Effects of Transcranial Alternating Current Stimulation in the Theta Frequency on Associative Memory consolidation

Abstract

Neural oscillations in the theta frequency range (4-8 Hz) are thought to underlie effective communication between brain regions subserving associative memory (e.g., prefrontal-hippocampal circuitry). Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation technique that may entrain endogenous theta oscillations. Application of tACS during memory encoding has been shown to modulate associative memory encoding; however, few studies have investigated whether and how associative memory consolidation is affected by tACS at theta frequency (i.e., theta-tACS). Using an interleaved EEG/tACS approach, we have evaluated electrophysiological (i.e., frontal-midline theta power) and behavioral (i.e., memory task performance) effects of frontal theta-tACS, applied during memory consolidation. In a counter-balanced cross-over design, 30 participants (50% F, mean age 24 years) received 20 minutes of either sham tACS or active tACS (5 Hz, 2 mA peak-to-peak) during the consolidation phase of an associative memory task. Results showed no significant difference between stimulation conditions on our outcome measures. Our study provides no evidence of an effect of frontal theta-tACS on associative memory performance or frontal-midline theta power.