HC selectivity ... was Re: Physiological models of cochlea activity - alternatives to the travelling wave (Matt Flax )


Subject: HC selectivity ... was Re: Physiological models of cochlea activity - alternatives to the travelling wave
From:    Matt Flax  <flatmax@xxxxxxxx>
Date:    Fri, 28 Sep 2007 12:55:18 +1000
List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>

Hi Martin and others, I agree, mathematical models are expert systems. There are a lot of expert systems out there. I can not see the link between CF-tuned hair cells and cochlea amplification - currently ... the hair cells need to actuate some form of mechanical model ... right ? Further on the topic of CF-tuning of hair cells ... as you point out (e-mail included below) it is widely accepted that there is frequency selectivity [1], [2], [3]. This point of view is linear and flawed ... read on ... The basic point of view which argues for hair cell frequency selectivity - at the moment - is as follows : Conductance changes form the basis of time constant selectivity in hair cells . The time constant of interest is across the basolateral membrane of the hair cells. The combination of the membrane conductance and membrane capacitance is hypothesised to generate a first order filter. As the membrane conductance is proposed to change, the cut off frequency of the first order membrane circuit changes. The conductance change is due to varying ion channel counts - which change with the size of the cell. Larger cells in the apex of the cochlea have more ion channels then the smaller basal cells. This point of view is based on a linear first order model. The linear first order model is of the basolateral HC membrane. The basolateral HC membrane is nonlinear - in physiology - and the current point of view is flawed in this respect. With respect to a hair cell at rest ... take the following general values for membrane resistance and capacitance : R= 40 Meg Ohms ... taken from [4] for example C= 1 pF ... taken from [5] for example The first order cut-off frequency would be about 25 kHz. fc=25 kHz. The hair cell at rest has a very high cut off frequency. Much much higher then that proposed by Housley [1] for example ... it is quite possible that all experiments probing the cut off frequency of hair cells are introducing parasitic impedances - thus they are recording very small cut off frequencies. Further the membrane conductance and capacitance are nonlinear. This nonlinearity is dependent on the forcing frequency and level. Thus the frequency selectivity will change depending on the forcing signal. I do not think that HC frequency selectivity has anything to do with the frequency selectivity of the Cochlea amplifier - over the range of interest. Matt [1] @xxxxxxxx{housley:1992, author = {Housley, GD and Ashmore, JF}, title = {{Ionic currents of outer hair cells isolated from the guinea-pig cochlea}}, journal = {The Journal of Physiology}, year = {1992}, volume = {448}, pages = {73--98}, number = {1} } [2] @xxxxxxxx{ramanathan:1999, title={{A molecular mechanism for electrical tuning of cochlear hair cells.}}, author={Ramanathan, K. and Michael, TH and Jiang, GJ and Hiel, H. and Fuchs, PA}, journal={Science}, volume={283}, number={5399}, pages={215--7}, year={1999} } [3] @xxxxxxxx{fettiplace:1999, title={{MECHANISMS OF HAIR CELL TUNING}}, author={Fettiplace, R. and Fuchs, PA}, journal={Annual Review of Physiology}, volume={61}, number={1}, pages={809--834}, year={1999}, publisher={Annual Reviews} } [4] @xxxxxxxx{Dallos:1983, author = {Dallos, P.}, title = {Some electrical circuit properties of the organ of Corti. I. Analysis without reactive elements}, journal = {Hearing Research}, year = {1983}, volume = {12}, pages = {89-119}, number = {1}, month = {Oct.} } [5] @xxxxxxxx{Russell:1978, author = {Russell, I. J., and Sellick, P. M.}, title = {Intracellular studies of hair cells in the mammalian cochlea}, journal = {The Journal of Physiology (London)}, year = {1978}, volume = {284}, pages = {261-290} } On Thu, Sep 27, 2007 at 07:14:42PM +0200, Martin Braun wrote: > Dear Matt and others, > > If the available data on mammalian cochlea function are considered > reasonably and nonselectively (!), there is no need for a mathematically > formulated model. For all non-mammalian ears, where the principle of > frequency selectivity by CF-tuned hair cells is already widely accepted, > there was never a demand for mathematically formulated cochlear models. > > The "gold rush" of recent decades for mathematically formulated models of > mammalian cochlear function can perhaps best be compared with the gold rush > of the alchemists in the Middle Ages. > > Martin > > --------------------------------------------------------------------- > Martin Braun > Neuroscience of Music > S-671 95 Klässbol > Sweden > web site: http://w1.570.telia.com/~u57011259/index.htm -- http://www.flatmaxstudios.com/ http://www.flatmax.org Public Projects : http://sourceforge.net/search/?type_of_search=soft&words=mffm http://www.psysound.org


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