# Pre-stimulus alpha power modulates trial-by-trial variability in theta rhythmic multisensory entrainment strength and theta-induced memory effect

## TL;DR

The study shows that brain activity before a task affects how well multisensory stimulation improves memory.

## Contribution

The paper introduces the role of pre-stimulus alpha power in modulating multisensory entrainment and memory effects.

## Key findings

- Pre-stimulus alpha power modulates sensory region entrainment strength during rhythmic multisensory stimulation.
- Stronger entrainment predicts better subsequent memory formation.
- Synchrony between stimulation and theta phase is crucial for memory enhancement.

## Abstract

Binding multisensory information into episodic memory depends partly on the timing of the hippocampal theta rhythm which provides time windows for synaptic modification. In humans, theta rhythmic sensory stimulation (RSS) enhances episodic memory when the stimuli are synchronised across the visual and auditory domain compared to when they are out-of-synchrony. However, recent studies show mixed evidence if the improvement in episodic memory is the result of modulating hippocampal theta activity. In the current study, we investigated whether pre-stimulus brain state could explain part of this variance in the neural and behavioural effects induced by the RSS, via recording 24 participants’ brain activity with MEG during a multisensory theta RSS memory paradigm. Our findings suggest that pre-stimulus alpha power modulates entrainment strength in sensory regions, which in turn predicts subsequent memory formation. These findings suggest that for non-invasive brain stimulation tools to be effective it is crucial to consider brain-state dependent effects.

Synchronised rhythmic multisensory entrainment enhances episodic memory performance only when the trials’ actual theta phases follow the stimulation faithfully. Pre-stimulus alpha plays a role in modulating the upcoming trials’ entrainment strength.