Spatiotemporal patterns of transcranial electrical stimulation can strengthen the metamemory of individual episodic memories in humans

Long-term retention of memories critically depends on consolidation processes, which occur during slow-wave oscillations (SWOs) in non-rapid eye movement (NREM) sleep. We designed a non-invasive system that can tag one-shot experiences of naturalistic episodes within immersive virtual reality (VR) with unique spatiotemporal amplitude-modulated patterns (STAMPs) of transcranial electrical stimulation (tES). We demonstrate that these STAMPs can be re-applied during UP states of SWOs on two consecutive nights to achieve a 19.43% improvement in the metamemory of targeted episodes at 48 hours after the one-shot viewing, compared to the control episodes. Further, we found an interaction between pre-sleep metamemory of targeted episodes and the number of STAMP applications for those episodes during sleep, and that STAMPs elicit increases in left temporal slow-spindle (9-12 Hz) power that are predictive of overnight metamemory improvements. These results prescribe an optimal strategy to leverage STAMPs for boosting metamemory based on pre-sleep performance and tracking the STAMP-induced biomarker during sleep, and suggest that real-world episodic memories can be modulated in a targeted manner even with coarser, non-invasive spatiotemporal stimulation.