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And the experiment then is to
if you're recording electrodes,
record from the
auditory nerve fibers,
get a single nerve fiber,
and take its tuning curve.
And that's what's shown
on this top graph.
So tuning curves from the
normal region of the cochlea
are normal shaped.
They have sharp tips and
tails, normal sensitivity.
In the region of the cochlea
when the drug treatment has
lesioned the outer hair
cells, the tuning curves
look extremely abnormal.
There's a tail, whatever tip
there is is a tiny little tip,
and there's a tremendous loss
of sensitivity, as much as 60
or more dB lost.
Basically, these are
tipless tuning curves.
And now we know that
the outer hair cells
have their
electromotility function.
They are the cochlea amplifier.
Without the amplifier, you lose
the tip on the tuning curve.
So that should be a mini review.
This is the way the outer
hair cells originally
thought-- or discovered
to be important
in the sense of
hearing, to provide
the normal sensitivity
and a sharp tuning.
You can get all kinds of tuning
curve abnormalities depending
on whether you, in this case,
lose all the outer hair cells.
You cause disarray
of the stereocilia.
You have partial loss
of the outer hair cells.
All these kinds of things can
be found after noise damage
depending on the place of
the cochlea you look at,
the type of noise, the
length of the noise exposure,
and the animal.
There's a lot of variability
in noise damage from exposures
to 10-- 10 different
animals, you
can have 10 different types
of loss of hair cells.
Noise damage is
tremendously variable
from subject to subject.