Episodic memory encoding fluctuates at a theta rhythm from 3-10 Hz

Why do some experiences endure in memory better than others? Here, we explore the possibility that learning fluctuates rhythmically several times per second, with fortuitously timed experiences being more memorable. Although such fleeting opportunities for encoding would evade our awareness, they are predicted by a prominent model describing how theta rhythms in the brain coordinate memory – the Separate Phases for Encoding and Retrieval (SPEAR) model. Here, in a pre-registered study, we adapted a dense sampling approach to reconstruct the millisecond time-course of memory encoding in n=125 participants. We found that memory encoding fluctuated at a theta rhythm (3-10 Hz), that these rhythms were not a byproduct of rhythmic attention, and that—like theta rhythms in the brain—memory rhythms were modulated by putative markers of acetylcholine. Our findings provide behavioral evidence consistent with the SPEAR model of episodic memory.