People with lots of Facebook friends have denser grey matter in three regions of the brain, a study suggests
When I heard about this, my heart sank. The Facebook area of the brain? It had all the hallmarks of a piece of media neuro-nonsense: a hook (Facebook!), a simplistic neo-phrenological story (bigger brains are better!)… so I was expecting to discover that the fuss was all about some tiny, statistically questionable study, which wasn’t really about what the newspapers said it was, as is so often the case.
So I was very surprised to find that it’s actually an extremely good paper.
Kanai et al from London took 125 young Facebookers (mostly students) and correlated their friend count with grey matter density across the brain. They found some correlations:
The numbers seem solid. It was a large study. They used whole-brain correction for multiple comparisons (a=0.05 FWE corrected), controlling for age, gender and overall brain grey matter.
Most importantly, they included a replication sample, something that very few neuroscience papers do. After having done the first 125 people, they got another 40, and looked in the areas where they’d previously found results. They found the same correlation in all three cases – in fact, it was even stronger.
They even made sure to only display the scatterplots from the replication sample, thus avoiding the dreaded voodoo correlations problem that so often plagues such graphs. Note that the correlations are actually with the square root of the number of friends.
As if this wasn’t enough, they confirmed a previously reported correlation between amygdala size and social network size, in both of their samples. And to cap it all, they show that Facebook friends are correlated (albeit not hugely) with other measures of number of friends.
So, as unlikely as it sounds, this Facebook finding is stronger than a good 90% of similar papers.
What does it mean that the size of the amygdala, left MTG, right STS and right entorhinal cortex are correlated with your Friend count? Good question. The authors discuss the result in terms of the known functions of these areas, e.g. the entorhinal cortex is involved in learning to associate pairs of stimuli, such as matching names to faces, which might be related to keeping track of your friends… but frankly this is just a post-hoc story.
You could tell an equally convincing tale about almost any part of the brain, if you found a correlation there. And as the authors point out, they didn’t find correlations with other “social” areas you might expect like the mirror neuron system.
But that doesn’t change the fact that the results of the study seem rock solid. So what’s going on? It could be that having lots of friends makes your brain bigger. Or it could be the reverse, that having a certain kind of brain wins you friends, or at least Facebook ones. Or it could be that there’s some third factor underlying the correlation, although who knows what that is.
Kanai, R., Bahrami, B., Roylance, R., & Rees, G. (2011). Online social network size is reflected in human brain structure Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2011.1959