Input-output curves of low and high spontaneous rate auditory nerve fibers are exponential near threshold

Abstract

Input-output (IO) properties of cochlear transduction are frequently determined by analyzing the average discharge rates of auditory nerve fibers (ANFs) in response to relatively long tonal stimulation. The ANFs in cats have spontaneous discharge rates (SRs) that are bimodally distributed, peaking at low (<0.5 spikes/s) and high (∼60 spikes/s) rates, and rate-level characteristics differ depending upon SR. In an effort to assess the instantaneous IO properties of ANFs having different SRs, static IO-curves were constructed from period histograms based on phase-locking of spikes to the stimulus waveform. These curves provide information unavailable in conventional average rate-level curves. We find that all IO curves follow an exponential trajectory. It is argued that the exponential behavior represents the transduction in the IHC and that the difference among ANFs having different SRs is predominantly a difference in gain attributed most likely to synaptic drive. © 2018 The authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Phase Locking of Auditory-Nerve Fibers Reveals Stereotyped Distortions and an Exponential Transfer Function with a Level-Dependent Slope

“…3C). Refractoriness therefore is not the mechanism responsible for skewing the period histograms, in contrast to what has been proposed (Horst et al, 2018), or for preventing peak clipping at high SPLs.…”

“…When P(t) is a sinusoid, Equation 8 yields the von Mises distribution (Ashida et al, , 2013van Hemmen, 2013) scaled to represent an instantaneous rate. Such an equation has been used previously to model period histograms from ANF responses to low-frequency tones of low and moderate stimulus levels (Siebert, 1970;Colburn, 1973;Johnson, 1974;Heinz et al, 2001;Colburn et al, 2003;Horst et al, 2018). The concentration parameter of the von Mises distribution is equal to the dimensionless product BP 1 of the slope factor B and the amplitude of the sinusoid, P 1 .…”

“…Refractoriness limits the spike rate of ANFs and also slightly alters the shapes of the period histograms relative to those that would be observed in the absence of refractoriness (Avissar et al, 2013). Refractoriness has also been proposed to be responsible for the temporal asymmetry of period histograms (Horst et al, 2018). We removed the effects of refractoriness from each spike train to yield period histograms showing the recovered instantaneous rate of presumed synaptic release events rather than the rate of spikes ( Fig.…”

“…For display purposes, period histograms in A, C, and F were shifted by a constant phase for each ANF such that their peaks occur at ϳ/2. sponses show little, if any, compression (Robles and Ruggero, 2001), and mechanoelectrical transduction in the peripheral auditory system is thought to obey a static sigmoidal nonlinearity (Meddis, 2006;Zilany et al, 2009;Altoè et al, 2018;Horst et al, 2018).…”

Inconsistent effects of stochastic resonance on human auditory processing

“…Ward et al 22 argue that SR might also be observed in the case of a "soft threshold", i.e., a non-linear transfer function between instantaneous input and output, such as an exponential or logistic function, if sufficiently steep. The phase-locked period histograms of mammalian auditory-nerve fibers to low-frequency tones can be well described by exponential transfer functions relating the instantaneous stimulus pressure to the instantaneous spike rate (e.g., 26,27 ). However, it appears from comparing the data in these studies with the findings of Ward et al 22 (their Figure 6) that at the low, near-threshold stimulus levels the transfer functions are not steep enough to allow for SR. Later, Greenwood et al 28 reported that for SR to occur it is important that the signal is located near a transition between a relatively flat and an increasing portion (an 'edge') of the transfer function, while the slope of the function, in itself, would not be of great importance.…”