Validation : measuring the fraction of surface area of the cortical GM-WM surface comprising concave surface patches (predominantly sulci) in 50 healthy adults. (a)-(d) Proposed surface descriptors for the frontal, parietal, temporal, and occipital lobes, respectively. The asymmetry between the left and right halves, i.e. concave and convex patches, is consistent with published clinical studies [Van-Essen and Drury (1997); Zilles et al. (1988)]. Note the reduced left-right asymmetry in (d) relative to (a)-(c).