Great Minds Think Alike: Friends' Brains Work in Similar Ways, Neuroimaging Shows

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A woman looks at a functional magnetic resonance image (fMRI) in London on March 27, 2012. MIGUEL MEDINA/AFP/Getty Images

You and your friends may literally think alike. Friends' brain activity were more similar, especially in certain regions, than activity in the brains of more distant acquaintances. Researchers behind the study could even predict which people were likely to be friends based on this brain activity.

However, plotting to get your friends to hop into a brain scanner would be a waste of time right now. "We can't disentangle cause and effect here," University of California, Los Angeles social neuroscientist Carolyn Parkinson told Newsweek about her work, published Tuesday in Nature Communications. (Parkinson did the work while a postdoctoral fellow at Dartmouth College.)

That is, it's impossible to say whether you became friends with someone because you perceived the world in similar ways to begin with or if experiences you've shared after becoming friends have shaped the way your brains function.

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Aya Attal, 17, of Crafton, Pennsylvania, hugs a friend at an Eid al-Fitr celebration, marking the end of Ramadan, on June 25, 2017 in Pittsburgh. Justin Merriman/Getty Images

A wide variety of factors can contribute to who people count as friends as well as the way people perceive the world. Age, gender, personality traits and even genetics may all play a role. But even if demographic factors are taken into account, Parkinson and her team found, brain activity is still a factor on its own.

Activity in specific brain regions—measured by a functional magnetic resonance imaging machine—seemed particularly similar between friends. Some of these regions, like the parietal lobules, the nucleus accumbens, and the amygdala, have been linked with emotion and processing facial expressions. However, Parkinson said, drawing firm conclusions about what that activity means would be a mistake. "Some of the brain regions implicated here are functionally heterogeneous—they're involved in many different things," she said.

Still, it's possible that the activity may reflect similarities in how friends respond emotionally to what they see, she said, which would fit with the videos that subjects were shown.

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A pupil reassures a friend in the courtyard of a primary school on the first day of school in Paris. MARTIN BUREAU/AFP/Getty Images

Those videos, which were clips of comedies, documentaries, debates and sports games, were all selected to provoke an emotional response. And the use of those videos, University of Maryland psychologist Elizabeth Redcay said, made the study particularly interesting because it captured "how dynamic and complex" the real world is.

Given that all the participants clearly had some things in common—after all, they all wound up at the same graduate program—Redcay said she was surprised they could find these differences in the scans. "They're probably a lot more in common than they are different."

Of the nearly 280 students surveyed as part of the research, almost everyone had friends within the program—almost. One of the figures of the paper shows all the students surveyed as dots, with lines connecting each to their friends. (Friends, in this case, were defined as people who both agreed that the other person was a friend.) However, one dot—a person—had no mutual connections to his or her classmates; no one whom that person called a friend returned the sentiment.

If that makes you sad, don't worry. First of all, the person behind that dot had some connections to other students, though none were reciprocated. And Redcay took an optimistic view about that person's larger social network. "That dot probably has a lot of other friends, other than in that graduate program," she said. "That's what I thought."