My Brain is My Best Friend: How many friends has your brain got?

28 May

David Di Salvo of “The Daily Brain” published two posts this past week on the neuroscience of forming and maintaining social relationships. So what role does your brain play in how many friends you have?

Your Facebook page might say 300+, but apparently the optimal number of relationships your brain can maintain is half that number.  So who makes your brain’s list?

Professor Robin Dunbar famously known for identifying 150 as the optimal number (the “Dunbar Number”) of social relationships your brain can manage, has recently focused his investigations on the brain areas that may be linked to maintaining friendships.

Dunbar’s recent paper noted that the size of the orbital prefrontal cortex (associated with higher-level thinking) is correlated with the number of friendships one can manage.  This research suggests that the social complexities of friendships may require certain higher-level cognitive skills of the frontal lobe.  According to Professor Dunbar, Mentalizing is one important cognitive process by which we hierarchically follow others’ mental states, with managing 5 mental states as the natural upper limit for most adults.

“We found that individuals who had more friends did better on mentalizing tasks and had more neural volume in the orbital frontal cortex. Understanding this link… helps us understand the mechanisms that have led to humans developing bigger brains than other primate species.”Professor Dunbar, Science Daily.

Further research at the Vanderbilt University suggests that the difference between socialites and social-mights may lie in two main areas underlying memory formation and how we respond to new stimuli – the hippocampus and the amygdala. Functional MRI was used to examine the brain in those with uninhibited temperaments and inhibited temperaments, while images of unfamiliar faces were presented multiple times. Adults with uninhibited temperaments exhibited habituation to the images, while inhibited temperament individuals failed to habituate to the stimuli regardless of the number of times the stimuli were repeated. In other words, responses to the new stimuli in the hippocampus and amygdala did not decrease over time in inhibited individuals, as was the case with the uninhibited individuals.

“This failure to habituate provides a novel neural mechanism for understanding the shy and cautious behavior that is characteristic of inhibited individuals, [who] may find encounters with new people overwhelming and thus avoid new social experiences…”Jennifer Urbano Blackford, lead author of the study.


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