Abstract
Magnetic resonance imaging (MRI) of the human brain has provided converging evidence that visual deprivation induces regional changes in white matter (WM) microstructure. It remains unclear how these changes modify network connections between brain regions. Here we used diffusion-weighted MRI to relate differences in microstructure and structural connectedness of WM in individuals with congenital or late-onset blindness relative to normally sighted controls. Diffusion tensor imaging (DTI) provided voxel-specific microstructural features of the tissue, while anatomical connectivity mapping (ACM) assessed the connectedness of each voxel with the rest of the brain. ACM yielded reduced anatomical connectivity in the corpus callosum in individuals with congenital but not late-onset blindness. ACM did not identify any brain region where blindness resulted in increased anatomical connectivity. DTI revealed widespread microstructural differences as indexed by a reduced regional fractional anisotropy (FA). Blind individuals showed lower FA in the primary visual and the ventral visual processing stream relative to sighted controls regardless of the blindness onset. The results show that visual deprivation shapes WM microstructure and anatomical connectivity, but these changes appear to be spatially dissociated as changes emerge in different WM tracts. They also indicate that regional differences in anatomical connectivity depend on the onset of blindness.
Highlights
Structural and functional alterations in the brain related to visual deprivation have been widely studied in both animals and humans to unravel the underlying plastic mechanisms [1,2,3]
No significant differences were found in the whole-brain anatomical connectivity mapping (ACM) between normally sighted (NS) and late blind (LB) group, but LB group differed from congenitally blind (CB) group (p < 0.05), suggesting that only CB individuals are affected in terms of brain connectivity
Diffusion tensor imaging (DTI) is sensitive to the local microstructural tissue environment, and we find that mainly the primary visual pathway is largely affected by visual loss, expressed as decreased fractional anisotropy (FA) driven by increased radial diffusivity (RD), in CB and LB individuals compared to NS
Summary
Structural and functional alterations in the brain related to visual deprivation have been widely studied in both animals and humans to unravel the underlying plastic mechanisms [1,2,3]. Cross-modal plasticity refers to the ability of the blind brain to functionally recruit the visual cortex to process a variety of nonvisual tasks such as audition and language [7,8,9,10], tactile discrimination and spatial navigation [11,12,13,14], and even olfaction [15] (for review see Kupers and Ptito [6, 16]). This raises the question of whether the functional recruitment of the visual cortex during nonvisual tasks involves plastic changes in the anatomical connections. Linking such regional microstructural changes in white matter (WM) tracts to the altered patterns of brain connectivity can hold important information on the rewiring of the blind brain
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