WEDNESDAY, May 17, 2006 (HealthDay News) -- The human brain may have a built-in mechanism for keeping racially or politically distinct groups apart, a new Harvard study suggests.
U.S. researchers observed the brain activity of liberal college students who were asked to think about Christian conservatives. As they did so, a brain region strongly linked to the self and to empathy with others nearly shut down, while another center -- perhaps linked to stereotypic thoughts -- swung into high gear.
"It's as if you think that 'they' don't think like you do -- it's like you believe they are governed by a different set of rules when they think," explained study author Dr. Jason Mitchell, a postdoctoral researcher at Harvard University's department of psychology.
His team published its findings in the May 18 issue of Neuron.
According to Mitchell, social psychologists have long known that people engage different mental criteria when thinking about the possible thoughts and actions of people within their own ethnic, cultural or political group, vs. those outside that group.
The neurological mechanisms governing this process has been much less clear, however.
"Our work is about 'other-ness,' " Mitchell said. "There's this question of 'How do I figure out what's going on inside your head? How do I make inferences about what you are feeling?' "
One theory that's gained credence among social neuroscientists is that people look to themselves when thinking about people they already include in their "group."
"If you and I are similar, then I can use what I know about myself to figure out what you are thinking," said Mitchell, who will become an assistant professor of psychology at Harvard in July.
Previous studies have shown that an area toward the front of the brain, called the medial prefrontal cortex (mPFC), always lights up when people think about themselves or people they consider similar to themselves.
But which part of the mPFC activates when people think about those outside their group?
To find out, the Harvard team hooked up a group of liberal Boston college students to a functional MRI machine, which tracks real-time changes in brain energy use.
They then asked the students to read detailed profiles of two people: one, a liberal-minded person much like themselves, and the other, a fundamentalist Christian conservative with views and activities very different from their own.
"We showed that there are distinct brain regions active in the mPFC," depending on the political stripe of the object in question, Mitchell said.
When the students thought about the liberal person, the mPFC's ventral region -- strongly associated with thoughts about the self -- got very active. But it quieted down when the subject was the Christian conservative -- instead, the mPFC's dorsal area took over.
"The dorsal region is a lot more mysterious," Mitchell said. "It's more engaged when I think about a dissimilar other."
"These data challenge the naive view that we bring the same mental orientation to bear when we think about those who are similar or different from us," said study co-author Dr. Mahzarin Banaji, a professor of social ethics in Harvard's department of psychology. "In particular, it raises questions about who can, objectively speaking, sit in judgment on whom."
Mitchell stressed that scientists currently have no way to tell what kinds of thoughts get processed in the dorsal mPFC. But he suspects it could be responsible for stereotypic thoughts that fail to take similarities between people into account, and instead stress their dissimilarities. So, people may consult the dorsal mPFC when they make snap judgments that assume that the "other" does not think or act like they do.
That's unfortunate, Mitchell said, because when people of different political, racial or cultural backgrounds focus on what they have in common, tensions ease. "If I can find a way to reach common ground -- for example, we both love baseball -- that might be enough to trump our dissimilarities," he said.
Another social neuroscientist who's worked in this field praised the study.
"We already knew much of this from psychology, but what we know now is more about how this is represented in the prefrontal cortex," said Dr. Elizabeth Phelps, a professor of psychology and neural science at New York University in New York City.
She said it's natural that humans lean to stereotypes when thinking about those outside their circle.
"We evolved to be in groups, and somebody who is part of your group is seen as less of a threat than somebody who is not," she said. "And it's a natural thing to assume that people who are not like you are going to have a different set of qualities."
But Phelps also believes that we might be able to override our ingrained "dorsal" response to strangers. "I imagine that you can think compassionately, highlighting similarities between you and another person that will change your interpretation of their actions," she said.
Mitchell agreed. He said a new set of fMRI experiments will soon get under way to see if that neural switch can easily occur. But, he said, there are limits to empathy, of course.
For example, for most people, finding out that Adolf Hitler loved dogs "isn't going to be enough" to mentally allow him into one's group -- even for the most hardened dog-lover, Mitchell said.
"It's not everyday that you interact with Hitler, however," he added. "Hopefully, in your everyday life you'll encounter less extreme examples."
Learn more about brain imaging at the U.S. National Institute on Drug Abuse.