Rhythmic Sampling Supports Episodic Memory Formation

Theta oscillations (3-9 Hz) in the hippocampus have been posited to mitigate the trade-offs between encoding and retrieval by segregating them in time (i.e. at opposite phases). However, there is limited behavioral evidence that humans cognitively cycle in and out of encoding and retrieval states at this rhythm. Here, I adapted the behavioral oscillation paradigm to investigate if episodic memory formation is rhythmic. In the present experiment (n=79) I found that associative retrieval performance oscillated at the theta frequency (5-6 Hz) with respect to a cue-image delay during the time of encoding. This same rhythmicity was not found for an attention task performed during the time of encoding, suggesting rhythmicity in memory formation was found over and above rhythmicity in perceptual processing. These data provide the first evidence demonstrating that human memory formation oscillates at a similar frequency as neural oscillations in the hippocampus known to underlie memory formation.M.A