Theta-frequency sensory entrainment promotes episodic memory consolidation

Neural oscillations in the theta frequency range have been implicated in episodic memory processes. Previous work using EEG neurofeedback and non-invasive brain stimulation has demonstrated that enhancing theta activity immediately after encoding can improve long-term memory retention. The present study examined whether audio-visual entrainment combined with cranio-electro stimulation (AVE + CES), a noninvasive and accessible method, may similarly support early stages of consolidation. Sixty-nine undergraduate participants were assigned to one of three oscillatory sensory entrainment conditions: Theta 3 Hz and Theta 5.5 Hz (to examine frequency-specific theta effects), or Beta 16 Hz (as a control condition). Participants completed three study-test cycles of an episodic free-recall task, followed by 20 min of AVE + CES during which they were exposed to rhythmically flashing lights, pulsing tones, and mild earlobe electrical stimulation. Memory performance was assessed immediately after entrainment, after 24 h, and after one week. Baseline-corrected retention scores were computed relative to pre-entrainment performance. No group differences were observed prior to entrainment and baseline-corrected retention did not differ between groups immediately following entrainment. However, both theta groups exhibited significantly reduced forgetting relative to the beta group after 24 h and one week, with no differences between the two theta frequencies. These findings suggest that theta-frequency sensory entrainment broadly enhances episodic memory consolidation, highlighting AVE + CES as a promising and accessible approach for promoting mnemonic retention.