Theta oscillations and memory performance effects of transcranial alternating current stimulation

Poster Session F - Tuesday, April 16, 2024, 8:00 – 10:00 am EDT, Sheraton Hall ABC

Fenne M. Smits^1,2,3 (f.m.smits-2@umcutrecht.nl), Elbert Geuze^1,2, Dennis J.L.G. Schutter³; ¹Department of Psychiatry, UMC Utrecht Brain Center, University Medical Center Utrecht, The Netherlands, ²Brain Research & Innovation Centre, Ministry of Defence, the Netherlands, ³Experimental Psychology, Helmholtz Institute, Utrecht University, the Netherlands

Introduction: Neural activity in the theta frequency (4-7 Hz) is involved in memory. Several studies showed memory performance improvements after theta-frequency transcranial alternating current stimulation (tACS). However, effects of tACS on the targeted oscillatory brain activity show mixed results. Moreover, transcranial stimulation is typically applied during memory encoding while effects on memory consolidation are less understood. Therefore, we investigated effects of tACS interleaved with brain activity recordings during a memory consolidation phase. Methods: In two cross-over studies, healthy volunteers (Study I: n=39; Study II: n=32) underwent sham and active tACS in separate sessions (5 Hz, 2 mA peak-to-peak, F3/F4 montage). Twenty minutes of total stimulation time was divided into short periods (1 or 4 minutes) interleaved by resting-state EEG recordings (30 or 60 seconds). Memory encoding was performed pre-stimulation, and memory retrieval was tested post-stimulation. Memory performance was assessed by a face-scene associative memory task (Study I) and a free word recall task (Study II). Additionally, Study II assessed working memory during stimulation using a change detection task. Results: Preliminary analyses of grand average oscillatory power in frontocentral EEG electrodes at the stimulation frequency (5 Hz) or in the broader theta band (4-7 Hz) show no significant differences between active vs. sham tACS. Further analyses are ongoing. Results will be presented on the poster. Conclusion: Preliminary evidence shows no entrainment of frontocentral theta activity during the interleaved tACS-EEG protocol. Effects of theta-tACS on memory consolidation, and dependence on individual differences in theta activity are topics of further investigations.

Topic Area: METHODS: Electrophysiology