Patterning the mammalian cerebral cortex

When and how is the area map of the cerebral cortex set up during developme nt? Recent studies indicate that regional pattern emerges early in cortical neurogenesis, and that this pattern does not require cues from extrinsic i nnervation. Studies of mutant mice indicate a role for embryonic signaling centers and for specific transcription factors in regionalizing the cortex. Thus, it is increasingly probable that the cortex is partitioned using the same types of mechanisms - and in some cases, the same gene families - tha t are used in patterning other parts of the embryo. This emerging model is likely to be the basis for many future studies. However, new evidence also confirms the special nature of the cerebral cortex, in that cues from devel oping connections appear to modify and refine the final area map.