|Humans are a social species|
Now a report in the latest issue of Nature Neuroscience provides new support for this hypothesis. Using MRI brain imaging and a metric called the Social Network Index, Kevin Bickart and colleagues report that the volume of the amygdala is strongly correlated with both the size and complexity of an individual's social network.
|The size of the amygdala is greater in people |
with larger and more complex social networks
(image from scienceblogs.com/neurotopia)
When interpreting such results, it's important to remember that correlation does not equal causation. The social brain hypothesis would suggest that increased amygdala size facilitates greater social functioning. However, it's possible these are co-occurring but unrelated phenomena. Alternatively, causation could work in the opposite direction: maybe being more social increases the size of the amygdala, much like a muscle grows with increased use.
|How do we define a social network?|
|In the brain, is bigger really better?|
Despite these caveats, the present results are intriguing and provide further support for the social brain hypothesis and the idea that the amygdala plays a central role in social functioning. The study's authors are quick to point out that their results don't really provide answers but rather should be viewed as preliminary findings that "provok[e] an interesting question." The real answers await future studies that will continue to elucidate the complex entangled ways in which our brains and social capacities evolved.
Original article: Bickart KC, Wright CI, Dautoff RJ, Dickerson BC, Barrett LF (2011). Amygdala volume and social network size in humans. Nature Neuroscience 14(2): 163-164.