A pioneer in research on play, Dr. Stuart Brown says humor, games, roughhousing, flirtation and fantasy are more than just fun. Plenty of play in childhood makes for happy, smart adults -- and keeping it up can make us smarter at any age.

Stuart Brown's research shows play is not just joyful and energizing -- it's deeply involved with human development and intelligence. Through the National Institute for Play, he's working to better understand its significance.