Social connections influence brain structure of rhesus macaques
Date:
April 13, 2022
Source:
University of Pennsylvania
Summary:
Scientists have found that social connections influence the
brain structure of rhesus macaques. Specifically, the number of
grooming partners an individual had predicted the size of brain
areas associated with social decision-making and empathy.
FULL STORY ========================================================================== 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.
Previous research on human social networks has hinted at this
relationship, says Michael Platt, the James S. Riepe Penn Integrates
Knowledge University Professor. "The literature, for example, ties
variation in the size of the amygdala to the number of Facebook friends
that you have. But it's hard to get granular data on human social
interactions because we can't follow people around all day long," he says.
With the rhesus macaques living on Cayo Santiago, an island off the coast
of Puerto Rico, however, it's a different story. Platt and colleagues
have studied this group of free-ranging nonhuman primates for more
than a decade. Part of that research has focused on grooming partners,
which represent direct and important relationships for the macaques,
as well as looking at the animals' broader social networks, representing individuals they interact with indirectly.
After Hurricane Maria hit the island, for example, the researchers
examined whether the macaques grew or shrunk their social networks in
the face of more limited resources. Testard, who joined the lab in 2018,
led the analysis for that study, which found that the animals became more social and more accepting of one another, forming new relationships in
addition to those they already had.
========================================================================== Building on that and on previous work from collaborator Je'ro^me Sallet of Inserm, Testard also designed the current study. Here, the team recorded
the detailed interactions of a social group of 68 adult rhesus macaques
on Cayo Santiago, 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."
Though all these findings relate specifically to free-ranging rhesus
macaques, they have possible implications for human behavior, in
particular to understanding neurodevelopmental disorders like autism,
according to Platt.
Such connections, however, are still in the distance. For now, the team is moving ahead with additional research studying Cayo Santiago's population
of macaques, looking at facets like whether a natural disaster such
as Hurricane Maria affects the animals' brain structure and how social connectedness influences long-term survival. They'll continue to dive
deeper into their most recent findings, too.
"This is not some lab phenomenon. This is real life, the real world,"
Platt says. "This work provides a baseline for understanding how these
animals navigate. It's really thrilling and gratifying that this work
done in the field is synergizing work we've been doing in the lab for a
long time." Funding for this research came from the National Institutes
of Health (grants R01MH118203, U01MH121260, R01MH096875, R01AG060931,
and R00AG051764), the National Science Foundation (Grant 1800558),
the Royal Society (Grant RGS/R1/ 191182), the National Center for
Research Resources and the Office of Research Infrastructure Programs
(Grant P40OD012217-25), the Blavatnik Family foundation, an IDEXLYON
"IMPULSION 2020" grant (IDEX/ IMP/2020/14), and the Wellcome Centre for Integrative Neuroimaging (grants 203139/Z/16/Z and WT101092MA).
========================================================================== Story Source: Materials provided by University_of_Pennsylvania. Original written by Michele W. Berger. Note: Content may be edited for style
and length.
========================================================================== Journal Reference:
1. Camille Testard, Lauren J. N. Brent, Jesper Andersson, Kenneth
L. Chiou,
Josue E. Negron-Del Valle, Alex R. DeCasien, Arianna Acevedo-Ithier,
Michala K. Stock, Susan C. Anto'n, Olga Gonzalez, Christopher
S. Walker, Sean Foxley, Nicole R. Compo, Samuel Bauman, Angelina
V. Ruiz-Lambides, Melween I. Martinez, J. H. Pate Skene,
Julie E. Horvath, Cayo Biobank Research Unit, James P. Higham,
Karla L. Miller, Noah Snyder-Mackler, Michael J. Montague,
Michael L. Platt, Je'ro^me Sallet. Social connections predict
brain structure in a multidimensional free-ranging primate
society. Science Advances, 2022; 8 (15) DOI: 10.1126/ sciadv.abl5794 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/04/220413141613.htm
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