The 5-HTT gene (SLC6A4) is regulated by a common polymorphism in the promoter region (5-HTTLPR), which has functional consequences. Two major alleles have been observed and shown to have differential transcriptional activity with the long (L) allele having greater gene expression than the short (S) allele. 5-HTTLPR appears to modulate depression, anxiety and personality traits such as neuroticism. Additionally, a significant influence of 5-HTTLPR genotype on amygdala reactivity in response to fearful stimuli has been reported. Moreover, 5-HTTLPR seems to impact on the role of stressful life events (SLEs) in the development of depression. An elevated risk of depression and suicidal behaviors has been found in carriers of at least one low expressing S allele who had experienced SLEs, suggesting a gene x environment interaction. However, a recent meta-analysis showed that several findings failed to replicate this finding. Since genetic polymorphisms of the dopaminergic and serotonergic neurotransmission interact at the molecular, analyses with another polymorphism of the dopaminergic system, the dopamine D4 receptor (DRD4) was included to consider these likely gene-gene interactions (epistasis). The aim of this series of studies was to investigate the role 5-HTTLPR and SLEs on the endocrine stress response in different age samples. While newborns have been examined by a heel prick, stress responses were provoked in children (8-12 yrs) and younger adults (19-31 yrs) and older adults (54-68 yrs.) with the Trier Social Stress Test (TSST). The Life History Calendar (LHC) and Life Events Questionnaire (LEQ) were used to acquire data on SLEs. While in newborns the S/S genotype showed a significantly higher acute endocrine stress response than L/L or S/L genotypes, no significant difference between genotype groups was found in children. In the younger adult sample, the genotype impacted on cortisol stress responsiveness was reversed. Adults carrying the more active L allele of the 5-HTTLPR polymorphism showed a significantly larger cortisol response to the TSST than individuals carrying at least one of the lower expressing S allele. In older adults, no significant difference between genotype groups was found. However, results point in the same direction with showing highest cortisol response in individuals with L/L genotype. These data suggest that the association between 5-HTTLPR and endocrine stress reactivity seems to alter across lifespan, more specific the effects of genotype turns around. In addition, a significant interaction effect of 5-HTTLPR and SLEs has been found in the sample of younger adults, i.e. that early SLE as well as a severe number SLEs across the entire lifespan seem to modulate the interaction between HPA axis activity and 5-HTTLPR genotype. Additionally, a DRD4 by 5-HTTLPR interaction emerged which point to independent and joint effects of these polymorphisms on stress responsivity with regard to the concept of genegene interaction.

Beeinflusst unsere Variabilität, wie wir über andere denken? Betrifft die Veränderung unserer Persönlichkeitszustände mehr als uns selbst? Wie beeinflussen andere unsere Persönlichkeitsentwicklung? Wie wirkt sich Selbstbezug auf das Denken über andere aus? In dieser Arbeit werden die vielfältigen Beziehungen zwischen unserer Persönlichkeit und der Beziehung zu und Interaktion mit anderen Menschen in verschiedenen Bereichen der Persönlichkeitspsychologie untersucht. Neben der Zusammenfassung der vier Veröffentlichungen, wird der theoriegeleitete Ansatz erläutert und in Persönlichkeitsdynamik und -prozesse eingeführt. Zentral sind die Konzepte der Persönlichkeitsmerkmale, der innerpersonellen Variabilität, der Persönlichkeitsentwicklung, des Selbstfokus, des Egozentrismus und der egozentrischen Verzerrung–im Rahmen ihrer Bedeutung für die Theory of Mind (ToM). Publikation 1 schlägt ein zweistufiges Model vor, wie die innerpersonelle Variabilität die ToM durch Erweiterung und Relativierung des Egozentrismus einer Person erleichtern kann. Publikation 2 fürht die Terminologie und die statistischen Werkzeuge der dynamischen Systemtheorie für die Untersuchung von Persönlichkeitszuständen ein und diskutiert Anwendungsfälle. Publikation 3 stellt ein Klassifizierungssystem vor, mit dem systematisch zwischen persönlichen und kollektiven Lebensereignissen unterschieden werden kann, wobei die unterschiedlichen Mechanismen berücksichtigt werden, durch die beide Arten von Lebensereignissen die Persönlichkeitsentwicklung beeinflussen können. Publikation 4 präsentiert Belege für eine kleine, aber robuste positive Beziehung zwischen achtsamer Selbstfokussierung und ToM. Nach der Reflektion der Beiträge zum Fachgebiet werden drei Forschungsansätze aus dem Risikomanagement, der Persönlichkeitspsychologie und den Neurowissenschaften diskutiert, die auf die Forschung zu innerpersönlicher Variabilität und Persönlichkeitsentwicklung sowie zu Egozentrismus und ToM einzahlen könnten. / Does our own variability affect how we think about others? Do personality states changes involve more than ourselves? How do others affect our personality development? How does focusing on oneself affect thinking about others? This dissertation explores the many relationships between an individual’s personality and ther relation to and interaction with other people across multiple areas of personality psychological research. Before summarizing four publications of this cumulative project, I explain my theory-driven approach and introduce the field of personality dynamics and processes. In particular, I focus on the concepts of personality traits, within-person variability, personality development, self-focus, egocentrism, egocentric bias–often in light of their relevant for Theory of Mind. The first publication proposes a two-tier framework of how within-person variability can facilitate Theory of Mind by broadening and relativizing a person’s egocentrism. The second publication introduces the terminology and statistical tools of dynamic systems theory to the investigation of personality state levels and presents possible use cases. The third publication introduces a classification system to differentiate between personal and collective live events in a systematic way that is sensitive to the different mechanisms by which both kinds of life events can affect personality development. The fourth publication presents evidence for a small but robust positive relationship between mindful self-focus and Theory of Mind. Finally, I reflect on the publications’ contributions to the field and suggest three lines of research stemming from risk management, personality psychology, and neuroscience that could inform research on within-person variability and personality development as well as on egocentrism and Theory of Mind further in the future.