Spatial plasticity of the auditory cortex in single-sided deafness.

OBJECTIVES/HYPOTHESIS: To evaluate spatial plasticity of the auditory cortex in single-sided deafness (SSD).

STUDY DESIGN: Cross-sectional study comparing a cohort with adult-onset, idiopathic SSD to a cohort with normal hearing.

METHODS: Demographic, audiometric, magnetoencephalographic imaging, and magnetic resonance imaging data were collected for 13 SSD adult subjects and 13 normal-hearing controls. Locations of peak activation corresponding to the M100 response in auditory cortices ipsilateral and contralateral to tonal stimuli (0.5 kHz and 4 kHz) were extracted from advanced biomagnetic source imaging analyses. Spatial extent of frequency representation across the 0.5 kHz to 4 kHz zone was computed for the two hemispheres.

RESULTS: Spatial separation distance between peak locations for 0.5 kHz and 4 kHz stimuli in SSD showed increased activation spread distance in the hemisphere contralateral to the only hearing ear and decreased distance in the ipsilateral hemisphere. In contrast, normal hearing controls had nearly the same activation spread distance in the two hemispheres for ipsilateral and contralateral inputs. The difference between interhemispheric activation spread distance in SSD is significantly increased to 6.5 mm, when compared to 1.7 mm in normal controls (P < .05).

CONCLUSIONS: Loss of unilateral peripheral input in SSD is associated with spatial reorganization of the auditory cortex in both hemispheres. This change in central auditory functional organization may in turn lead to higher order hearing deficits that rely on interhemispheric processing. Hearing optimization in the only hearing ear may require remediation of both spatial and temporal central auditory changes in SSD.

LEVEL OF EVIDENCE: NA Laryngoscope, 126:2785-2791, 2016.