A new study by a North­eastern Uni­ver­sity researcher and her col­leagues indi­cates that the size of a cer­tain part of the human brain plays a sig­nif­i­cant role in deter­mining the breadth of social relationships.

Sci­en­tists found that the amyg­dala, a small struc­ture in the tem­poral lobe of the brain, appears to be impor­tant to a rich and varied social life among adult humans. Their finding, pub­lished in the journal Nature Neu­ro­science, pro­vides insight into how abnor­mal­i­ties in regions of the brain may affect social behavior in neu­ro­logic and psy­chi­atric disorders.

The inter­dis­ci­pli­nary study, led by Dis­tin­guished Pro­fessor of Psy­chology Lisa Feldman Bar­rett, advances Northeastern’s research mis­sion to solve soci­etal issues with a focus on global chal­lenges in health, secu­rity, and sustainability.

We know that pri­mates who live in larger social groups have a larger amyg­dala, even when con­trol­ling for overall brain size and body size,” said Bar­rett. “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.”

The researchers asked 58 par­tic­i­pants to com­plete stan­dard ques­tion­naires that reported on the size and the intri­ca­cies of their social net­works. They mea­sured the number of reg­ular con­tacts each par­tic­i­pant main­tained, as well the number of social groups to which these con­tacts belonged.

Par­tic­i­pants also had a mag­netic res­o­nance imaging brain scan to gather infor­ma­tion about var­ious brain struc­tures, including the volume of the amyg­dala. The authors found that indi­vid­uals with larger amyg­dala reported larger and more com­plex social net­works. This link was observed for both older and younger indi­vid­uals, and for both men and women.

Bar­rett noted that the study find­ings are con­sis­tent with the “social brain hypoth­esis,” which sug­gests that the human amyg­dala might have evolved par­tially to deal with an increas­ingly com­plex social life.

Exploratory analysis of other struc­tures deep within the brain indi­cates that the amyg­dala is the only area with com­pelling evi­dence of affecting social life in humans.

Bar­rett, who is also a research neu­ro­sci­en­tist at the Mass­a­chu­setts Gen­eral Hos­pital (MGH) Psy­chi­atric Neu­roimaging Research Pro­gram and the Mar­tinos Center for Bio­med­ical Research, col­lab­o­rated with Brad Dick­erson of the MGH Depart­ment of Neu­rology and other col­leagues. The researchers are con­tin­uing to inves­ti­gate the cor­re­la­tion between regions of the brain and human social behavior.