Speech-Evoked and Resting-State Functional Connectivity as a Measure of Visual Cross-Modal Reorganization in Pre-Lingual Early-Implanted Adult Cochlear Implant Users

Background: Visual cross-modal reorganization (VCMR), once considered a “hostile take-over” of auditory areas by visual areas, is a top-down mechanism thought to account for some of the variability in speech perception among cochlear implant users (CIU). However, evidence on whether VCMR refllects maladaptive neural reorganization remains conflicting, with most prior work targeting post-lingually deaf adults. We used functional Near Infrared Spectroscopy (fNIRS) to assess, for the first time in pre-lingually deaf, early-implanted CIU, how intra-modal and cross-modal (CMC) auditory–visual connectivity differs from that of normal hearing (NH), whether these differences depend on the type of speech perceived, and whether they persist at rest, with the aim of distinguishing intrinsic network reorganization from task-specific adaptation.

Methods: Twelve pre-lingually deaf adult CIU and 12 NH controls underwent fNIRS imaging over bilateral temporal and occipital cortices. A block-design speech task included auditory-only (AO), audiovisual (AV), and visual-only (VO) conditions, and a 5-minute resting-state recording. Intra-modal (IMC) and left and right CMC (LCMC, RCMC) connectivity estimates were analyzed using linear mixed-effects models and were correlated with speech perception scores in quiet and in noise.

Results: CIU showed preserved IMC but increased CMC connectivity, with significantly stronger RCMC, most prominently during AO condition. Resting-state patterns showed preserved IMC and bilaterally increased cross-modal connectivity in CIU. Connectivity measures were not correlated with speech-perception scores.

Conclusion: Early-implanted pre-lingual CIU demonstrated increased CMC and preserved IMC connectivity, with similar patterns observed during rest, suggesting intrinsic network reorganization rather than task-dependent functional adaptation. These findings do not support the interpretation of increased cross-modal connectivity as a maladaptive form of neural reorganization.