The assembly of neurons into circuits may to some extent be independent of the spatial relationships between these neurons, due to the existence of conserved, location-independent molecular controls. Input neurons (in black) connect to intracortically projecting neurons (in green), which project to output neurons (in blue). A current limitation in testing this hypothesis is our generally limited ability to establish unambiguous correspondences in cell types across species/conditions. Reeler mouse, see ref. 74; L4 FEZF2 overexpression, see ref. 56.