans, observing the difference between the desired outcome and the actual outcome, and updating the models for a future attempt.
=== Information based control ===
An alternative to model based control is information based control. Informational control strategies organize movements and actions based on perceptual information about the environment, rather than on cognitive models or representations of the world. The actions of the motor system are organized by information about the environment and information about the current state of the agent. Information based control strategies often treat the environment and the organism as a single system, with action proceeding as a natural consequence of the interactions of this system. A core assumption of information based control strategies is that perceptions of the environment are rich in information and veridical for the purposes of producing actions. This runs counter to the assumptions of indirect perception made by model based control strategies.
==== Direct perception ====
Direct perception in the cognitive sense is related to the philosophical notion of naïve or direct realism in that it is predicated on the assumption that what we perceive is what is actually in the world. James J. Gibson is credited with recasting direct perception as ecological perception. While the problem of indirect perception proposes that physical information about object in our environment is not available due to the ambiguity of sensory information, proponents of direct perception (like Gibson) suggest that the relevant information specified in ambient optic array is the distal physical properties of objects. This specifying information reveals the action opportunities the environment affords. These affordances are directly perceivable without ambiguity, and thus preclude the need for internal models or representations of the world. Affordances exist only as a byproduct of the interactions between an agent and its environment, and thus perception is an "ecological" endeavor, depending on the whole agent/environment system rather than on the agent in isolation.
Because affordances are action possibilities, perception is directly connected to the production of actions and movements. The role of perception is to provide information that specifies how actions should be organized and controlled, and the motor system is "tuned" to respond to specific type of information in particular ways. Through this relationship, control of the motor system and the execution of actions is dictated by the information of the environment. As an example, a doorway "affords" passing through, but a wall does not. How one might pass through a doorway is specified by the visual information received from the environment, as well as the information perceived about one's own body. Together, this information determines the pass-ability of a doorway, but not a wall. In addition, the act of moving towards and passing through the doorway generates more information and this in turn specifies further action. The conclusion of direct perception is that actions and perceptions are critically linked and one cannot be fully understood without the other.
==== Behavioral dynamics ====
Building on the assumptions of direct perception behavioral dynamics is a behavioral control theory that treats perceptual organisms as dynamic systems that respond to informational variables with actions, in a functional manner. Under this understanding of behavior, actions unfold as the natural consequence of the interaction between the organisms and the available information about the environment, which specified in body-relevant variables. Much of the research in behavioral dynamics has focused on locomotion, where visually specified information (such as optic flow, time-to-contact, optical expansion, etc.) is used to determine how to navigate the environment Interaction forces between the human and the environment also affect behavioral dynamics as seen in by the Neural control of limb stiffness.
== Planning in motor control ==
=== Individual movement optimization ===
There are several mathematical models that describe how the central nervous system (CNS) derives reaching movements of limbs and eyes. The minimum jerk model states that the CNS minimizes jerk of a limb endpoint trajectory over the time of reaching, which results in a smooth trajectory. However, this model is based solely on the kinematics of movement and does not consider the underlying dynamics of the musculoskeletal system. Hence, the minimum torque-change model was introduced as an alternative, where the CNS minimizes the joint torque change over the time of reaching.
Later it was argued that there is no clear explanation about how could the CNS actually estimate complex quantities such as jerk or torque change and then integrate them over the duration of a trajectory. In response, model based on signal-dependent noise was proposed instead, which states that the CNS selects a trajectory by minimizing the variance of the final position of the limb endpoint. Since there is a motor noise in the neural system that is proportional to the activation of the muscles, the faster movements induce more motor noise and are thus less precise. This is also in line with the Fitts' Law and speed-accuracy trade-off. Optimal control theory was used to further extend the model based on signal-dependent noise, where the CNS optimizes an objective function that consists of a term related to accuracy and additionally a term related to metabolic cost of movement.
Another type of models is based on cost-benefit trade-off, where the objective function includes metabolic cost of movement and a subjective reward related to reaching the target accurately. In this case the reward for a successful reach within the desired target is discounted by the duration of reaching, since the gained reward is perceived less valuable when spending more time on it. However, these models were deterministic and did not account for motor noise, which is an essential property of stochastic motor control that results in speed-accuracy trade-off. To address that, a new model was later proposed to incorporate the motor noise and to unify cost-benefit and speed-accuracy trade-offs.
=== Multi-component movements ===
Some studies observed that the CNS can split a complex movement into sub-movements. The initial sub-movement tends to be fast and imprecise in order to bring the limb endpoint into vicinity of the target as soon as possible. Then, the final sub-movement tends to be slow and precise in order to correct for accumulated error by the first initial sub-movement and to successfully reach the target. A later study further explored how the CNS selects a temporary target of the initial sub-movement in different conditions. For example, when the actual target size decreases and thus complexity increases, the temporary target of the initial sub-movement moves away from the actual target in order to give more space for the final corrective action. Longer reaching distances have a similar effect, since more error is accumulated in the initial sub-movement and thus requiring more complex final correction. In less complex conditions, when the final actual target is large and the movement is short, the CNS tends to use a single movement, without splitting it into multiple competents.
== See also ==
Motor learning
Motor skill
Motor coordination
Motor cortex
Multisensory integration
Proprioception
Sensory processing
Sensory-motor coupling
Two-alternative forced choice
Psychomotor learning
== References ==
== Further reading ==
=== Research in athletes === | Wikipedia/Motor_function |
In the subject area of control theory, an internal model is a process that simulates the response of the system in order to estimate the outcome of a system disturbance. The internal model principle was first articulated in 1976 by B. A. Francis and W. M. Wonham as an explicit formulation of the Conant and Ashby good regulator theorem. It stands in contrast to classical control, in that the classical feedback loop fails to explicitly model the controlled system (although the classical controller may contain an implicit model).
The internal model theory of motor control argues that the motor system is controlled by the constant interactions of the “plant” and the “controller.” The plant is the body part being controlled, while the internal model itself is considered part of the controller. Information from the controller, such as information from the central nervous system (CNS), feedback information, and the efference copy, is sent to the plant which moves accordingly.
Internal models can be controlled through either feed-forward or feedback control. Feed-forward control computes its input into a system using only the current state and its model of the system. It does not use feedback, so it cannot correct for errors in its control. In feedback control, some of the output of the system can be fed back into the system's input, and the system is then able to make adjustments or compensate for errors from its desired output. Two primary types of internal models have been proposed: forward models and inverse models. In simulations, models can be combined to solve more complex movement tasks.
== Forward models ==
In their simplest form, forward models take the input of a motor command to the “plant” and output a predicted position of the body.
The motor command input to the forward model can be an efference copy, as seen in Figure 1. The output from that forward model, the predicted position of the body, is then compared with the actual position of the body. The actual and predicted position of the body may differ due to noise introduced into the system by either internal (e.g. body sensors are not perfect, sensory noise) or external (e.g. unpredictable forces from outside the body) sources. If the actual and predicted body positions differ, the difference can be fed back as an input into the entire system again so that an adjusted set of motor commands can be formed to create a more accurate movement.
== Inverse models ==
Inverse models use the desired and actual position of the body as inputs to estimate the necessary motor commands which would transform the current position into the desired one. For example, in an arm reaching task, the desired position (or a trajectory of consecutive positions) of the arm is input into the postulated inverse model, and the inverse model generates the motor commands needed to control the arm and bring it into this desired configuration (Figure 2). Inverse internal models are also in close connection with the uncontrolled manifold hypothesis (UCM), see also here.
== Combined forward and inverse models ==
Theoretical work has shown that in models of motor control, when inverse models are used in combination with a forward model, the efference copy of the motor command output from the inverse model can be used as an input to a forward model for further predictions. For example, if, in addition to reaching with the arm, the hand must be controlled to grab an object, an efference copy of the arm motor command can be input into a forward model to estimate the arm's predicted trajectory. With this information, the controller can then generate the appropriate motor command telling the hand to grab the object. It has been proposed that if they exist, this combination of inverse and forward models would allow the CNS to take a desired action (reach with the arm), accurately control the reach and then accurately control the hand to grip an object.
== Adaptive Control theory ==
With the assumption that new models can be acquired and pre-existing models can be updated, the efference copy is important for the adaptive control of a movement task. Throughout the duration of a motor task, an efference copy is fed into a forward model known as a dynamics predictor whose output allows prediction of the motor output. When applying adaptive control theory techniques to motor control, efference copy is used in indirect control schemes as the input to the reference model.
== Scientists ==
A wide range of scientists contribute to progress on the internal model hypothesis. Michael I. Jordan, Emanuel Todorov and
Daniel Wolpert contributed significantly to the mathematical formalization. Sandro Mussa-Ivaldi, Mitsuo Kawato, Claude Ghez, Reza Shadmehr, Randy Flanagan and Konrad Kording contributed with numerous behavioral experiments. The DIVA model of speech production developed by Frank H. Guenther and colleagues uses combined forward and inverse models to produce auditory trajectories with simulated speech articulators. Two interesting inverse internal models for the control of speech production were developed by Iaroslav Blagouchine & Eric Moreau. Both models combine the optimum principles and the equilibrium-point hypothesis (motor commands λ are taken as coordinates of the internal space). The input motor command λ is found by minimizing the length of the path traveled in the internal space, either under the acoustical constraint (the first model), or under the both acoustical and mechanical constraints (the second model). The acoustical constraint is related to the quality of the produced speech (measured in terms of formants), while the mechanical one is related to the stiffness of the tongue's body. The first model, in which the stiffness remains uncontrolled, is in agreement with the standard UCM hypothesis. In contrast, the second optimum internal model, in which the stiffness is prescribed, displays the good variability of speech (at least, in the reasonable range of stiffness) and is in agreement with the more recent versions of the uncontrolled manifold hypothesis (UCM). There is also a rich clinical literature on internal models including work from John Krakauer, Pietro Mazzoni, Maurice A. Smith, Kurt Thoroughman, Joern Diedrichsen, and Amy Bastian.
== See also ==
Repetitive control
Efference copy
== References == | Wikipedia/Internal_models |
Alpha (α) motor neurons (also called alpha motoneurons), are large, multipolar lower motor neurons of the brainstem and spinal cord. They innervate extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction. Alpha motor neurons are distinct from gamma motor neurons, which innervate intrafusal muscle fibers of muscle spindles.
While their cell bodies are found in the central nervous system (CNS), α motor neurons are also considered part of the somatic nervous system—a branch of the peripheral nervous system (PNS)—because their axons extend into the periphery to innervate skeletal muscles.
An alpha motor neuron and the muscle fibers it innervates comprise a motor unit. A motor neuron pool contains the cell bodies of all the alpha motor neurons involved in contracting a single muscle.
== Location ==
Alpha motor neurons (α-MNs) innervating the head and neck are found in the brainstem; the remaining α-MNs innervate the rest of the body and are found in the spinal cord. There are more α-MNs in the spinal cord than in the brainstem, as the number of α-MNs is directly proportional to the amount of fine motor control in that muscle. For example, the muscles of a single finger have more α-MNs per fibre, and more α-MNs in total, than the muscles of the quadriceps, which allows for finer control of the force a finger applies.
In general, α-MNs on one side of the brainstem or spinal cord innervate muscles on that same side of the body. An exception is the trochlear nucleus in the brainstem, which innervates the superior oblique muscle of the eye on the opposite side of the face.
=== Brainstem ===
In the brainstem, α-MNs and other neurons reside within clusters of cells called nuclei, some of which contain the cell bodies of neurons belonging to the cranial nerves. Not all cranial nerve nuclei contain α-MNs; those that do are motor nuclei, while others are sensory nuclei. Motor nuclei are found throughout the brainstem—medulla, pons, and midbrain—and for developmental reasons are found near the midline of the brainstem.
Generally, motor nuclei found higher in the brainstem (i.e., more rostral) innervate muscles that are higher on the face. For example, the oculomotor nucleus contains α-MNs that innervate muscles of the eye, and is found in the midbrain, the most rostral brainstem component. By contrast, the hypoglossal nucleus, which contains α-MNs that innervate the tongue, is found in the medulla, the most caudal (i.e., towards the bottom) of the brainstem structures.
=== Spinal cord ===
In the spinal cord, α-MNs are located within the gray matter that forms the ventral horn. These α-MNs provide the motor component of the spinal nerves that innervate muscles of the body.
As in the brainstem, higher segments of the spinal cord contain α-MNs that innervate muscles higher on the body. For example, the biceps brachii muscle, a muscle of the arm, is innervated by α-MNs in spinal cord segments C5, C6, and C7, which are found rostrally in the spinal cord. On the other hand, the gastrocnemius muscle, one of the muscles of the leg, is innervated by α-MNs within segments S1 and S2, which are found caudally in the spinal cord.
Alpha motor neurons are located in a specific region of the spinal cord's gray matter. This region is designated lamina IX in the Rexed lamina system, which classifies regions of gray matter based on their cytoarchitecture. Lamina IX is located predominantly in the medial aspect of the ventral horn, although there is some contribution to lamina IX from a collection of motor neurons located more laterally. Like other regions of the spinal cord, cells in this lamina are somatotopically organized, meaning that the position of neurons within the spinal cord is associated with what muscles they innervate. In particular, α-MNs in the medial zone of lamina IX tend to innervate proximal muscles of the body, while those in the lateral zone tend to innervate more distal muscles. There is similar somatotopy associated with α-MNs that innervate flexor and extensor muscles: α-MNs that innervate flexors tend to be located in the dorsal portion of lamina IX; those that innervate extensors tend to be located more ventrally.
== Development ==
Alpha motor neurons originate in the basal plate, the ventral portion of the neural tube in the developing embryo. Sonic hedgehog (Shh) is secreted by the nearby notochord and other ventral structures (e.g., the floor plate), establishing a gradient of highly concentrated Shh in the basal plate and less concentrated Shh in the alar plate. Under the influence of Shh and other factors, some neurons of the basal plate differentiate into α-MNs.
Like other neurons, α-MNs send axonal projections to reach their target extrafusal muscle fibers via axon guidance, a process regulated in part by neurotrophic factors released by target muscle fibers. Neurotrophic factors also ensure that each muscle fiber is innervated by the appropriate number of α-MNs. As with most types of neurons in the nervous system, α-MNs are more numerous in early development than in adulthood. Muscle fibers secrete a limited amount of neurotrophic factors capable of sustaining only a fraction of the α-MNs that initially project to the muscle fiber. Those α-MNs that do not receive sufficient neurotrophic factors will undergo apoptosis, a form of programmed cell death.
Because they innervate many muscles, some clusters of α-MNs receive high concentrations of neurotrophic factors and survive this stage of neuronal pruning. This is true of the α-MNs innervating the upper and lower limbs: these α-MNs form large cell columns that contribute to the cervical and lumbar enlargements of the spinal cord. In addition to receiving neurotrophic factors from muscles, α-MNs also secrete a number of trophic factors to support the muscle fibers they innervate. Reduced levels of trophic factors contributes to the muscle atrophy that follows an α-MN lesion.
== Connectivity ==
Like other neurons, lower motor neurons have both afferent (incoming) and efferent (outgoing) connections. Alpha motor neurons receive input from a number of sources, including upper motor neurons, sensory neurons, and interneurons. The primary output of α-MNs is to extrafusal muscle fibers. This afferent and efferent connectivity is required to achieve coordinated muscle activity.
=== Afferent input ===
Upper motor neurons (UMNs) send input to α-MNs via several pathways, including (but not limited to) the corticonuclear, corticospinal, and rubrospinal tracts. The corticonuclear and corticospinal tracts are commonly encountered in studies of upper and lower motor neuron connectivity in the control of voluntary movements.
The corticonuclear tract is so named because it connects the cerebral cortex to cranial nerve nuclei. (The corticonuclear tract is also called the corticobulbar tract, as the target in the brainstem—which is medulla—is archaically called the "bulb.") It is via this pathway that upper motor neurons descend from the cortex and synapse on α-MNs of the brainstem. Similarly, UMNs of the cerebral cortex are in direct control of α-MNs of the spinal cord via the lateral and ventral corticospinal tracts.
The sensory input to α-MNs is extensive and has its origin in Golgi tendon organs, muscle spindles, mechanoreceptors, thermoreceptors, and other sensory neurons in the periphery. These connections provide the structure for the neural circuits that underlie reflexes. There are several types of reflex circuits, the simplest of which consists of a single synapse between a sensory neuron and a α-MNs. The knee-jerk reflex is an example of such a monosynaptic reflex.
The most extensive input to α-MNs is from local interneurons, which are the most numerous type of neuron in the spinal cord. Among their many roles, interneurons synapse on α-MNs to create more complex reflex circuitry. One type of interneuron is the Renshaw cell.
=== Efferent output ===
Alpha motor neurons send fibers that mainly synapse on extrafusal muscle fibers. Other fibers from α-MNs synapse on Renshaw cells, i.e. inhibitory interneurons that synapse on the α-MN and limit its activity in order to prevent muscle damage.
== Signaling ==
Like other neurons, α-MNs transmit signals as action potentials, rapid changes in electrical activity that propagate from the cell body to the end of the axon. To increase the speed at which action potentials travel, α-MN axons have large diameters and are heavily myelinated by both oligodendrocytes and Schwann cells. Oligodendrocytes myelinate the part of the α-MN axon that lies in the central nervous system (CNS), while Schwann cells myelinate the part that lies in the peripheral nervous system (PNS). The transition between the CNS and PNS occurs at the level of the pia mater, the innermost and most delicate layer of meningeal tissue surrounding components of the CNS.
The axon of an α-MN connects with its extrafusal muscle fiber via a neuromuscular junction, a specialized type of chemical synapse that differs both in structure and function from the chemical synapses that connect neurons to each other. Both types of synapses rely on neurotransmitters to transduce the electrical signal into a chemical signal and back. One way they differ is that synapses between neurons typically use glutamate or GABA as their neurotransmitters, while the neuromuscular junction uses acetylcholine exclusively. Acetylcholine is sensed by nicotinic acetylcholine receptors on extrafusal muscle fibers, causing their contraction.
Like other motor neurons, α-MNs are named after the properties of their axons. Alpha motor neurons have Aα axons, which are large-caliber, heavily myelinated fibers that conduct action potentials rapidly. By contrast, gamma motor neurons have Aγ axons, which are slender, lightly myelinated fibers that conduct less rapidly.
== Clinical significance ==
Injury to α-MNs is the most common type of lower motor neuron lesion. Damage may be caused by trauma, ischemia, and infection, among others. In addition, certain diseases are associated with the selective loss of α-MNs. For example, poliomyelitis is caused by a virus that specifically targets and kills motor neurons in the ventral horn of the spinal cord. Amyotropic lateral sclerosis likewise is associated with the selective loss of motor neurons.
Paralysis is one of the most pronounced effects of damage to α-MNs. Because α-MNs provide the only innervation to extrafusal muscle fibers, losing α-MNs effectively severs the connection between the brainstem and spinal cord and the muscles they innervate. Without this connection, voluntary and involuntary (reflex) muscle control is impossible. Voluntary muscle control is lost because α-MNs relay voluntary signals from upper motor neurons to muscle fibers. Loss of involuntary control results from interruption of reflex circuits such as the tonic stretch reflex. A consequence of reflex interruption is that muscle tone is reduced, resulting in flaccid paresis. Another consequence is the depression of deep tendon reflexes, causing hyporeflexia.
Muscle weakness and atrophy are inevitable consequences of α-MN lesions as well. Because muscle size and strength are related to the extent of their use, denervated muscles are prone to atrophy. A secondary cause of muscle atrophy is that denervated muscles are no longer supplied with trophic factors from the α-MNs that innervate them. Alpha motor neuron lesions also result in abnormal EMG potentials (e.g., fibrillation potentials) and fasciculations, the latter being spontaneous, involuntary muscle contractions.
Diseases that impair signaling between α-MNs and extrafusal muscle fibers, namely diseases of the neuromuscular junction have similar signs to those that occur with α-MN disease. For example, myasthenia gravis is an autoimmune disease that prevents signaling across the neuromuscular junction, which results in functional denervation of muscle.
== See also ==
Beta motor neuron
Anterior grey column
== References ==
== External links ==
NIF Search - Alpha Motor Neuron Archived 2016-03-04 at the Wayback Machine via the Neuroscience Information Framework | Wikipedia/Alpha_motor_neurons |
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