Neural stem cells are present both in the developing nervous system and in the adult nervous system of all mammals, including humans. Little is known, however, about the extent to which stem cells in adults can give rise to new neurons. There is extensive evidence indicating that new neurons are generated in the dentate gyrus of the adult mammalian hippocampus, a region of the brain that is important for learning and memory. Several studies have new shown that enriched environment, voluntary movement enhance the survival of newly generated cells in the hippocampus. Exposure to stressful experiences, glucocorticoids decreased the numbers of new neurons in the dentate gyrus; this occurs not by altering the survival of new cells but by downregulating cell proliferation. Now that it has been established that new neurons are in face added to the adult brain, the question becomes what are their functions. Adult neurogenesis has been offered as a possible key to understanding and even treating such phenomena as depression, Alzheimer's disease, and schizophrenia. It would be wonderful if further study of adult neurogenesis could shed light on any or all of these CNS conditions.
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