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Abstract

The experience of loneliness, the painful feeling that the quantity or especially the quality of interpersonal relationships does not meet one's own needs, is markedly increased in patients diagnosed with borderline personality disorder. The development of loneliness is multifactorial, involving biological, intra-, and interpersonal as well as environmental factors such as adverse childhood experiences. Since chronic loneliness is not only one of the more stable symptoms of borderline personality disorder but is also associated with a variety of negative physical and psychological symptoms, the aim of this thesis was to contribute to the understanding of vulnerability factors for loneliness in patients with borderline personality disorder. The interplay of potential vulnerability factors for loneliness was investigated on the three domains of the bio-psycho-social model in four studies. Study 1 investigated the polygenic score for loneliness in patients with borderline personality disorder as a biological vulnerability factor and its influence on the association of adverse childhood experiences with loneliness. Study 2 examined alterations in the evaluation of an interaction partner’s benevolence following the induction of social rejection and acceptance with and without a provided external explanation as a potential psychological vulnerability factor for loneliness in patients with borderline personality disorder. Study 3 investigated the interplay of different types of adverse childhood experiences, borderline personality features together with dimensions of attachment and perceived social support as psychological vulnerability factors for loneliness. Study 4 examined the influence of social network size and contact frequency as social vulnerability factors and alterations in the appraisal of social touch in patients diagnosed with borderline personality disorder as a psychological vulnerability factor for loneliness during the COVID-19 pandemic. Regarding biological vulnerability, a shared genetic contribution to borderline personality disorder and loneliness as well as a higher polygenic score for loneliness in the investigated groups of patients with borderline personality disorder were found. Nevertheless, the genetic vulnerability for loneliness did not significantly moderate the association between adverse childhood experiences and loneliness in the group of patients with borderline personality disorder. Regarding psychological vulnerability factors, alterations in outcomes of complex social cognitive evaluation processes were identified in patients with borderline personality disorder. More specifically, lower benevolence appraisals of a social partner in the borderline personality disorder group that were less positively influenced by acceptance and external explanations than in the healthy control group were found. Furthermore, the data indicated that insecure attachment and lower perceived social support as two potential vulnerability factors for loneliness partly explain the association of the severity of adverse childhood experiences and borderline personality features. In addition, insecure attachment was associated with a less positive appraisal of social touch in patients with borderline personality disorder, which in turn was associated with more loneliness during the COVID-19 pandemic. With regard to social vulnerability factors, a higher severity of adverse childhood experiences and smaller social networks were associated with higher loneliness. Overall, the findings indicate that the elevated levels of loneliness in patients with borderline personality disorder are influenced by alterations in all three domains of the bio-psycho-social model, which were associated with each other and are partly ascribable to adverse childhood experiences. Therefore, in the treatment of loneliness in patients with borderline personality disorder, this complex interplay has to be addressed. Therapeutic interventions for loneliness in patients with borderline personality disorder should aim to improve psychological dispositions (e.g. personality features, insecure attachment), alterations in social information processing (e.g. perception of the benevolence of social partners and social touch) and current social factors (e.g. social network size, contact frequency). The investigation of interaction effects between biological, psychological, and social factors in relation to loneliness did not yield significant results in the studies of this thesis and thus represents a topic that would benefit from further investigation in future research.