Individuals with methamphetamine use disorder (MUD) commonly exhibit socially problematic behaviours. Investigating the prosocial decision-making of individuals with MUD could enable a better understanding of their impaired social functioning and help improve their social relationships. We conducted two studies to examine the performance of individuals with MUD and healthy controls on a modified dictator game. In Study 1, 55 male individuals with MUD and 34 healthy male participants made a series of choices between two pairs of monetary prizes for themselves and for others. In Study 2, 62 male individuals with MUD and 31 healthy male participants made the same choices as in Study 1 after a brief exposure to methamphetamine-related pictures. In both studies, we consistently found a context dependency of decreased prosociality in individuals with MUD. That is, individuals with MUD made fewer prosocial choices than healthy individuals in disadvantageous contexts (but not advantageous contexts). The results of the computational model suggested that the lower prosociality of individuals with MUD in disadvantageous contexts could be attributed to the lower weight placed on others' benefits. Moreover, when exposed to methamphetamine-related pictures, individuals with MUD showed less caution and slower encoding/motor speed than healthy individuals, and individuals with MUD with a longer history of methamphetamine use tended to respond less cautiously. Our findings provide evidence that in disadvantageous contexts, individuals with MUD show reduced prosociality and less consideration of others' benefits. Identifying the origin of the alterations in prosocial decision-making has implications for diagnosis and treatment.
Keywords: computational modelling; drift-diffusion model; methamphetamine; prosociality; social cognition.
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