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In humans, new neurons are continually born throughout adulthood in two regions of the brain: *The subgranular zone (SGZ), part of the dentate gyrus of the hippocampus.〔 *The striatum; however the adult-born neurons are a type of interneuron, not a type that projects to other brain areas. In other species of mammals, particularly rodents, adult-born neurons also appear in the olfactory bulb. In humans, however, few if any olfactory bulb neurons are generated after birth. Much more attention has been paid to neurogenesis in the dentate gyrus than in the other areas. Many of the newborn dentate gyrus neurons die shortly after they are born, but a number of them become functionally integrated into the surrounding brain tissue. Early neuroanatomists, including Santiago Ramón y Cajal, considered the nervous system fixed and incapable of regeneration. The first evidence of adult mammalian neurogenesis in the cerebral cortex was presented by Joseph Altman in 1962, followed by a demonstration of adult neurogenesis in the dentate gyrus of the hippocampus in 1963. In 1969, Joseph Altman discovered and named the rostral migratory stream as the source of adult generated granule cell neurons in the olfactory bulb. Up until the 1980s, the scientific community ignored these findings despite use of the most direct method of demonstrating cell proliferation in the early studies, i.e. 3H-thymidine autoradiography. By that time, Shirley Bayer (and Michael Kaplan) again showed that adult neurogenesis exists in mammals (rats), and Nottebohm showed the same phenomenon in birds sparking renewed interest in the topic. Studies in the 1990s finally put research on adult neurogenesis into a mainstream pursuit. Also in the early 1990s hippocampal neurogenesis was demonstrated in non-human primates and humans. More recently, neurogenesis in the cerebellum of adult rabbits has also been characterized. Further, some authors (particularly Elizabeth Gould) have suggested that adult neurogenesis may also occur in regions within the brain not generally associated with neurogenesis including the neocortex. However, others have questioned the scientific evidence of these findings, arguing that the new cells may be of glial origin. Recent research has elucidated the regulatory effect of GABA on neural stem cells. GABA's well-known inhibitory effects across the brain also affect the local circuitry that triggers a stem cell to become dormant. They found that diazepam (Valium) has a similar effect.〔http://www.nature.com/nature/journal/vaop/ncurrent/full/nature11306.html〕 ===Role in learning=== The functional relevance of adult neurogenesis is uncertain, but there is some evidence that hippocampal adult neurogenesis is important for learning and memory. Multiple mechanisms for the relationship between increased neurogenesis and improved cognition have been suggested, including computational theories to demonstrate that new neurons increase memory capacity, reduce interference between memories, or add information about time to memories. Experiments aimed at ablating neurogenesis have proven inconclusive, but several studies have proposed neurogenic-dependence in some types of learning, and others seeing no effect. Studies have demonstrated that the act of learning itself is associated with increased neuronal survival. However, the overall findings that adult neurogenesis is important for any kind of learning are equivocal. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Adult neurogenesis」の詳細全文を読む スポンサード リンク
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