Date Published: 2 February 2012

Orbital prefrontal cortex size linked to number of friends

Researchers ask if the size of part of the brain could determine how good people are at maintaining friendships.

Recent research at Liverpool University suggests there is a link between the number of friends people have and the size of the region of the brain called the orbital prefrontal cortex which is located just above the eyes. Studies have shown that this region of the brain is larger in people who have a larger number of friendships. The study also suggests that people need to employ a set of cognitive skills to maintain a number of friends. These skills are described by social scientists as 'mentalising' or 'mind-reading' and involve the capacity to understand what another person is thinking. The recent study suggests that competency in these skills is determined by the size of key regions of our brains and in particular, the frontal lobe.

The researchers took anatomical magnetic resonance images (MRI) of the brains of 40 volunteers at Liverpool University's Magnetic Resonance and Image Analysis Research Centre to measure the size of the prefrontal cortex, the part of the brain used in high-level thinking. Participants were asked to make a list of 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 mentalising.

Dr Joanne Powell, from Liverpool University's Institute of Psychology, Health and Society, said:

" 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 mentalising skills. What this tells us is that the size of your brain determines your social skills, and it is these that allow you to have many friends."

Professor Robin Dunbar, from Oxford University's Institute of Cognitive and Evolutionary Anthropology, said:

" Mentalising is where one individual is able to follow a natural hierarchy involving other individuals' mind states. For example, in the play 'Othello', Shakespeare manages to keep track of five separate mental states: he intended that his audience believes that Iago wants Othello to suppose that Desdemona loves Cassio. Being able to maintain five separate individuals' mental states is the natural upper limit for most adults.

_ We found that individuals who had more friends did better on mentalising tasks and had more neural volume in the orbital frontal cortex, the part of the forebrain immediately above the eyes. 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."

The study is published in the journal, Proceedings of the Royal Society B.

More about this Research:
The study was carried out as part of the British Academy Centenary 'Lucy to Language' project, led by Professor Robin Dunbar from Oxford University in collaboration with Dr Joanne Powell and Dr Marta Garcia-Finana at Liverpool University, Dr Penny Lewis at Manchester University and Professor Neil Roberts at Edinburgh University.
The Lucy to Language Project aims to explore how the early hominid brain evolved from its essentially ape-like beginnings among the earliest australopithecines (around 3.5 million years ago) to the modern human potential of the Upper Palaeolithic Revolution (around 50,000 years ago) and its final expression in the dramatic social and economic changes of the last 10,000 years, i.e. throughout human evolution. It is funded by a seven-year programme grant awarded by the British Academy.

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