Landmarks were identified in three dimensions on the laboratory grand average FA image in common space (Rohlfing et al. 2010). The genu and splenium were identified in the midline at the center of their maximum extent and the left and right superior cingulate bundles at the level of the anterior margin of pons. Each landmark was dilated with a morphological operator to produce a cube as the fiber tracking target. Sources were defined as planes anterior and posterior to the superior cingulate, a perpendicular midline plane anterior to the genu and a similar plane posterior to the splenium. The targets and sources in common space were then transformed into each subject’s native space for fiber tracking (left panel of Fig. 3).
