In a recent study, brain MRI scans showed that the more varied social network an individual has, the bigger his/her amygdala will be. The study was carried out by researchers from Massachusetts General Hospital (MGH) in the US. The findings appear in the 26 December advance online issue of Nature Neuroscience.
The amygdala consists of 2 symmetrically placed small almond shaped structures located deep into the temporal lobe. It is connected to various brain structures and amygdala is involved in a wide range of behavioral functions. "We considered a single primate species, humans, and found that the amygdala volume positively correlated with the size and complexity of social networks in adult humans. They found the link was just as strong when they adjusted for age (older people have on average smaller amygdala volumes than younger people) and when they analyzed left and right amygdalas separately, indicating no lateralization of the effect" said Dr. Lisa Feldman Barrett, the study co-leader, from MGH's Psychiatric Neuroimaging Research Program and a Distinguished Professor of Psychology at Northeastern University.
Dr. Bradford C Dickerson, of MGH's Department of Neurology and the Martinos Center for Biomedical Research, also a co-leader of the study, said "This link between amygdala size and social network size and complexity was observed for both older and younger individuals and for both men and women." The study involved 36 men and 22 women, age between 19 and 83. They were asked to complete a survey discussing their social lives, the size and variation of their social networks. The participants answered questions designed according to two scales of the Social Network Index. Using the collected data, researchers measured the total number of regular contacts each participant indicated in addition to the number of different groups each of them contributed to. Two criteria were identified for each participant; the overall social network size and the network complexity.
Brain MRI scans were performed on the involved population in order to review several structures in the brain along with the volume of the amygdala. Researchers reported that there was a strong link between amygdala volume, social network size and complexity. The link was mainly involving the amygdale and not any other sub-cortical brain structure. The researchers wrote "An exploratory analysis of subcortical structures did not find strong evidence for similar relationships with any other structure, but there were associations between social network variables and cortical thickness in three cortical areas, two of them with amygdala connectivity,"
They also added that there was no link between the volume of the amygdala and other social variables such as life support or social satisfaction. Researchers concluded that their study and its findings "indicate that the amygdala is important in social behavior"Dr. Barrett reported that the results of the study were confirming the previous findings of other studies that discussed the link between the volume of brain structures and the size and complexity of social groups in other primate species. She said "We know that primates who live in larger social groups have a larger amygdala, even when controlling for overall brain size and body size," However, she added that her study was the first to indicate a "between amygdala volume and social network characteristics within a single species"