Differences in the major fiber-tracts of people with congenital and acquired blindness.

In order to better understand how our visual system processes information, we must understand the underlying brain connectivity architecture, and how it can get reorganized under visual deprivation. The full extent to which visual development and visual loss affect connectivity is not well known. To investigate the effect of the onset of blindness on structural connectivity both at the whole-brain voxel-wise level and at the level of all major white-matter tracts, we applied two complementary Diffusion-Tension Imaging (DTI) methods, TBSS and AFQ. Diffusion-weighted brain images were collected from three groups of participants: congenitally blind (CB), acquired blind (AB), and fully sighted controls. The differences between these groups were evaluated on a voxel-wise scale with Tract-Based Spatial Statistics (TBSS) method, and on larger-scale with Automated Fiber Quantification (AFQ), a method that allows for between-group comparisons at the level of the major fiber tracts. TBSS revealed that both blind groups tended to have higher FA than sighted controls in the central structures of the brain. AFQ revealed that, where the three groups differed, congenitally blind participants tended to be more similar to sighted controls than to those participants who had acquired blindness later in life. These differences were specifically manifested in the left uncinated fasciculus, the right corticospinal fasciculus, and the left superior longitudinal fasciculus, areas broadly associated with a range of higher-level cognitive systems.