Does unfairness evoke anger or disgust? A quantitative neurofunctional dissection based on 25 years of neuroimaging.

Over the last decades, the traditional 'Homo economicus' model has been increasingly challenged by converging evidence highlighting the critical impact of emotions on decision-making. A classic example is the perception of unfairness in the Ultimatum Game, where humans willingly sacrifice personal gains to punish fairness norm violators. While emotional mechanisms underlying such costly punishment are widely acknowledged, the distinct contributions of moral emotions, particularly anger and disgust, remain debated, partly due to methodological limitations in conventional experiments. Here, we leverage a quantitative neurofunctional dissection approach that integrates recent advances in neuroimaging meta-analyses, behavioral-level, network-level, and neurochemical-level decoding, drawing on data from 3266 participants from functional neuroimaging studies to determine the common and distinct neural representations between unfairness and the two moral emotions. Our results reveal that experiencing unfairness engages a widespread bilateral network encompassing insular, cingulate, and frontal regions, with dorsal striatal regions mediating the decision to reject unfair offers. Disgust engages a defensive-avoidance circuit encompassing amygdalar, occipital, and frontal regions, while anger engages non-overlapping systems including mid-cingulate, thalamic, and frontal regions. Unfairness shares common activation with both anger and disgust, respectively, in the anterior and mid-insula, while the latter additionally shows common recruitment of ventrolateral prefrontal and orbitofrontal cortices. Multimodal network, behavioral, and serotonergic decoding provide a more refined dissection of these results. Collectively, our results suggest a shared neuroaffective foundation through which emotions impact unfairness-induced punishment behavior, supporting the existence of a core brain circuit evolutionarily shaped to protect individuals from personal harm and enforce social norms.