Common and distinct contributions of the dorsomedial prefrontal and posterior parietal cortices to social episodic memory

The self-reference effect (SRE) refers to the robust mnemonic advantage for self-relevant information and is characterized by a graded pattern spanning the self, close others, and distant others. Despite extensive behavioural evidence, causal evidence for the neural mechanisms supporting the SRE remains limited, particularly during incidental encoding and across source memory, metacognition, and emotional valence. We investigated the causal contributions of the dorsomedial prefrontal cortex (dmPFC) and posterior parietal cortex (PPC) to self-other episodic memory and metacognition using focal transcranial direct current stimulation (tDCS). One hundred participants completed an incidental encoding task in which trait adjectives were rated with reference to the self, a close friend, or a celebrity, under anodal or sham stimulation to either region. Recognition tests assessed item and source memory sensitivity (d') and metacognitive efficiency (meta-d'/d') as a function of agent and emotional valence. Across stimulation conditions, a graded advantage for self-related information was observed in both item and source memory, extending to metacognitive efficiency. Anodal stimulation to either region attenuated the SRE, with significant effects at the dmPFC. PPC stimulation additionally biased source memory away from positive and towards negative information. These findings demonstrate shared and dissociable causal roles of dmPFC and PPC in self-other episodic memory.