Older Adults Show Altered Network Connectivity during Fairness Decisions with Similar and Dissimilar Partners

Fairness-related decisions depend on both offer value and partner identity, yet how aging reshapes the network-level connectivity supporting these decisions across social contexts remains unknown. Younger (18-35) and older (65-80) adults underwent fMRI while responding to offers in an ultimatum game from ostensible partners similar or dissimilar in age. We modeled trial-by-trial choices by offer size, age group, and partner similarity, and examined whole-brain activation and task-dependent connectivity of the default mode (DMN) and executive control (ECN) networks. Participants accepted fairer offers more often, but behavioral sensitivity did not differ reliably by age group or partner similarity. Whole-brain activation analyses revealed no significant age-by-partner-similarity effects. Connectivity analyses, however, revealed opposing age-related patterns. Younger adults showed stronger fairness-modulated DMN-anterior cingulate connectivity for similar than for dissimilar partners, whereas older adults showed the reverse. Age also moderated the relationship between individual sensitivity to fairness norm violations and ECN-medial prefrontal connectivity: this association was negative in younger adults and positive in older adults. These findings suggest that decisions regarding fairness in younger and older adults may be supported by different patterns of large-scale network connectivity.