Unilateral hearing loss during adulthood disrupts binaural integration in the auditory midbrain

An increasing number of subjects with single-sided deafness (SSD) undergo cochlear implant (CI) surgery to improve sound localization, which is a key factor for understanding speech in noise. However, asymmetrical hearing experience in SSD may disrupt binaural integration circuits in the auditory system that encode interaural time differences (ITDs) and other features of sound location, preventing the full binaural benefits from being realized.

Here, we induce SSD in adult gerbils using aminoglycosides. After 15 days of deafness, the animals receive bilateral CIs, and we characterize neural coding of electric ITDs in the inferior colliculus. Normal hearing (NH) gerbils served for comparison.

The degree of neural ITD sensitivity in SSD animals was significantly degraded, and ITD response patterns were significantly altered. The relative activation of neuronal populations to electric ITDs showed a high degree of asymmetry between hemispheres and displayed a clear reduction in sharpness of ITD tuning. Moreover, discrimination thresholds of single neurons to electric ITDs were significantly increased compared to NH animals.

This data highlights the evolving degradations in binaural integration in the adult auditory system even after short SSD durations. Similar changes may relate to poor directional hearing abilities in human CI subjects with a history of single-sided hearing impairment or deafness.

Publication History

Publication Date:
23 April 2019 (online)