The Neurobiology of Play

Taking Play Seriously, by Robin Marantz Henig, appears today in the New York Times Magazine.  Henig draws on ethology, neuroscience, and developmental psychology to highlight advances in research on play.  Play strikes many of us as deeply essential, but what the heck is it for?  It’s not precisely clear. 

Today I’ll cover some of the interesting developments about the neurobiology of play mentioned in Taking Play Seriously.  So John Byers first.  Byers is a zoologist at the University of Idaho who noticed that the developmental trajectory of play looks like an inverted U across many species, increasing during the juvenile period and dropping off during puberty.  This pattern corresponded quite well with the growth curve of the cerebellum.  The article summarizes the implications: 

The synchrony suggested a few things to Byers: that play might be related to growth of the cerebellum, since they both peak at about the same time; that there is a sensitive period in brain growth, during which time it’s important for an animal to get the brain-growth stimulation of play; and that the cerebellum needs the whole-body movements of play to achieve its ultimate configuration.

But why the match?  It’s important to look at the function of the cerebellum.  So here’s Wikipedia for us: “The cerebellum (Latin: “little brain”) is a region of the brain that plays an important role in the integration of sensory perception and motor control. In order to coordinate motor control, there are many neural pathways linking the cerebellum with the cerebral motor cortex (which sends information to the muscles causing them to move) and the spinocerebellar tract (which provides proprioceptive feedback on the position of the body in space). The cerebellum integrates these pathways, like a train conductor, using the constant feedback on body position to fine-tune motor movements.” 

The medial prefrontal cortex is also implicated in play, given that juvenile rats deprived of play (by living only with adults) had a more immature pattern of neuronal connections than normally-raised rats.  Sergio Pellis, the force behind this research, “interprets his observation of a more tangled, immature medial prefrontal cortex in play-deprived rats to mean that the rat will be less able to make subtle adjustments to the social world.” 

For more on the medial prefrontal cortex, we can turn to this 2007 article by Cowen and McNaughton: 

The medial prefrontal cortex (mPFC) plays a critical role in the organization of goal-directed behaviors and in the learning of reinforcement contingencies… As hypothesized, stimulus-selective, prospective delay activity was observed during sequences in which both elements contributed to the prediction of reward. Unexpectedly, selective delay responses were associated with slight variations in head position and thus not necessarily generated by intrinsic mnemonic processes. Interestingly, the sensitivity of neurons to head position was greatest during intervals when reward delivery was certain. These results suggest that a significant portion of delay activity in the rat mPFC reflects task-relevant sensorimotor activity, possibly related to enhancing stimulus detection, rather than stimulus–stimulus associations… These results also indicate that considerable attention must be given to the monitoring and analysis of sensorimotor variables during delay tasks because slight changes in position can produce activity in the mPFC that erroneously appears to be driven by intrinsic mechanisms [emphasis added].

 Finally, Taking Play Seriously discusses the work of Jaak Panksepp, who has linked play to the thalamus.  What does the thalamus do?  Again, Wikipedia: “The thalamus is believed to both process and relay sensory information selectively to various parts of the cerebral cortex, as one thalamic point may reach one or several regions in the cortex…  The thalamus plays a major role in regulating arousal, the level of awareness and activity.”  In other words, the thalamus acts as a moderator of sensory information to the cortex, highlighting the role of play in the integration of sensory and behavioral processing. 

We can also throw emotion into the mix.  Other research by Panksepp and colleagues points to a role for social play in brain development of emotion-related pathways: “Rough and tumble (R&T) play is assumed to have beneficial effects in developing organisms. To evaluate this idea, brain derived neurotrophic factor (BDNF) gene expression was evaluated in 32-day-old juvenile rats that were allowed to play for 30 min prior to sacrifice. In situ hybridization for BDNF mRNA revealed that the amygdala and dorsolateral frontal cortex had significantly elevated BDNF mRNA expression as a result of play. These effects suggest that play may help program higher brain regions involved in emotional behaviors.” 

What does all this research suggest about the functional role of play in brain and behavioral development?  First, what is striking is how play is involved in the integration of different types of processing—sensory, movement, emotion, decision making. Older views of play are that it helps a juvenile test out immature versions of skills (say, practicing how to hunt) or to produce a wider behavioral repertoire.  For example, Millicent Ficken in a 1977 article on Avian Play wrote, “Play evolved independently in the two groups probably because of similar selection pressures acting on the developmental process to produce flexibility of behavior and the perfection of certain motor skills.” 

But as Greg has argued in his recent post on the Sapir-Whorf hypothesis, the outdated modular view of unitary capacities and specific functions are not a productive way to think about the relationship between brains, behavior and environments.  Greg has consistently argued for the role of different systems collaborating together in the production of language or balance.  But how does that happen? 

One idea is through play.  Taking Play Seriously relates, “The physical movements of playfighting provide the environmental input needed to prune the developing cortex, as Sergio Pellis’s research suggested. This pruning is one way an animal achieves the ability to predict and respond to another animal’s shifting movements.” 

In developing species that need environmental-and-state specific behavioral response and modulation, we cannot assume that the coordination of different brain systems happens naturally, simply on its own.  That would bring us back to a nature-versus-nurture view, where the brain develops coordinated action on its own. 

Why not have a behavior that promotes this process?  Combining sensory information, emotional states, cognitive framing, bodily movement, and decision making is not an easy thing.  In itself, it takes practice.  Practice that brains use to develop appropriately as they connect sensory and body information with contingent responding to the environment. 

Play, in my mind, represents one preferential way to achieve this skilled engagement with ecologically and socially complex environments.  Given how “what fires together, wires together” and the evolutionary origins of behavior in “fixed action patterns,” a central challenge for our brains is to work against local circuits producing too much stereotypy and automaticity, of behaviors becoming so pervasive they are almost compulsive (like addiction).  If a species’ social environments are complex and its foraging strategies are complex, there is likely a selective advantage for brains whose related pathways can work together in producing contingent yet appropriate responses.  Play sounds like a fun way to do that. 

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