The cerebral cortex is composed of a heterogenous population of cells that give rise to different cell types. The majority of these cells are derived from radial glia migration that form the different cell types of the neocortex and it is a period associated with an increase in neurogenesis. Similarly, the process of neurogenesis regulates lamination to form the different layers of the cortex. During this process there is an increase in the restriction of cell fate that begins with earlier progenitors giving rise to any cell type in the cortex and later progenitors giving rise only to neurons of superficial layers. This differential cell fate creates an inside-out topography in the cortex with younger neurons in superficial layers and older neurons in deeper layers. In addition, laminar neurons are stopped in S or G2 phase in order to give a fine distinction between the different cortical layers. Laminar differentiation is not fully complete until after birth since during development laminar neurons are still sensitive to extrinsic signals and environmental cues.