Personal Rhythms of Memory: Investigating Individual Effects of Preferred Theta Phase Lag between Sensory Inputs on Associative Memory

Episodic memory formation requires integrating multisensory information. Inspired by animal research on how hippocampal theta oscillations modulate long-term potentiation, recent human studies have demonstrated that memory for auditory and visual stimuli modulated synchronously at theta frequency (4 Hz) is better than when those stimuli are modulated asynchronously; the so-called Theta-Induced Memory Enhancement (TIME) effect. However, recent failures to replicate the TIME effect question its robustness and dependence on other variables. One such variable may be inter-individual differences in neural sensitivity to the precise phase lag between auditory and visual streams. In this online study, we therefore test a wider range of phase lags between 4 Hz modulated audio and visual stimuli to test whether the TIME effect shows a different optimal phase lag in each participant. Using simulation methods from Zoefel et al. (2019), we estimated the sample size to achieve 90% statistical power to detect a participant-dependent effect of phase lag. Finding such an effect would provide further support for the role of theta oscillations in associative memory in humans, and could potentially inform future experimental designs to investigate this further.