22 Oct 2015 --- We take it for granted that our body can regenerate cells that become injured or simply wear out and die. For most of the 20th century, however, scientists were convinced that one organ—the brain—lacked that ability. Shortly after birth, they thought, our brains had as many neurons as they were ever going to have, and if we lost brain cells because of injury or aging, we were never going to make more of them.
