Scientists demonstrate empathy in rats

December 7, 2011

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(Science/AAAS)
A rat works to liberate his comrade, in an apparent demonstration of empathy.

Chicago researchers say it’s time to take another look at the noble rat. They’ve demonstrated what they call the first clear example in rodents of empathy, a quality previously only observed in primates.

Scientists have known that rodents show a primitive kind of empathy called “emotional contagion,” meaning a rat near another rat in distress will also feel distress. But the University of Chicago team designed an experiment to see if a rat would actually go out of its way to help a comrade.

They placed two rats in a cage. One roamed free while the other was trapped in a transparent stall in the center of the cage. The stall could only be opened by the other rat. Once he figured it out, the free rat would quickly move to liberate his cagemate.

“The trapped rat is now liberated and he runs around the arena,” said neurobiology professor Peggy Mason. “And the free rat runs after him. And jumps on him. And licks him. And it looks like a celebration.”

The scientists, beginning with graduate student Inbal Ben-Ami Bartal, then refined the experiment to be sure it really was empathy they were observing. They rigged the setup so that the liberator would not be able to play with his newly freed cagemate, to see if the action was motivated by wanting the reward of social interaction. But the behavior didn’t change even when there was no reward. They also tested whether the free rat would open the stall if it was empty, or if it contained a toy rat. He did not.

Finally, they put in a second stall, containing a handful of chocolate chips. To the scientists’ shock, the free rat would still release the trapped rat first before going for the chocolate -- about half the time.

“That was spectacularly clear, and what it tells us is that liberating a trapped cagemate is on a par with chocolate. And these are rats that like chocolate,” Mason said.

Even more staggering is that the free rat left some chocolate for his cagemate, rather than gobbling up all of it as they do when there’s no companion to think of.

Washington State University neuroscientist Jaak Panksepp wrote an analysis accompanying the research article, which appears in the journal Science. Panksepp said in an email that this experiment is the clearest-yet demonstration of behavior of this kind, but that further research is needed to untangle the motivation, be it empathy or "social stimulus enrichment."

The University of Chicago's Peggy Mason believes she's controlled for that possibility, and says she's certain that empathy is what's on display in the rat cage. She says the results suggest empathy goes back much farther in our evolutionary history than previously thought, and is therefore a deep and fundamental part of our very animal nature.

“What it basically tells us is that if we obey our biological inheritance, we’ll help each other,” Mason said. “To not help another person takes a conscious suppression of a natural biological tendency.”