The Regulation of Interpersonal Functioning by Serotonin in Adults at Risk for Depression

Humans are social animals. Good social interactions are imperative for mental health. Interpersonal factors often contribute to the onset, severity, and duration of psychiatric disorders. They do so by altering brain functions, which in turn may influence a person?s social environment. The neurobiology of human interpersonal functioning has been a relatively neglected research area. This may be due to (1) limited availability of relevant laboratory tasks and (2) limited generalizability to everyday life of data obtained using these tasks. Most laboratory studies have focused on accurate emotion labelling of static images of strangers? faces. In reality, however, emotions expressed in faces are highly dynamic social signals. Additionally, everyday life interactions typically involve known others, rather than strangers. Who the other person is moderates psychological and physiological reactions to interpersonal events. I propose to study how serotonin, an evolutionarily ancient neurotransmitter that modulates a wide range of functions, regulates interpersonal functioning in individuals at risk for major depressive disorder (MDD), a psychiatric disorder often characterized by irritability, rejection sensitivity, and social withdrawal. Moreover MDD is a risk factor for cardiovascular disease (CVD). In Study 1, during transient serotonin depletion, participants complete a novel laboratory task that uses dynamic video stimuli to measure their perceptions of others affective states. Study 2 uses ecological momentary assessment to measure, while participants are taking the serotonin precursor tryptophan, their affects, behaviours, cognitions, and perceptions of others behaviours during everyday social interactions. Both studies measure heart rate variability as a correlate of cardiovascular function in a social context. Results will provide insight into the role of serotonin in modulating psychological and physiological reactions to interpersonal stimuli in individuals at risk for MDD. The hypothesized positive effects of serotonin will be particularly relevant to the population studied, given their vulnerability for MDD and possibly CVD.