Cross-modal functional plasticity after cochlear implantation

Despite evidence that cross-modal effects after hearing loss and cochlear implantation are primarily driven by synaptic gain and efficacy, few studies have evaluated cross-modal functional connectivity (CMFC) to assess plasticity. This study, inspired by the psychophysiological interaction (PPI) method, addresses its limitations and provides a robust approach for assessing task-induced CMFC. Twenty-three postlingually deafened cochlear implant (CI) recipients and 17 normal-hearing (NH) participants took part in the study. Functional near-infrared spectroscopy was used to measure brain activity during audio-only and visual-only speech tasks, with resting-state FC as a baseline, at 1 month and 1 year postimplantation. CI users' speech understanding was assessed 1 year postimplantation. Significant negative correlations were observed between contralateral task-induced CMFC and speech outcomes, particularly in links from the angular gyrus (AG) to the visual cortex. One year after CI activation, higher task-induced CMFC was found in AG compared to the superior temporal gyrus, reflecting neural efficiency principles. Task-induced CMFC remained elevated in CI users compared to NH even after 1 year. These findings suggest task-induced CMFC as a significant marker of cross-modal plasticity and speech performance in CI recipients.