Perturbation of theta-gamma coupling at the temporal lobe hinders verbal declarative memory

Publication date: Available online 25 December 2017
Source:Brain Stimulation
Author(s): Gabriel Amador de Lara, Ivan Alekseichuk, Zsolt Turi, Albert Lehr, Andrea Antal, Walter Paulus
BackgroundPhase-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 communications 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.MethodsIn 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.ResultsGamma 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.ConclusionsOur results demonstrate direct evidence regarding the importance of theta-gamma coupling in verbal long-term memory formation.



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