Social exclusion is a common part of life. At some point, we've all felt ostracized at work, by our partner, or even snubbed by friends. On the surface, the pain of being excluded seems pretty different from physical pain, but it turns out that these experiences share a common biological basis in the brain.
It's easy to imagine how our physical pain system could have evolved to register social pain. Primates—and particularly humans—have a long infancy, which means that maintaining social connections at an early age is critical for survival. If being separated from a caretaker is a threat to survival, feeling hurt or pained by this separation could offer an adaptive edge, keeping caretakers close at hand. Perhaps those infants that were best at using their pain system as an alarm when abandoned were the ones who thrived, resulting in a system that serves two purposes.
In 2003, UCLA neuroscientists Naomi Eisenberger and Matt Lieberman conducted an experiment. They began by asking volunteers to take part in a computer game known as Cyberball. At first glance, Cyberball appears to be an onscreen version of catch with two other players whose computer is networked to your own. Each of you has a character on screen and you can toss a virtual ball back and forth amongst you using a joystick. Even though you can't see the other people playing, you're told a little something about them—their name, age, and background. For a while, the two other players throw the ball regularly to your character, but at some point they stop and only toss the ball to each other, ignoring you completely. There's nothing you can do but sit there and watch as you are excluded.
In reality, there aren't any other players. The game is controlled by a pre-programmed computer, but of course volunteers in the experiment don't know this. In fact, when people are first introduced to Cyberball, they're given an elaborate cover story so they really believe they are playing a virtual game of catch with others.
The UCLA researchers were particularly interested in what parts of the brain come alive when people are excluded in Cyberball and, specifically, if they could find evidence for a common brain biology underlying social rejection and physical injury. So, while people played Cyberball, Eisenberger and Lieberman used fMRI to peer inside the heads of the volunteers. What they found was that a network of brain regions involved in registering physical pain—including the anterior cingulate cortex (ACC) and the insula—tracked social pain as well.
If social and physical pain share a common brain biology, then you would imagine that some of the same factors that reduce physical pain might also alleviate social pain. In their next set of studies, Eisenberger and Lieberman set out to test this idea. The scientists asked people to take a daily dose of acetaminophen (Tylenol) or a placebo pill for three weeks. Because acetaminophen is believed to reduce people's experience of pain by acting on the central nervous system, the researchers hypothesized that acetaminophen might attenuate activity in neural areas known to play a role in both physical and social pain.
People took one 500-mg pill when they woke up each morning and another 500-mg pill before they went to sleep each night. Every evening, volunteers also filled out the Hurt Feelings Scale, which asks for a report on how much social pain a person experienced that day. People responded to questions such as, "today, being teased hurt my feelings" on a scale ranging from "not at all" to "a lot."
Across the three weeks of the study, people who took the acetaminophen pills reported a progressive decrease in their hurt feelings. This wasn't the case for the placebo group. Importantly, there was no difference in each of the group's reports of hurt feelings at the beginning of the study. Only by the study's end did people taking the acetaminophen pill report less daily social pain than those who took the placebo pill.
And, when Eisenberger and Lieberman peered inside the brains of volunteers while they played Cyberball after having taken either acetaminophen or a placebo for several weeks, they found that people who took the acetaminophen showed less activity in the ACC and insula when they were rejected and reported less distress about the rejection experience. A daily dose of acetaminophen, a painkiller used to reduce physical pain, diminishes the hurt feelings that often go hand in hand with being socially rejected likely because it reduces the sensitivity of our neural circuit involved in pain.
The idea that we use the same brain systems to register social and physical pain makes economical sense. Rather than creating an entirely new brain area to register social rejection, we seem to have just jimmy-rigged our more evolutionarily ancient pain system to do the same thing. Perhaps Stanford biologist Robert Sapolsky said it best, "evolution is a tinkerer and not an inventor," duct taping the experience of social stress to whichever pre-existing brain areas provided the closest fit. As it happens, we deal with social pain the best way we know how; we take it literally.
For more on the connections between body and mind, check out my book Choke.
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Eisenberger, N. I. (2012) Broken hearts and broken bones: A neural perspective on the similarities between social and physical pain. Current Directions in Psychological Science, 21, 42-47.