Abstract: Amid escalating ecological crises, such as climate change and resource consumption, promoting pro-environmental behavior(PEB) has become critical for sustainable development. PEB often unfolds within social dilemmas that require individuals to prioritize collective and ecological well-being over immediate self-interest. However, because the benefits of such behaviors are typically delayed and uncertain, maintaining sustained engagement remains challenging. Social norms serve as essential social cues that regulate individual behavior and guide collective decision-making. Although both injunctive and descriptive norms can promote PEB, previous studies have suggested that they operate through distinct psychological mechanisms. Although morally prescriptive, injunctive norms often lack enduring motivational strength. By contrast, descriptive norms, which reflect perceptions of group consensus, tend to be adopted more readily and demonstrate greater intervention effects. Scholars have suggested that activating individuals' moral identities may offer a promising solution for enhancing the effectiveness of injunctive norms. Moral identity, which reflects the extent to which moral values are incorporated into one's self-concept, can enhance an individual's likelihood of regarding environmental behavior as an ethical obligation, thereby intensifying their responsiveness to injunctive cues.
To systematically examine the moderating role of moral identity across different types of social norms and uncover the underlying neural mechanisms, the present study used the Greater Good Game paradigm in combination with functional near-infrared spectroscopy(fNIRS). Participants engaged in a decision-making task that involved trade-offs among self-interest, cooperation, and pro-environmental options under injunctive or descriptive norm conditions. Moral identity activation was experimentally manipulated to examine its moderating role and cortical hemodynamic responses were recorded concurrently recorded.
Behavioral choice data and multinomial processing tree(MPT) model analyses indicated that, under the moral identity activation condition, injunctive norms significantly enhanced individuals' PEB and latent pro-environmental tendencies compared with descriptive norms. In contrast, in the control condition without moral identity activation, descriptive norms exhibited relatively higher latent pro-environmental tendencies than injunctive norms, although the difference in behavioral choice proportions did not reach statistical significance. The neuroimaging results further demonstrated that moral identity activation elicited stronger activation in the dorsolateral prefrontal cortex(dlPFC), reflecting enhanced cognitive control and inhibition of self-serving tendencies. Moreover, the combination of injunctive norms and moral identity elicited substantial activation in the orbitofrontal cortex(OFC) and medial prefrontal cortex(mPFC), regions linked to moral valuation, emotional regulation, and social decision-making. In contrast, descriptive norms primarily stimulate the right temporoparietal junction(rTPJ), a region associated with social cognition and perspective-taking.
In conclusion, this study reveals the distinct neural pathways through which social norms shape PEB and highlights the crucial role of moral identity in enhancing normative interventions. These findings have important implications for policy and practice. By combining injunctive norms with moral identity, educational or promotional interventions can guide individuals to regard PEB as an ethical obligation, thereby effectively promoting such behavior. Simultaneously, leveraging descriptive norms—through community role models, media coverage, or collective initiatives—provides stable and broadly applicable behavioral references, reinforcing public engagement in environmental practices. Taken together, these insights support the development of neuroscience-informed strategies to promote sustainable behavior.

Key words: pro-environmental behavior, social norm types, moral identity, Greater Good Game, fNIRS