What Drives Play

What's the motivation behind animal's desire to play?

Posted Sep 19, 2019

Rolf Dietrich Brecher via Wikimedia Commons
Who’s there?
Source: Rolf Dietrich Brecher via Wikimedia Commons

From Part 1 of this series:  But, you may ask:  What did the animals actually learn?  Were they really playing the game?  Did the animals actually enjoy the game?  Were they actually playing just for the fun and joy of it?

Play, laughing at play, and let's play more please!

Many aspects of the animals' activity suggested that they had really learned something about "hiding and seeking" and had developed some appropriate game-playing strategies.  For example, when the experimenter hid in random (non-predictable) locations from one trial to the next, the rats took longer to find the experimenter than when the experimenter consistently hid in one location across a series of five trials. 

In such consistent trials, the animals searched for the experimenter increasingly quickly and directly – making a beeline toward where she was hidden with scarcely a pause – showing that they remembered where the experimenter had hidden on the previous several trials.  Also, when they were the hiders (but not as seekers), the animals showed a clear and significant preference for the opaque and cardboard boxes over the transparent "see-through" boxes.  

In the wild, rats are most active during the night and so most of their play will occur in darkness.  Rather than a visual cue to signal that they want to play, such as a puppy's "play bow" or a monkey's "open mouth," adolescent rats of the type the researchers studied (the Long-Evans hooded strain) give a variety of different vocal chirps or calls. These calls are ultrasonic vocalizations at a frequency of close to 50 kHz, and are emitted during social play with peers, and during other positive affective states, such as when they are being "tickled" by human handlers.  

Such "calls to play" or play signals are especially frequent in juvenile or adolescent rats. The chirping calls, and their specific timing – such as anticipatory calls given just before launching a playful nape attack or chase – seem to help maintain a playful mood or motivation, and to promote cooperative play.

A close look at the vocalizations of the rats during the researchers' hide-and-seek sessions showed that for both seek and hide trials, the animals' calls (all of which were inaudible to the experimenter but visible on the Audacity recordings) sharply increased at those times when the rats were enthusiastically darting away from the start box. There were also many such calls during the tickling and finger-chase-play interactions with the experimenter but fewer when the animals were quietly choosing where to "hide" and also during their hiding time.  

The timing and patterns of the animals' chirping calls suggested that the animals were indeed enjoying the hide-and-seek game.  

And like young toddlers who often exclaim "do it again, do it again!" or "more, more!" when they love the playful motions or sounds that their parents or adults are making, so the adolescent rats often seemed to want to prolong the hiding portion of the game, darting away from the experimenter to a new "hiding place" even when they'd clearly been found out in their hiding place. These and other behavioral indicators, such as their quick and lively search, and springy "joy jumps," all converged in an impression that this was all good fun.  

Motivational and reward systems in the brain

What, then, was happening in the brains of these small creatures as they enthusiastically played this complex socially-interactive rule-based game? To find out, the researchers focused their attention on a region at the front of the brain – the medial prefrontal cortex – known to be involved in social play and reward-based play motivation in rats. After the animals had learned the hide-and-seek game, the experimenters implanted electrodes (tetrodes) in the medial prefrontal cortex of five of the anesthetized animals. Then, after they'd recovered from the surgery and were again happily playing hide-and-seek, the researchers tracked the patterns and changes in the firing activity of individual neurons as the rats now took on the role of the seeker, and then that of the hider.   

The electrode recordings revealed that the patterns of brain cell firing differed markedly depending on specific timepoints and the animals' particular role in the game. Firing of neurons increased strongly in nearly 30% of the 177 neurons the researchers were able to record from at the timepoint when the start box lid was closed – the environmental signal that the rat was, on the next trial, to be in the "seeker" role.  

Analyses of the patterns of firing showed that some clusters of neurons were mostly active during the seeking phase of the game.  Other groups of neurons were most active during hiding.  Still other clusters of neurons were especially active during the brief periods of intense experimenter-rat interaction (touching and hand games) that ended each seeking or hiding trial.  

The play-to-play hypothesis

Despite the central role that play and play-like activities have in our own lives and those of other animals, probing and fully charting out the complex social, cognitive, motivational, and neurobiological bases of such activitites in many animals has been challenging.  There has been extensive research on some sorts of play in a few species – for example, play fighting has been much studied in adolescent rats, but many other types of play, such as object play, have been less often studied.

The Berlin-based researchers used a creative play format that gave small creates the opportunity to themselves make choices about where and how they will hide, or where and how they will seek out a hidden playmate. The initials findings from these experiments open new opportunities and challenges for researchers of play: Their findings suggest that by using experimental procedures that give other animals more room for choice, and more room for play, we might be able to learn much more about what "drives play" and the motivation of playing just to play.  Hide-and-seek anyone?

To think about

  • The particular strain of rats used in the hide-and-seek study (Long-Evans) has, in other research, been characterized as typically "bold" or exploratory rather than shy and reticent (e.g., they quickly raise themselves up on their hind legs to look about them, and move more quickly into the center of an exposed field).  Would comparatively "shy" rats also learn the hide-and-seek game and learn to quickly switch their roles between hiding and seeking?  
  • In this study, adolescent playful rats learned to play hide-and-seek with the human experimenter. Would older rats also successfully learn the two different roles required during hiding and seeking? Could they enjoy the game as much as the younger animals?  Or could the game be changed in ways that would increase their playfulness and playful enjoyment?  
  • We often learn from watching others.  How much could younger or older animals learn by observing other animals in the game?  
  • Why do we so often focus on extrinsic rewards in thinking about what moves us, rather than also intrinsic rewards, such as our desire for play?
  • A recent report on "the power of play" in the clinical journal Pediatrics affirmed, "Play is not frivolous; it is brain building" (p. 5).  Much of the evidence for substantial brain changes related to the opportunities for play has been found using juvenile rats.  For example, rats that were denied the opportunity to play as pups (kept in sparse cages without any toys) were less adept problem-solvers later and showed markedly impaired (immature) medial prefrontal cortex development.  Why do we tend to downplay the many social and health-promoting roles of play, not only for children but also for youth and adults of all ages?  What playful counter-moves can we let loose, hoist, or heave against such heavy anti-play sentiment?

References

Bell, H. C., McCaffrey, D. R., Forgie, M. L., Kolb, B., & Pellis, S. M. (2009). The role of the medial prefrontal cortex in the play fighting of rats.  Behavioral Neuroscience, 123, 1158–1168.

Panksepp, J., & Burgdorf, J. (2003). "Laughing" rats and the evolutionary antecedents of human joy?  Physiology & Behavior, 79, 533–547.

Pellis, S. M., Pellis, V. C., Pelletier, A., & Leca J-B. (2019). Is play a behavior system, and, if so, what kind?  Behavioural Processes, 160, 1–9.

Peskin, J., & Ardino, V. (2003). Representing the mental world in children's social behavior: Playing hide-and-seek and keeping a secret.  Social Development, 12, 496–512.

Reinhold, A. S., Sanguinetti-Scheck, J. I., Hartmann, K., & Brecht, M. (2019). Behavioral and neural correlates of hide-and-seek in rats. Science, 365 (Sept. 13), 1180–1183.

Weiss, A., & Neuringer, A. (2012).  Reinforced variability enhances object exploration in shy and bold rats.  Physiology & Behavior, 107, 451–457.

Yogman, M., Garner, A., Hutchinson, J., Hirsh-Pasek, K., & Golinkoff, R. M. (2018).  The power of play: A pediatric role in enhancing development in young children. Pediatrics, 142, 1–16.