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Effects of transcranial alternating current stimulation and context reinstatement on wakeful episodic memory consolidation

Poster Session A - Saturday, March 7, 2026, 3:00 – 5:00 pm PST, Fairview/Kitsilano Ballrooms

Jonathan S. Morrow¹ (jonmorrow@ucla.edu), Jesse Rissman¹; ¹University of California, Los Angeles

Previous research has shown that the application of theta-frequency transcranial alternating current stimulation (tACS) to frontal midline brain areas during a period of wakeful rest immediately following memory encoding can boost subsequent recall (Shtoots et al., 2024). A putative mechanism for the beneficial effect of theta tACS is that it entrains neural activity conducive to awake hippocampal replay. If this is the case, it might be possible to influence which recently encoded memories benefit most from stimulation through targeted reactivation during consolidation, as has been demonstrated in prior sleep studies. In the present double-blind tACS experiment, healthy adult participants studied two sets of 30 visual objects, with each set associated with a unique video background context. After two study/test cycles of each set, participants received frontal midline theta-frequency (N=30) or sham (N=32) stimulation for 20 minutes as one of the two video contexts was played. After a 2-hour break, participants returned to complete a free recall test, followed by a four-alternative forced-choice recognition task. Contrary to expectations, neither theta stimulation nor context reinstatement yielded a significant increase in subsequent memory recall or recognition. Preliminary results from an in-progress follow-up study isolating the effect of stimulation by removing the context reinstatement factor seems to replicate this null result. Ultimately, the results of this project suggest that the effect of theta-frequency tACS on waking post-encoding memory consolidation is more difficult to capture than previously thought, and that a more robust effect could potentially emerge after sleep-dependent consolidation processes occur.

Topic Area: LONG-TERM MEMORY: Episodic