Adult Neurogenesis

Early neuroanatomists believed that the adult mammalian central nervous system (CNS) was not capable of neurogenesis (the production of new neurons). This long-standing belief began to be overturned in the 1960s, when Joseph Altman pioneered studies demonstrating proliferation of neurons in rat brain. Subsequent work has established the presence of such populations in seemingly all mammals. Although the role of adult neurogenesis is still not fully understood, it has been suggested to be involved in processes of learning or CNS repair.

Adult neurogenesis occurs from the division of neural stem cells (NSCs) in two well-defined regions of the brain:

1. The subventricular zone (SVZ), located beneath the lateral ventricles, from where cells migrate via the rostral migratory stream (RMS) to the olfactory bulbs.
2. The dentate gyrus of the hippocampus, where cells migrate only a short distance to form synapses with other hippocampal and entorhinal cortical cells.

Adult neurogenesis is present in primates, although at levels much lower than in rodents. In 1998, adult neurogenesis was demonstrated for the first time in the hippocampus of humans. The robustness of neurogenesis and migration in the human SVZ has been heavily debated; recent work has indicated, however, that neurogenesis in the SVZ is present only in young children and virtually nonexistent in adults. Neurogenesis has been identified in the SVZ and hippocampus of adult macaques.
Unfortunately, studies of adult neurogenesis in non-human hominids are lacking. However, studies to date make clear that, if anything, it is a relative reduction in the degree and time course of adult neurogenesis that may be uniquely human.