Amygdala Size and Social Complexity
The Amygdala and Social Behavior
It has been shown earlier that, in the great apes, there is a connection between a brain structure know as the amygdala and the complexity of the social group and behavior. Primates living in larger and more complex social groups tend to have a larger amygdala, even after a statistical correction for both brain and body size.
The amygdala consist out of two almond shaped groups of nuclei, deep in the medial temporal lobes of the brain, and is found in complex vertebrates, including humans. So far, its primary role appears to be the processing and remembering of emotional reactions (specifically anger and fear).
Figure 1: Location of the amygdala in the brain.
New research shows that, in humans too, the size of this brain structure seems to be connected to the intricacies of the social life.
American researchers had 58 test subjects between the ages of 19 and 83 answer questions about their social contacts and the social groups in which they felt they belonged. Subsequent brain scans revealed that the volume of the amygdala of the test subjects was correlated with the size and complexity of their social network.
This correlation could be found in both young and old people, and men and women. The volume of this particular brains structure did not, however, correlate with other social variables, such as social contentment.
The Social Brain Hypothesis
These results provide some support for the so-called social brain hypothesis, which states that the amygdala might have evolved in human beings to support a more complex social life, with more social contacts and a more intricate social network.
The next step the researchers are planning to take in their investigation, is testing how abnormalities in this little brain structure might influence a normal social life and how these anomalies might possibly create neurological and psychiatric conditions. There are already some indications for this in social phobias.
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- Bickart, K.C.; Wright, C.I.; Dautoff, R.J.; Dickerson, B.C. & Barrett, L.F. (2011). Amygdala volume and social network size in humans. Nature neuroscience. 14, pp. 163 – 164.
- Irle, E.; Ruhleder, M.; Lange, C.; Seidler-Brander, U.; Salzer, S.; Dechent, P.; Weniger, G.; Leibing, E. & Leichsenring, F. (2010). Reduced amygdalar and hippocampal size in adults with generalized social phobia. Journal of Psychiatry & Neuroscience. 35(2), pp. 126 – 131.
- Todd, R.M. & Anderson, A.K. (2009). Six degrees of separation: the amygdala regulates social behavior and perception. Nature neuroscience. 12, pp. 1217 – 1218.