Changes in thalamocortical connectivity as a potential mechanism of cross-modal plasticity in congenitally blind individuals
Cross-modal plasticity in blind individuals has been reported over the past decades showing that non-visual information is carried and processed by visual brain structures. However, the structural underpinnings of cross-modal plasticity in congenitally blind individuals remain unclear despite multiple efforts. We mapped thalamocortical connectivity and assessed cortical thickness and integrity of white matter of ten congenitally blind individuals and ten sighted controls. We hypothesized an aberrant thalamocortical pattern of connectivity taking place in the absence of visual stimuli from birth as a potential mechanism of cross-modal plasticity. In addition to the increased cortical thickness of the primary visual cortex and reduced integrity of visual white matter bundles, we observed structural connectivity changes between the thalamus and occipital and temporal cortices. Specifically, the thalamic territory dedicated to connections with the occipital cortex was smaller and displayed weaker connectivity in congenitally blind individuals. In contrast, those connecting with the temporal cortex showed greater volume and increased connectivity compared to sighted controls. The abnormal pattern of thalamocortical connectivity included the lateral and medial geniculate nuclei and the pulvinar nucleus. For the first time in humans, a remapping of structural thalamocortical connections involving both unimodal and multimodal thalamic nuclei has been demonstrated, shedding light on the possible mechanisms of cross-modal plasticity in humans. The present findings may help understand the functional adaptations commonly observed in congenitally blind individuals.