In our brains there is a structure called the amygdala. It is within our medial temporal lobe, shaped something like an almond, and has been widely studied due to the important role it plays in human emotion.
But according to at least two recent studies, the amygdala may also play a role in what has been called the "social brain."
The "social brain" hypothesis comes from the idea that our relatively large brains may have evolved to help guide and shape our social behavior. For an excellent overview of this hypothesis and some of the research that supports it, see my Caltech colleague Ralph Adolph's essay, The Social Brain. Recently, researchers (like Adolphs and others) have been trying to determine which brain structures might be involved in guiding our social behavior.
The first of these recent studies appeared in Current Biology, coauthored by Justin S. Feinstein, Ralph Adolphs, Antonio Damasio, and Daniel Tranel. In this study, "The Human Amygdala and the Induction and Experience of Fear," the authors discuss an unusual human subject they call "SM." SM is unusual because she has focal bilateral amygdala lesions, and as the authors of the study point out, SM's behavior "repeatedly demonstrated an absence of overt fear manifestations and an overall impoverished experience of fear." Otherwise, SM appears to have most other typical emotional reactions. SM's behavior leads the authors of this study to conclude that the amygdala plays an important role in the fear response. And as fear is an important aspect of our social interactions, this study implies that the amygdala plays a role in shaping our social behavior.
The second study appeared in Nature Neuroscience. This paper, "Amygdala volume and social network size in humans," by Kevin C. Bickart Christopher I. Wright, Rebecca J. Dautoff, Bradford C. Dickerson, and Lisa Feldman Barrett, found that amygdala volume correlates with reported social network size and complexity. The larger the volume of the subject's amygdala, the larger and more complex was the subject's reported social network. This study, like Feinstein et al., also reinforces the hypothesis that the amygdala plays an important role in guiding our social interactions.
It has long been known that the amygdala plays a role in guiding our emotions. But these studies suggest that the amygdala might play a broader role, in that it appears to be involved in shaping our social lives -- how we react to, and interact with, other people. This provides support for hypothesis that the amygdala appears to play an important role in the "social brain." I'm sure that we will see additional studies like these in the near future examining how the amygdala -- and other brain structures -- influence other forms of social behavior, especially our economic and political interactions.
NOTE: Amygdala image from the National Institute of Mental Health, National Institutes of Health, Department of Health and Human Services.