Unilateral Hearing Loss During Development and Adulthood Differently Disrupts Binaural Integration in the Gerbil Auditory Midbrain

Subjects with single-sided deafness (SSD) increasingly undergo cochlear implant surgery (SSD-CI users) to restore directional hearing. However, asymmetric hearing may disrupt the hemispheric balance of central auditory circuits supporting spatial hearing. In an animal model, we test whether interaural time difference (ITD) coding in auditory midbrain neurons is differently impacted by unilateral hearing loss during development or during adulthood.

Single unit recordings were performed in the inferior colliculus of gerbils. First, responses to acoustic ITDs were characterized in normal hearing (NH) juveniles to identify the critical period for binaural integration. Second, juvenile and adult animals were unilaterally deafened. After 15 days of deafness, animals received bilateral round window electrodes, and neural responses to electric ITDs were recorded. NH adults served as controls.

In hearing animals, mature-like ITD coding occurred around P23. In SSD animals, degradations in ITD sensitivity and increases in discrimination thresholds were observed across all ages. However, animals deafened prior the closure of the critical period (P23) showed hemisphere-independent changes, whereas animals deafened later in life demonstrated more pronounced degradations in the hemisphere contralateral to the deaf ear.

In summary, ITD coding matures relatively late during development. ITD coding in auditory midbrain neurons was differently impacted by unilateral hearing loss during development and adulthood. The observed asymmetric changes in ITD coding between hemispheres may contribute to the poor directional hearing in SSD-CI users. It remains speculative whether differential therapeutic strategies are necessary to restore binaural hearing in juvenile versus adult SSD-CI users.

Poster-PDF A-1470.PDF

Publication History

Article published online:
10 June 2020