Abstract
Rodent research indicates that the hippocampus naturally oscillates between memory encoding and retrieval phases at theta rhythm, indicating that the timing of when information reaches the hippocampus can determine encoding success. However, non-invasively probing such oscillations is challenging in humans. Here, we employed a recently developed dense sampling approach to construct a time course of memory encoding success. Using an attention-grabbing cue expected to reset theta phase, we varied the delay between the cue and to-be-remembered stimulus. Experiment 1 replicated recent finding that human associative memory performance fluctuates with theta rhythmicity, with the best fitting frequency at 8 Hz. Experiment 2 tested and confirmed a new prediction that memory precision also fluctuates with theta rhythmicity, consistent with hippocampal models postulating oscillations in the relative engagement of alternative processing pathways. Together, these findings suggest that the rapid neural fluctuations underpinning memory processes are robust enough to be observed using the dense behavioral sampling approach. Moreover, this work substantiates models of episodic memory and provides new avenues to study models of hippocampal function in humas noninvasively, providing evidence from a purely behavioral approach that human mnemonic discrimination fluctuates with theta rhythm.