The production of new, maturing neurons by neural stem and progenitor cells is called neurogenesis.
Rapid neurogenesis occurs in the fetal brain in humans and other animals. It occurs in all species of animals except the porifera(sponges) and placozoans.
During embryonic development, the mammalian central nervous system, brain and spinal cord is derived from the neural tube, which contains neural stem cells that will later generate neurons.
Adult neurogenesis has been shown to occur at low levels compared with development, and in only two regions of the brain: the adult subventricular zone (SVZ) of the striatum and the dentate gyrus of the hippocampus.