Aims: Social decision making has recently been evaluated in alcohol use disorder (AUD) using the ultimatum game (UG) task, suggesting a possible deficit in aversive emotion regulation elicited by the unfairness during this task. Despite the relevance to relapse of this possible faulty regulation, the brain correlates of the UG in AUD are unknown.

Methods: In total, 23 AUD and 27 healthy controls (HC) played three consecutive fMRI runs of the UG, while behavioral and brain responses were recorded.

Results: Overall, acceptance rate of unfair offers did not differ between groups, but there was a difference in the rate of behavioral change across runs. We found significant anterior insula (aINS) activation in both groups for both fair and unfair conditions, but only HC showed a trend towards increased activation during unfair vs. fair offers. There were not overall whole-brain between-group significant differences. We found a trend of signal attenuation, instead of an increase, in the aINS for AUD when compared to HC during the third run, which is consistent with our recent findings of selective insula atrophy in AUD.

Conclusion: We found differential group temporal dynamics of behavioral response in the UG. The HC group had a low acceptance rate for unfair offers in the first two runs that increased markedly for the third run; whereas the AUD group was consistent in their rejection of unfair offers across the three runs. We found a strong significant decrease in neural response across runs for both groups.

Short summary: This fMRI study of UG in alcohol use disorder found behavioral group differences in acceptance rate across runs, which together with significant BOLD-signal decrease across runs in UG-related regions in both groups, highlights the impairment of strategy in AUD and the effect of repetitive exposure to unfairness in this task.