Effort Expenditure Reduces Prosocial Decision-Making: Computational Principles and Neural Mechanisms

Charitable giving is a costly prosocial act in which individuals donate money or other resources to benefit others. Although the relationship between effort and prosocial behavior has been explored, how effort expenditure affects subsequent prosocial decisions and the underlying neurocognitive processes remains poorly understood. We conducted two experiments to address this, using cognitive modeling of behavioral responses in Experiment 1 and electrophysiological recordings in Experiment 2. In both experiments, participants received cues indicating the effort type required (effort vs. no-effort) before completing a task involving either physical effort or rest. They earned monetary rewards based on performance or unconditionally and then decided whether to accept donation offers at low, medium, or high costs. Behavioral results in both experiments revealed that participants were more likely to reject donation offers after exerting effort, particularly for medium- and high-cost offers. Analysis using a hierarchical drift diffusion model revealed that participants accumulated information more rapidly and required less evidence for decision-making in the effort condition compared to the no-effort condition. Electrophysiological results revealed that effort expenditure heightened reward-sensitive neural responses upon receiving monetary feedback, as reflected by increased reward positivity, fb-P3, and fb-delta power. Moreover, higher amplitudes of reward positivity and fb-P3 in response to effort-earned feedback were associated with less generous prosocial donations. These findings demonstrate that effort expenditure amplifies reward sensitivity, expedites the accumulation of self-interest, simplifies the decision-making process, and ultimately strengthens proself choices during decision-making.