The expression of the limbic system-associated membrane protein (LAMP), a marker of specific functional regions of the cerebral cortex, has been used to determine the environmental signals that regulate cortical regionalization. Transplant and cell culture studies have shown previously that the fate of precursor cells, based on LAMP expression, is amenable to regulation by exposure to novel environmental stimuli. This has been demonstrated in vitro to be dependent upon exposure to transforming factor-alpha and collagen type IV. Results following exposure to the inductive signals for a specific duration indicate a cell cycle dependence on the decision to become a limbic or nonlimbic cortical neuron. It appears, therefore, that areal and laminar fates are both influenced by mechanisms that specify commitment early in cortical development.