Great minds think alike, so goes the saying. Greatness notwithstanding, a study in PNAS finds that the minds of friends do appear to share patterns of activity. “A lot of us have the intuition that our friends are kind of similar to us,” says senior author Carolyn Parkinson, a social neuroscientist at the University of California, Los Angeles. The new work suggests that there’s some neurological basis behind that suspicion.
Parkinson and colleagues focused on a rural village in South Korea. Co-corresponding author Yoosik Youm, a sociologist at Yonsei University in Seoul, had been following the villagers as part of a larger project studying the social lives and health of aging individuals. He was intrigued by Parkinson’s 2018 report that the brain activity of graduate students viewing video clips was more similar between friends than between more distantly linked peers in the same training program.
The researchers teamed up to ask whether MRI scans from the villagers of Township K, in the county of Ganghwa-gun, would correlate with social ties. Youm and colleagues had mapped the social network of 591 of the village’s 860 residents, mostly older adults, based on who was a self-reported direct tie, a friend of a friend, or more distantly linked. To define those ties, the researchers asked people with whom in their circles they discussed “important things.” Though some subjects named their spouses, biological kin were not included, says Youm.
For 64 of those individuals, the scientists also had access to brain scans from screenings for neurocognitive disorders. Participants were asked to rest quietly without closing their eyes or napping. The resulting functional MRI scans indicated which areas of the brain tended to activate at the same time. These patterns are specific to individuals, like a fingerprint (See for example recent work on mapping neural identities). “This pattern can predict aspects of people’s behavior, such as how well they pay attention and remember information,” says Monica Rosenberg, a cognitive neuroscientist at the University of Chicago. (See Core Concept: Resting-state connectivity)
At UCLA, first author Ryan Hyon asked whether machine learning, a form of artificial intelligence, could be trained to predict social ties from the brain connectivity data. Indeed, the computer often hit upon the truth. In fact, says Youm, the correlations between the prediction and actual social ties were “very, very high” in terms of statistical significance. People with more similar brain connectivity were likely to have closer social ties. The link between brains and friendships was even stronger among those who lived near each other.
“This is a groundbreaking study that focuses on the important idea that similarities across individuals might explain why some people have closer connections to one another than to others,” says Leonhard Schilbach, a psychiatrist at the LVR Clinic Düsseldorf in Germany.
Among the key questions that remain: What causes this strong correlation between neural and social networks? Rosenberg, who wasn’t involved in the study, says she’s confident in the correlation—“but I’m pretty uncertain about what’s driving it.”
It could be that people with already-similar brain patterns somehow find each other and build relationships. Or it could be that once those relationships form, people’s thought patterns, reflected in their brain connections, slowly become more alike. Youm and Parkinson think both of these possibilities are likely to be true, as does Schilbach. “I would expect that it is a combination,” he says.
Alternately, Rosenberg speculates, some other factor or factors—for example, what people are likely to think about while in the scanner, or perhaps how sleepy they get—could correlate with both social relationships and with brain connectivity, making the two appear linked. The researchers controlled for factors such as gender and personality, but a third factor is “definitely possible,” agrees Parkinson, the senior author on the work.
Another caveat is that this set of older Korean islanders, who have fairly stable relationships, cannot be said to represent humans as a whole. (Hyon notes that a UK-based study of girls aged 12 to 14 found no such correlation.) “It would be interesting to study similar patterns in a younger population, where the social networks may be subject to change more frequently,” says Tobias Kaufmann, a neuroscientist at the University of Tübingen in Germany.
That’s precisely what Youm and Parkinson hope to do. They plan to recruit a freshman class of high school students, start monitoring them before they’ve built close bonds with their classmates, and follow their brain connectivity and social networks over time as both evolve. This might let them tease out whether the connectivity patterns or the friendships happen first.
Other recent papers recommended by Journal Club panelists: