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Beyond conventional audiograms : thresholds in quiet and noise and their diagnostic potential for noise-induced cochlear synaptopathy Ma, Ainsley


Purpose: Studies in rodents, and more recently humans, suggest that noise exposure can cause permanent damage to synaptic ribbons between cochlear inner hair cells and auditory nerve synapses. Because this damage occurs before it is apparent in outer hair cells, it remains undetectable on traditional clinical assessments. Individuals may present with difficulty listening to speech in noise, tinnitus, hyperacusis, or a combination. This neuropathy, known as cochlear synaptopathy, or “hidden hearing loss”, is relatively uninvestigated, and there is currently no known test protocol to detect it. This study aims to identify the diagnostic potential of thresholds in quiet and noise on noise-induced cochlear synaptopathy. Methods: 42 young adults (mean age = 20 years) were recruited. Twenty music students with normal hearing (≤ 25 dB, HL 250-8000 Hz) and 22 normal-hearing controls with limited noise exposure were tested. Lifetime noise exposure, hearing thresholds 250-16 000 Hz in quiet, and TEN test thresholds at 1000 Hz and 4000 Hz were recorded. Bayesian inference was used to analyze differences between thresholds by group, and interactions between noise exposure and thresholds in quiet and in noise. Results: Threshold differences between groups were found at 1000 Hz TEN. There was a trend for a negative association between thresholds in quiet and thresholds in noise in most multiple regression models; however, unexpected results were found with two outcomes involving lifetime noise exposure as an additional predictor. Though trends were observed, none of them were overtly conclusive. Conclusion: The present study found inconclusive evidence for differences between thresholds in quiet or in noise between early-career musicians and non-musicians. It is possible that the cohort tested did not yield conclusive results due to the nature of noise exposure, or other inherent characteristics of the group such as age and clinical symptoms. Further research is required to develop a reliable behavioural test battery sensitive to cochlear synaptopathy in humans.

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