Diffusion weighted data were collected on a 3.0-Tesla GE magnetic resonance scanner using whole brain echo planar imaging (repetition time = 12,000 ms; echo time = 93.4 ms; 36 × 3.0 mm thick axial slices; in plane voxel resolution 1.875 × 1.875). Diffusion gradients were applied in 15 directions with 4 averages and a b-value of 2,000 s/mm2. Raw images were uniformly pre-processed by analyzers (TM and SB), blind to participant group status, to correct for: (1) eddy-current distortions using Functional Magnetic Resonance Imaging of the Brain's (FMRIB) Diffusion Toolbox (FDT; 2D with 6 degrees-of-freedom) (Smith et al., 2004); (2) head motion by registering the diffusion images to the b0 image as a reference, and (3) susceptibility distortions by applying field map unwarping (Smith et al., 2006). FA values were computed using a log-linear estimation procedure to fit each data point to a diffusion tensor model via FDT (Basser et al., 1994). FA maps from each participant were submitted to Tract-Based Spatial Statistics (TBSS) (Smith et al., 2006), which involved 3 steps: (1) all datasets were nonlinearly registered and aligned
