Distinct generation of subjective vividness and confidence during naturalistic memory retrieval in angular gyrus

Subjective experience of remembering is a hallmark of episodic memory, which enables us to monitor experiences, identify mistakes, and adjust our decisions accordingly. A fundamental and enduring puzzle is the origin of confidence in memory; for example, does the confidence during episodic retrieval depend upon the subjective sensed vividness, or does confidence and vividness reflect dissociable introspective processes? The angular gyrus (AnG) exhibits a sensitivity to subjective experience of remembering, but its direct contribution to the monitoring of internal subjective mnemonic experience has hitherto been lacking. Here we combined a novel naturalistic video-watching paradigm with repetitive transcranial magnetic stimulation (rTMS) and resting-state functional magnetic resonance imaging (fMRI) to test the idea that vividness and confidence are generated differently during retrieval. We found that pre-retrieval rTMS targeting the left AnG selectively alters the vividness efficiency compared to control stimulation while keeping metacognitive efficiency and objective memory accuracy unaffected. Using trial-wise data, we showed that vividness mediates the association between confidence and objective memory accuracy and such mediation was eradicated by AnG stimulation. Furthermore, resting-state functional connectivity of hippocampus and AnG was specifically associated with vividness efficiency, while the connectivity of hippocampus and medial prefrontal cortex was associated with metacognitive efficiency across individuals. These findings identify a role for the AnG in gauging the vividness, but not the confidence, of memory, thereby providing evidence for a differentiation account of conscious assessment of memory by functionally and anatomically dissociating the monitoring of vividness from confidence.