Social Rejection Linked to Inflammation

Aug. 6, 2010— -- Social rejection isn't just bad for your ego, it may be harmful to your health.

At least that's the implication of a small study linking rejection to increases in inflammatory markers associated with disorders such as asthma, arthritis, cardiovascular disease, and depression.

The study, conducted in the lab among 124 healthy adults, found a test of social rejection triggered increases in oral levels of two inflammatory markers, Shelley Taylor, PhD, and colleagues at the University of California Los Angeles reported.

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Further testing in 31 of those participants found that one of the two inflammatory markers was associated with greater activity in brain regions linked to processing rejection-related distress, Taylor and colleagues wrote online in the Proceedings of the National Academy of Sciences.

While the study was small, the findings start to pin down the neural pathways that are involved in reactions to acute social stress and may help explain the "considerable variability" in susceptibility to disorders with an inflammatory component, the researchers argued.

Volunteers Deliberately Snubbed by Researchers

Taylor and colleagues conducted a two-part experiment -- a standard stress test involving speaking and calculating under pressure in public and a functional magnetic resonance imaging study of brain regions active when participants were socially rejected.

In the first, 124 healthy adult volunteers took the Trier Social Stress test, which involves composing and delivering an impromptu speech to a panel of nonresponsive judges. Then they were asked to perform difficult mental arithmetic -- counting backward from 2,935 by 7s and by 13s -- while being urged to go faster by an "apparently exasperated experimenter," Taylor and colleagues wrote.

Before and after the test, the researchers collected saliva from the participants and analyzed it levels of two markers of inflammatory activity.

As expected, Taylor and colleagues wrote, levels of both markers increased significantly, and the increases were positively and significantly correlated.

Volunteers Played Video Games While Having Their Brains Scanned

The volunteers were asked to complete a second experiment -- playing a computer game called Cyberball while getting their brains scanned with functional magnetic resonance imaging (fMRI). All told, 31 participants were eligible and took part.

In the game, participants had to throw a virtual ball back and forth to two other "players" but did not know that the other players were actually computer-generated. In one game, the ball was shared equally, but in the other, the volunteer got a few passes at the beginning and then was ignored for the rest of the 60-throw game.

The researchers correlated levels of the two markers, as measured after the previous stress test, with activity in regions of the brain previously linked with rejection-related stress -- the dorsal anterior cingulate cortex (dACC) and the anterior insula.

As expected, Taylor and colleagues wrote, those who had high levels of one of the markers on the stress test had significantly elevated activity in both regions of the brain during the game in which they were excluded, as compared with the game in which they were included.

"These data demonstrate that neural responses to social rejection are associated with potentiated inflammatory responses to an episode of acute social stress," the researchers argued.

Taylor and colleagues cautioned that the observed associations were correlational, so that causality can't be determined. As well, they said, more research is needed to see if neural responses to social rejection are uniquely related to differences in inflammatory responses or if they are part of a more general system that can be activated by several types of negative events.