But often, says Dr. Brown at the National Institute for Play, a lot is happening all at once. He cites the time he tried to do a brain scan of his then-4-year-old grandson at play with his stuffed tiger.
"He was clearly playing," Brown recalls.
"And then he says to me, 'Grandpa, what does the tiger say?' I say, 'Roar!' And then he says, 'No, it says, "Moo!" ' and then laughs like crazy. How are you going to track that? He's pretending, he's making a joke, he's interacting."
This is one reason Brown says play has been discounted – both culturally and, until relatively recently, within the academic community, where detractors argue that play is so complex it cannot be considered one specific behavior, that it is an amalgamation of many different acts. These scientists – known as "play skeptics" – don't believe play can be responsible for all sorts of positive effects, in part because play itself is suspect.
"It is so difficult to define and objectify," Brown notes.
But most researchers agree that play clearly exists, even if it can't always be coded in the standard scientific way of other human behaviors. And the importance of play, Brown and others say, is huge.
Brown became interested in play as a young clinical psychiatrist when he was researching, somewhat incongruously, mass murderers. Although he concluded that many factors contributed to the psychosis of his subjects, Brown noticed that a common denominator was that none had participated in standard play behavior as children, such as interacting positively with parents or engaging in games with other children. As he continued his career, he took "play histories" of patients, eventually recording 6,000. He saw a direct correlation between play behavior and happiness, from childhood into adulthood.