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Re: Cochlea Amplifier models : a new list

Dear A.J. and others,

In my mind there is such a close correlation between measurements of BM motion and of auditory nerve fiber responses that it's hard to believe that BM motion is not involved in cochlear function.

Yes, BM motion is involved in cochlear function. But which one? Here, the "relation between BM motion and auditory nerve fiber responses" indeed gives strong clues, which are highly compelling.

1) At low sound levels:
Here the outer hair cells (OHC) respond to sound pressure gradients in the endolymph, generate motility, and excite the inner hair cells (IHC) via the given hydromechanical coupling of the subtectorial space. Nowotny and Gummer (2006) have reported interesting data on this subject:


A side effect of this BM motility are basilar membrane (BM) excursions. Hence the close correlation between BM tuning and neural tuning "at near-threshold stimulus levels" (quoting Mario Ruggero from the abstract of his Science paper):



Rémy Pujol and his colleagues in France state on their outstanding inner ear website:

"The traveling wave tends now to be considered an epiphenomenon."


where you have to go to "cochlea", then "physics", then last paragraph.

2) At high sound levels:
Here BM tuning is shifted by about half an octave towards the base of the cochlea, whereas neural tuning remains unchanged. The effect of this shift is that BM vibrations absorb acoustical energy, before it reaches the OHCs that are tuned to the same sound frequencies. Thus it is evident that this mechanisms must contribute to the protection of OHCs from overstimulation.


In summary, at low sound levels BM vibrations are an epiphenomenon of OHC motility, and at high sound levels they are specifically tuned to absorb energy for overload protection.

In engineering, tuned membranes for absorption of acoustic energy, called silators, are applied for noise control of machines:





Martin Braun
Neuroscience of Music
S-671 95 Klässbol
web site: http://w1.570.telia.com/~u57011259/index.htm

----- Original Message ----- From: "A.J. Aranyosi" <aja@xxxxxxx>
To: <AUDITORY@xxxxxxxxxxxxxxx>
Sent: Tuesday, October 09, 2007 6:51 PM
Subject: Re: Cochlea Amplifier models : a new list