Pathways of Cross-Modal Access to the Visual Cortex in Late Blindness

This study investigated how auditory and tactile inputs reach the visual cortex in late-blind (LB) adults, a population for whom the neural mechanisms supporting cross-modal plasticity remain incompletely understood. Using magnetoencephalography (MEG), we measured neural responses to tactile finger stimulation and preceding auditory cues in LB and sighted controls (SC). When analyses were time-locked to the tactile stimulus, LB individuals showed markedly earlier and stronger activations in primary visual cortex (V1) than SC, with responses emerging at 35 ms versus 59 ms, suggesting the recruitment of a fast, likely monosynaptic thalamo-cortical, pathway in LB but not in SC. In contrast, analyses time-locked to the auditory cue revealed a common sequence in both groups: activation of the thalamus (~ 20 ms), followed by primary auditory cortex (A1, 35-38 ms), and then V1 (49-53 ms), consistent with direct A1-to-V1 transmission. Connectivity analyses showed enhanced thalamus-to-V1 alpha-band connectivity in LB for both auditory and tactile inputs, and increased beta-band connectivity only in the auditory modality. These effects did not depend on duration or onset age of blindness. Overall, the findings indicate that auditory and tactile signals reach V1 through distinct but complementary pathways in late blindness, highlighting substantial cross-modal reorganization in adulthood.