“There are all these YouTube videos from pet owners that say their animals love to do this.” That’s how neuroscientist Michael Brecht of the Bernstein Center for Computational Neuroscience at the University of Humboldt in Berlin got the idea of teaching rats to play hide and seek. See how this both absurd and fascinating study managed to shed light on rats’ cognitive abilities.

To accomplish their goal of studying the behavior of these rodents while at play, the research team transformed their laboratory into a playground. In the first case, a member of the team placed a rat in a closed box and hid. The scientist then opened the box using a remote control… and the rat began looking for the experimenter. Once he found his target, the rodent was rewarded with petting and tickling. The animals are very fond of such forms of social interaction.

In the other (more complex) case, the roles were reversed. The rat was placed in the box, but the lid was left open, letting him know that it was his turn to hide. The experimenter crouched down next the rat while it exited the box and went to hide in one of the seven opaque or transparent boxes placed around the room. Again, when the scientist found the animal, it was entitled to the same petting and tickling as before.

It only took two weeks for five teenage male rats (out of six at the beginning of the experiment) to learn to play hide and seek without changing roles in the middle of a game. To confirm the results, another series of experiments with four other rodents was carried out with success.

What did the scientists observe during their hide-and-seek games with the rats? The rats preferred to hide in an opaque box, and when they decided to change hiding places, they did so as quietly as possible. The scientists were particularly surprised to see that the rats, who could go from one hiding place to another, would move to a box where their playmate had already looked (as if they thought that he or she wouldn’t look there again). What if rats could imagine things from someone else’s perspective? This would suggest a complex cognitive ability (known as “theory of mind”).

The scientists also tried to find out if the rats enjoyed playing hide-and-seek. They gradually abandoned the principle of reward in favor or just playing the game. Moreover, when the rats found their target, they performed something like “joy jumps” and made contented vocalizations. Finally, once they’d been found, they often went to a new hiding spot as if they wanted to keep playing the game.

Throughout the experimental protocol, the research team also recorded the rats’ brain activity (using an implant) and detected a set of neurons in the prefrontal cortex that were sensitive to the game’s structure.

In conclusion, Annika Stefanie Reinhold and her colleagues indicate that playing hide-and-seek requires cognitive skills to know where your “adversary” will mostly likely look or to find the best hiding place. And this study tends to show that rats could have these abilities, which had until now only been observed in primates.