The role of loneliness in the neurocognitive processing of psychosocial stress and trauma

Abstract

Loneliness is a ubiquitous problem in modern societies due to its detrimental psychological and physiological health effects. Loneliness is closely associated with psychosocial stress, a link further exacerbating mental health problems and subjective suffering. The following thesis tried to shed light on the interconnection between the physiological and psychological phenotypes of stress and loneliness and investigate their consequences for mental well-being. Thus, study 1 examined alexithymia as a predictor for psychosocial stress during social transition phases with an additional focus on how loneliness contributes to this connection. Therefore, alexithymia, loneliness, and perceived stress were monitored in first-year students and functional magnetic resonance imaging (fMRI) was conducted at the beginning and six months after their transition to university. The results demonstrated that alexithymia predicted higher psychosocial stress via enhanced loneliness levels. On a neural level, insula reactivity mediated the connection between alexithymia and loneliness. Study 2 investigated romantic relationships and current living situations as possible protective factors for loneliness and stress during the COVID-19 lockdown. To that end, momentary loneliness and cortisol levels were assessed. The study revealed that romantic relationships and living with others could protect against loneliness, whereas romantic relationships might even reduce neuroendocrine stress response showing the protective quality of social connectedness during challenging times. To elucidate the role of loneliness as a potential risk factor for psychopathology, study 3 applied an experimental trauma paradigm to elicit intrusive thoughts in a sample of lonely and non-lonely subjects. Prior to trauma exposure, an fMRI scan was conducted to examine loneliness-related changes in neural fear processing. Results showed an interaction of sex and loneliness, with high lonely men exhibiting more intrusive thoughts and an amygdala hyperreactivity to fear signals implying increased vulnerability after trauma exposure. Moreover, a literature review (study 4) was conducted as part of this thesis to outline structural and functional neural changes related to loneliness. To summarize, the presented results confirm that loneliness acts directly on the neuroendocrine and neural stress systems, potentially enhancing the malicious effects of stress on psychopathology. Hence, new studies should focus on deepening the understanding of the neural pathways of loneliness to tailor new neuroscientifically informed therapies targeting perceived social isolation.