Monkey brain size is influenced by social interactions, a new study revealed, finding more friends in a group leads to larger social regions in the brain.
A team of researchers from the University of Pennsylvania in Philadelphia studied the brains and social interactions of a group of rhesus monkeys that lived on Cayo Santiago, an island off the coast of Puerto Rico.
They found that the number of social connections predicted the size of key nodes in parts of the brain responsible for social decision-making and empathy.
While all of these findings relate specifically to free-ranging rhesus monkeys, the team says they have potential implications for human behavior, particularly for understanding neurodevelopmental disorders such as autism.
Monkey brain size is influenced by social interactions, new study revealed, finding more friends in a group leads to larger social regions in the brain
Researchers found that, for macaques with more grooming partners, the mid-superior temporal sulcus (STS) and ventral-dysgranular insula increased in size.
They found no such association between brain structure and other variables such as social status within the group — it simply depended on the number of partners.
“For the first time, we can relate the complexity of the social life of a group of living primates to brain structure,” said Camille Testard, lead author of the paper.
Previous research into human social networks has suggested this relationship, according to Michael Platt, co-author of the study and head of the lab conducting the tests.
‘For example, the literature links variation in the size of the amygdala to the number of Facebook friends you have. But it’s difficult to get detailed data on human social interactions because we can’t track people all day,” he says.
However, with the rhesus monkeys that live on Cayo Santiago, an island off the coast of Puerto Rico, it’s a different story.
A team of researchers from the University of Pennsylvania in Philadelphia studied the brains and social interactions of a group of rhesus monkeys that lived on Cayo Santiago, an island off the coast of Puerto Rico. Stock image
Platt and colleagues have been studying this group of free-range nonhuman primates for more than a decade, with an emphasis on grooming partners.
RHESUS MACAC MONKEYS (MACACA MULATTA) OFTEN USED IN RESEARCH
The rhesus (Macaca mulatta) monkey stands between 19-21 in length with a 8.1-9.0 in long tail.
It is an old-fashioned monkey with between six and nine recognized subspecies.
The primate is native to South, Central and Southeast Asia and has the widest range of all non-human primates.
It can be found at various elevations in Asia and lives in grasslands as well as arid and forested areas.
They have also been found near human settlements, with wild colonies in the US – probably from human release.
The macaque is mostly herbivorous – eating fruits, but will also consume seeds, roots, buds, bark and grains.
Like other macaques, the rhesus monkey is a herd animal with flocks of 20-200 individuals.
A woman’s rank is determined by that of her mother, and rhesus monkeys live in a female-led society.
This is an important factor, as it represents direct and important relationships for the macaques, Platt explained. They also looked at the animals’ wider social networks, which represent individuals with whom they interact indirectly.
After Hurricane Maria hit the island, for example, the researchers examined whether the macaques grew or shrinked their social networks despite limited resources.
Testard, who joined the lab in 2018, led the analysis for that study, which found that the animals became more social and accepting of each other, forming new relationships in addition to the ones they already had.
Building on that and on previous work by collaborator Jérôme Sallet of Inserm, Testard also designed the current study.
The team recorded the detailed interactions of a social group of 68 adult rhesus monkeys on Cayo Santiago and then examined five factors of their lives.
These included social status, number of grooming partners, physical distance from other monkeys, affiliation with popular monkeys in the network and what the researchers termed “in-between,” or the ability to act as a bridge between disconnected parts of the social network.
They also collected brain scans for each individual in the social group, including 35 juvenile and young macaques.
Analyzing the adult data, Testard and colleagues found that the more caregivers a person had, the larger their mid-STS and ventral dysgranular insula.
“It was very interesting to find these regions, because their importance for social cognition in humans is known,” Sallet said.
“We also identified the mid-STS region in another study showing that activity in this region is modulated by the predictability of the behavior of others.”
They found that the number of social connections predicted the size of key nodes in parts of the brain responsible for social decision-making and empathy. Stock image
An unexpected finding focused on the babies, according to Testard and colleagues, who said the work showed that young macaques were not born with these differences in brain structure, but rather the differences arose with development.
“There’s something about the skills needed to make and maintain a lot of friendships that you get from parents,” explains Platt.
Monkeys around: Howler monkeys use PLAY to avoid conflict and reduce group tension, study shows
By Shivali Best
Howler monkeys live up to their name and love to “monkey” around — especially if it’s during a tense situation, a new study has revealed.
Researchers at Anglia Ruskin University have revealed that adult monkeys play more when faced with scarce resources, as a way to break the tension within the group.
“Despite its appearance and our own perception of what play means, play is not always associated with frivolity or nurture,” explains Dr Jacob Dunn, co-author of the study.
“Instead, we think it fulfills an important function in howler monkey society by decreasing tension when there is competition for scarce resources.”
“You’d think it’s written into your brain at birth, but it seems more likely to come from the patterns and interactions you have.
“Maybe that means if your mom is sociable and you have the ability to be sociable, your brain can mature in a way similar to the findings we discovered.” That’s intriguing.’
This negative result is telling, Sallet said, adding that “if we had seen the same correlation, it could mean that if you were born to a very popular mother, you somehow have a brain that predisposes you to to become more popular.’
“Instead, I think it suggests that the modulation we observe is strongly driven by our social environment, perhaps more than by our innate predisposition.”
While all of these findings relate specifically to free-running rhesus monkeys, they have potential implications for human behavior.
Platt said this would be especially helpful in gaining a better understanding of non-neurotypic individuals, including those with autism, although such connections are still in the offing and require significantly more research.
For now, the team is moving forward with additional research on Cayo Santiago’s macaque population, looking at facets such as whether a natural disaster like Hurricane Maria affects the animals’ brain structure and how social connectedness affects long-term survival.
They will also dive deeper into their most recent findings, because “this is not a laboratory phenomenon. This is real life, the real world,” Platt said.
‘This work provides a foundation for understanding how these animals navigate. It’s really exciting and gratifying that this work in the field is synergistic work that we’ve been doing in the lab for a long time.”
The findings are published in the journal Science Advances.
THE SIGNS AND SYMPTOMS OF AUTISM
According to the Centers for Disease Control and Prevention, people with autism have problems with social, emotional, and communication skills that usually develop before age three and persist throughout a person’s life.
Specific signs of autism include:
- Reactions to smell, taste, appearance, feel, or sound are unusual
- Difficulty adapting to changes in routine
- Unable to repeat or repeat what is said to them
- Difficulty expressing desires using words or movements
- Unable to talk about their own feelings or those of others
- Difficulty with acts of affection such as hugging
- Prefer to be alone and avoid eye contact
- Difficulty getting along with other people
- Unable to point or look at objects when others are pointing at them