Concurrent Compensation for Auditory and Visual Processing in Individuals With Single-Sided Deafness.

Abstract

Objectives: Auditory deprivation results in functional enhancement of the remaining intact visual modality, and the underlying mechanisms include cross-modal recruitment of additional resources from the auditory cortex and compensatory reorganization of the visual network in bilateral deafness. However, how resources are allocated between hearing and vision has not been determined in patients with partial auditory deprivation. This study aimed to investigate the relationship between functional plasticity of the visual and auditory pathways in patients with congenital single-sided deafness (SSD), a typical partial deprivation condition.

Design: The cross-sectional cohort was comprised of 25 patients with congenital SSD (mean age ± SD = 31.6 ± 5.2 years, 13 males) and 25 normal hearing (NH) controls (mean age ± SD = 30.9 ± 7.5 years, 13 males). Both visual-evoked potentials (VEPs) and auditory-evoked potentials (AEPs) were assessed for all participants. For assessment of AEPs, auditory stimuli were presented unilaterally through the hearing ear in the SSD group, while the auditory stimuli were presented unilaterally (left and right) and bilaterally in the NH group. Event-related potential analyses focused on the differences in latency and amplitude of VEPs and AEPs between groups. Dipole source analyses of VEPs and AEPs were implemented to measure the dipole strengths and latencies of the bilateral primary visual and auditory cortex and comparisons were made both within and between groups.

Results: For VEPs, SSD patients exhibited a greater amplitude and a shorter latency than NH controls. For dipole source analysis of VEPs, no interhemispheric asymmetry or between-group difference was observed. For AEPs, the amplitude of SSD patients was greater than that of NH controls under the monaural condition but did not exceed that evoked by binaural stimuli in NH controls. For dipole source analysis of AEPs, interhemispheric strength asymmetry was observed in NH controls in response to monaural stimuli but was less clear in SSD subjects. Considering the side of deafness, interhemispheric strength asymmetry was hardly observed in left SSD (LSSD) patients, and was also weakened in right SSD (RSSD) patients. The interhemispheric difference index of dipole strength in LSSD patients was significantly lower than that in NH controls in response to right monaural stimuli. Furthermore, the dipole strength of the ipsilateral hemisphere in both LSSD and RSSD patients was greater than that in NH controls in response to monaural stimuli.

Conclusions: Neural activity and efficiency in the early stage of cortical visual processing in SSD patients were enhanced. The monaural responses of the auditory pathway have lost the typical contralateral organization, becoming more symmetric due to the increased ipsilateral pathways. These findings suggest concurrent compensation for auditory and visual processing in SSD patients.