Does the size of your social network predict how big certain parts of your brain are?
Camille was the lead author on this study. She is a 5th year graduate student at the University of Pennsylvania with Dr. Michael Platt. She wants to understand the evolution and neurobiological mechanisms of social relationships in primates using approaches from behavioral ecology of primates in the wild to single cell electrophysiology in the lab!
or technically,
Social Connections predict brain structure in a multidimensional free-ranging primate society
[See original abstract on PubMed]
Authors of the study: 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. Antón, 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, Jérôme Sallet
When I think of neuroscience, I think of scientists in white lab coats examining brains under a microscope. While it’s true that neuroscience these days typically takes place in a laboratory environment, some would argue that this isn’t the best way to study the brain. If we want to study how the brain works naturally, why would we study it in an artificial environment, such as a lab?
While of course there are some topics that are better suited to be studied in labs like how individual neurons in the brain function and work together, topics like social behavior, which is what Camille and her colleagues were interested in, may benefit from more naturalistic experimental conditions. In particular, Camille and her colleagues wanted to know how the size of an individual’s social network can affect their brain structure and function. To do this they studied the behavior and brains of rhesus macaque monkeys living in a semi-free range colony on Cayo Santiago Island in Puerto Rico.
In their paper, the researchers examined the behavior of a single social group composed of 103 individual monkeys of which 39 were male and 64 were female. For each monkey in the colony, the researchers looked at two measures of social behavior. The first measure was the monkey’s social network, which was based on the number of grooming interactions a given monkey had with other monkeys. The more grooming partners a monkey had, the larger its network was. The second measure they looked at was the monkey’s social status, which was based on aggressive interactions given and received that a given monkey encountered with others (threats, chases, submissions, etc.).
Camille and her team observed each monkey’s behavior for 3 months prior to measuring their brain structure using a technique known as MRI, or magnetic resonance imaging. With this technique, they were able to determine the size of different brain areas in each monkey. Then, they wanted to see if there was a relationship between a given monkey’s social behavior and any part of the monkey’s brain.
Interestingly, the researchers found that there was a positive correlation between the social network size (i.e, number of grooming partners) of a monkey and the size of two specific brain regions (see Figure 1). The first brain region is called the mid superior temporal sulcus (mid-STS, for short). In previous studies, the mid-STS has been found to be involved in responding to social scenes. This region is also thought to be involved in deciding whether to cooperate versus compete with a partner. The second brain region is called the ventral dysgranular insula (vd-insula, for short). In previous studies, this region has been found to be involved in grooming behavior in macaques and empathy in humans!
Because social interactions between monkeys are multi-faceted, just as in humans, Camille also looked at several other nuances of the monkeys’ social network to see if they predicted the size of these brain regions. For example, they looked at “betweenness” (was a given monkey able to bridge connections between distant members of the colony?) and “closeness” (how close was a given monkey to every other monkey in the colony?). These other measures did not correlate with any brain region in these monkeys. Because of this, the researchers took a closer look at social network size, which did show a correlation with brain size. Since this measure was determined by grooming interactions, they were curious if the direction of the grooming mattered: whether the monkey actively groomed other individuals or was being groomed. When they looked at the data this way, they found that how many individuals in the colony that groomed a given monkey more closely predicted its brain size.
Finally, the researchers wondered if the relationship that they found between social network size and brain size in adult monkeys was also true for infant monkeys. These monkeys are too young to form complex social networks so the researchers instead used the social network of the mothers of these infants. They reasoned that they might still see a relationship because previous studies showed that an infant macaque’s social network mimick the social network of his/her mother. However they found no clear relationship between a mother’s social network and her infant’s brain size. The authors suggested that the infants were perhaps too young for their brains to have fully developed and any size differences to be observable. These results led the researchers to believe that the brain-size differences that they see in adult macaques are due to the increased sociability that occurs during development.
In summary, Camille’s research offers incredible insight into how the size of specific brain regions is related to the ability of mammals to form large social networks in their natural environment. Her team determined the social network size of each monkey in the colony and found a significant correlation with two socialization-related brain regions, the mid-STS and the vd-Insula. Furthermore, this relationship could not be found in infant monkeys, leading them to believe that increased sociability during development leads to the observed differences in brain structure seen in adult monkeys. Camille’s work is important because her discoveries in wild, free-ranging monkeys emphasize that complex social forces, for instance in human societies, can powerfully drive the physical expansion of socially related areas in the brain.
About the brief writer: Jafar Bhatti
Jafar is a PhD Candidate in Maria Geffen’s lab. I’m broadly interested in brain networks involved in auditory processing and decision-making.