House of Mind

Amygdala volume correlates with the size and complexity of social networks in humans

Evolutionarily, one of the most important social challenges is to be able to distinguish between friend and foe, which can aid in survival. The social brain hypothesis, which suggests that living in larger and complex social groups selected for larger brain regions capable of performing relevant computations. One of these brain regions is the amygdala, a critical structure for learning, memory and emotion that has been implicated in mood disorders, social behavior, and interpersonal relationships (i.e. mother-infant interactions). Because of its central functional role and anatomical position, the authors proposed that amygdala volume should be associated with size of social network (size is typically considered an indicator of processing capacity. Moreover, neuroimaging studies done in nonhuman primates have supported this association between an enlarged amygdala and larger social groups.Thus, there is a notion that a larger amygdala volume enables increased processing of social demands that form part of life in a social group or hierarchy.

In a 2011 study, Bickart et al. examined whether amygdala volume varies as a function of individual variation in the size and complexity of social groups within humans. The group examined the social networks, the number of people that the individual maintains or “regular contacts” (also an indication of overall network size), in approximately 58 healthy adults (healthy= absence of DSM-IV diagnoses). The group also employed another social scale to measure the number of different groups that the contacts belonged to, reflecting network complexity. Furthermore, the performed quantitative morphometric analyses of MRI data. According to Bickart, linear regression analyses revealed that subjects with larger and more complex social networks had larger amygdala volume (even when controlling for variables such as age) with no lateralization of effect. The group found no significant differences in other non-social brain structures like the hippocampus and other subcortical structures. 

Sources:

Bickart, et al. (2011). Amygdala volume and social network size in humans. Nature Neuroscience. 14:163-164. doi:10.1038/nn.2724

Image: http://www.nature.com.ezproxy.med.nyu.edu/neuro/journal/v14/n2/fig_tab/nn.2724_F1.html