Our brain structure may be related to our social networks-the bigger our amygdala, the bigger and more complex our networks seem to be.
In an article inNature, a team of researchers from Boston University and Harvard University report on their study of 58 adults whose social networks were described and whose amygdala volume was measured by MRI data and other technological means. They found the individuals with the largest amygdalas were regularly in contact with the largest numbers of people, and that their networks were the most complex, meaning that the members of their network could be divided into many distinct groups.
The amygdala is perhaps most popularly known as the seat of human anxiety and fear. Scientists have spent years studying a woman whose amygdala was destroyed in childhood by a congenital disorder. A DiscoveryNews storydescribes the woman’s documented neutrality toward snakes, spiders and physical peril, and tells how her inability to be frightened has led her into danger.
But the amygdala has many complex functions. It is closely connected to nearly every structure in the brain, and is essential in determining friend or foe and providing information for a variety of social decisions. Much remains to be learned-some scientists have associated an enlarged amygdala with bipolar disorder, and a smaller or malfunctioning amygdala with autism and schizophrenia. The size of the left and right sides of the amygdala has also been associated with extroversion and introversion.
The Harvard and Boston University researchers did not find any correlation between social networks and the size of the hippocampus or other subcortical brain region. However, their research suggested an association with social connectivity and three regions in the cerebral cortex of the brain, two of which are connected to the amygdala. Interestingly, theNaturestory reports no association between amygdala volume and social satisfaction or happiness.
We may not have as much control over our networks as we’d like to imagine. Nicholas Christakis and James Fowler, in the book Connected, write that our genes influence not only the size and structure of our networks, but our positions in them. Studying more than 90,000 adolescents from 142 schools, they found that genetic factors accounted for 47 percent of how popular the kids were-and how big their networks were. That’s not surprising, because appearance and social status influence popularity. But they also found that people in the center of networks had different genetic makeup than people on the peripheries, and that people whose network connections knew each other differed genetically from people whose connections were strangers or members of diverse groups.
Scientists think a larger amygdala has evolved over eons as civilization has placed increasing demands on our ability to process complex social information. Yun Xie, of Wired, wonders whether people create bigger social networks because they born are with bigger amydalas or whether the amygdala grows as people discover more friends and foes.