The human brain reacts quickly when encountering physical pain. But psychological pain takes longer to register.
A team led by Mary Helen Immordino-Yang in the University of Southern California used functional MRI to study the brains of 13 people as they responded to stories designed to provoke a range of emotions.
Immordino-Yang reported in the online edition of the Proceedings of the National Academy of Sciences
that it was easy to get people's brains to react to another person's physical pain. All it took was a few seconds of video.
"For example, a tennis player reaching for an outside shot," Immordino-Yang says. "And then you just see her ankle break as she lands on it."
In their experiments they found that it took the brain up to six seconds to react to a complex emotion like emotional pain, while reactions to physical pain occurred almost instantly.
The response is immediate because people are born hard-wired to react to other people experiencing simple emotions like pain or fear, Immordino-Yang says. That's why when one baby starts crying, other babies tend to join in.
Scientists know quite a bit about which parts of the brain make us wince when we witness a physical injury. They're the same parts of the brain that respond when we're injured ourselves.
And there's evidence that a basic ability to feel another's pain emerged pretty early in human evolution, says Antonio Damasio, a co-author of the study. Damasio is the David Dornsife Professor of Neuroscience at USC and the director of USC's Brain and Creativity Institute.
Damasio says early humans were probably more likely to survive if they could tell when a friend needed help or a foe was in pain.
"It probably took longer in evolution to get to a stage in which human beings could look at another human being, not see anything externally wrong with them, but imagine that there was something quite wrong in terms of their feelings, in terms of their mental pain," he says.
Damasio says people still aren't born with this sort of compassion. They have to learn it.
Immordino-Yang says the team was able to induce that sort of compassion using recordings of real stories told by real people. One involved a woman with cerebral palsy who had given up hope of having a romantic relationship, Jon Hamilton reported for National People's Radio.
They also found that reactions to emotional pain also took much longer to dissipate. And that is something to build on.