Cochlea Amplifier models : a new list

["reinifrosch@xxxxxxxxxx" <reinifrosch@xxxxxxxxxx>]

Dear Dick,

I'll try to answer below, using Fig. 14 of the review by 
Robles & Ruggero (2001).

----UrsprÃngliche Nachricht----
Von: DickLyon@xxxxxxx
Datum: 18.10.2007 23:48
An: <reinifrosch@xxxxxxxxxx>, <AUDITORY@xxxxxxxxxxxxxxx>
Betreff: Re: Cochlea Amplifier models : a new list

>Matt says you are pointing out two distinct peaks.  So I
>repeat my question from before:  does the data support
>only that interpretation?  Or can the two (active and 
>passive) peaks be just as well interpreted as two ends of
>a level-dependent continuum, reflecting a degree of active
>involvement?

That Fig. 14 features the panoramic view. The 55dB curve
of BM-displacement versus x_a contains two peaks, namely
a broad passive peak at x_a = 15.86 mm and a narrower
active peak at x_a = 14.47 mm. The same is true for the
curve at 60 dB. At 60 dB, the OHC's generate as much
energy as they can. At >60 dB, therefore, the active peak
in dB is reduced. Indeed there is, from 60 dB to 110 dB or
so, a transition of the whole profile from the two-peaked
shape observed at 60 dB to the one broad peak at
110 dB (not shown) which has the same shape as the
passive peak which would probably occur at all levels post
mortem. That broad passive peak has its maximum at
x_a = 15.86 mm.
 
>Active traveling-wave models as I know them show a
>continuous behavior between low-level active and
>high-level passive, with degree of activity also influenced
>by efferent control and local adaptation state.  Do you
>believe the data support that notion?  Or contradict
>it?  Or neutral?

I agree, i.e., I do not contradict, nor am I neutral.
With one grain of salt: Even at low level, the TW between
base and x_a = 15.5 mm (the basal limit of the
active-peak x_a-region) is, in my opinion, entirely passive,
i.e., the OHC's feed no energy into that basal part of the TW.

Reinhart.