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DOI: 10.1101/2023.05.20.541280

The role of serotonin and of perceived social differences in infering the motivation of others

M.Moutoussis J. M. Barnby A. Durant M. Croal R. Rutledge L. Mason
Attributing motives to others is a crucial aspect of mentalizing, which is disturbed by prejudice and is also affected by common psychiatric disorders. Thus it is important to understand in depth the neuro-computational functions underpinning mentalizing and social reward. We hypothesized that people quickly infer whether the motives of others are likely beneficial or detrimental, then refine their judgment. Such 'Classify-refine', active inference models of mentalizing motives might improve on traditional models, and hence allow testing the hypothesis that serotonergic antidepressant drugs improve function partly by inducing more benign views of others. In a week-long, placebo vs. Citalopram study using an iterated dictator task, 'Classify-refine' models accounted for behaviour better than traditional models. Citalopram did not lead to more magnanimous attributions of motives, but we found evidence that it may help refine attributions about others' motives through learning. With respect to social differences, model comparison clearly indicated that ethnicity-dependent, in-task biases played no role in attributing motives for the large majority of participants. This is a very encouraging result which further research should seek to replicate, and, if replicated, celebrate. Lower subjective socio-economic status was associated with lower attributions of harm intent to others. We discuss how classify-refine social cognition may be highly adaptive. Future research should examine the role of Serotonergic antidepressants in clinical studies over longer time spans.