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

Unilateral hearing loss (UHL) alters binaural cues affecting speech comprehension and sound localisation. While many patients with UHL perform poorly on binaural tasks, some are able to adapt to monaural deficit. We aimed to identify patients with UHL who use compensatory strategies and to explore the neural correlates of this adaptation using Mismatch Negativity (MMN). We recruited 21 patients with UHL and we separated them into three groups using cluster analysis based on measures of binaural processing. The resulting groups were referred to as the better, moderate and poorer performers clusters (BPC, MPC and PPC). We measured the MMN elicited by deviant sounds located 10°, 20° or 100° away from a standard sound. We found that the BPC group had a significant MMN for all three deviant sounds, as in a group of normal-hearing controls. In contrast, the PPC group and normal-hearing controls with an earplug did not have a significant MMN for the 10° and 20° deviations. For the 100° deviation, the scalp distribution was found to be maximal over central regions in the BPC group, while the PPC group showed a more frontal distribution. Differences were also found for the N100 evoked by standard sounds, with the BPC group showing a contralateral pattern of activation, as in the controls, and the PPC group showing more symmetrical hemispheric activation. These results indicate that patients with UHL can develop adaptive strategies that are reflected by sound processing differences at the cortical level.