Mechanisms of hearing question

F. Frank LeFever flefever at ix.netcom.com
Mon Dec 14 22:12:04 EST 1998


Well, I am learning things from this discussion.  Don't know when I'll
find the time to look systematically at the distinctionns between
retina and cochlea that Didier describes, but a nagging question about
the implications will be lurking in the back of my mind and will I'm
sure make things leap out from my casual reading that would not have
otherwise ("Chance favors the prepared mind"--variously attributed to
Louis Pasteur and/or Claude Bernard).

I will venture one more question from the depths of my raw
half-knowledge: there has been much attention in the past couple of
years to the idea that neural noise enhances detection of extremely
weak signals: is this relevant to the point Dider makes about cats
detecting signals below the level of Brownian movement?  Would this
make a sufficiently "non-passive" cochlea?

"P.S." after re-reading the comments below: is this what is meant by
"unstable oscillator"?

F. LeFever



In <753gqr$jqv$1 at hecate.umd.edu> didier at Glue.umd.edu (Didier A.
Depireux) writes: 
>
>TONYJEFFS (tonyjeffs at aol.com) wrote:
>: >
>: > but why do you invoke higher centers in this "tuning"? 
>: Because the common theory is that the Inner hair cells only send
messages   to
>: the brain, while the OHCs mostly (90%) receive messages from the
brain, and I
>
>If you really want to know all the details, they can be found in one
of the
>7 "Green Books", edited by Art Popper and published by
Springer-Verlag. One
>of the green books (vol 8, I think) is entitled 'The cochlea'.
>
>There is a big difference between the retina and the cochlea, in that
the
>local inhibitory circuit that's found in the retina itself doesn't
appear
>in the auditory pathway until the cochlear nucleus. In the auditory
nerve,
>about 5 % of the auditory nerve fibers course from the CNS to the
cochlea,
>whereas the rest goes the other way. The descending fibers all target
outer
>hair cells (and nothing else), whereas the ascending fibers connect
only to
>inner hair cells. In other words, the only possible lateral inhibition
>would be from descending fibers, although I should point out that if
this
>were the mechanism for lateral inhibition, anatomy tells us it would
have
>to be through the superior olivary complex.
>
>The truth is that no one knows what the descending pathway does,
really.
>Cats can detect sounds at a -15 dB level (re SPL), at which power
level the
>sound vibrations in the cochlea are about 1/10th of the average
brownian
>motion. What this means in all likelihood is that OHCs are very
unstable
>oscillators, that amplify very weak vibrations. Look at Bialek's
article in
>Physics Letters A (1987 or so) to see an interesting analysis of the
fact
>that a passive cochlea cannot account for our perception.
>
>I should probably stop here! I don't want to go on and on...
>
>					Didier
>
>--
>Didier A Depireux                              didier at isr.umd.edu
>Neural Systems Lab                 http://www.isr.umd.edu/~didier
>Institute for Systems Research          Phone: 301-405-6557 (off)
>University of Maryland                                -6596 (lab)
>College Park MD 20742 USA                     Fax: 1-301-314-9920




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