Fiber-tract differences in people with congenital and acquired blindness

Visual deficits can lead to differences in both the gray and white matter of the brain. Previous research has shown that there are connectivity differences (functional and structural) between sighted and blind individuals, with further differences in cortical activation between those with congenital and acquired blindness. The current study sought to determine the differences in major white matter tracts between congenitally blind and acquired blind participants, as well as to determine how they each differ from sighted subjects. Diffusion-weighted images were collected from three groups of participants: congenitally blind (CB), acquired blind (AB), and sighted controls with normal/corrected-to-normal visual acuity (SC). Each participant's data was processed using the Automated Fiber Quantification (AFQ) software package, which automatically groups fibers into a set of 20 fiber bundles using a two ROI-based approach (Yeatman et al., 2012). This method allows for accurate between-group comparisons without the use of co-registration algorithms, and thus tolerates greater variation at the level of individual fibers. For each subject, a partially-weighted mean fractional anisotropy (FA) was calculated at 100 nodes between the two ROIs for each fiber bundle. Comparisons of the FA values between the three groups showed several fiber bundles where the FA was greater for the AB group than for both the CB and sighted groups. Specific tracts that appeared to be particularly distinct in the AB participants included the cingulum, corticospinal, inferior fronto-temporal, and uncinated fasciculi bilaterally, as well as the right inferior longitudinal fasciculus. Interestingly, in fiber-tracts where all groups deviated from one another, the CB participants appeared to be more similar to the sighted group than to the AB group. These results suggest that the level of white matter reorganization in major fiber tracts is dependent on the onset of blindness.