Development of the cerebral cortex

Abstract The cerebral neocortex is the largest segment of the mammalian brain. In humans, it consists of multiple folds that contain a vast number of neurons, glia, and myelin. This allows the size of the skull to remain relatively small. The neocortex consists of six laminar layers made up of Glu-containing excitatory neurons and GABA-containing inhibitory neurons. The lamina develop sequentially from neuronal precursors in the subventricular zone with layer VI neurons migrating first, being overlaid sequentially with neurons forming layers V, IV, etc. Layer I contains mostly axons and dendrites. Radial glia form scaffolds along which neuronal migration occurs. Several tropic/trophic factors and receptor systems are involved in this migration. The GABAergic neurons develop later in a lower region of the forebrain called the ganglionic eminences. These neuronal precursors migrate tangentially until they encounter the axons of projection neurons from the cortex. They then migrate along these axons until reaching their final destinations in the cortical lamina. Various tropic/trophic factor–receptor interactions are important in this migratory flow.