Hide and squeak: Scientists reveal playful lives of rats

The next time you come across a rat darting furtively for cover, consider this: It might just want to have a playful game of hide-and-seek.
A group of neuroscientists in Germany spent several weeks hanging out with rodents in a small room filled with boxes, finding the animals were surprisingly adept at the cross-cultural childhood game — even though they weren’t given food treats as a reward.
Instead, the rats appeared to genuinely enjoy both finding their sneaky human companions and being caught by them, as shown by their joyful leaps (what the Germans called “freudensprung”) and ultrasonic giggles that previous work has found is a sign of happiness.
The researchers’ paper was published in the influential journal Science, and beyond the cuteness factor (or creepiness, depending on one’s perspective), it offers new insight into play behaviour, an important evolutionary trait among mammals.
“When you work a lot with rats over the years, you see how intelligent these animals are and how social,” co-author Konstantin Hartmann from the Humboldt University of Berlin, where the other members of the team are also based, said.
“But it was still very surprising to us to see how well they did,” he said.
Working with adolescent male rats in a room of 30 square metres (320 square feet), a scientist would either find a cardboard box to crouch behind in a hiding role, or give the rat a headstart to find cover while the scientist searched.
Over a period of one to two weeks, the rats were taught that starting the game inside a closed box that was opened remotely meant they were seeking, while starting the game with the box open meant they were hiding.
They quickly developed advanced strategies, including re-visiting spots humans had previously hidden when they were seeking, and choosing to take cover in opaque rather than transparent boxes when they were hiding.
To help train them, the authors rewarded the rats not with food or water, which would invalidate the experiment, but with positive social interaction in the form of physical contact, explained Hartmann.
“They chase our hand, we tickle them from the side, it’s like a back and forth a little bit like how you play with small kittens or puppies,” he said.
The scientists suspect though that the rats were motivated not just by this interaction but that they also liked to play for the sake of play itself.
The animals would let out high-pitched giggles three times above the human audible range and would execute so-called “joy jumps” during the game —both associated with feelings of happiness.
Once they were discovered, the rats often jumped away and “playfully rehid” at a new location, sometimes repeating the process several times — indicating they wanted to prolong the play session and delay the reward.
Play is an important part of cognitive development for adolescent mammals, and rats make for ideal models to study brain activity in humans because of their evolutionary proximity to us, which is also why they are often used in the study of disease.