Regionalization of cell-cycle kinetics of cortical precursors has been described in non-human primates and rodents indicating a fate map of areal 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 areas17 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 two areas involve an orchestration of diverse phenomena including differential rates of proliferation, migration and tangential expansion.
