The origin and migration of cortical neurones: new vistas

The principal neuronal types of the cerebral cortex are the excitatory pyra midal cells, which project to distant targets, and the inhibitory nonpyrami dal cells, which are the cortical interneurones. This article reviews evide nce suggesting that these two neuronal types are generated in distinct prol iferative zones. Pyramidal cells are derived from the neuroepithelium in th e cortical ventricular zone, and use the processes of radial glia in order to migrate and take their positions in the cortex in an 'inside-out' sequen ce. Relatively few nonpyramidal cells are generated in the cortical neuroep ithelium: the majority is derived from the ganglionic eminence of the ventr al telencephalon. These nonpyramidal neurones use tangential migratory path s to reach the cortex, probably travelling along axonal bundles of the deve loping corticofugal fibre system.