Rumination on the feeling of loneliness explains the loneliness-depression relationship

Abstract

Previous literature has suggested a significant association between loneliness and depression. Importantly, research has shown that rumination can mediate the tightly connected loneliness-depression relationship. Chapter 1 of the present thesis provided an overview of the upcoming chapters in the rest of the thesis. In Chapter 2, a comprehensive literature review was conducted on the definitions, epidemiology, health impacts, theoretical frameworks, and brain mechanisms underlying loneliness and rumination. Chapter 3 contains a meta-analysis and systematic review of the neural correlates underlying loneliness and rumination (or perseverative cognition) across healthy and depressed populations and looks for the joint brain regions underpinning both processes The results suggested that the medial frontal gyrus is the pivotal overlapping region that both loneliness and rumination primarily work on. Importantly, there is a shift from a combination of anterior and posterior regions recruited by healthy individuals to a more medial frontal orientation in depressed individuals. The medial prefrontal cortex is essential in self-referential processes and were suggested as an important pathway in the psychopathology of depression. This implies the potential mechanism that loneliness and rumination work jointly to contribute to the development of depression through excessive self-referential processes that hyperactivate the medial frontal gyrus. Chapter 4 went further to evaluate the hypothesis that rumination mediates the loneliness-depression relationship at an item level utilizing a network analysis approach. In a large community adult sample (N = 900), we constructed the Loneliness-Depression and Loneliness-Rumination-Depression network using a cross-sectional design. The results suggested that loneliness has no robust association with depressive symptoms. Instead, a connection between a specific ruminative thought (“think about how alone you are”) and a specific loneliness item (“how often do you feel alone”) is essential in maintaining the Loneliness-Rumination-Depression network (partial r = .307). The findings indicated that ruminating on the feeling of loneliness was the key underlying factor that modulated the loneliness-depression relationship. Interventions for depression should focus on ameliorating ruminative thoughts, especially on loneliness feelings. Chapter 5 discussed the main findings, the implications of the thesis to the current theoretical framework and clinical practice, and the potential limitations and future directions. Finally, the thesis closed with Chapter 6 summarizing the major findings and significance of the thesis.