The Default Network in the Human Brain Is Associated with Loneliness

Post by Amanda McFarlan

What's the science?

Humans have evolved to rely on socialization and, therefore, so has the human brain. What happens to the brain when an individual’s social expectations are not met? Since socialization is such a quintessential part of being human, it is thought that loneliness may result in distinct changes in the brain. Research has shown that loneliness is associated with reduced activity in reward areas of the brain as well as a greater vigilance and detection of negative social information. Still, the study of loneliness in higher-order brain regions that make up the “social brain” is lacking. This week in Nature Communications, Spreng and colleagues used a multimodal approach to investigate whether loneliness is associated with structural and functional changes in the brain.

How did they do it?

The authors used data collected for the UK Biobank initiative to investigate whether differences in brain structure and connectivity between brain regions exist between individuals who self-reported as being lonely and those that did not. In the first set of analyses, the authors used the Bayesian hierarchical approach to examine whether loneliness is associated with variations in gray matter volume, for both regional (localized) brain structure and large-scale brain networks. Next, they investigated how resting-state functional connectivity (which identifies brain regions with correlated activity, termed functional networks) relates to loneliness. Finally, the authors explored whether loneliness was associated with the integrity of white matter tracts in the brain. The authors also examined whether biological sex was associated with loneliness for all three neuroimaging approaches.

What did they find?

The authors found that gray matter volume for brain structures including the posterior superior temporal sulcus, the left temporoparietal junction, the left fusiform gyrus, the right inferior temporal gyrus, right posterior parietal lobe, and the right dorsal anterior cingulate cortex were positively associated with loneliness (high volume associated with high loneliness). Conversely, volume in several regions such as the left dorsal anterior cingulate cortex, the dorsolateral prefrontal cortex, the right central operculum, the right inferior parietal lobule, the left retrosplenial cortex, and the inferior visual cortex was negatively associated with loneliness. At the network level, the authors showed that loneliness was most strongly related to variations in gray matter volume in the default network (a network of brain regions that are typically more active when a person is not paying attention to the external world, i.e. daydreaming).

Next, the authors determined that individuals who self-reported as being lonely had greater resting-state functional connectivity between brain regions in the same network. This link between connectivity pattern and loneliness was expressed more strongly in men compared to women. Finally, the authors found that the structural integrity of white matter tracts originating from the hippocampus was greater in lonely individuals. This anatomical relationship between white matter tracts and loneliness was more prominent in men compared to women.

What’s the impact?

This study shows that loneliness is associated with distinct changes in gray matter volume, white matter tract integrity, and functional connectivity within brain regions. Notably, the authors identified the default network as the network most strongly associated with the neural expression of loneliness. Altogether, the link between loneliness and the default network may reflect increased mental simulation of inner social events in the absence of real-world social interaction.

Spreng et al. The default network of the brain is associated with perceived social isolation. Nature Communications (2020). Access the original scientific publication here.