Abstract
The increasing ubiquity of web-based social networking services is a striking feature of modern human society. The degree to which individuals participate in these networks varies substantially for reasons that are unclear. Here, we show a biological basis for such variability by demonstrating that quantitative variation in the number of friends an individual declares on a web-based social networking service reliably predicted grey matter density in the right superior temporal sulcus, left middle temporal gyrus and entorhinal cortex. Such regions have been previously implicated in social perception and associative memory, respectively. We further show that variability in the size of such online friendship networks was significantly correlated with the size of more intimate real-world social groups. However, the brain regions we identified were specifically associated with online social network size, whereas the grey matter density of the amygdala was correlated both with online and real-world social network sizes. Taken together, our findings demonstrate that the size of an individual's online social network is closely linked to focal brain structure implicated in social cognition.
Highlights
Web-based social network services such as Facebook or MySpace consist primarily of a representation of each user and their social links [1]
We examined the relationship between real-world social network size and the grey matter density at the loci identified by our voxelbased morphometry (VBM) analysis in a subset of 65 participants who completed the social network size questionnaire and magnetic resonance imaging (MRI) scan
We computed partial correlation between real-world social network size and grey matter density while regressing out the factor of FBN. This showed significant correlation at right amygdala (T62 1⁄4 2.410, R 1⁄4 0.293, p, 0.05), but nowhere else. These results together suggest that the three cortical loci, i.e. left middle temporal gyrus (MTG), right superior temporal sulcus (STS) and right entorhinal cortex, are associated with online social network size, whereas the right amygdala is associated with real-world social network size, while these two variables exhibited some degree of correlation
Summary
Web-based social network services such as Facebook or MySpace consist primarily of a representation of each user and their social links [1]. In all the three cortical loci of interest showing whole-brain-corrected relationships with online social network size (i.e. from experiment 1 left MTG, right STS and right entorhinal cortex), we observed significant (T38 1⁄4 2.52, R 1⁄4 0.379, p , 0.05; T38 1⁄4 2.97, R 1⁄4 0.435, p , 0.01; T38 1⁄4 3.41, R 1⁄4 0.484, p , 0.01, respectively) correlation between the FBN and local grey matter density in those areas (figure 2). We examined the relationship between real-world social network size and the grey matter density at the loci identified by our VBM analysis (see experiment 1) in a subset of 65 participants who completed the social network size questionnaire (experiment 1) and MRI scan (either experiment 1 or experiment 2). These results together suggest that the three cortical loci, i.e. left MTG, right STS and right entorhinal cortex, are associated with online social network size, whereas the right amygdala is associated with real-world social network size, while these two variables exhibited some degree of correlation (figure 3)
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