How is it that people can sometimes show such empathy when other times our ability to feel compassion seems to be in such short supply? A study published in the Cell Press journal Current Biology on January 15 shows that stress is a major factor.

A drug that blocks stress hormones increases the ability of college students and mice to “feel” the pain of a stranger, the study shows. That phenomenon, known as “emotional contagion of pain,” is one form of empathy. In even better news, a shared round of the video game Rock Band worked just as well as the drugs among those undergrads.

“We found what in some sense might be thought of as the ‘secret’ to empathy; that is, what prevents it from occurring more often between strangers,” says Jeffrey Mogil of McGill University in Montreal. “The secret is–quite simply–stress, and in particular the social stress of being in close proximity with a stranger.”

Earlier studies had shown that mice and humans both have empathy for another’s pain, especially when the individual in pain is someone they know. It was also clear from those studies that stress levels rise in both mice and people when in the presence of a stranger.

To test for a direct connection between stress and empathy, Mogil and his colleagues treated male mice with a stress hormone-blocker called metyrapone and watched their response to the pain of other mice.

They found that the drug allowed greater empathy as mice began reacting to strangers in a manner normally reserved for familiar cagemates. In other tests, the researchers found that when they put mice under stress, the mice showed less empathy when their peers were in pain. In other words, biochemical changes related to stress were preventing emotional contagion in the animals.

The researchers went on to test for signs of empathy in undergraduate students by pairing them with either a friend or a stranger and having them rate the pain associated with holding a hand in ice water. Again, undergrads treated with metyrapone showed a greater sense of empathy toward strangers. After taking the drug, participants not only reported a greater experience of pain, but they also showed more pained facial expressions and more often touched their own hands when witnessing another’s pain.

This doesn’t mean that Mogil would recommend that anyone with the goal of becoming more empathetic take a pill. There is an easier way: A simple psychosocial interaction–a game of Rock Band–worked just as well as the drugs in boosting empathy toward another person, the researchers report.

The findings are the first to suggest an important role for the stress axis in the brain and endocrine system in modulating our response to other people, the researchers say. They also suggest that mice and humans are surprisingly similar when it comes to social behaviors.

“It is quite intriguing indeed that this phenomenon appears to be identical in mice and humans,” Mogil says. “First, it supports the notion that mice are capable of more complex social phenomena than is commonly believed. Second, it suggests that human social phenomena might actually be simpler than commonly believed, at least in terms of their organizing principles. This is an emerging theme of much research currently ongoing in my lab; when it comes to social behavior, ‘mice are people too.'”

A game of Rock Band, anyone?