ALL your friends praise a film you just watched. Instead of admitting how dull you found it, you agree. We all sometimes mute our own beliefs like this, but it seems there is more to this than a little white lie. Conforming to others’ views can cause a real shift in your own opinion.

That’s the conclusion of Jamil Zaki at Harvard University and colleagues, who asked men to rate how attractive they found a series of photos of women’s faces. The men were then given the average rating for each photo, said to be determined by a previous group. In reality, these ratings were randomly generated by a computer. Thirty minutes later, the participants reassessed the same photos while having their brains scanned using fMRI.

As expected, the men’s ratings changed to match the consensus scores more closely. However, Zaki’s team found that if the participant decided a woman was more attractive than they first thought, there was a spike of activity in the orbitofrontal cortex and nucleus accumbens; if they decided she was not as pretty, activity decreased in these areas.

Previous research has shown that the higher the activity in these brain regions, the more a person values a certain stimulus. In other words, the researchers argue, the participants were not just modifying their appraisals for the sake of appearances: the so-called average results had genuinely changed their opinion of the photos. The work will appear in Psychological Science.

“We know that we adopt the beliefs and perceptions of people around us, but one of the big issues is whether conformity represents a true shift in opinion or just a kind of a white lie,” says Zaki. “The brain regions [we studied] specifically track how you regard something and they recapitulated the shift in opinion,” he says.