Auditory and cognitive functioning in hidden hearing loss due to noise exposure, aging, and tinnitus: A systematic review

Abstract

Purpose: Since the inception of the term cochlear synaptopathy, extensive research is carried out to study the effects of noise and age on suprathreshold hearing in individuals with otherwise normal hearing. Yet, there is a lack of a standard test battery. We hypothesize that this variability in the results across studies may be due to the use of “cochlear synaptopathy” or “hidden hearing loss” as a blanket term to refer to auditory deficits seen in individuals with noise exposure, aging, and tinnitus with normal hearing. The present study aimed to systematically review the literature on hidden hearing loss due to noise exposure, aging, and tinnitus. Method: Keywords were combined using Boolean operations, and an electronic search was carried out through PubMed, ScienceDirect, ResearchGate, and Google Scholar databases. Screening for abstracts, title, and full text resulted in 46 articles eligible for data extraction. Results: Among the 46 studies considered for the review, 30 studies included human participants and 16 included animal participants. The possibility of noise-induced synaptopathy was assessed in 30 studies; age-induced synaptopathy in 6 studies; and synaptopathy in normal-hearing individuals with tinnitus in 10 studies. The results revealed conclusive findings of synaptopathy in animals; however, the evidence in studies involving human participants was inconclusive. Conclusions: Auditory brainstem response (ABR), histopathology, and middle ear muscle reflex (MEMR) are the widely used measures of synaptopathy in animals. Human studies indicated that temporal processing, speech perception in the presence of background noise, and working memory are majorly affected in individuals with hidden hearing loss. Specifically, speech perception in noise (SPiN), temporal resolution, MEMR, ABR wave I amplitude growth, and electrocochleography (ECochG) are identified as the potential measures of hidden hearing loss due to noise exposure. Further, the effect of common recreational noise on these measures is less compared to high life-time noise exposure. The results of synaptopathy due to aging or tinnitus are inconclusive.