Rats may not be, well, such rats after all. In the first study of its kind, researchers show that rats engage in empathy-driven behavior, helping to free a trapped cagemate for no reward other than relieving its fellow rat’s distress. Rats chose to help each other out of traps, even when a stash of delicious chocolate chips was on the line.
Although previous research has suggested that empathy isn’t just the province of humans, this is the first study to show such pro-social behavior in rodents. Researchers say the basic understanding of empathy in lower animals could help scientists’ understand it better, and even increase it in people. “It’s a neat new experimental procedure that may facilitate the empirical understanding of empathy,” says Jaak Panksepp, a pioneer in the study of emotions in animals, who wrote a commentary that appeared alongside the new research in the journal Science.
In the study, same-sex rats were first housed in pairs in the same cage for two weeks. Then, during the testing sessions, one rat was allowed to run free, while the other was trapped in a plastic restraining tube. The restraining device was designed so that the free rat could liberate the trapped one, if it could figure out how to tip over the door. In control conditions, the restrainer was either empty or contained a toy rat.
“We wanted to have a cool paradigm to look at whether rats understand another’s state of mind, and also act on it intentionally,” says the study’s senior author, Jean Decety, professor of psychology and psychiatry at the University of Chicago.
He explains that prior research on empathy in rats had looked only at their reactions to other animals in fear and pain. While those studies show that rats pick up the fear and stress of other rats and become frightened themselves, a phenomenon known as “emotional contagion,” they can’t demonstrate whether they want to help or whether they are just sensitive to the other animal’s condition and fear they will be hurt next.
High levels of fear actually wouldn’t be likely to lead to altruism. Studies in children show that those who are especially sensitive and become highly distressed by the pain of others, are less likely to behave empathetically because they have to soothe themselves before they can help. “Too much sensitivity is actually bad,” says Decety, noting that “it doesn’t help a surgeon to shake or be afraid [of hurting the patient].” (Oversensitivity may also be why some autistic people withdraw rather than seek to connect; they can be highly emotionally sensitive, but get easily overwhelmed by it.)
In the rat experiments, researchers observed that the free rats immediately liberated their trapped partners, once they figured out how to open the restraint — which took about a week. Rats that were exposed to empty restrainers or a trapped toy rat ignored them.
“They are very smart and figure out if they pitch their nose up, they can open the door,” says Decety. “It’s not easy and it doesn’t happen by chance. They try hard and circle around.” The researchers did not teach the rats how to nudge the door open or give them any incentive to. Even when opening the door would release its companion into a separate compartment, rats freed each other.
Research suggests that females show more empathetic behavior than males, and this was borne out in the study. All of the female rats in the study learned to open the door and free their partners, while 17 of the 24 males did.
In an ingenious twist, researchers then placed free rats in a cage with two restraining tubes. One contained a fellow rat, while the other held chocolate chips. Rats, like most of humans, love chocolate. Would the rats go for the chips and leave their friend locked up, or open both doors and share the goodies?
As it turns out, about half the time, rats chose to free their cagemates and share. They also didn’t take longer to release their cagemates when the chocolate was available. Even though control rats that had a choice between a restrainer containing chips and an empty one ate all the chips most of the time, in 51% of trials where rats could share with friends, they did.
“They open both doors and share the chocolate,” says Decety. “That’s amazing. They could eat all of the chocolate, but they didn’t.” The researchers did expect the rats to try to help, but were surprised by how much they shared.
“This paper gives us one of the very best experimental models that exists so far,” says Panksepp. “What this model provides is reasonably good evidence for empathy, and [it] also provides a model system to study the underlying processes further.”
Decety and his colleagues, for example, will study whether rats that have previously been restrained themselves are faster to help other rats who have not had that experience. They’re also studying the biology underlying the rats’ actions, looking at chemicals like the “love hormone” oxytocin, which is involved in social bonding and nurturing behavior.
“There’s no reason to think that only humans are pro-social and have empathy,” says Decety.
Nor is there reason anymore to believe that we are “naturally selfish” or that selfishness is our default position. “We’re a social species,” says Decety. “It’s good for us to help, it makes us feel good, it’s connected with dopamine and that’s good for everybody.”