When one baby starts crying, so do other babies. That's because infants are hard-wired to react to simple emotions, like fear or physical pain, in other people. But it takes years before children are able to feel another person's psychological pain. And now scientists are beginning to understand how the brain learns that sort of compassion.
NPR's Jon Hamilton has the story.
JON HAMILTON: Scientists at the University of Southern California scanned the brains of 13 people as they responded to stories designed to provoke a range of emotions. Mary Helen Immordino-Yang says it was easy to get their brains to react to another person's physical pain. All it took was a few seconds of video.
Dr. MARY HELEN IMMORDINO-YANG (Scientist, University of Southern California): For example, a tennis player reaching for an outside shot, and then you just see her ankle break as she lands on it.
Dr. ANTONIO DAMASIO (University of Southern California, Brain and Creativity Institute) : Ouch.
Dr. IMMORDINO-YANG: Right.
HAMILTON: The person reacting there is Antonio Damasio of USC's Brain and Creativity Institute. He's also an author of the study. Damasio says 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 register when we're injured ourselves.
And he says that ability seems to have appeared pretty early in human evolution. Even animals need to know when a friend needs help or a foe has been hurt.
Dr. ANTONIO DAMASIO (University of Southern California, Brain and Creativity Institute): 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.
HAMILTON: Damasio says we have to learn some kinds of compassion. And he says the brain scans showed it's a lot harder to get a reaction to psychological pain than physical pain. The USC team asked people to listen to recordings of real stories told by real people, including this woman with cerebral palsy.
Unidentified Woman: I've never been kissed. And I have to be honest, I don't see myself in a romantic relationship at all.
HAMILTON: People's brains had to work a lot harder before they showed compassion. But Damasio says even the most complex psychological emotions engaged many of the same brain systems that respond to physical states.
Dr. DAMASIO: They end up recruiting parts of the brain that are normally used to regulate our own life, which to put it in a very simple way, is like saying that these emotions go deep in our brain, and they also go deep in our body, in our flesh.
HAMILTON: The study found another difference between the brain's response to another person's broken leg, rather than their broken heart.
Dr. IMMORDINO-YANG: The reaction that people had to compassion for physical predicaments happened much more quickly in the brain than the reaction that they had to compassion for social or psychological predicaments, which was a much slower process to ramp up.
HAMILTON: Antonio Damasio says that finding raises questions about the effects of news programs and video games in which a traumatic psychological event may flash by in just a second or two. Damasio says that could be a problem for children who are still developing compassion.
Dr. DAMASIO: And what if this is happening to a child who does not have parents or guardians around that can say, well, wait a minute, there are terrible implications for the person who just underwent that particular event.
HAMILTON: Damasio says compassion matters because it helps anchor moral systems and society itself. The new research appears in the online edition of "The Proceedings of the National Academy of Sciences."
Jon Hamilton, NPR News.