(a) Boundary definitions for thickness measurement. The inner, outer, and Neumann boundaries are defined and the label of the neocortex is used as a solution domain in thickness computation. (b), (c) Histology atlas13, 14 shows a Nissl-stained slice along with anatomical annotations. Note that the six cortical layers stack up from inner boundary towards the outer boundary, and they converge laterally to the Neumann boundary in parallel, which is denoted with the arrow, as shown in (a). (d) Laplacian vector field is shown from axial and sagital view. Note that mathematically derived layers are similar to cortical layers in (c). (e) Thickness map is computed by the boundary definition of (a). Streamlines used to measure cortical thickness are represented as randomly colormapped stripes.