In a series of experiments, Fernando Nottebohm and his research team showed that the numbers of neurons in the forebrains of male canaries dramatically increased during the mating season. But in the early 1980s, a scientist trying to understand how birds learn to sing suggested that neuroscientists look again at neurogenesis in the adult brain and begin to see how it might make sense. These discoveries about neurogenesis in the adult brain were surprising to other researchers who didn’t think they could be true in humans. In 1979, another scientist, Michael Kaplan, confirmed Altman’s findings in the rat brain, and in 1983 he found neural precursor cells in the forebrain of an adult monkey. He later reported that newborn neurons migrated from their birthplace in the hippocampus to other parts of the brain. In 1962, scientist Joseph Altman challenged this belief when he saw evidence of neurogenesis (the birth of neurons) in a region of the adult rat brain called the hippocampus. But scientists believed that once a neural circuit was in place, adding any new neurons would disrupt the flow of information and disable the brain’s communication system. As children we might produce some new neurons to help build the pathways - called neural circuits - that act as information highways between different areas of the brain. Until recently, most neuroscientists thought we were born with all the neurons we were ever going to have.
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