Population variability in social brain morphology for social support, household size and friendship satisfaction

Abstract

The social brain hypothesis proposes that the complexity of human brains has coevolved with increasing complexity of social interactions in primate societies. The present study explored the possible relationships between brain morphology and the richness of more intimate 'inner' and wider 'outer' social circles by integrating Bayesian hierarchical modeling with a large cohort sample from the UK Biobank resource (n = 10 000). In this way, we examined population volume effects in 36 regions of the 'social brain', ranging from lower sensory to higher associative cortices. We observed strong volume effects in the visual sensory network for the group of individuals with satisfying friendships. Further, the limbic network displayed several brain regions with substantial volume variations in individuals with a lack of social support. Our population neuroscience approach thus showed that distinct networks of the social brain show different patterns of volume variations linked to the examined social indices.

Keywords: Bayesian hierarchical modeling; big data; population neuroscience; social behavior.

Fig. 1

Social brain atlas. Thirty-six brain regions were previously automatically separated into (i) visual sensory network (red), (ii) limbic network (green), (iii) intermediate-level network (yellow) and (iv) highly associative network (blue). For details on the topographical definition, see Alcala-Lopez et al. (2018).

Fig. 2

Population volume effects in the visual sensory network of the social brain. Boxplots depict four different subgroups in the context of (A) social support, (B) number of people living in the same household and (C) friendship satisfaction. (A) Men with less social support showed divergent volume effects in the right middle temporal V5 area (MT/V5_R) and left fusiform gyrus (FG_L) compared to men with more social support. (B) Women living with others showed divergent volume effects in the right fusiform gyrus (FG_R) and left middle temporal V5 area (MT/V5_L). (C) Large volume effects were observed in the right and left posterior superior temporal sulcus (pSTS_R, pSTS_L) and left middle temporal V5 area (MT/V5_L) in men and in the right posterior superior temporal sulcus (pSTS_R), right fusiform gyrus (FG_R) and left middle temporal V5 area (MT/V5_L) in women with satisfying friendships. These analyses were conducted in the whole social brain, of which we show obtained marginal posterior distributions for the visual sensory network.

Fig. 3

Population volume effects in the limbic network of the social brain. Boxplots depict four different subgroups in the context of (A) social support, (B) number of people living in the same household and (C) friendship satisfaction. (A) Large volume effects were observed in the amygdala (AM), ventromedial prefrontal cortex (vmPFC) and rostral anterior cingulate cortex (rACC) in women and in the right nucleus accumbens (NAC_R) in men with less social support. (B) Volume effects were incongruent in the right amygdala (AM_R) in women and in the ventromedial prefrontal cortex (vmPFC) in men living with others. (C) Volume effects were uncovered in the left amygdala (AM_L) and ventromedial prefrontal cortex (vmPFC) in women and in the right nucleus accumbens (NAC_R) in men who are not happy with their friendships. These analyses were conducted in the whole social brain, of which we show obtained marginal posterior distributions for the limbic network.

Fig. 4

Population volume effects in the intermediate-level network of the social brain. Boxplots depict four different subgroups in the context of (A) social support, (B) number of people living in the same household and (C) friendship satisfaction. (A) Volume effects were incongruent in the anterior midcingulate cortex (aMCC), left anterior insula (AI_L), left supramarginal gyrus (SMG_L), right supplementary motor area (SMA_R), right inferior frontal gyrus (IFG_R) and left cerebellum (Cereb_L) in women with more social support and in the anterior midcingulate cortex (aMCC), right anterior insula (AI_R) and left inferior frontal gyrus (IFG_L) in men with less social support. (B) Men living with others displayed volume effects in the right supramarginal gyrus (SMG_R) and left supplementary motor area (SMA_L) compared to men living alone. (C) Men who are not happy with their friendships showed large volume effects in the anterior midcingulate cortex (aMCC) and inferior frontal gyrus (IFG). These analyses were conducted in the whole social brain, of which we show obtained marginal posterior distributions for the intermediate network.

Fig. 5

Population volume effects in the higher associative network of the social brain. Boxplots depict four different subgroups in the context of (A) social support, (B) number of people living in the same household and (C) friendship satisfaction. (A) Volume effects were revealed in the frontal pole (FP), right middle temporal gyrus (MTG_R), right and left temporal pole (TP_R, TP_L) and posterior mid-cingulate cortex (pMCC) in men with more social support and in the frontal pole (FP) and posterior mid-cingulate cortex (pMCC) in women with less social support. (B) Household size analysis showed a volume effect in the frontal pole (FP) for women living with others. (C) The volume effects were incongruent in the dorsomedial prefrontal cortex (dmPFC), right temporoparietal junction (TPJ_R) and posterior mid-cingulate cortex (pMCC) in women with happy friendships and in posterior mid-cingulate cortex (pMCC) for men with unhappy and in frontal pole (FP) for men with happy friendships. These analyses were conducted in the whole social brain, of which we show obtained marginal posterior distributions for the higher associative network.