Researchers know that play isn’t just for kids. Play—or scientifically speaking, voluntary recreational activity—is widespread in the animal kingdom, with dolphins, cats, dogs, otters, ravens and even crocodiles engaging in forms of play. But studying the neuroscience behind play in a controlled setting requires more than watching animals frolick; by definition, play must be spontaneous and voluntary.
That’s why researchers at Humboldt University of Berlin recently taught a group of rats to play hide-and-seek. And another win for future experiments: the animals thoroughly enjoyed the game, they report this week in the journal Science.
Annika Reinhold, a graduate researcher in neuroscientist Michael Brecht’s lab, was already familiar with how much lab rats like chase and rough house with one another when Brecht asked her to teach them hide—perhaps, an otherwise odd request.
To begin, she selected six young rats and let them frolick in a 300-square-foot room with plenty of boxes and obstacles that a wily rodent or human could hide behind, reports Ed Yong at The Atlantic. By stroking, chasing and tickling them (something rats love!), she was able to get them used to having her around. After about a month, she taught them to seek her out in the room and eventually schooled them in finding just the right hiding place. Eventually, social interaction was enough incentive to get the rats to play along, instead of food or other rewards. All six rats successfully learned to seek, and five of them learned the ins-and-outs of hiding.
The rats started out in closed box that was remotely opened and eventually, they learned that being in the box meant it was their turn to seek out a human researcher, reports Issam Ahmed at Agence France-Presse. The rats seemed to be enthusiastic about the game and got good at it quickly, learning to hide in opaque boxes instead of transparent boxes. They even noticed the spots their skilled human playmates hid, using those spots later in the game. They were also good at staying in their hiding spot until the human seeker found them.
It appears they actually enjoyed the playtime quite a bit. During the hide-and-seek sessions, they would emit ratty giggles. (Though they are three times higher than audible range of humans.) They also performed little freudensprung or “joy jumps,” which previous research found is an indication they are happy. In some cases, when the rats were found they would jump away and re-hide, trying to make the play session last even longer, an indication that they were more interested than the joy of game than a tickle reward.
The neuroscience part of the research came into play when the team implanted wireless electrodes on five of the rats’ medial prefrontal cortex—a part of the brain that, in humans, is associated with decision making, theory of mind and social interaction. Because play is spontaneous and free flowing, it’s been hard for researchers to understand what parts of the brain are associated with these social activities. During the hide and seek sessions, certain neurons lit up at certain times, like when the rats were sealed in the starting box. It’s hoped that from this data the team can start to figure out what the brain is doing during playtime.
But the biggest revelation from the study is that little rats will play with giant humans, something that was not a given. Exactly why the rats took to hide and seek so well is a matter of debate. George Dvorsky at Gizmodo reports that there are two hypotheses. In the shaped-to-play scenario, it's possible the rats were classically conditioned to learn to play due to the desire for the reward, the tickling and tummy rubs. The other hypothesis is called play-to-play, which means the rats played the game simply for the enjoyment of it. The team favors play-to-play because the rats showed clear signs of enjoyment during the game.
Not everyone is completely convinced that the rats were really into hide and seek. “I would question whether rats are really playing the game or just engaging in typical behavior in which they seek out shelter,” Jennifer Vonk, an expert in animal cognition at Oakland University, tells Dvorsky. “But the authors do show that the preference for opaque boxes is stronger when they are playing the hiding role, which means they don’t just prefer covered areas generally.”
She says to confirm that the rats are playing the game, the researchers should repeat the experiment using a doll to see if they were really engaging with another live being.
If the rats are indeed playing, they can help answers lots of questions within neuroscience. “The rats are doing incredible behaviors that involve many things that neuroscience is preoccupied with, like decision making,” co-author Juan Ignacio Sanguinetti-Scheck, also of Humboldt University tells The Atlantic’s Yong. “There are many things that we can now use hide-and-seek to start studying.”