Many of the other important studies on play and the brain have come from the lab of Jaak Panksepp, a behavioral neuroscientist who trained most of the neurological investigators in the field during the three decades he was at Bowling Green State University in Ohio (though Pellis, who studied at Australia’s Monash University, was not among them). In the 1980s, Panksepp and a graduate student, Stephen Siviy, located the play drive in the thalamus, a primitive region of the brain that receives sensory information and relays it to the cortex. More recently, Panksepp has been exploring the connections among the play drive and certain human conditions, in particular attention deficit hyperactivity disorder (A.D.H.D.).
Panksepp has been studying A.D.H.D. in rats since the 1990s. In one experiment, to create a rat model of A.D.H.D., he and his colleagues took 32 newborn rats and destroyed in each the right frontal cortex, the region of the brain responsible for paying attention, planning ahead and being sensitive to social cues. (Human studies have shown that in children with A.D.H.D., frontal-lobe development is often delayed.) As a control, they performed sham surgery on 32 other rats, making the incisions but leaving the brain intact to be sure that any observed change would be due to the cortical destruction rather than the surgery itself. When the scientists compared the play behavior of the two groups, they found that the rats with the damaged right frontal cortex had higher levels of overall activity, as well as increased rates of rough and- tumble play, as compared with the controls. The rats with damaged frontal cortices behaved much like children described as hyperactive.
Panksepp and his colleagues then exposed these super players to extra opportunities for play. One extra hour a day of play, which generally took the form of play-fighting during a critical early stage, sufficed to reduce hyperactivity. The scientists thought similar play therapy might work for children with A.D.H.D., particularly if it was undertaken in early childhood — between ages 3 and 7 — when the urges are ‘‘especially insistent.’’
Panksepp’s current view of human A.D.H.D., he told me from his office at Washington State University, where he moved two years ago, is that it is in part ‘‘over activity of play urges in the nervous system.’’ His ideas have made some impression on the human A.D.H.D. community, but not much. Benedetto Vitiello, the head of child and adolescent treatment and research at the National Institute of Mental Health, remembers hearing Panksepp give a talk at the institute around the time his article appeared in 2003. But he said he has not heard of any clinical studies since then that investigate whether extra play in early childhood helps ease the symptoms of A.D.H.D. Besides, Vitiello adds, there are many differences between a rat with a brain injury and a child with an intact but slowly developing brain. So even though he considers Panksepp’s research ‘‘interesting,’’ he says that it has not quite led to a complete animal model of A.D.H.D.
Animal-play experiments have focused largely on the most vivid form of play — social play, in particular the kind of social play known as play-fighting. But it’s clear to anyone who thinks about it that play-fighting is a very narrow definition of play. Wrestling is not the same as chasing. For that matter, playing tag is not the same as playing dress up; playing in a soccer league is not the same as shooting hoops in a neighborhood park; and none of these are the same as playing Scrabble or Uno or video games. For all its variety, however, there is something common to play in all its protean forms: variety itself. The essence of play is that the sequence of actions is fluid and scattered. In the words of Marc Bekoff, an evolutionary biologist at the University of Colorado, play is at its core ‘‘a behavioral kaleidoscope.’’
In fact, it’s this kaleidoscopic quality that led Bekoff and others to think of play as the best way for a young animal to gain a more diverse and responsive behavioral repertory. Thus, the currently fashionable flexibility hypothesis, a revival of an idea Bekoff first proposed in the 1970s. If a single function can be ascribed to every form of play, in every playful species, according to this way of thinking, it is that play contributes to the growth of more supple, more flexible brains.
Check back next week for a continuation of this great article on "Play".