Computational, psychological and neural mechanisms of prosocial motivation

Prosocial behaviours are essential for healthy social interactions, with established impacts on life satisfaction, mental and physical health, and economic success. Yet, how willing people are to act prosocially varies considerably between individuals and across contexts. When making decisions that can result in others' pain, people can be highly prosocial, and will typically not profit from other's harm. In contrast, people are much less motivated to exert effort to benefit others compared to themselves. However, the psychological and neural mechanisms of these behaviours remain largely unknown. In this thesis, I examine the affective, cognitive, and neural processes that underpin harm aversion and effortful prosocial behaviours and their variability between people. First, I propose a theoretical framework where individual differences in prosocial behaviour across domains are due to idiosyncratic sensitivities to personal costs and others' benefits, giving a conceptual and methodological overview on what factors might be hypothesised to influence cost-benefit prosocial evaluations. Second, I show that harm aversion and prosocial effortful actions share variance despite their differences at group level, and are linked by responses in the anterior cingulate cortex (ACC) and the anterior insula (AI) to others' benefits. Third, I identify an affective profile characterised by high empathy and low apathy as crucial for predicting prosociality. Fourth, I find that people who are highly hypocritical, i.e. fail to live up to their moral standards, are more sensitive to effort costs, suggesting motivational aspects in moral hypocrisy. Fifth, I disentangle the role of ACC and AI in others' rewards representations, with the dorsal AI linked to interoceptive processes and the ACC linked to motivational aspects of others' rewards. Finally, I propose a new experimental framework to investigate prosocial motivation, examining how the alternative opportunities in the environment shape prosociality. In sum, in this thesis I show that being motivated to benefit others depends on cost-benefit evaluations, which are modulated by affective traits and interoceptive sensibility, with crucial, but differential, roles of ACC and AI in prosocial behaviour.