Physiological assays of suprathreshold hearing are consistent with widespread deafferentation of the human auditory periphery

Abstract

Multiple animal models have robustly shown the effects of noise-exposure and aging can have on the afferent synapses between the cochlea and the auditory nerve. This cochlear synaptopathy can affect responses to suprathreshold stimuli while leaving audiometric thresholds intact. However, currently, there is much debate on whether these same changes occur in humans with significant noise-exposure or with middle age. Our study examined two different physiological responses in which these afferent synapses are a crucial component, the auditory brainstem response (ABR) and the middle ear muscle reflex (MEMR). Versions of these measures were completed in both a clinical setting and a laboratory. Responses to both measures in both testing environments demonstrated significant age and noise-exposure effects. Moreover, these effects remained significant even after statistically accounting for variability in audiometric sensitivity and otoacoustic emissions, suggesting that despite clinically normal audiograms, cochlear synaptopathy may be a widespread occurrence in humans with both acoustic-overexposure and normal aging. Finally, our results suggest that a battery combining ABR and MEMR measures may be viable as a non-invasive assay of synaptopathy and can help examine the perceptual sequelae of such damage. Multiple animal models have robustly shown the effects of noise-exposure and aging can have on the afferent synapses between the cochlea and the auditory nerve. This cochlear synaptopathy can affect responses to suprathreshold stimuli while leaving audiometric thresholds intact. However, currently, there is much debate on whether these same changes occur in humans with significant noise-exposure or with middle age. Our study examined two different physiological responses in which these afferent synapses are a crucial component, the auditory brainstem response (ABR) and the middle ear muscle reflex (MEMR). Versions of these measures were completed in both a clinical setting and a laboratory. Responses to both measures in both testing environments demonstrated significant age and noise-exposure effects. Moreover, these effects remained significant even after statistically accounting for variability in audiometric sensitivity and otoacoustic emissions, suggesting that despite clinically normal audiograms, c...