Characterizing noise-induced hidden hearing loss in veterans

Cochlear synaptopathy, the partial loss of auditory nerve synapses onto inner hair cells, has been proposed as a possible source of hyperacusis, some forms of tinnitus, and difficulty understanding speech in background noise. In animal models, cochlear synaptopathy is associated with a reduction in the amplitude of wave I of the auditory brainstem response (ABR) and can occur even when auditory thresholds are normal. This presentation will discuss noise exposure-related changes to several auditory physiological measures, including the ABR, in young military Veterans with clinically normal pure tone thresholds. Veterans show differences from non-Veteran controls even after statistically adjusting for group differences in sex and otoacoustic emissions, suggestive of synaptic or neuronal loss. While these physiological changes do not appear to be associated with decreased performance on standard speech-in-noise tests, they are associated with the report of frequent or constant tinnitus. Although post-mortem histological analysis would be necessary for confirmation, these data are consistent with animal models of cochlear synaptopathy and suggest that synaptopathy or “hidden hearing loss” may occur in response to high intensity noise exposure in humans and be correlated with tinnitus.