Reorganization of thalamocortical connections in congenitally blind humans

Cross-modal plasticity in blind individuals has been reported over the past decades showing that nonvisual information is carried and processed by visual brain structures. However, despite multiple efforts, the structural underpinnings of cross-modal plasticity in congenitally blind individuals remain unclear. We mapped thalamocortical connectivity and assessed the integrity of white matter of 10 congenitally blind individuals and 10 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 impaired microstructure 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, whereas those connecting with the temporal cortex showed greater volume and increased connectivity. 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.

Automated summary

Cross-modal plasticity in blind individuals refers to the ability of their visual brain structures to process nonvisual information. However, the structural basis of this plasticity in congenitally blind individuals is not clear. This study investigates the thalamocortical connectivity and white matter integrity in 10 congenitally blind individuals and 10 sighted controls, revealing changes in connectivity between the thalamus and occipital and temporal cortices. The findings demonstrate a remapping of thalamocortical connections and provide insights into the functional adaptations in congenitally blind individuals.