Background: Phase-amplitude cross-frequency coupling (PAC) is characterized by the modulation of the power of a fast brain oscillation (e.g., gamma) by the phase of a slow rhythm (e.g., theta). PAC in different sub- and neocortical regions is known to underlie effective neural communication and correlates with successful long-term memory formation. Objective/Hypothesis: The present work aims to extend earlier observational data, by probing the functional role of theta-gamma PAC in the left temporal cortex in humans during verbal long-term memory encoding. Methods: In three double-blinded, placebo-controlled experiments (n = 72), we employed cross-frequency transcranial alternating current stimulation (tACS) to externally modulate ongoing PAC during a verbal-associative learning task. Three types of cross-frequency tACS protocols were used: bursts of high gamma tACS were coupled to the peak or trough of the theta tACS cycle, and a control condition where gamma tACS was continuously superimposed at theta tACS cycles. Results: Gamma bursts coupled to the trough of theta tACS induced robust behavioral impairment in memory performance (p < .01), whereas gamma burst coupled to the peak or continuously superimposed with theta tACS had no significant behavioral effects. Conclusions: Our results demonstrate direct evidence regarding the importance of theta-gamma coupling in verbal long-term memory formation.
Bibliographical noteFunding Information:
We thank Christine Crozier for language editing of the manuscript. This work was supported by the Deutsche Forschungsgemeinschaft ( PA 419/15-1 ) awarded to WP.
© 2017 Elsevier Inc.
Copyright 2018 Elsevier B.V., All rights reserved.
- Long-term memory
- Phase-amplitude cross-frequency coupling
- Temporal lobe
- Verbal episodic memory
PubMed: MeSH publication types
- Journal Article
- Research Support, Non-U.S. Gov't
- Controlled Clinical Trial