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STUDY: Social connections influence brain structure of rhesus macaques

Analyzing the data, researchers discovered that the more grooming partners macaque individuals had, the larger their mid-STS and ventral-dysgranular insula were, as is the case for social cognition in humans.

UNIVERSITY OF PENNSYLVANIA: What’s the link between social life and brain structure? Researchers from the University of Pennsylvania, the Stem Cell and Brain Research Institute at Inserm, and elsewhere are now one step closer to understanding this connection for rhesus macaques. In work published in Science Advances, the team found that for these nonhuman primates the number of social connections predicted the size of key nodes in parts of the brain responsible for social decision-making and empathy.

Specifically, the researchers determined that, for macaques with more grooming partners, the mid–superior temporal sulcus (STS) and ventral-dysgranular insula grew larger. They found no such link between brain structure and other variables like social status. “For the first time, we’re able to relate the complexity of social lives of a group of living primates with brain structure,” says Camille Testard, a fourth-year doctoral student in the Platt Labs at Penn and lead author of the paper…

The team recorded the detailed interactions of a social group of 68 adult rhesus macaques on Cayo Santiago [an island off the coast of Puerto Rico], then examined five factors: social status, number of grooming partners, physical distance with other monkeys, connectedness to popular monkeys in the network, and what the researchers called “betweenness,” or the ability to act as a bridge between disconnected parts of the social network. They also collected brain scans for every individual in the social group, including 35 juvenile and infant macaques.

Analyzing the adult data, Testard and colleagues discovered that the more grooming partners individuals had, the larger their mid-STS and ventral-dysgranular insula were. “It was very interesting to find these regions, as their importance is known for social cognition in humans,” Sallet says. “We also identified the mid-STS region in another study showing that activity in this region is modulated by the predictability of others’ behaviors.” One unexpected finding centered around the infants. According to Testard and colleagues, the work showed that young macaques weren’t born with these differences in brain structure but, rather, the differences arose with development…

“There’s something about the skills it takes to make and maintain a lot of friendships that you get from parents. You’d think it would be written into your brain when you’re born, but it seems more likely to emerge from the patterns and interactions that you have,” Platt says. “Perhaps that means that if your mother is social and you’ve got the capacity to be social, your brain can mature in the way that looks like the findings we’ve uncovered. That’s intriguing.”

This negative result is telling, Sallet says. “If we had seen the same correlation, it could mean that if you are born from a very popular mother then somehow you have a brain that predisposes you to become more popular later in life. Instead, what I think it suggests is that the modulation we observe is strongly driven by our social environments, maybe more than by our innate predisposition”. SOURCE…


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