Effect of Sound Amplification on Central Auditory Plasticity: Endbulb of Held as a Substrate

Background: Hearing loss is known to cause structural and functional abnormalities in the central auditory pathways. Interventions with hearing aids that amplify acoustic signals have been developed to combat hearing loss. However, little is known about how such devices may affect the brain and mitigate the progression of hearing loss. We hypothesized that timely intervention that amplifies acoustic signals would delay further progression of hearing loss by maintaining central auditory activity and neural structure. Method: To that end, we provided eight weeks of acoustic stimulation tailored to compensate for subject-specific patterns of frequency loss in two mouse models of progressive hearing loss. We evaluated the effects of sound amplification on endbulb of Held anatomy at different ages of intervention in mice with early-onset (DBA/2) and late-onset (C57Bl/6) hearing loss. Results: We observed in both strains that endbulbs undergo rapid and progressive atrophy in untreated control subjects exposed to a baseline, unamplified, sound environment. In contrast, endbulb atrophy was significantly slowed in treated mice (p < 0.05). Conclusions: These data provide a possible explanation for how the brain benefits from sound amplification via hearing aid devices.