The Relative and Combined Effects of Noise Exposure and Aging on Auditory Peripheral Neural Deafferentation: A Narrative Review

Abstract

Animal studies have shown that noise exposure and aging cause a reduction in the number of synapses between low and medium spontaneous rate auditory nerve fibers and inner hair cells before outer hair cell deterioration. This noise-induced and age-related cochlear synaptopathy (CS) is hypothesized to compromise speech recognition at moderate-to-high suprathreshold levels in humans. This paper evaluates the evidence on the relative and combined effects of noise exposure and aging on CS, in both animals and humans, using histopathological and proxy measures. In animal studies, noise exposure seems to result in a higher proportion of CS (up to 70% synapse loss) compared to aging (up to 48% synapse loss). Following noise exposure, older animals, depending on their species, seem to either exhibit significant or little further synapse loss compared to their younger counterparts. In humans, temporal bone studies suggest a possible age- and noise-related auditory nerve fiber loss. Based on the animal data obtained from different species, we predict that noise exposure may accelerate age-related CS to at least some extent in humans. In animals, noise-induced and age-related CS in separation have been consistently associated with a decreased amplitude of wave 1 of the auditory brainstem response, reduced middle ear muscle reflex strength, and degraded temporal processing as demonstrated by lower amplitudes of the envelope following response. In humans, the individual effects of noise exposure and aging do not seem to translate clearly into deficits in electrophysiological, middle ear muscle reflex, and behavioral measures of CS. Moreover, the evidence on the combined effects of noise exposure and aging on peripheral neural deafferentation in humans using electrophysiological and behavioral measures is even more sparse and inconclusive. Further research is necessary to establish the individual and combined effects of CS in humans using temporal bone, objective, and behavioral measures.

Neural adaptation at stimulus onset and speed of neural processing as critical contributors to speech comprehension independent of hearing threshold or age

“…When subjects were grouped into three categories based on their PNOT (poor, standard, and good), there was a better correlation between these categories and the subjects’ self-reported evaluation of their comprehension ability when listening to speech in quiet than that when subjects were categorized by age (Figure 7). Although this correlation was only a statistical tendency it strengthen previous findings of no correlation between self-reported speech comprehension ability and age (Shehabi et al, 2022).…”

Effects of Age and Noise Exposure History on Auditory Nerve Response Amplitudes: A Systematic Review, Study, and Meta-Analysis

“…Longitudinal studies are warranted to assess changes in AN function across the lifespan and how such changes in AN function relate to AN structure evaluated post-mortem (for reviews and similar recommendations, see Bramhall et al, 2019; Le Prell, 2019; Shehabi et al, 2022).…”

“…To date, the specific pathology underlying reduced AN response amplitudes can only be identified with post-mortem histological assessment. Longitudinal studies are warranted to assess changes in AN function across the lifespan and how such changes in AN function relate to AN structure evaluated post-mortem (for reviews and similar recommendations, see Bramhall et al, 2019; Le Prell, 2019; Shehabi et al, 2022).…”

Noise Exposure in Palestinian Workers Without a Diagnosis of Hearing Impairment: Relations to Speech-Perception-in-Noise Difficulties, Tinnitus, and Hyperacusis

“…Evidence from several animal species suggests that noise exposure and aging may damage the cochlear synapses that connect the inner hair cells with the auditory nerve well before cochlear hair cells are damaged ( Kujawa & Liberman, 2009 , 2015 ; Lin et al, 2011 ; Shehabi, Prendergast, & Plack, 2022 ; Valero et al, 2017 ). Low-to-medium spontaneous-rate (SR) high-threshold auditory nerve fibers (ANFs) were observed to be particularly vulnerable to this cochlear synaptopathy (CS) in guinea pigs and gerbils ( Furman et al, 2013 ; Schmiedt et al, 1996 ), but not in CBA/CaJ mice, in which high-SR fibers were equally affected ( Suthakar & Liberman, 2021 ).…”

“…Adults with NIHL and/or ARHL have been consistently observed to perform worse in SPiN tests compared to their counterparts with normal hearing ( Acton, 1970 ; Dubno et al, 1984 ; Frisina & Frisina, 1997 ; Quist-Hanssen et al, 1978 ; Smoorenburg, 1992 ). However, no clear association has been found between lifetime noise exposure and SPiN performance in audiometrically normal young adults (for reviews, see Bramhall et al, 2019 ; Le Prell, 2019 ; and Shehabi, Prendergast, & Plack, 2022 ). In contrast, an age-related decline in SPiN performance among older adults with normal or near-normal audiometric profiles has been consistently documented in the literature ( Babkoff & Fostick, 2017 ; Füllgrabe et al, 2015 ; S. Kim et al, 2006 ; Patro et al, 2021 ; Pichora-Fuller et al, 1995 ; Vermeire et al, 2016 ).…”