How stress kills our ability to feel compassion

Stress isn't just bad for our physical and mental health -- it may also inhibit our ability to empathize with others, according to new McGill University research.

The study, recently published in the journal Current Biology, found that a drug that blocks stress hormones can increase the ability of both humans and mice to "feel" others' pain.

The researchers studied the phenomenon known as "emotional contagion of pain," a key component of empathy which has to do with our ability to experience the pain of strangers.

Previous research by the same team has shown that both mice and humans have this ability, particularly when the person in pain is somebody they know. That research also showed that stress levels rose in mice and humans when they were around strangers, inspiring the researchers to investigate a potential link between stress and empathy.

In the first part of the experiment, the researchers gave mice metyrapone, a stress hormone blocker, which caused the mice to react to strangers in pain the same as they responded to cagemates in pain -- thereby suggesting a boost in empathy. Another test found that when the mice were put under stress, they showed less empathy towards their cagemates.

The researchers explained that biochemical changes related to stress seemed to be preventing emotional contagion in the mice.

"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."

In a second test on humans, students were paired with either a friend or a stranger, as asked to evaluate the pain of their partner when holding their hand in ice water. When the undergraduates were then treated with the stress hormone blocker, they showed a greater empathy towards strangers -- they both reported a greater experience of pain, and also showed more pained facial expressions and bodily movements when witnessing their partner's pain.

The findings suggest that the stress response may play an important role in dictating how we respond to social situations.

"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.'"

However, while this study didn't note any gender differences in empathic response, previous research has shown that stress has a different effect on empathy and prosocial behavior for men and women. Earlier this year, Italian researchers found that while stress undermines empathic abilities in men, but boosts these abilities in women. Namely, their research showed that stress rendered men more self-centered and less able to distinguish their own emotions from those of other people.

"To be truly empathic and behave prosocially it's important to maintain the ability to distinguish between self and other, and stress appears to play an important role in this," lead researcher Giorgia Silani said in a statement.