Brain plasticity and auditory spatial adaptation in patients with unilateral hearing loss

The ability to localize sounds in patients with Unilateral Hearing Loss (UHL) is usually disrupted due to alteration in the integration of binaural cues. Nonetheless, some patients are able to compensate deficit using adaptive strategies. In this study, we explored the neural correlates underlying this adaptation. Twenty-one patients with UHL were separated into 3 groups using cluster analysis based on their binaural performance. The resulting clusters were referred to as better, moderate, and poorer performers cluster (BPC, MPC, and PPC). We measured the mismatch negativity (MMN) elicited by deviant sounds located at 10 degrees, 20 degrees, and 100 degrees from a standard positioned at 50 degrees ipsilateral to the deaf ear. The BPC exhibited significant MMN for all 3 deviants, similar to normal hearing (NH) subjects. In contrast, there was no significant MMN for 10 degrees and 20 degrees deviants for the PPC and for NH when one ear was plugged and muffed. Scalp distribution was maximal over central regions in BPC, while PPC showed more frontal MMN distribution. Thus, the BPC exhibited a contralateral activation pattern, similar to NH, while the PPC exhibited more symmetrical hemispheric activation. MMN can be used as a neural marker to reflect spatial adaptation in patients with UHL.