For most of the history of neuroscience, it was widely believed, despite isolated reports to the contrary (1 ), thatde novogeneration of neurons in the mammalian CNS did not persist past perinatal development. It was not until the last decade of the twentieth century that the existence, within the CNS of fully developed mammals, of a persistent germinal zone containing neural stem cells (NSCs) with the capacity to differentiate into both neurons and glia became widely accepted (2 ). It is now known that in vivo genesis of new neurons occurs throughout life, and is restricted primarily to the periventricular subependymal zone (SEZ), which generates neurons destined for the olfactory bulb, and the subgranular layer of the hippocampus, which generates neurons destined for the dentate gyrus (3 ,4 ).
