Special Session: Uncovering Hidden Hearing Loss: Noise Exposure, Tinnitus and AgingNoise-Induced Hidden Hearing Loss: What We Can Learn from Military Veterans OBJECTIVES: Although noise-induced cochlear synaptopathy has been demonstrated in a number of animal species, including non-human primates, synaptopathy is a type of “hidden” hearing loss and cannot be confirmed in living humans. This leaves us with two big unanswered questions about the impact of noise-induced cochlear synaptopathy on humans: 1) Does noise-induced cochlear synaptopathy occur in humans? and 2) Does synaptopathy have perceptual consequences? METHODS: High levels of noise exposure from sources such as weapons fire, aircraft, and explosions are often encountered during military service. This makes Veterans an ideal sample population for exploring questions about noise-induced synaptopathy. Although synaptopathy can only be confirmed through post-mortem temporal bone analysis, several auditory physiological measures that are sensitive to synaptopathy have been identified in animal models, including the auditory brainstem response, the envelope following response and the middle ear muscle response. RESULTS: Data from young Veterans with normal audiograms illustrate relationships between physiological indicators of cochlear synaptopathy and noise exposure history that parallel those observed in animal models. Perception of tinnitus in young Veterans is associated with similar changes in these physiological indicators. CONCLUSIONS: These results suggest that noise-induced cochlear synaptopathy occurs in humans and has auditory perceptual consequences. Given these findings, the ability to diagnose cochlear synaptopathy in individual patients will be vital for developing treatment options and guiding clinical care. Auditory physiological measurements hold promise for future clinical diagnosis of cochlear synaptopathy.
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