DTI data were used to evaluate structural connectivity between PPC and DLPFC regions. White matter integrity was measured with DTI indices FA, MD, AD, and RD in tracts subserving left and right frontoparietal connections, including the superior longitudinal fasciculus and genu of corpus callosum (see Figure 1). DTI data processing (see Bava et al., 2010 for details) included correction for head motion and eddy current distortion, using FSL tools (Smith et al., 2004). Preprocessed images underwent tensor decomposition to derive scalar diffusion indices (i.e., FA, MD, AD, and RD) for each voxel (Le Bihan et al, 2001), and statistical analyses were performed on FA maps using Tract-Based Spatial Statistics (TBSS; Smith et al., 2006) to co-align each subject’s FA image, create a mean FA image from which a white matter skeleton was derived, and project individual transformed FA images onto the skeleton. Partial-volume effects and areas of high inter-subject variability were minimized by thresholding values at 0.2. Values from individuals’ nearest relevant tract center were assigned to the skeleton through a perpendicular search for the maximum value within the skeleton.
