Theta Stimulation Enhances Early Consolidation of Semantic Memory

Abstract This study investigates the role of theta frequency transcranial alternating current stimulation (tACS) in enhancing the consolidation of newly acquired semantic knowledge. Although postencoding theta oscillatory power increase has been reported to benefit episodic memory consolidation, its influence on semantic memory retention has not been examined. In this experiment, 175 participants were taught fundamental immunology concepts and were then randomly assigned to receive either theta or beta tACS, applied through midline frontal, left parietal, or bilateral parietal montages, or sham stimulation as a passive control condition. Memory for that newly acquired knowledge was assessed before and shortly after the intervention, 24 hr later, and 1 week later, to evaluate both acute and longer-lasting effects of the stimulation. Results indicated that theta tACS significantly enhanced memory consolidation compared with both sham and beta conditions, especially when applied using a parietal montage targeting the area of the left angular gyrus. The resulting improved performance was consistent across all stages of assessment, indicating a robust effect of postencoding theta stimulation on the persistence of semantic memory. This suggests that some processes and substrates of early memory consolidation are common to episodic and semantic memories. These findings hold practical implications for educational and therapeutic contexts, suggesting that theta tACS might be used to reinforce learning, in both healthy and memory-challenged individuals.