Large, Rich Social Network Linked To Bigger Amygdala Deep In The Brain

The richer and more diverse social network of people, the more their amygdala, the structure deep in the brain, which was related to the size and complexity of social groups in other primate species, said researchers from Massachusetts General Hospital (MGH) in the U.S..

You can read about their study in the Dec. 26 advance online issue of Nature Neuroscience.

Tonsils includes a pair of symmetrically placed small almond-shaped structure deep within the temporal lobe. It has many links with other regions of the brain and is believed to be involved in different behavioral functions.

Study co-leader Dr. Lisa Feldman Barrett, of the MGH Psychiatric Neuroimaging Research Program and a professor emeritus of psychology at Northeastern University told the press that:

"We looked at one species of primates, humans, and found that the amygdala volume is positively correlated with the size and complexity of social networks among adults."

They found the relationship was as strong when they are adjusted for age (older people, on average, smaller amygdala volumes than younger people), and when they analyzed the left and right amygdala separately, indicating a lack of laterality effect. "

Co-author Dr. Bradford C Dickerson, Department of Neurology at MGH and the Martinos Center for Biomedical Research, said:

"This relationship between the size of the amygdala and social network size and complexity was observed for both older and younger men and for men and women."

Dickerson is also an adjunct professor of neurology at Harvard Medical School.

For the study, Barrett, Dickerson and colleagues invited 36 men and 22 women aged between 19 and 83 years and the average age of 52.6 years, to fill in a survey about their social lives, and give information on the size and complexity of their social networks Answering questions based on the two scales of social networks Index.

From the responses, researchers were able to measure the total number of regular contacts maintained by each participant plus a number of different groups of contacts belonged. The first measure of the total social network size, and the second is a measure of the complexity of the network.

Then the researchers took magnetic resonance imaging (MRI) brain scans of participants to study the structure of different regions, and the volume of the amygdala.

They found that the relationship between amygdala volume and social network size and complexity was just as strong when adjusted for total brain volume, and seems to be characteristic of the amygdala, but not other subcortical structures.

"Research analysis of subcortical structures have not found convincing evidence for a similar relationship with any other structure, but there was no connection between social network variables and cortical thickness in three regions of the cortex, two of them connect with the amygdala," they write.

They also found that the volume of the amygdala was not associated with other social variables in human life, such as life support or social satisfaction.

They concluded that their findings "suggest that the amygdala plays an important role in social behavior."

Barrett said that their findings were similar to the results of other studies that compared the size and complexity of social groups and in other primate species:

"We know that primates who live in large social groups have a larger amygdala, even when controlling for overall brain size and body size," she said.

But she and her colleagues wrote that to their knowledge, this study is the first to show the relationship between the volume of the amygdala and social network characteristics within a species. " They also wrote that their findings are consistent with the "social brain hypothesis", who wishes that human tonsils were developed partly to deal with increasing complexity of social life.

Barrett said that further research to explore other aspects of human social behavior that may be associated with the amygdala and other brain regions.

They also hope to figure out how to "violations in these brain regions may lead to violations of social behavior in neurological and psychiatric disorders," she added.

"Amygdala volume and size of social network for people." Kevin C Bickart, Christopher I Wright, Rebecca J Dautoff, Bradford Dickerson C & Lisa Feldman Barrett. Nature Neuroscience, Published online: December 26, 2010. DOI: 10.1038/nn.2724

Additional Massachusetts General Hospital press release.

Author: Catherine Paddock, PhD