Memory’s pulse: episodic memory formation is theta-rhythmic

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 SPEAR (Separate Phases for Encoding and Retrieval) model. In a pre-registered study, we adapted a dense sampling approach to reconstruct the time-course of how well 125 people formed memories across milliseconds. We found that memory formation 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. Critically, our findings provide behavioral evidence for the SPEAR model and reveal the finest timescale at which experience is carved up into memories.