NRSC 4132 Blog

The age old question of size has finally been answered and it turns out it does matter. If you want to be popular then being big is best, but not in the way you think. New England researchers reported in the prestigious journal Nature Neuroscience (December 26, 2010) that human amygdala size correlates with the extent and complexity of one's social life.

Using a technique from Harvard called FreeSurfer which reconstructs brain images from structural MRI scans and has the capability to overlay fMRI data, the researchers measured the sizes of multiple brain structures and cortical thicknesses of 58 adult men and women. Then they questioned the participants about their social lives, looking to find out how many regular contacts they had and also looking at how complex their social lives were, using the number of distinct social networks within the whole social life as a measure. Participants had anywhere from 4 to 50 contacts and 1 to 7 distinct networks.

They found that the amygdalas of the participants varied in size considerably with the largest being over twice the volume of the smallest. The regression coefficients they found were pretty solid at 0.38 for the relation between the number of contacts and amygdala size and 0.44 for the relation between number of networks and amygdala size. They also measured a bunch of other brain structures to check for correlations but didn't find any except for some slight matches between cortical thickness in three areas that would be expected to contribute to social competency, the anterior cingulate gyrus, for instance.

How exactly that relationship comes about is a topic for discussion. The amygdala is usually thought of as the fear center of the brain so seeing that it's correlated with a larger social network is a somewhat surprising result. Does a larger amygdala make it easier to suppress fear and so people feel less anxiety in social situations, leading to a more active social life, or is the largeness of the amygdala an indicator that a person is generally more fearful and so cleaves to their social life in an effort to buffer themselves from the fearsome natural world? The researchers believe that the larger amygdala helps people distinguish between welcoming and threatening social situations, thus leading to greater social competency and greater social capacity.

It's also possible that the amygdala has more than one distinct function. Maybe it's not just the subcortical structure that makes people feel fear but can also process social data. It would be terribly interesting to find a way to turn the activity of the amygdala down and then measure people on their ability to understand social cues or their accuracy when trying to determine whether certain social situations are dangerous or not. The connection is really very exciting and opens up a whole new area of research opportunities.

Most important of all is what it could mean for everyday life. Understanding the mechanisms that link the amygdala size to social success could highlight a set of social skills that would help people enhance their social lives. Maybe people who aren't as socially successful could improve their social lives just by paying closer attention to whether social situations present a risk, for instance.

This is exciting news that helps make steps toward simplifying the great mystery of social living, this one as simple as knowing where the danger lies as a key to success.