Brain Plasticity and Clinical Consequences of Adult-Onset Asymmetric Hearing Loss

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PROJECT SUMMARY Permanent sensorineural asymmetric hearing loss (AHL) disrupts extraction of interaural information for binaural processing. Using a cutoff of at least 15 dB interaural difference as definition of AHL, prevalence estimates vary widely, from 1% to 50%. Among cohorts with occupational noise exposure, AHL prevalence ranges from 15%- 49%. Critical clinical consequences include difficulty with sound target identification in noisy environments and degradation of spatial hearing. Beyond those impairments, the aidable poorer ear in AHL is at risk for accelerated decline and often burdened by tinnitus. There is a wide gap in our understanding of the relationship between central nervous system changes along the continuum of AHL magnitudes, audiological and psychoacoustical outcomes, and tinnitus perception. Closing this knowledge gap would be the first step to advance diagnostic tools and inspire innovative treatments for AHL. Informed by anchoring neuroimaging and audiological data from normal hearing and single-sided deafness, the most extreme form of AHL, we propose to close this knowledge gap. A comprehensive study on the clinical consequences of AHL should address hearing performance under adverse conditions, spatial hearing, and tinnitus outcomes, and their central neural correlates. We propose a longitudinal within-subject neuroimaging features and clinical assessments study of AHL before and after treatment by amplification. We will use resting-state magnetoencephalographic imaging (RS-MEGI) and functional magnetic resonance imaging (RS-fMRI), task-based MEGI, and diffusion MRI to examine temporal, functional and structural features, and audiological and psychoacoustical tests to evaluate hearing performance and tinnitus outcomes. This observational study will collect data from participants who will be treated by routine amplification with individualized tinnitus sound therapies, as required, for AHL. We will evaluate test-retest reliability of neuroimaging features, and assess neuroimaging features, hearing performance, and tinnitus outcomes at baseline and at months 3, 6 and 12 following treatment. The specific aims of this research are to examine: 1) AHL clinical outcomes, 2) AHL auditory interhemispheric temporal organization using MEGI, and 3) AHL whole brain functional and structural neuroimaging features using resting-state MEGI and fMRI (functional), task-based MEGI (functional), and diffusion MRI (structural).