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

## TL;DR

Late-blind adults use different neural pathways for auditory and tactile signals to reach the visual cortex, showing significant brain reorganization.

## Contribution

The study reveals distinct and complementary cross-modal pathways in late-blind individuals, offering new insights into adult brain plasticity.

## Key findings

- Late-blind individuals show earlier and stronger visual cortex activation in response to tactile stimuli.
- Auditory cues activate a common sequence involving the thalamus, auditory cortex, and visual cortex in both blind and sighted groups.
- Enhanced thalamus-to-visual cortex connectivity is observed in late-blind individuals for both auditory and tactile inputs.

## Abstract

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.