You can’t win if you don’t play

Posted by Susan Lubejko on September 7, 2023 in Behavioral Neuroscience, Developmental Neuroscience, Mood, Neuroscience, Social Neuroscience | Leave a comment

When I think about the happiest moments from my childhood, I’ll often reflect on the times my sister and I played “school” (as the younger sibling, I was always the student…), when my best friend and I played with Barbies and dress-up clothes in her basement, or when we played hide-and-seek with other kids in the neighborhood on summer afternoons. You will undoubtedly have your own precious memories, but what many of these recollections have in common is the importance of play during childhood, specifically the concept of social play. 

Play is a well-known yet difficult to define instinctive behavior due to the many forms it can take (try to define play vs. other instinctive behaviors such as fight-or-flight responses and aggression, for instance). For this reason, the motivations that lead to play, the role play has in our development, and the neurobiological factors underlying play behavior have been challenging to study. Importantly, scientific studies in recent years have endeavored to not only define play, but also determine the brain activity that underpins it. Notably, this has involved using animals like rats that, believe it or not, play like you and me.

What is play and what role does it perform in humans?

As mentioned, play is an easy-to-understand concept with details that are difficult to define. Psychology researcher G.M. Burghardt uses a five point structure which includes the following criteria to categorize an activity as “play”:

1. The behavior isn’t really all that functional in the situation that it is done in – i.e. it doesn’t contribute to necessary survival
2. The activity is spontaneous, rewarding, and “done for its own sake”
3. It differs from functional behaviors by being incomplete or exaggerated, among other aspects that make play not a fully formed, useful behavior
4. Play is performed repeatedly and similarly during at least a portion of development
5. It is performed when the animal or person is in a relaxed state and all other needs are met (healthy, fed, clothed, etc) [1].

The American Psychological Association defines play as “activities that appear to be freely sought and pursued solely for the sake of individual or group enjoyment”. Additionally, the APA suggests that there are three main types of play: locomotor play (which involves vigorous and repetitive movement), object play (which occurs when the play is focused around a toy, for instance), and social play. For the purposes of this article, we will focus mostly on social play, which is considered by the APA as “play that involves interacting with others for fun or sport”.

Much like any of our instinctive behaviors, it would be unlikely for social play to be such a big part of our lives without a functional purpose. So what is the point of playing, an energy-intensive and possibly dangerous endeavor that your brain and body might otherwise avoid to conserve its resources?

While we can’t know exactly the reasons for play, we can make hypotheses based on the type of play children and the young of other primate species take part in during their development. The available theories appear to boil down to just a few factors: skill development, social learning, and stress management. Play often involves the honing of fine motor, but also creative and cognitive, skills that drive the player to better learn to interact with their environment and possibly practice skills that will be useful later in life. Additionally, social play specifically provides an unmatched training ground for developing useful social dexterity. This includes learning “social rules,” which govern how individuals in a group are expected to interact with each other, and promoting social bonding within a group. In many species, rough-and-tumble play fighting helps to establish social rank without the need to progress to actual brawls [2]. Finally, play can help manage stress, a factor that surely solidifies the importance of doing tasks simply for the purpose of enjoyment well into adulthood [3, 4]. Overall, studies of humans and primates have shown that babies that begin to engage in social play with their mother, and then develop to share these behaviors with peers, progress more quickly in developing motor and social skills [4]. 

Which brain chemicals are involved in play behavior?

Due to its nature as an extremely variable and spontaneous behavior, there is not much neuroscientific evidence for the brain mechanisms responsible for the different aspects of social play in humans. Therefore, scientists have turned to observing and manipulating play in animals to assess the neurobiology at work. It is easy for us to imagine a few animal species that appear to engage in play, such as primates or dogs (for example, dogs have been shown experimentally to re-engage a human in play after that interaction had been interrupted [5], indicating their preference for playing). What you may not expect, however, is that much of what we know about play in the laboratory comes from an animal model that is commonly studied, but not commonly interacted with by most: the rat. 

Popular attention to using the rat to study play was achieved in 2016 after a high-impact scientific publication found that rats respond to being tickled and chased by human researchers by emitting ultrasonic vocalizations (shorts pips that can be recorded but are beyond the range of frequencies that human ears can hear). Put simply, rats “laugh” when they are enjoying themselves. The study additionally showed that the somatosensory cortex, the area of the brain in which touch signals are processed, responded to and encoded the rats’ perception of being tickled [6]. 

While this study brought the most attention to the field, playfulness in rats has actually been studied in the laboratory for 40 years, pointing to brain chemicals and regions that may be involved in and necessary for play. Several neurotransmitters and neuromodulatory chemicals present in the brain have been implicated in social play. Endogenous opioids, similar to the opioid drugs we may be familiar with but produced naturally within the body, are released during play and are likely involved in the rewarding feelings produced by play that make us feel good. Dopamine, a neurochemical often associated with our brains’ reward pathways, is released during play to drive the motivation to seek out and continue playing. Serotonin, which we typically associate with mood regulation, may play a more complicated role, sometimes being shown to decrease social play behavior but hypothesized by others to provide cues to modulate play based on the social context. Additionally, other major neurochemicals, such as cannabinoids, noradrenaline, and vasopressin have been implicated in brain signaling that contributes to play, suggesting that this complicated behavior relies on complex and brainwide chemical signaling [1,7]. 

What regions of the brain allow us to play?

Although the cerebral cortex (the outermost, wrinkly layer of our brain) acts as the major information processor and controller of our thoughts and behavior, it has actually been shown to not be all that important for play [8], suggesting that the brain areas crucial for this behavior are deeper in the brain and more evolutionarily conserved among species. One brain area that has been implicated as important for play behavior is the parafascicular nucleus of the thalamus (Pf). The thalamus on the whole acts as a switchboard in the center of the brain for incoming sensory information to be routed throughout the cerebral cortex. The Pf sends and receives information to and from many other brain regions, positioning it as a master regulator of many types of behavior associated with play, including learning and behavioral switching [1]. In rats, destruction of the Pf leads to almost complete loss of behavior associated with play, such as pinning during wrestling [9].

Most recently, the same research group that introduced rat laughter in response to play and tickling provided evidence for another brain region that they believe is necessary for play [10]. Their study found that activity in the midbrain periaqueductal gray (PAG), a brain region with many diverse roles in things such as defensive behavior, vocalizations, and the pain relief provided by opioid drugs, is strongly influenced during tickling or play. Not only did the researchers find that this activity change occurs during social play (including play with another rat or interspecific play with a human researcher), they also found that the PAG is in fact necessary for play as experimental blockade of activity in this brain region prevented both play behavior and the laughter vocalization elicited by tickling. Additionally, the activity of PAG neurons generated during play was decreased when the rat was feeling anxiety, which supports the suggestion we discussed much earlier that play can only be achieved when the needs of the organism are met and outside negative factors are absent. 

Taken together, it appears that there are multiple neurochemicals and brain regions in rats that likely work together to govern the ability to and motivation for play. These brain regions also exist in humans and primates, making it possible that our brains function in similar ways when we play. 

Play is for everyone

Reflecting back on childhood, it should be obvious that play has an influential role in our development. Perhaps as you were reading, you came up with your own list of play-related memories that fit with the detailed definition of play that scientists use. However, the importance of play certainly doesn’t end with our development as children and actually appears to extend throughout the entirety of our lives. The non-profit National Institute for Play that endeavors to gather the knowledge of the top play researchers worldwide boldly displays on its website that “play isn’t just for kids”. While our play may look different now than when we were kids as our interests and patience for certain tasks have changed with our developing brains (remember: play is only play if you’re enjoying it), play simply for the purpose of enjoyment throughout adult life remains an important factor in refining our social skills, decreasing stress, improving mental health, and particularly important for older adults, keeping our brains flexible and sharp. So, despite the feelings we sometimes get that play takes away from our time to be productive on more important tasks, take this as your sign to get out there and do something fun – your brain will thank you!

References

1. Kellman J, Radwan K (2022) Towards an expanded neuroscientific understanding of social play. Neuroscience and Biobehavioral Reviews, 132:884-891
2. Maynard Smith J, Price GR (1973) The logic of animal conflict. Nature, 246: 15-18
3. Lents NH (2017) Why play is important. Psychology Today. Accessed August 29, 2023.https://www.psychologytoday.com/us/blog/beastly-behavior/201705/why-play-is-important
4. Palagi E (2018) Not just for fun! Social play as a springboard for adult social competence in human and non-human primates. Behavioral Ecology and Sociobiology, 72:90
5. Horschler DJ, Bray EE, Gnanadesikan GE, Byrne M, Levy KM, Kennedy BS, MacLean EL (2022) Dogs re-engage human partners when joint social play is interrupted: a behavioral signature of shared intentionality? Animal Behaviour, 183:159-168
6. Ishiyama S, Brecht M (2016) Neural correlates of ticklishness in the rat somatosensory cortex. Science, 354(6313):757-760
7. Marijke Achterberg EJ, Vanderschuren LJMJ (2023) The neurobiology of social play behaviour: Past, present, and future. Neuroscience and Biobehavioral Reviews, 152:105319
8. Panksepp J, Normansell L, Cox JF, Siviy SM (1994) Effects of neonatal decortication on the social play of juvenile rats. Physiology & Behavior, 56(3):429-443
9. Panksepp J, Siviy S, Normansell L (1984) The psychobiology of play: theoretical and methodological perspectives. Neuroscience & Biobehavioral Reviews, 8:465-492
10. Gloveli N, Simonnet J, Tang W, Concha-Miranda M, Maier E, Dvorzhak A, Schmitz D, Brecht M (2023) Play and tickling responses map to the lateral columns of the rat periaqueductal gray. Neuron, 111:1-12

Cover Image Source: Gratisography/Free Range Stock