When Inbal Ben-Ami Bartal was a master’s student in Israel researching immunosuppression after surgery, she noticed a strange phenomenon in her laboratory rats. When rats were brought to the room where she regularly conducted surgical procedures, they grew extremely agitated.
“It was very obvious that rats could sense what was going on with other rats,” Bartal said. “They freaked out and were affected by the emotional state of the other rats once they were removed from the cages.”
Other researchers had previously noticed this phenomenon in both humans and animals and gave it the name “emotional contagion,” describing when the distress or pain of one individual spreads to others. In 2006, Jeffrey Mogil of McGill University found evidence of this effect in mice, observing that when one mouse is given a mildly painful stimulus, a second mouse viewing the first mouse’s pain will exhibit increased sensitivity to pain. When that paper was published, it was considered by some to be the first evidence for empathy in a rodent. But Bartal, having started as a graduate student advised by Jean Decety, Irving B. Harris Professor of Psychology and Psychiatry at the University of Chicago, wanted to find more definite proof of rat compassion.
Collaborating with the laboratory of Peggy Mason, professor of neurobiology, Bartal designed a test to see whether emotional contagion could actually drive a rat to take action. Two rats who live together in the same cage were placed in a special arena, with one held in a transparent, tube-shaped restrainer and one allowed to roam free. The restrainer’s door could be opened by a nudge from the outside, though the free rat – at least initially – didn’t know that. But after several sessions where the free rat was visibly agitated by his trapped companion’s distress, he figured out how to pop open the restrainer. As you can see in this video from Science, once the free rat learned this trick, he would take action almost immediately upon being placed in the arena during subsequent sessions.
“We are not training these rats in any way,” Bartal said. “These rats are learning because they are motivated by something internal. We’re not showing them how to open the door, they don’t get any previous exposure on opening the door, and it’s hard to open the door. But they keep trying and trying, and it eventually works.”
Proving that the free rat’s actions were motivated by empathy required more experimental conditions. When the restrainer was left empty, or when researchers put a stuffed toy rat in the tube, the free rat showed no interest in opening the restrainer door. He did, however, when the arena was rigged so that opening the restrainer released the trapped rat into a separate compartment from the free rat, showing that the free rat was not motivated by the “reward” of social interaction. The experiments left behavior motivated by empathy as the simplest explanation for the rats’ behavior.
“There was no other reason to take this action, except to terminate the distress of the trapped rats,” Bartal said. “In the rat model world, seeing the same behavior repeated over and over basically means that this action is rewarding to the rat.”
For the strongest test of empathy’s power in driving rat behavior, the researchers introduced a wild card in the form of chocolate chips. Mason’s previous research proved that rats are big fans of chocolate, so the researchers placed a second restrainer into the arena holding the delicious snack and posing an ethical dilemma for the free rat. If he opened the chocolate tube first, he could dine in peace while his cagemate remained trapped. If he freed the cagemate first, the free rat would have to share his chocolate prize. Surprisingly, the rats did both, choosing to free the cagemate or the chocolate first with roughly equal preference.
“The rat can hog the entire chocolate stash if he wants to, and he does not,” Mason said. “On average he shares one and a half chips – that may not seem like a lot, but for rats that’s amazing. It said to us that, essentially, relieving a cagemate’s distress is on a par with chocolate. Not more important than chocolate, but certainly not less important.”
Taken together, the experiments are the first evidence of an empathy in rats that runs deeper than emotional contagion, a drive to help a companion in distress that is equally as motivating as the lust for sweets.
“This is the first evidence of helping behavior triggered by empathy in rats,” said Decety. “There are a lot of ideas in the literature showing that empathy is not unique to humans, and it has been well demonstrated in apes, but in rodents it was not very clear. We put together in one series of experiments evidence of helping behavior based on empathy in rodents, and that’s really the first time it’s been seen.”
Having an animal model of empathy-driven behavior will now allow researchers to study the biological mechanisms that underlie empathy, looking at brain anatomy, stress hormones, and other factors that could motivate a rat to help – or not help. In a more philosophical sense, it shows that helping another individual in need is not a social construct, but a behavior with evolutionary roots that go beyond our own sometimes selfish species.
“When we act without empathy we are acting against our biological inheritance,” Mason said. “If humans would listen and act on their biological inheritance more often, we’d be better off.”