Acoustic Middle-Ear-Muscle-Reflex Thresholds in Humans with Normal Audiograms: No Relations to Tinnitus, Speech Perception in Noise, or Noise Exposure

Hannah Guest,Kevin J Munro,Christopher J Plack

doi:10.1016/j.neuroscience.2018.12.019

Abstract

The acoustic middle-ear-muscle reflex (MEMR) has been suggested as a sensitive non-invasive measure of cochlear synaptopathy, the loss of synapses between inner hair cells and auditory nerve fibers. In the present study, clinical MEMR thresholds were measured for 1-, 2-, and 4-kHz tonal elicitors, using a procedure shown to produce thresholds with excellent reliability. MEMR thresholds of 19 participants with tinnitus and normal audiograms were compared to those of 19 age- and sex-matched controls. MEMR thresholds did not differ significantly between the two groups at any frequency. These 38 participants were included in a larger sample of 70 participants with normal audiograms. For this larger group, MEMR thresholds were compared to a measure of spatial speech perception in noise (SPiN) and a detailed self-report estimate of lifetime noise exposure. MEMR thresholds were unrelated to either SPiN or noise exposure, despite a wide range in both measures. It is possible that thresholds measured using a clinical paradigm are less sensitive to synaptopathy than those obtained using more sophisticated measurement techniques; however, we had good sensitivity at the group level, and even trends in the hypothesized direction were not observed. To the extent that MEMR thresholds are sensitive to cochlear synaptopathy, the present results provide no evidence that tinnitus, SPiN, or noise exposure are related to synaptopathy in the population studied.

Highlights

Cochlear synaptopathy, the loss of synapses between inner hair cells and auditory nerve fibers, has been convincingly demonstrated in rodent and recently primate models as a consequence of noise exposure and aging (Fernandez et al, 2015; Furman et al, 2013; Kujawa & Liberman, 2009; Sergeyenko et al, 2013; Valero et al, 2017)
Some studies have reported a relation of self-report noise exposure to wave I amplitude (Bramhall et al, 2017; Stamper & Johnson, 2015), or to the ratio of wave I amplitude to wave V amplitude, or to the ratio of summating potential amplitude to action potential amplitude (SP/AP; Liberman et al, 2016), with the latter two measures having been proposed as differential measures of synaptopathy
The present paper reports an analysis of previously unpublished middle-ear-muscle reflex (MEMR) threshold data collected as part of two published studies examining the relation between tinnitus, speech perception in noise (SPiN), and electrophysiological measures of synaptopathy in listeners with normal audiometric hearing (Guest et al, 2017b; Guest et al, 2018c)

Summary

Introduction

The loss of synapses between inner hair cells and auditory nerve fibers, has been convincingly demonstrated in rodent and recently primate models as a consequence of noise exposure and aging (Fernandez et al, 2015; Furman et al, 2013; Kujawa & Liberman, 2009; Sergeyenko et al, 2013; Valero et al, 2017). Is to select a measure of an assumed underlying cause - for example, self-report noise exposure - as a predictor variable and ask if this variable is associated with an outcome measure assumed to reflect synaptopathy - for example, wave I of the auditory brainstem response (ABR), which reflects auditory nerve function and is related to histological measures of synaptopathy in the rodent models (Kujawa & Liberman, 2009; Sergeyenko et al, 2013). A problem with this approach with respect to noise exposure is that self-report measures are inherently highly variable, we have argued previously that the measurement error is small compared to the range of exposures in the population (Prendergast et al, 2017a)

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Discussion

Conclusion