EEG-triggered TMS of dorsomedial prefrontal cortex selectively modulates working memory performance depending on the phase of endogenous theta oscillation

Abstract

The theta-oscillation of the prefrontal cortex is associated with multiple cognitive functions such as memory retention and processing. The phases of this oscillation represent different states of excitability. The objective of this thesis was to determine whether a phase-specific stimulation, either targeting the negative or positive peak of the ongoing theta rhythm in the dmPFC, results in different effects on working memory performance and is superior to random phase stimulation. 16 healthy subjects participated in this study with 4 sessions on separate days, with 3 of the sessions including an EEG-triggered phase-dependent TMS intervention. The stimulation was applied in 400 triple-pulses either targeted at the negative peak, positive peak, or at a random phase. The working memory performance was assessed with a modified Sternberg task. The negative peak stimulation resulted in a significant improvement in the reaction times in the Sternberg task and showed a significant difference compared to the random stimulation. The results on healthy subjects indicate that this designed method of an EEG-triggered phase-dependent TMS could help refine current TMS therapy protocols and, thereby, improve response rates of TMS therapy.