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Sensitivity to social rejection and physical pain linked by a common gene

August 19, 2009 |  5:43 pm

The hurt of social rejection or exclusion is emotional. But there must be a reason why we so often experience it -- and talk about it -- as if it were a physical pain. One feels "burned" by a partner's infidelity, "wounded" by a friend's harsh words, "heartache" when spurned by a lover.

It turns out, there is a good reason we use such terms: The same circuits in the brain that are responsible for processing physical pain are also called into play when one feels the sting of social rejection. And a new study finds that people who have a rare variation of a gene that programs cells in those circuits are acutely sensitive to physical pain and to the hurt that comes from social rejection.

One class of brain cells that plays a key role in physical and social pain are mu-opioid receptors. They're best known for their role in dampening pain when an opiate drug or one of the body's own painkillers appears in their midst. But they are at work when we seek out or feel pleasure as well. The gene OPRM-1 helps govern the function of these mu-opioid receptors. Scattered through the family of man are several variants of OPRM-1.

Research already has shown that those who have the rarest variant of that gene are keenly sensitive to physical pain. The latest study suggests that this same population reacts strongly when, in an experimental situation, they are drawn into a group and then excluded from its activities. The study was published Friday in the early online edition of the Proceedings of the National Academies of Science, and due in print in the coming weeks. 

After collecting saliva from 122 subjects to determine which variation of the OPRM-1 gene they had, the researchers -- all from UCLA -- had subjects answer a survey of questions determining their level of sensitivity to social rejection. They found a strong relationship between those with a rare variant of the gene and those who agreed strongly with such questions as "I am very sensitive to the signs that a person might not want to talk to me."

Under scrutiny in a scanner that pinpoints bursts of activity in the brain, those subjects with the rare variant of OPRM-1 also showed acute discomfort when they played a virtual game of "catch" in which their presumed playmates progressively left them out of the game. By comparison, the brains of subjects who had the more common variant of OPRM-1 shrugged off the slight.

Here's an interesting fact: While the social-sensitivity variant of the OPRM-1 gene appears rarely in Caucasian populations tested to date, it appears to be far more common in those of Asian descent. That may offer some insight into the many rituals, customs and social conventions that govern social interaction in many Asian cultures: If social exclusion is painful, adherence to clearly delineated rules of intercourse would be an important way to prevent such discomfort.

Naomi Eisenberger, a researcher at UCLA who is one of the study's authors, said that, for humans, it may be highly adaptive to experience the sting of social rejection as physical pain. Pain is nature's way of alerting us to dangers such as poisonous animals and proximity to fire. Perhaps, said Eisenberger, psychological pain was an effective way to keep us from withdrawing from family and friends who help us tend our young, catch our food and protect us from predators. It is no surprise that two functions might eventually have evolved to use the same brain circuitry, said Eisenberger.

 "It helps us make sure we stay connected."

-- Melissa Healy

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