Objective markers of altered neural gain dissociate tinnitus and self-reported listening problems in individuals with exceptional hearing thresholds
Many individuals experience problems that are undetected by standard hearing tests, such as persistent tinnitus and difficulties understanding speech in background noise. Here, we report evidence of altered neural gain in young adults with self-reported listening problems despite exceptional hearing thresholds. Individuals reporting persistent tinnitus (the daily percept of sound in the absence of an external source) exhibited elevated thresholds of the middle ear muscle reflex, suggestive of altered gain in brainstem reflexive circuits, and reduced cortical responses to auditory spatial cues conveyed in the temporal fine structure of low-frequency sounds. Moreover, in both groups, greater self-reported speech-in-noise difficulties were associated with higher magnitude cortical responses, particularly at the highest stimulus intensity, consistent with elevated neural gain. Using a conceptual model, we demonstrate how damage to high-threshold auditory nerve fibres innervating cochlear nuclei can account for reduced activity of binaural neurons sensitive to the temporal fine structure of low-frequency sounds, generating a compensatory increase in neural gain in higher brain centres that impacts listening in complex environments.