Scientists say they can predict who you're friends with based on brain patterns alone

  • Psychologists who scanned the brains of graduate students said they accurately predicted who people were friends with based on how their brains lit up while watching a video.
  • Did the students pick out friends with similar brains, or could they be shaping the way their friends see the world? The study authors say it could be a little of both.

Maybe your friends really do “just get you” after all.

At least, that’s what a new study of graduate students at an Ivy League school suggests.

For that study, published Tuesday in the journal Nature Communications, a group of brain researchers and social psychologists at Dartmouth College looked at the brains of 42 students, and monitored their reactions as they watched some retro video clips.

The students watched America’s Funniest Home Videos, saw an astronaut at the International Space Station, peeked in on a wedding ceremony, and glanced at footage of the discontinued CNN show “Crossfire.”

MRI scans showed that friends watching the same clips reacted in strikingly similar ways: some of the same brain areas lit up, notably those associated with motivation, learning, affective processing, and memory.

The researchers said the similarities in brain reaction patterns were so striking, they could actually use them to predict who the participants’ friends were. (The scientists based their assessment of students’ friendships on the results of an online survey taken by the participants, as well as the other 279 students in their graduate program, about who their friends were.)

Conversely, people who weren’t friends had different reactions to the same clips. The activity patterns were less similar in friends of friends, and even more divergent in people who were in separate social groups.

“Our results suggest that friends process the world around them in exceptionally similar ways,” lead author Carolyn Parkinson said in a release.

The authors think that’s because spending time with people who think like us feels pretty good. In their paper, they wrote that having close friends whose brains respond like ours “may be rewarding because it reinforces one’s own values, opinions, and interests.”

Dartmouth business professor Adam Kleinbaum, who co-authored the study, told Business Insider that it’s not clear whether people are seeking out friends whose brains are already like theirs, or if friends change the ways each other’s brains react to stimuli.

“We think both are happening,” he said.

An important caveat to note about this study, however, is that it only looked at how the brains of graduate students at one university react. The ways people choose and interact with friends at school are not necessarily representative of how everyone picks their pals.

College and graduate students are often the subjects in psychological studies, since there are so many students near research labs. But social scientists have argued for years that college students aren’t necessarily like the rest of us. In 1986, psychologist David Sears wrote in the Journal of Personality and Social Psychology that using college students as research subjects might skew the ways we perceive human nature.

“Compared with older adults, college students are likely to have less-crystallised attitudes, less-formulated senses of self, stronger cognitive skills, stronger tendencies to comply with authority, and more unstable peer group relationships,” Sears wrote.

A 2010 paper in the journal Behavioural and Brain Sciences argued that college students are “WEIRD” research subjects: they’re generally Western, Educated, Industrialized, Rich, and Democratic.

Still, there’s a growing body of research that suggests the way we pick out friends has a lot to do with the shape of our brain and our body.

A 2014 study of 1,932 adults (of all ages) showed that people tend to pick out friends with similar genotypes to their own. The researchers found that the genetic similarities of friend “pairs” were, on average, as close as those of fourth cousins.

A new study by Korean researchers, which was released this month, also notes differences in the brains of people who have more friends. When lots of people reported being friends with a given individual, that person was found to have a bigger neocortex, an area sometimes referred to as the “social brain” since it’s believed to play a role in social interaction. Those study participants weren’t college students at all: they were Koreans over the age of 60.

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