"Neurogenesis," or the formation of new neurons, is known to take place before birth. But some evidence suggests that it can continue throughout the human lifespan. (Image credit: CHRISTOPH BURGSTEDT/SCIENCE PHOTO LIBRARY via Getty Images) The developing human brain gains billions of neurons while in the womb, and tacks on some more during childhood. For most of the 20th century, the conventional wisdom was that the brain cells grown before adulthood would be the only ones we would have for the ...