University thesis:
Dissertation, Universität Freiburg, 2020
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Description:
Abstract: The hormone and neuropeptide oxytocin is critically involved in monogamous pair bonding behavior in mammals. In human couples, trust is widely considered to be one of the most important preconditions for stable and satisfactory long-term romantic relationships. While studies using intranasal administration of oxytocin confirmed intriguing effects on human social behavior, including increased trust during interactions with unfamiliar interaction partners, psychoendocrine regulation mechanisms of trust in couples remain nebulous. However, these mechanisms could be of critical importance for a comprehensive understanding of the specific evolutionary role oxytocin plays within our highly social species. This thesis aims to close this research gap by providing and validating a standardized tool for the quantitative assessment of trust towards a romantic partner, and implementing this tool in an experimental setting that examines the effects of oxytocin on partner-specific trust behavior compared to a placebo. In chapter 1, literature reviews on trust, the current approaches to measure the construct, its importance in romantic relationships, and the psychobiological model of trust are provided as a general introduction to this dissertation. Chapter 2 presents a comprehensive validation study of the newly developed Trust Game for Couples, an interactive paradigm in which trust is operationalized as the willingness to invest financial resources in pro-relationship attitudes of the partner. Results from 35 couples (N = 70) confirm excellent convergent and discriminant validity of our paradigm, being associated not only with explicit self-report measures of partnership quality, but also with implicit relationship-related measures based on response times. In chapter 3, we review initial studies and recent advances in oxytocin research, and present data from an extensive double-blind placebo-controlled randomized controlled trial on oxytocin’s effects on partner-specific trust compared to a placebo control condition in 60 couples (N = 120). While there was no main effect of oxytocin on trust decisions in the Trust Game for Couples, we found conditional effects dependent on self-reported trait perceptions of partner-specific and general interpersonal trust in the social environment. Subsequent analyses indicate that oxytocin primarily decreased trust behavior towards the partner in cases of lower trait levels of partner-specific and general interpersonal trust (and to a lesser extent increased trust behavior in cases of higher trait levels of trust), effects that were more pronounced in women. In support of the increasingly popular social salience hypothesis, these results contribute to a complex model of psychoendocrine regulation mechanisms of trust in couples, suggesting that oxytocin holds the potential to decrease the stability of romantic relationships if prior experiences with the partner or the social environment signal suboptimal preconditions for shared offspring. Finally, chapter 4 provides a general discussion of our results in an attempt to clarify what trust in couples is made of, how previous theoretical frameworks can be expanded to a psychobiological model of trust in couples, and which limitations should be addressed in future studies. We would like to invite researchers to make use of our newly developed behavioral and implicit relationship-related measurement tools to further investigate social, psychological, physiological or psychopathological mechanisms of human romantic relationships. Furthermore, we hope that our findings on psychoendocrine regulation mechanisms of trust in couples contribute to a differentiated psychobiological model of monogamous romantic relationships as well as our understanding of the evolutionary purpose of oxytocin in humans