Abstract
Transcranial alternating current stimulation (tACS) has been repeatedly demonstrated to modulate endogenous brain oscillations in a frequency specific manner. Thus, it is a promising tool to uncover causal relationships between brain oscillations and behavior or perception. While tACS has been shown to elicit a physiological aftereffect for up to 70 min, it remains unclear whether the effect can still be elicited if subjects perform a complex task interacting with the stimulated frequency band. In addition, it has not yet been investigated whether the aftereffect is behaviorally relevant. In the current experiment, participants performed a Shepard-like mental rotation task for 80 min. After 10 min of baseline measurement, participants received either 20 min of tACS at their individual alpha frequency (IAF) or sham stimulation (30 s tACS in the beginning of the stimulation period). Afterwards another 50 min of post-stimulation EEG were recorded. Task performance and EEG were acquired during the whole experiment. While there were no effects of tACS on reaction times or event-related-potentials (ERPs), results revealed an increase in mental rotation performance in the stimulation group as compared to sham both during and after stimulation. This was accompanied by increased ongoing alpha power and coherence as well as event-related-desynchronization (ERD) in the alpha band in the stimulation group. The current study demonstrates a behavioral and physiological aftereffect of tACS in parallel. This indicates that it is possible to elicit aftereffects of tACS during tasks interacting with the alpha band. Therefore, the tACS aftereffect is suitable to achieve an experimental manipulation.
Highlights
Transcranial alternating current stimulation is a relatively novel method that has been demonstrated to modulate endogenous brain oscillations in a frequency specific manner (Herrmann et al, 2013; Reato et al, 2013; Helfrich et al, 2014b)
While most studies on physiological effects of Transcranial alternating current stimulation (tACS) rely on aftereffects of the stimulation and performed resting-state measurements
While there were no effects on participants’ reaction times, performance in the mental rotation task was significantly enhanced in the stimulation group as compared to sham
Summary
Transcranial alternating current stimulation (tACS) is a relatively novel method that has been demonstrated to modulate endogenous brain oscillations in a frequency specific manner (Herrmann et al, 2013; Reato et al, 2013; Helfrich et al, 2014b). For example, that task complexity and cognitive load modulate event-related-desynchronization (ERD) patterns in the alpha band (Van Winsun et al, 1984; Boiten et al, 1992; Dujardin et al, 1995) It is largely unclear whether the elicited physiological changes affect behavioral measures such as reaction times or task performance. Additional evidence supporting the functional role of alpha desynchronization during mental rotation arises from studies using neurofeedback training (NFT) and repetitive transcranial magnetic stimulation (rTMS) In these studies, ERD in the alpha band was increased by enhancing alpha power in a reference period before stimulus onset (Klimesch et al, 2003; Hanslmayr et al, 2005; Zoefel et al, 2011). The amplitude of these components might be enhanced after tACS in the alpha band
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