December 26th, 2010
01:01 PM ET
All the people you interact with on a daily basis may be influencing a structure in your brain - or maybe your brain is influencing how many people you socialize with, new research suggests.
It all comes back to the amygdala, the almond-shaped structure found in the temporal lobe of both hemispheres of the brain. It is connected to almost every other brain region, and participates in many different kinds of social and psychological phenomena including the "flight or fight" response. The amygdala plays a part in fear, emotion, vision, memory, and social interaction, among other things.
A new study in the journal Nature Neuroscience finds that the amygdala appears to be larger in people who have larger and more complex social networks.
Researchers asked 58 participants, who ranged in age from 19 to 83, about the number of people they interact with regularly per week and what roles those people play in their lives. They had "complex" social networks if their close contacts had multiple roles in their lives - for instance, if friends were also co-workers, for example.
Study authors then looked at the volume of the amygdala, controlling for the size of the overall brain, in each participant. The relative size of the amygdala was not associated with perceived social support, satisfaction with social interactions, or how much participants enjoy interacting with people in general. It did, however, correlate well with the size and complexity of individuals' social networks.
The association between amygdala size and social network size and complexity appeared fairly consistent among men and women, and among old and young participants.
Because the study does not show causation, it is impossible to know whether the amygdala actually grows in size because of social interaction, or if people with larger amygdalae gravitate toward larger groups of friends, or both. This study cannot make conclusions about that topic, but it is the subject of ongoing research.
Lead study author Lisa Barrett, professor of psychology at Northeastern University and associate neuroscientist at Massachusetts General Hospital, does not believe that people born with larger amygdalas are destined to have broader social networks.
"You're never destined for anything. Your brain gives you the potential for things, it doesn’t dictate that those things will materialize," Barrett said.
Still, looking across different species of animals, those who live in larger social groups also have larger amygdalas, even when you control for body and brain size, she said.
"It does seem like the amygdala to some extent evolved in size under the pressure for more complex social interactions," she said.
But keep in mind that the brain is plastic, and it's possible that the amygdala does increase in size in response to social activity.
There may be a link between how big your amygdala is and how many friends you have on a social networking website like Facebook, but there has not been a complete study on this topic, Barrett said.
Having a large social network is not necessarily advantageous all the time, Barrett said. In some cases, interacting with more people could also create more opportunities for stress, she said.
About this blog
Get a behind-the-scenes look at the latest stories from CNN Chief Medical Correspondent, Dr. Sanjay Gupta, Senior Medical Correspondent Elizabeth Cohen and the CNN Medical Unit producers. They'll share news and views on health and medical trends - info that will help you take better care of yourself and the people you love.