Cross-modal reorganization in cochlear implant users: Auditory cortex contributes to visual face processing.

There is converging evidence that the auditory cortex takes over visual functions during a period of auditory deprivation. A residual pattern of cross-modal take-over may prevent the auditory cortex to adapt to restored sensory input as delivered by a cochlear implant (CI) and limit speech intelligibility with a CI. The aim of the present study was to investigate whether visual face processing in CI users activates auditory cortex and whether this has adaptive or maladaptive consequences. High-density electroencephalogram data were recorded from CI users (n=21) and age-matched normal hearing controls (n=21) performing a face versus house discrimination task. Lip reading and face recognition abilities were measured as well as speech intelligibility. Evaluation of event-related potential (ERP) topographies revealed significant group differences over occipito-temporal scalp regions. Distributed source analysis identified significantly higher activation in the right auditory cortex for CI users compared to NH controls, confirming visual take-over. Lip reading skills were significantly enhanced in the CI group and appeared to be particularly better after a longer duration of deafness, while face recognition was not significantly different between groups. However, auditory cortex activation in CI users was positively related to face recognition abilities. Our results confirm a cross-modal reorganization for ecologically valid visual stimuli in CI users. Furthermore, they suggest that residual takeover, which can persist even after adaptation to a CI is not necessarily maladaptive.

Rapid bilateral improvement in auditory cortex activity in postlingually deafened adults following cochlear implantation.

OBJECTIVE: Cochlear implants (CIs) can partially restore hearing, but the cortical changes underlying auditory rehabilitation are not well understood. METHODS: This prospective longitudinal study used electroencephalography (EEG) to examine the temporal dynamics of changes in the auditory cortex contralateral and ipsilateral to the CI. Postlingually deafened CI recipients (N=11; mean: 59years) performed an auditory frequency discrimination task after <1week, 8weeks, 15weeks, and 59weeks of CI use. RESULTS: The CI users revealed a remarkable improvement in auditory discrimination ability which was most pronounced over the first eight weeks of CI experience. At the same time, CI users developed N1 auditory event-related potentials (AEP) with significantly enhanced amplitude and decreased latency, both in the auditory cortex contralateral and ipsilateral to the CI. A relationship was found between the duration of deafness and the ipsilateral AEP latency. CONCLUSIONS: Postlingually deafened adult CI users show rapid adaptation of the bilateral auditory cortex. Cortical plasticity is limited after long duration of auditory deprivation. SIGNIFICANCE: The finding of rapid and limited cortical changes in adult CI recipients may be of clinical relevance and can help estimate the role of plasticity for therapeutic gain.