New research suggests rats are capable of learning to play hide-and-go-seek with humans—and they appeared to legitimately enjoy the game. Rats, as this new research demonstrates, just wanna have fun.
Fascinating new research published today in Science describes how neuroscientists in Berlin taught rats to play the classic children’s game, hide-and-seek. Incredibly, the rats were capable of playing the game either as the hider or the seeker, and they appeared to enjoy the matches, exhibiting joyful jumps, employing strategies, and actively prolonging the game.
Scientific research involving rats is traditionally based on strict control and conditioning. Here, the scientists, including Michael Brecht and Annika Reinhold from Humboldt University, had an opportunity to loosen up a bit, choosing to explore the ways in which rats might naturally and spontaneously participate in playful behaviors. Teaching rats to play-hide-and-seek might seem like a weird thing for scientists to do, but the exercise offers new insights into the cognitive capacities of rodents and possibly other “simple” mammals.
That rats like to play games with humans is a surprising result. This kind of playful behavior carries no tangible benefit to the rat outside of the gameplay itself. In this case, the rats were motivated to play the game simply for the sake of it. As the researchers pointed out in their study, “the animals looked like they are having fun.”
Konstantin Hartmann, a co-author of the new study and a Ph.D. candidate at Brecht’s lab, knew going into the study that rats have “strongly developed cognitive capacities,” he told Gizmodo in an email. But watching how fast they learned to play hide-and-seek, and how good they got at it, “was a big surprise, even for us.” An even bigger surprise, said Harmann, was watching the rats use “smart strategies” when playing the game, and how they actively prolonged the game “in a way that tells us that they enjoyed the game itself and not only the social interaction at the end of each round.”
Six different rats were used for the experiment. Training started at a very young age, when the rats were just 3 weeks old—a time when rats are naturally playful. The hide-and-seek experiments were conducted while the rats were between 5 and 23 weeks of age. The training environment in a well-lit room, and the researchers used a series of cardboard boxes as potential hiding places, in addition to small boxes, either opaque or transparent, for the rats. When in seeker mode, the rats were placed in a closed box, which the researcher opened with a remote control device, setting the game into motion.
Needless to say, teaching rats to play hide-and-seek wasn’t easy. As Hartmann pointed out, it’s not possible to talk to the animals to explain the rudiments of the game. Instead, the researchers took incremental steps to teach the animals how to play. The initial step was to make the rats comfortable with the scientists, which they did by playing with them and spending lots of time with them, similar to how a person interacts with a pet.
“Once familiar to us, they actively pursued interaction with us,” said Hartmann. “We used this to teach them the seeker role of the game. First, we ‘hid’ in plain sight, and when the animals came to us, we rewarded them with a playful interaction. You can tickle a rat, chase it playfully with your hand, and it will also chase your hand,” he said.
Next, the researchers started hiding behind a cover, namely the cardboard box, and whenever a rat found the hider, the researchers would once again playfully interact with the rat before returning it back to the starting position.
Teaching the rat to play in the hider mode, however, proved to be more challenging.
“We started placing the animal in a box and sat next to it,” said Hartmann. “Once the animal jumped out, we again played with it. Later we only played with it after it walked away from us and the box. Continually, we only played with the animal once it was close to an appropriate hiding location. Last step was that the animal had to properly hide before we played with it.” This proved to be a time consuming process, but it eventually worked.
It’s important to point out that the rats were rewarded only with playful human interaction—not with food. Eventually, however, as the rats got into the game, the interactions seemed less important to the animals than playing the game itself.
In addition to prolonging the game, the rats became increasingly strategic in their behaviors, whether in the seeker or hider roles. For example, they systematically searched the space in search of visual cues, they targeted previous hiding locations, they preferred to hide in the dark boxes, and they made sure to be very quiet when changing hiding locations, according to the paper.
“All rats we trained did learn the game and performed very well,” said Hartmann. “One rat was only taught to seek and wasn’t trained to hide. This was just because it was the first animal we used in this study.”
So why did the rats play this game? In the study, the researchers invoked two possibilities: either the shaped-to-play hypothesis, in which the rats were classically conditioned to play the game on accounts of the rewards, or the play-to-play hypothesis, in which the rats played the game simply for the enjoyment aspect. Of these possibilities, the researchers preferred the play-to-play hypothesis, offering four specific reasons, as described in the new study:
First, the animals looked like they are having fun. Behaviors that signify eagerness to observers include the following: quick, directed locomotion; frantic search; teasing of the experimenter; and execution of freudensprung (“joy jumps”). Rats were highly vocal and eager to engage in the game but appeared tired toward the end of a 20-trial session. Thus, motivational aspects differ from....food-reward conditioning, where there is little evidence for vocalizations and where rats tirelessly do hundreds of trials. Second, the rats’ behavior seemed purposeful. They preferred to hide in opaque over transparent boxes as if they were hiding to hide rather than hiding to be found. Third, hiding rats tended to be silent when being found, contrary to the excitement about being found predicted by the shaped-to-play hypothesis. Fourth, when found, rats often ran away and re-hid. Contrary to the shaped-to-play hypothesis, rats prolonged the game by re-hiding. By succeeding at hiding, they inherently delayed the reward.
Taken together, the authors say their observations “tentatively, but not conclusively” favor the play-to-play hypothesis. But because we can’t yet peer inside the mind of rats and fully understand their true intentions and motivations, “further work is needed to understand rat play behavior.”
In addition to the observations chronicled by cameras, five of the rats had wireless implants placed on their medial prefrontal cortex (the part of the brain responsible for planning and decision making, among other complex behaviors), allowing the researchers to see which parts of the brain were active during the game. After the experiments, the researchers saw that different parts of the prefrontal cortex were engaged during seeker mode compared to when the rodents were in hiding mode, highlighting the distinct and complex neural signatures associated with playing hide-and-seek. Recording devices were also used to capture vocalizations made by the rats, some of which occur outside of the range of human hearing.
In terms of the scientific takeaway, Hartmann said the game allowed his team to study unrestricted playful behavior in rats. This is consequently telling us about the rodent brain and how it takes on roles and processes rules in a “more naturalistic and relevant context than most other studies have done in the past,” he said, adding that the new research “extends the repertoire of known behaviour in rodents and is the first proof of a game between humans and rodents.”
But were the rats truly playing hide-and-go seek in the sense of it being active play? We posed this question to Jennifer Vonk, a cognitive psychologist and expert in animal cognition at Oakland University.
“I would question whether rats are really playing the game or just engaging in typical behavior in which they seek out shelter,” said Vonk in an email to Gizmodo. “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.”
To more conclusively determine if the rats’ behavior was a form of play, Vonk said “it would be nice to see if rats respond similarly if an inanimate object, like a doll, is the partner, compared to a live experimenter. If the same behaviors are evidenced it would contradict the idea that they are engaging in play with another live agent,” she said, adding: “I would also love to see if the rats played with each other in the same way once they had learned both roles.”
These concerns aside, Vonk said she liked that the researchers experimented with different types of trials, and that the rats continued to search at sites previously occupied by the human hiders.
“I like that the researchers recorded their vocalizations so they could show that they vocalized less when hiding versus seeking,” said Vonk. “The fact that the researchers could measure brain activity during the game is fantastic and may help us understand the function of different brain areas in social interactions.”
Peggy Mason, a professor of neurobiology at the University of Chicago, said this was “absolutely good research.” The new study “once again reinforces how similar rats are to us,” she told Gizmodo during a telephone interview, and that “we don’t have to invoke any special human capacity for a pretty sophisticated game.” She wasn’t terribly impressed that rats can play a game, but she was impressed that “they do do it,” meaning they appeared to enjoy the activity. “Presumably that’s why human kids do it,” she said.
Mason also commended the researchers for embarking upon an experiment that, at the outset, wasn’t obviously going to work, and for doing something that was purely based on animals having fun.
“Scientists can get all tied up in knots, and make a big separation between humans and nonhumans,” she said. “Researchers shouldn’t be afraid to make a connection between the human and the nonhuman—they have to get over it,” she said. Clearly, this approach could be problematic if done uncritically, she said, but this kind of research showcases the “continuity of life.”
“This is what evolution tells us—that there shouldn’t be a chasm between us and the rest of the animals,” concluded Mason.