Number of Friendships Linked to Brain Size
By TRACI PEDERSEN Associate News Editor
Reviewed by John M. Grohol, Psy.D. on March 26, 2012
If you have a lot of friends, then you most likely have a bigger orbital prefrontal cortex — a brain region found just above the eyes — according to a new study, part of the British Academy Centenary “Lucy to Language” project.
The research shows that in order to maintain several friendships (not acquaintances), it is necessary to use what social scientists refer to as “mentalizing” or “mind-reading” — the capacity to understand what another person is thinking. This skill is crucial in handling a complex social world, including the ability to hold a conversation.
This study is the first to suggest that proficiency in these skills is linked to the size of key regions of the brain, particularly the frontal lobe.
“Perhaps the most important finding of our study is that we have been able to show that the relationship between brain size and social network size is mediated by mentalizing skills.
“What this tells us is that the size of your brain determines your social skills, and it is these that allow you have many friends,” said psychologist Dr. Joanne Powell from the University of Liverpool.
For the study, researchers used an MRI to scan the brains of 40 volunteers in order to measure the size of the prefrontal cortex, the region used in high-level thinking. Participants were then asked to list everyone they had had social (as opposed to professional) contact with over the previous seven days. They also took a test to determine their competency in mentalizing.
‘We found that individuals who had more friends did better on mentalizing tasks and had more neural volume in the orbital frontal cortex, the part of the forebrain immediately above the eyes,” said Robin Dunbar, Ph.D., of the University of Oxford and the Institute of Cognitive and Evolutionary Anthropology.
“Understanding this link between an individual’s brain size and the number of friends they have helps us understand the mechanisms that have led to humans developing bigger brains than other primate species. The frontal lobes of the brain, in particular, have enlarged dramatically in humans over the last half-million years.”
“All the volunteers in this sample were postgraduate students of broadly similar ages with potentially similar opportunities for social activities. Of course, the amount of spare time for socializing, geography, personality and gender all influence friendship size, but we also know that at least some of these factors, notably gender, also correlate with mentalizing skills.
“Our study finds there is a link between the ability to read how other people think and social network size,” added Dunbar.
The study is published in the journal Proceedings of the Royal Society B.
Source: University of Oxford