无私行为的生物学原理

AUDIE CORNISH, HOST: Turning to another study now, this one on altruism. New research suggestsextraordinary acts of kindness may be rooted in the brain. Michelle Trudeau reports.

MICHELLE TRUDEAU, BYLINE: Altruism is when you help somebody else at a cost to yourself. So you're sacrificing for another; you're taking a risk or suffering pain.

ANGELA SIMPSON: My name is Angela Simpson. I reside in Albany, New York, and I am 46 years old.

TRUDEAU: Angela is a graphic artist. She is also an extraordinary altruist. Back in 2010 Angela donated one of her kidneys to an unknown recipient.

SIMPSON: The only thing I knew about my recipient is that she was a female and she was residing in Bakersfield, California.

TRUDEAU: The surgery to remove Angela's kidney occurred at a transplant Hospital in New York City.

SIMPSON: And my kidney was shipped to California immediately after it was extracted.

TRUDEAU: Angela's altruistic act begs the question why would someone donate a perfectly healthy part of their body to a total stranger? Go through the risk of major surgery and do it willingly - even happily - for no pay, no remuneration and anonymously? Here's how Angela explains her decision.

SIMPSON: At that time in my life I was 42 years old. I was very single. I had no children; you know, very, very fortunate - loved my life. But I really felt like I would question often what is my purpose?

TRUDEAU: So when she heard about the critical need for kidney donations - over 100,000 people in the U.S. today are waiting for a kidney transplant...

SIMPSON: To really be able to help somebody unconditionally was, like, an awe moment.

TRUDEAU: So she did it, she says, simply because she could. Professor Abigail Marsh has her own story of altruism, too.

ABIGAIL MARSH: I think I was 20 years old and I was driving home to my parent's house in Tacoma, Washington.

TRUDEAU: Long story short - A freak highway accident. Her car spins around and stalls in the fast lane. A stranger stops, dodges through traffic, helps her to safety saving her life and then disappears. A true altruist - risking his own life to help someone he didn't know and would never see again. This propelled Abigail Marsh toward her professional career, one of today's leading researchers of altruism. Now at Georgetown University, Marsh studies what she calls extraordinary altruists - most recently a study of 19, including Angela from around the country who donated a kidney to a stranger.

MARSH: And we brought them to Georgetown for testing.

TRUDEAU: Psych testing, brain imaging studies, extensive background profiles, etc. But says Marsh...

MARSH: Most of the test that we did didn't show any differences between the altruistic donors and people who had not been donors.

TRUDEAU: All pretty normal - except for a telltale difference in a part of our brain called the amygdala. It's an almond shaped cluster of nerves; it's our emotional radar. And it was significantly larger in altruists compared to those who'd never donated an organ. Additionally, Marsh reports that the amygdala in altruists is supersensitive to fear or distress in another's face.

MARSH: They showed this very specific increase in amygdala activation in response to others' fear.

TRUDEAU: Now in previous research Marsh reports some polar opposite findings in a group of psychopaths. Using the same tests as with the altruists Marsh found that psychopaths have smaller, less active amygdalas. The brains' emotional radar in psychopaths was blunted and relatively unresponsive to someone else's distress or fear. For NPR News, I'm Michelle Trudeau.