Progressive acquisition of cortical phenotypes as a mechanism for specifying the developing cerebral cortex.

The formation of the cerebral cortex requires the assembly of a complex array of neurons that exhibit specific patterns of laminar distribution, connectivity, and macromolecular expression. The problem of how various areas become specified relies to a large extent on the ability to assay certain characteristics of a particular cortical area during development. Certain phenotypic features appear to be acquired early in histogenesis, whereas others have a relatively late onset of expression. This pattern of progressive acquisition of traits suggests that each feature may be regulated by a different set of genomic-environmental interactions. This would lead to an early framing of cortical regions through the commitment of cells to area-specific phenotypes, but allow modifications of later developing traits through changes in certain environmental features.