Modeling Early Auditory Processing Using GENESIS ("HARRY R. ERWIN" )

Subject: Modeling Early Auditory Processing Using GENESIS
From:    "HARRY R. ERWIN"  <herwin(at)OSF1.GMU.EDU>
Date:    Mon, 7 Jul 1997 13:48:43 -0400

Also posted to newsgroup bionet.audiology As a class project, I've been working on a GENESIS model of the neural pathway from the inner hair cell to the bushy cells of the cochlear nucleus. My advisor points out that the data I'd need for bat is mostly lacking, and I'm looking for pointers from the auditory community: 1. I'm using a vesicle release model at the inner hair cell that treats it as a poisson process, with rates of 100 vesicles/second (no signal) and 700 (pressure wave present). This model is suggested by Mountain and Hubbard's papers in Auditory Computation and by the know rates of spontaneous spiking in spiral ganglion neurons. Are there any bat data on this? The resulting conductance values at the type I spiral ganglion cell synapse seem to be very noisy. 2. The type I spiral ganglion cell is modeled as a synaptic structure at the inner hair cell, ten dendritic compartments, and a soma, where the spikes are generated. The synapse is ignited by the inner hair cell vesicle release process, and the resulting depolarization is passively transmitted down the dendrite to the soma. Is this valid? The reduction in the strength of the depolarization depends on the dendritic diameter, and specific membrane and axial resistance and seems to be related to the sensitivity of the cell. In any case, the cell starts spiking periodically (500-1000 Hz) very soon after the arrival of the wave of depolarization, bridging over and erasing any internal structure in the return. If elements of the internal structure of the return are to be used in downstream processing, they would have to be selected out by inhibiting the early ignition of the synapse. Again, this model is calibrated by using information related to spontaneous spiking rates in type I spiral ganglion neurons in cat and rat. Has anyone studied the phenomenon in bat? 3. The End Bulb of Held/Bushy Cell complex is modeled as a soma, a short dendritic tree, and a collection of excitatory axo-somatic synapses from the type I spiral ganglion cell. These synapses fire over a period of about 4 microseconds after the arrival of the action potential. (Valid in bat?) This complex seems to be an edge detector. I get an initial spike from the bushy cell at the beginning of a spike train from the type I spiral ganglion cell, and then the follow-on spikes in that train seem to prevent the bushy cell soma from resetting/respiking for a while. Has anyone looked at this in bat? -- Harry Erwin, Internet: herwin(at), Web Page: PhD student in computational neuroscience (how bats echolocate) Lecturer for CS 211 (data structures and advanced C++) Senior Software Analyst supporting the FAA

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