Abstract/Summary

Major depressive disorder is commonly associated with altered processing of social stimuli, as well as with impaired learning from non-social outcomes. While a plethora of research has examined these aspects in isolation, few integration attempts have been made. That is to say, studies that examine social learning in depression and link task-based measures to real-life interpersonal experiences are lacking. Given that learning from social outcomes is crucial for successful interpersonal interactions, it is important to assess how this process may be affected in depression. The current work aimed to address this question, on both the behavioural and the neural level. Specifically, study 1 explored task-based social learning in individuals with high (HD) and low (LD) depressive symptomatology and related learning parameters derived from computational modelling to reports of everyday social experiences. Study 2 extended this approach to the neural level, examining how the neural encoding of social learning signals is altered in HD subjects and how these alterations relate to real-life interpersonal experiences. Moreover, study 3 investigated the involvement of different neurotransmitters in the learning process by assessing neural and behavioural responses during social learning after dietary dopamine or serotonin (precursor) depletion in healthy volunteers. It was found that HD individuals demonstrated deficits in social learning, which were associated with increased experiences of negative interpersonal encounters (study 1) and reduced social engagement motivation (study 2) in everyday life. In addition, HD subjects displayed altered social reward prediction signals in the insula, temporal lobe and parietal lobe, the latter of which were linked to decreased real-life social engagement motivation (study 2). Notably, the changes in social reward prediction encoding observed in HD individuals closely resembled those found in healthy subjects after serotonin depletion, while predictionrelated dopamine depletion effects were mainly seen in frontal cortex areas (study 3). These findings suggest that depression symptoms are associated with impaired social learning responses, on both the behavioural and the neural level, which are linked to changes in reallife social experiences and may be underpinned by altered serotonin functioning.