Approved Research

Structural properties of the human brain associated with social isolation and loneliness

Lay summary

Social isolation and loneliness are risk factors for various diseases, including depression, cognitive decline, obesity, cancer and heart disease (Holt-Lunstad et al., 2010). Recently, countries where the number of older people is increasing such as the UK and Japan started big projects to prevent social isolation and loneliness. For these projects, developing preventative measures against social isolation and loneliness and the elucidation of recovery mechanisms are urgent issues, for which a psychological and neuroscientific understanding of social isolation and loneliness is essential. It has been reported that brain regions associated with loneliness include the dorsolateral prefrontal cortex, insular cortex, ventral striatum, posterior superior temporal gyrus, hippocampus and amygdala (Lam JA et al., 2021), and that grey matter volume in default mode network-related brain regions is associated with loneliness (Spreng RN et al., 2020). However, there are many aspects that require further detailed investigation, including the need to consider various confounding factors and covariate adjustment, such as health, mental health, stress and environmental characteristics, and the lack of sufficient studies distinguishing between social isolation and loneliness. In addition, some results are inconsistent across reports, and confirming reproducibility is also an important issue. In this study, we use the following sources: 1) Tohoku Medical Megabank (https://www.megabank.tohoku.ac.jp/), 2) Human Connectome Project (https://www.humanconnectome.org/), 3) UK Biobank (https:/!www.ukbiobank.ac.uk/). The main purpose of the present study is 1) to elucidate the brain mechanisms behind social isolation and loneliness in Japanese people and 2) to investigate cross-cultural effects related to social isolation and loneliness from neuroscience perspectives. Specifically, the data will be divided into three groups: 1) participants who are socially isolated but do not feel lonely, 2) participants who are socially isolated and feel lonely, and 3) participants who are neither isolated nor lonely, and the brain grey matter volume changes that characterise each group will be clarified. The next step is to determine whether social isolation and loneliness can mediate the association between grey matter volume and depression. As this study analyses data from three datasets, 1) findings that are common regardless of cultural background and 2) findings that are specific will also be examined. In addition, relevant covariate adjustments will be made at the time of analysis. The current project provides critical evidence for understanding, preventing, and policy making concerning the social isolation and loneliness.