Consensus. The brain fires in particular regions when an individual's rating of a face's beauty differs from the group's.

Adapted from V. Klucharev et al., Neuron 61 (15 January 2009)

The Brain's Pied Piper

From fashion trends to political movements, nothing is more human than following the crowd. Although history documents our lemminglike tendencies, neuroscience has been slower to explain them. Now, researchers have pinpointed a brain circuit that makes us want to act like our peers.

Psychologist Solomon Asch of Swarthmore College in Pennsylvania highlighted the power of conformity in a landmark 1951 study. He showed that adults will change their opinions on objective facts--whether one line drawn on a piece of paper is longer than another, for example--to mesh with the group's opinion, even if the group is obviously wrong. Since then, researchers have suggested that conformity helps people gain social acceptance and feel confident that their opinions or perceptions are correct. Other experiments have shown that bucking consensus, in contrast, can cause anxiety and confusion.

The findings suggested a role for the brain's reinforcement learning system, says Vasily Klucharev, a social neuroscientist at Radboud University in Nijmegen, the Netherlands. Previous studies have shown that the rostral cingulate zone and the nucleus accumbens, areas of the brain believed to be part of that learning system, activate when people make wrong predictions in a betting game and prompt a change in strategy. Klucharev and his colleagues wanted to determine whether the same areas are triggered when an individual's choice doesn't conform to the group's.

The researchers asked 21 young women to rate the attractiveness of 222 female faces while lying in an fMRI scanner. To avoid any confounding effects of race or sexual desire, all the test subjects and faces were white, and all the subjects were heterosexual. The volunteers saw each face for about 2 seconds and assigned it a score from 1 (least attractive) to 8 (most attractive). They were then told how another group of women had rated the face. These "group ratings" were actually generated by a computer that gave each face a different rating than the test subjects about two-thirds of the time. As the researchers suspected, the rostral cingulate zone and nucleus accumbens fired up when the group ratings did not match the subject's score. Moreover, brain areas associated with reward were less active when a subject’s predictions deviated from the group's score, the researchers report online today in Neuron.

To see if this perceived error might actually change behavior, the researchers asked the women to rate the same 222 faces again after leaving the fMRI scanner. On average, the test subjects scored the faces 0.2 points higher when the group rating had been more positive and about 0.4 lower when the group rating had been more negative.

The findings explain why going along with the group feels good, says Robert Cialdini, a social psychologist at Arizona State University in Tempe. But Gregory Berns, a neuroeconomist at Emory University in Atlanta, Georgia, cautions that the study examined decision-making only in a situation where the "correct" answer was subjective. He says that to get a complete sense of the brain's role in social conformity, he'd also like to see a study looking at how individuals respond to group consensus in making objective decisions.