Editor’s Note: We are pleased to bring you this arti­cle by Sian Beilock, thanks to our col­lab­o­ra­tion with the Greater Good Mag­a­zine. (Pic by Leigh Wells)

Ever won­der why some peo­ple have more friends than oth­ers? Why some run in large and com­plex social cir­cles while oth­ers have a small group of acquain­tances? There are no doubt a vari­ety of fac­tors that influ­ence the extent of our social net­works. New research shows, how­ever, that one fac­tor we may not have con­sid­ered before is right inside our head.

In a paper pub­lished recently in Nature Neu­ro­science, researchers showed that the num­ber of friends we have could be pre­dicted by the size of our amygdala—a small, almond-shaped region located deep inside our brains.

As I have blogged about before, the amyg­dala is a major player in our emo­tional reac­tions. Because of this, it makes sense that the amyg­dala would be at the cen­ter of a brain net­work impor­tant for social­iz­ing. This net­work helps us rec­og­nize whether some­body is a stranger or an acquain­tance, a friend or a foe—all impor­tant fac­tors in main­tain­ing social relations.

To get at the rela­tion between amyg­dala size and social net­works, researchers began by mea­sur­ing the size and com­plex­ity of about 60 adults’ social net­works. In terms of size, the researchers were inter­ested in the total num­ber of peo­ple with whom a per­son was in reg­u­lar con­tact. In terms of com­plex­ity, the researchers looked at the num­ber of dif­fer­ent groups these friends could be divided into (e.g., book club, child­hood friends, run­ning group, etc.). The size and com­plex­ity of each person’s social net­work was then com­pared to the size of their amyg­dala. Sure enough, the big­ger the amyg­dala, the larger and more com­plex a person’s social net­work tended to be.

Impor­tantly, amyg­dala vol­ume was not linked to a person’s life sat­is­fac­tion or the amount of social sup­port they felt in gen­eral, sug­gest­ing that it’s not that the big­ger the amyg­dala, the hap­pier a per­son is. Rather, amyg­dala size was specif­i­cally related to the makeup of one’s social network.

Researchers have known for some time that non-human pri­mates who live and oper­ate in larger social groups tend to have greater amyg­dala vol­ume rel­a­tive to those pri­mates that don’t, even after con­trol­ling for over­all body and brain size. This new research shows that, even within the same species, the big­ger the amyg­dala, the larger and more com­plex one’s social net­works tend to be.

This find­ing is excit­ing because it opens a win­dow into explor­ing how abnor­mal­i­ties in the amyg­dala may impair social func­tion­ing or con­tribute to cer­tain psy­chi­atric dis­or­ders. In short, it sets the stage to fur­ther our under­stand­ing of how par­tic­u­lar brain net­works guide our social interactions.

Of course, one big unan­swered ques­tion cen­ters around the direc­tion of this amygdala-social net­work rela­tion. Are some peo­ple born with a big­ger amyg­dala that helps them to forge more com­plex social net­works, or does amyg­dala size increase as we gain more friends? The jury is still out on this one, but given our knowl­edge of evo­lu­tion­ary influ­ences on the brain and the ever increas­ing evi­dence that expe­ri­ence can change the brain—even later in life—it’s prob­a­bly some of both.

— Sian Beilock is an asso­ciate pro­fes­sor of psy­chol­ogy at the Uni­ver­sity of Chicago and the author of Choke: What the Secrets of the Brain Reveal About Get­ting It Right When You Have To. This arti­cle orig­i­nally appeared on her Psy­chol­ogy Today blog. More on her work can be found at sianbeilock.com

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