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

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/).

Quantification of audiogram fine-structure as a function of hearing threshold.

We investigated the amount of fine-structure in the audiograms of patients with Menière's disease. Both ears (often an affected and an unaffected ear) were investigated. Data are presented from 39 ears of 21 patients with hearing thresholds varying from about 0 to 70 dB HL. The fine-structure was measured in the frequency range from 500 to 3500 Hz; this agrees with a part of the basilar membrane from 10 to 22.5 mm from the apex. The fine-structure was characterized by means of the number of peaks N(p) and the sum S(p) of the heights of all the peaks in an audiogram. From these quantities, we also determined average peak height H(p). We found a negative correlation between hearing loss and strength of fine-structure, i.e. the higher the thresholds the smaller N(p) and S(p) as well as H(p). Also N(p) and H(p) were correlated, i.e. the more peaks the higher the average peak height. The summated peak height S(p)=N(p)H(p) showed a strong dependence on the hearing loss. In cases of strong fine-structure, S(p) reached values around 200 dB.