The size of your amygdala might indicate how large and complex your social network is. Amygdala volume has been connected to social network and behavior in past research, as scientists have found that nonhuman primate species with larger social groups tend to have greater amygdala volumes. Kevin Bickart and his coauthors took the next logical step and examined how amygdala volume varies in humans with different social networks. Their results appear in a recent issue of Nature Neuroscience.

The researchers measured two social network factors in 58 adults. First, they calculated the size of a participant’s network, which is simply the total number of people that are in regular contact with the participant. Second, they measured the network’s complexity, based on how many different groups a participant’s contacts can be divided into. The authors then examined how well those two factors correlated with the size of a participant’s amygdala and hippocampus. The hippocampus served as a negative control, as it should not vary based on social networks.

Linear regression revealed a positive correlation in amygdala size with both social network size and complexity. This effect showed no lateralization, meaning both left and right amygdala volumes followed this relationship. In addition, the effect is relatively specific, as other social factors like life satisfaction and perceived social support failed to correlate with amygdala volume.

Social network size and complexity did not significantly correspond with the size of the hippocampus or other subcortical areas. The authors did find that three regions in the cerebral cortex of the brain (caudal inferior temporal sulcus, caudal superior frontal gyrus, and subgenual anterior cingulate cortex) might correlate with social networks. They propose that those regions might have evolved along with amygdala to deal with the complexities of growing social circles.

This is one of the first publications that demonstrates a relationship between amygdala volume and social networks in humans. It would be fascinating to determine if a cause and effect relationship can be established. Are certain people born with larger amygdala and therefore create bigger social networks, or does the amygdala grow as we gain more friends and foes?