Our capability to show empathy and compassion for the suffering of others can wax and wane, and when it comes to people we don't know it appears that normal "stranger danger" stress is the cause, researchers say.
Encountering someone who is a stranger to us can raise our stress levels, which in turn can make us less able to feel their pain or unhappiness, they explain.
"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 researcher Jeffrey Mogil at McGill University in Montreal. "The secret is -- quite simply -- stress, and in particular the social stress of being in close proximity with a stranger."
Previous research with both mice and humans has shown both possess empathy for the pain of another, particularly when the suffering individual is someone familiar.
However, in both that empathy can fall victim to the rise in stress levels when the other individual is a stranger, the researchers report in the journal Current Biology.
Reducing that social stress can elicit more empathy, they say.
When mice were given a drug known as metyrapone to block stress hormones it allowed for greater empathy, and they started reacting to strange mice in a manner usually reserved for more familiar cage mates, they found.
In another experiment, when student volunteers were given metyrapone they also showed more empathy toward strangers.
However, Mogil doesn't suggest taking a pill is the way to become a more empathetic person, pointing out there is a better and easier way.
Simple interaction of a psychosocial kind -- in the case of this study a shared session of playing a video game -- served just as well for increasing empathy between strangers, he says.
The takeaway findings of the study suggest people's normal response is to be empathetic but stress can inhibit that emotional ability by acting on the brain and our endocrine system, altering the way we respond to other people, the researchers say.
An extra result of the study is the discovery that humans and mice are much the same when it comes to social behaviors, Mogil says.
"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.'"
