mPFC-Dependent Valuation Shapes Information Sharing: Causal Evidence from tDCS and a Dyadic Social Media Paradigm

Information sharing drives the spread of both accurate and misleading content, yet its psychological and neural mechanisms remain unclear. We investigated whether perceived self- and social relevance influence sharing through downstream content evaluations, and whether this process depends on medial prefrontal cortex (mPFC) function. In a dyadic social media paradigm, 186 participants were assigned to anodal, cathodal, or sham tDCS over the mPFC. Senders judged 30 science news items (15 true and 15 false) on truthfulness, self-relevance, social relevance, interestingness, and importance before deciding whether to share each item with a real receiver. Structural equation modeling showed that self- and social relevance predicted sharing indirectly through evaluations of interestingness, importance, and truthfulness. mPFC stimulation did not reliably change sharing rates, but altered evaluative processing: it reduced perceived interestingness, and anodal stimulation produced a significant negative indirect pathway to sharing through reduced interestingness. Multi-group analyses indicated that these valuation pathways were invariant across true and false news. On the receiver side, social endorsement increased reading of shared items but had little effect on post-reading evaluations. Together, these findings support a causal contribution of mPFC-targeted neuromodulation to evaluative processing relevant to sharing, with limited evidence for a direct effect on sharing behavior.