Source analysis reveals plasticity in the auditory cortex: evidence for reduced hemispheric asymmetries following unilateral deafness

Abstract

Objective: To investigate the effect of acquired unilateral deafness on hemispheric asymmetries in adult humans using cortical auditory evoked potentials.

Methods: N1 cortical auditory evoked potentials were measured from 30 channels in 18 unilateral profoundly-deaf participants (6 right-sided and 12 left-sided deafness) and 18 audiogram-matched controls. Stimuli were 0.5-kHz and 4-kHz tones presented monaurally, and the data were analysed using global field power and dipole source analysis.

Results: There was a statistically significant difference in dipole source strength and orientation between the two groups. Similar changes (increased dipole strength and more medial orientation) were apparent after profound unilateral deafness of either ear and for both stimuli.

Conclusions: The results reveal evidence of central auditory system plasticity that is consistent with animal models having experimentally induced unilateral deafness.

Significance: The trend towards reduced hemispheric asymmetries was reflected in the dipole source model by changes in dipole strength, location and orientation. These findings may explain the inconsistencies reported in previous studies involving dipole source analysis where location and orientation have not always been considered.