Suppression in auditory-nerve fibers of cats using low-side suppressors III. Model resultsOr in other words…OptionsSo who’s responsible for two-tone suppression?Whose fault is it anyways?Bring it onModel - physiologicalModel - phenomenologicalGeneration of two-tone suppression?Results - OHCsSlide 11Results - IHCHigh SR vs. Low SR suppressionImplicationsLimitationsQuestions?Slide 17Model FormulationTone -pip responsesHigh-side SuppressionSuppression in auditory-nerve fibers of cats using low-side suppressors III. Model resultsYidao Cai and C. Daniel GeislerOr in other words…Another way to try understand the nature of the cochlear amplifier (CA).Why suppression? Why low-side suppressors?OptionsSo who’s responsible for two-tone suppression?•Probably related to CA•Seen in cochlea•Nonlinear•Active processes•OHC electromotility linked to CAProblem : OHC and IHC have similar mechanismsWhose fault is it anyways?Bring it onModel - physiologicalModel - phenomenological• Represents phenomena of cochlear amplifier•Full-wave rectifier Time average of OHC signal not equal to zero•Inverter As signal level increases, amplification from CA decreases•Gain-smoothing filter Prevents instantaneous change of gainGeneration of two-tone suppression?Start¾ cycle¼ cycleResults - OHCsModel ExperimentResults - OHCsModelExperimentResults - IHCModelHigh SR vs. Low SR suppressionImplications•Model simulates two-tone & low-side suppression–IHCs–BM–Temporal responses •similar to AN data for both High and Low – SR fibers–Amplitude responses •High-SR fibers --- AGREE•Low-SR fibers --- DISAGREELimitations•Physiologic and phenomenological model–Model of CA was “ad hoc” •Stronger suppressions of lower SR fibers not seen•Feedback signal for simulations was OHC current and not transmembrane voltage•OHC membrane filter attenuates high frequency signals–OHC current provides unfiltered signalQuestions?Model FormulationWhere Yohc(t)=OHC output which controls gain of CAYdmax(t)= maximum depolarization amplitude of OHC outputYhmax(t)= maximum hyperpolarization amplitude of OHC outputy(t)=normalized outputp(t)= BM displacement (input to OHC and IHC)Pd=BM depolarizing displacement producing half saturating outputPh=BM hyperolarizing displacement producing half saturating outputGraw= raw gainGrmax= maximum CA gain (1000 or 60 dB)Yohc(t) Yd maxp(t)Pd p(t),p(t) 0Yohc(t) Yh maxp(t)Ph p(t),p(t) 0Graw(t) max Gmax1 y(t) ,1 Gmaxmax imum.gain.of .CA 1000.or.60dBy(t) Yohc(t)Yd max(t),Yohc(t) 0y(t) Yohc(t)Yh max(t),Yohc(t) 0Tone -pip responsesHigh-side
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