Scientists are studying the link between chronic pain and depression. (Guang Niu, Getty Images )
Across cultures and language divides, people talk about the sting of social rejection as if it were a physical pain. We feel "burned" by a partner's infidelity, "wounded" by a friend's harsh words, "crushed" when a loved one fails us, "heartache" when spurned by a lover.
There's a reason for that linguistic conflation, says a growing community of pain researchers: In our brains too, physical and social pain share much the same neural circuitry. In many ways, in fact, your brain may scarcely make a distinction between a verbal and physical insult.
So the well-worn parental reassurance that "sticks and stones will break your bones, but names will never hurt you" is false, these scientists say. And they have the pictures to prove it.
University of Kentucky psychologist Nathan DeWall, a researcher in this young field, says the pain of social exclusion assaults each of us on average about once a day. "It's a big deal," he adds, one that's often unrecognized by friends and colleagues and is downplayed by the emotionally wounded themselves.
But when it comes to the human brain, evolution has been economical in allocating resources to the problem, DeWall adds. "Instead of creating an entirely new system to respond to social hurt, evolution piggybacked the system for emotional pain onto that for physical pain," he says.
Last week, new research offered further evidence of pain's shared circuitry in the brain. The study, published in the journal Proceedings of the National Academy of Sciences, established that two regions of the brain previously known only to process the sensation of physical pain come alive when a person gazes upon a photograph of a former lover and ponders the feelings of rejection that came with being jilted by that person.
"These results give new meaning to the idea that social rejection 'hurts,'" wrote the authors.
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The dual role of the brain's pain network offers a powerful example of the connection between body and mind, and may help explain how emotional distress can make us sick and human kindness sustains us in health. And it may yet shed light on an enduring medical mystery: why depression, a sort of emotional pain disorder, coexists so often in patients who also have chronic or neuropathic pain disorders.
At the same time, the overlap underscores the profound importance of social connection as an evolutionary imperative, key to our survival as individuals and a society.
"Physical pain obviously serves a purpose: It's uncomfortable and distressing, but it's a signal that something's wrong, that we need to take action to fix it," says UCLA psychologist Naomi Eisenberger. "I think we can say the same about social pain: It motivates us to reconnect socially and avoid social rejection in the future."
In 2002, Eisenberger was a graduate student at UCLA, using brain scans to see how the human brain responds to social rejection. Her office-mate and fellow psychology graduate student, Johanna Jarcho, was studying human pain perception and was using functional magnetic resonance imaging, or fMRI, in her own work.
"We noticed that there was so much overlap between our scans," Eisenberger says.
The resulting study, showing what Eisenberger called a "common neural alarm system for physical and social pain," was published in 2004 and has spawned a welter of research exploring the bonds that tie social pain and physical pain together.
Among them, two studies have provided new insights on the connection. One, published in August 2009, showed that sensitivity to both kinds of pain may be strongly influenced by genetics. Writing in the Proceedings of the National Academy of Sciences, Eisenberger and two UCLA colleagues reported that research subjects who carried a rare variant of a single gene known to increase pain sensitivity also were acutely vulnerable to feelings of rejection.
In December 2009, another pair of experiments, published in the journal Psychological Science, offered a "novel insight" on the link between social and physical pain. One found that daily doses of an over-the-counter painkiller — acetaminophen — made research participants less sensitive to daily social slights than their peers taking dummy pills. In the second, subjects in a brain scanner played a virtual game of "catch" in which their presumed playmates progressively excluded them from the game. Compared with subjects taking the placebo pills, those taking the painkiller exhibited less brain activation in those circuits that respond to both physical and social pain, even though they still reported feelings of hurt.