waypoint to constrain probabilistic tracts; a separate exclusion mask was created to further eliminate the likelihood of pathways in irrelevant white matter tracts, gray matter regions and CSF. Hippocampus and ACC masks were used as seed regions for the tracts, created using the Harvard-Oxford Subcortical Structural Atlas (http://www.cma.mgh.harvard.edu/fsl_atlas.html). Only streamlines that passed through seed regions and the waypoint were retained. The resulting streamlines were transformed to Montreal Neurological Institute (MNI) space. Given the large size and extent of cingulum streamlines, these paths were thresholded by 10% to reduce the likelihood of including extraneous tracts. An example thresholded probabilistic tract of the cingulum is provided in Figure 1. Fractional anisotropy was used as our measure of tract integrity, given that earlier studies have indicated it to be a reliable assessment of microstructural integrity of white matter fibers (35). Individual FA maps were linearly aligned to a standard MNI brain using FLIRT; mean FA for all streamlines was then extracted and entered into statistical analyses.
