Brain Basics: The Life and Death of a Neuron

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Neurogenesis in the adult human brain is still tricky for neuroscientists to show, let alone learn about, how it impacts the brain and its functions. Still, scientists are intrigued by current research on neurogenesis and the possible role of new neurons in the adult brain for learning and

Neurons are nerve cells that send messages all over your body to allow you to do everything from breathing to talking, eating, walking, and thinking. Until recently, most neuroscientists (scientists who study the brain) thought we were born with all the neurons we were ever going to have. As children, we might grow some new neurons to help build the pathways—called neural circuits—that act as information highways between different areas of the brain. However, scientists believed that once a neural circuit was in place, adding any new neurons would change the flow of information and break the brain’s communication system

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. He later reported that newborn neurons traveled from their birthplace in the hippocampus to other parts of the brain. In 1979, another scientist, Michael Kaplan, confirmed Altman’s findings in the rat brain; and in 1983, he found special kinds of cells—called neural precursor cells—with the ability to become brain cells like neurons, in adult monkeys.

These discoveries about neurogenesis in the adult brain were surprising to other researchers who thought they were not true in humans. Fortunately, in the early 1980s, a scientist trying to understand how birds learn to sing began to see how neurogenesis in the adult brain might make sense. In a series of experiments, Fernando Nottebohm and his research team showed that the numbers of neurons in the forebrains (areas controlling complex behaviors) of male canaries dramatically increased during the mating season, when the birds learn new songs to attract females.

Why did these bird brains add neurons at such an important time in learning? Nottebohm believed it was because newborn neurons helped store new song patterns within the pathways of the forebrain; these new neurons made learning new songs possible! If birds made new neurons to help them remember and learn, Nottebohm thought the brains of mammals—like humans—might too.

Other scientists, like Elizabeth Gould, later found evidence of newborn neurons in a distinct area of the brain in monkeys, and Fred Gage and Peter Eriksson showed that the adult human brain produced new neurons in a similar area.

Neurogenesis in the adult human brain is still tricky for neuroscientists to show, let alone learn about, how it impacts the brain and its functions. Still, scientists are intrigued by current research on neurogenesis and the possible role of new neurons in the adult brain for learning and memory.

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