The same human behavior arises for different reasons, and different behaviors have the same motivation. Behavioral data alone is not sufficient to identify psychological mechanisms underlying human behavior. The fMRI experiments provide researchers with opportunities to differentiate the important psychological processes. In this paper, we introduce our recent neuroimaging study on repeated prisoner's dilemma games. We have specifically explored the neural correlate of reciprocal interaction that has an immediate relevance to investigate the real dynamics in the society. Based on the evidence from the experiment, we examine the contribution of the neurocognitive approaches to deepening our understanding on human behavior. The article suggests the validity of the method and empirical knowledge in political science when we conduct the experiments in neuroscience.