Data Preprocessing

The data analyses consisted of three major steps: (1) data preprocessing, (2) probabilistic fiber tractography and network construction, and (3) network analyses. We performed the data preprocessing and fiber tractography using the FMRIB’s Diffusion Toolbox (http://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FDT). The data preprocessing included eddy current and motion artifact correction, and co-registration. Eddy current distortions and motion artifacts were corrected by applying affine alignment of each diffusion-weighted image to the b₀ image. After this process, the tensor elements were estimated and then the reconstructed tensor matrix was diagonalized to obtain three eigenvalues and eigenvectors [Behrens et al., 2003]. The probabilistic distribution of fiber orientations for each voxel was estimated with a two-tensor model following the instruction of the BEDPOSTX (Bayesian Estimation of Diffusion Parameters Obtained using Sampling Techniques with modeling crossing fibers within each voxel) program on FSL website [Smith et al., 2004] (http://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FDT/UserGuide).