Neurogenesis is the process of generation of new neurons from neuronal precursor cells, and was first described in adult mammals in 1965, where it was identified in rodents ( Altman and Das, 1965 ). Adult neurogenesis has subsequently been shown to occur in two specific regions of the adult brain, the subventricular zone of the olfactory bulb and the subgranular layer of the hippocampal dentate gyrus, where it has been identified in all mammals studied to date, including man ( Ehninger and Kempermann, 2008 ). Adult neurogenesis involves several distinct stages, beginning with the proliferation of resident neural stem and progenitor cells, followed by differentiation, migration, selection, and ultimately functional integration into the pre-existing circuitry ( Ehninger and Kempermann, 2008 ). The rate of turnover of cells is very low.