Context-sensitivity and longitudinal stability of the effects of depressive symptoms on social and reward decision-making

Depressive symptoms could affect decision-making in multiple ways, yet it remains unclear whether these effects are context-sensitive or stable over time. In this longitudinal study, 236 online participants (n=129 at 1-month follow-up) completed a social exchange task (Ultimatum Game) and a reward learning task (Reversal Learning). Mixed-effects regression analyses revealed consistent effects of depressive, but not anhedonic, symptoms on social decision-making. Specifically, participants with elevated depressive symptoms (BDI-II > 13) exhibited slower response times and lower acceptance of unfair offers in the Ultimatum Game across both time points relative to participants below the clinical threshold, regardless of anhedonic symptoms. In contrast, symptom-related effects in the Reversal Learning task were less consistent across time. Analyses using continuous symptom measures yielded weaker and less stable effects than the primary categorical models, suggesting that symptom–behavior relationships may be non-linear. Overall, these findings indicate that the effects of depressive symptoms on decision-making are context-sensitive and robustly expressed during social exchange. This work highlights the importance of considering both symptom dimension and decision context when identifying behavioral phenotypes relevant to depression.