0245 CLOSED-LOOP TACS DURING SWS BOOSTS SLOW-WAVE AND DELTA POWER AND POST-SLEEP MEMORY FOR THREAT DETECTION ON NOVEL STIMULI

Few studies have shown transcranial alternating current stimulation (tACS) applied in open loop during slow-wave sleep (SWS) could improve declarative memory performance following sleep. The present study investigates the mechanisms by which closed-loop tACS can enhance sleep consolidation more robustly. Participants (n=7) underwent a within-subjects counterbalanced protocol involving baseline, training, and post-training tests (immediate and morning). Similar to prior work in our lab, participants viewed static images, half of which contained a target signaling a potential threat. Subjects made a response (target present or absent), received feedback via a short video during training, and then were tested for two image types: repeated (identical from training to test) and generalized (same scene from training to test, but novel spatial viewpoint). During sleep after training, participants received 1.5 mA of closed-loop tACS (adapted to ongoing slow-wave oscillations) to F3 and F4 with returns on mastoids, or sham stimulation on different nights. Normalized spectral power changes in sleep EEG across stimulation events were correlated with performance changes over the night. We observed not only a robust performance improvement but also a significant post-stimulation increase in power of slow-wave (0.5–1.5 Hz), delta (1.2–3 Hz), spindle (11–16 Hz), and gamma (30–50 Hz) bands relative to pre-stimulation baseline (ps<0.002). Further, we identified a cluster in the delta band at 3–4 s post stimulation that significantly correlated with the overnight change in performance for generalized images (p=0.0160). Performance for repeated images did not change overnight due to ceiling effects. Our results suggest that closed-loop tACS during sleep increases slow-wave and delta activity, which then triggers spindle and gamma band activity. These mechanisms promote memory consolidation wherein performance becomes less tied to a specific event and instead more generalized to the goals of the task. This material is based upon work supported by the Defense Advanced Research Project Agency (DARPA) and the Army Research Office under Contract No. W911NF-16-C-0018. The views, opinions and/or findings expressed are those of the author and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government.