The concerted modulation of proliferation and migration contributes to the specification of the cytoarchitecture and dimensions of cortical areas.

Regionalization of cell cycle kinetics of cortical precursors has been described in nonhuman primates and rodents indicating a fate map of areas as distinct proliferative programs in the germinal zones of the neocortex. It remains to be understood how proliferative gradients during corticogenesis are transcribed into a stepwise function to form adult areal borders. Here we have used the monkey areas 17 and 18, which show striking cytoarchitectonic differences, as a model system for studying how developmental events establish areal boundaries in the adult. We present data indicating that the events that are involved in the formation of a sharp border separating 2 areas involve an orchestration of diverse phenomena including differential rates of proliferation, migration, and tangential expansion.