Like breathing, sleeping and eating, playing is innate in humans. But unlike those other functions, which could easily mean the difference between a long life and an early death, the usefulness of play isn’t quite as obvious. Brains at Play investigates play through the work of Jaak Panksepp, professor of integrative psychology and neuroscience at Washington State University, who conducted pioneering research on play. By performing surgery on rats, Panksepp discovered that the instinct to play exists in the primitive part of the mammalian brain, and has surprisingly important implications for social development.