Abnormal diffusion of cerebral white matter in early blindness

Early visual deprivation may lead to both abnormal and plastic changes in the visual and other systems of the brain. Such secondary changes in the gray matter of the early blind have been well studied, but not so well in the cerebral white matter whose subtle changes may be revealed by diffusion tensor imaging. The first purpose of this study is to explore the possible changed white matter regions of the early blind in whole brain manners, using voxel-based analysis (VBA) and tract-based spatial statistics (TBSS) methods. The second purpose is to investigate the changes of diffusion eigenvalues in the abnormal white matter fiber tracts using tractography based group mapping analysis. From VBA of fractional anisotropy (FA) images, the significant changed white matter regions were the geniculocalcarine tract (GCT) and its adjacent regions. This finding was validated by TBSS method. Then we studied the changes of mean diffusivity (MD), FA, primary (lambda(1)) and transverse diffusivities (lambda(23)) in the GCT using tractography based group mapping analysis. We found the early blind had significantly lower FA (P < 0.0001), higher MD (P = 0.001) and lambda(23) (P < 0.0001) in the GCT. This pattern of diffusion changes is similar to findings seen in immaturity or axonal degeneration. Thus, we suggest that transneuronal degeneration and/or immaturity may account for the abnormal diffusion changes in the GCT of the early blind.