There are two regions in the adult brain that exhibit neuronal stem and progenitor cells, generating new neurons postnatally and throughout adulthood. One is the so called subventricular zone the other is the dentate gyrus of the hippocampus. Adult neurogenesis is a physiological process representing an important functional impact for certain brain areas, especially the hippocampus. The hippocampal formation plays an important role in long-term memory and spatial navigation. Inhibition of adult neurogenesis in mice by chemotherapy or radiation is followed by significant deficits in hippocampal memory functions while hippocampus-independent memory is unaffected.