In 1949 Hebb proposed that learning linked neurons in new ways. He proposed that when two neurons fire at the same time repeatedly (or when one fires, causing another to fire), chemical changes occur in both, so that the two tend to connect more strongly. Hebb’s concept—actually proposed by Freud sixty years before—was neatly summarized by neuroscientist Carla Shatz: Neurons that fire together wire together.
