Abstract
Application of transcranial alternating current stimulation (tACS) is thought to modulate ongoing brain oscillations in a frequency-dependent manner. However, recent studies report various and sometimes inconsistent results regarding its capacity to induce changes in cortical activity beyond the stimulation period. Here, thirty healthy volunteers participated in a randomized, cross-over, sham-controlled, double-blind study using EEG to measure the offline effects of tACS on alpha and beta power. Sham and high current density tACS (1 mA; 10 Hz and 20 Hz; 0.32 mA/cm2) were applied for 20 min over bilateral sensorimotor areas and EEG was recorded at rest before and after stimulation for 20 min. Bilateral tACS was not associated with significant changes in local alpha and beta power frequencies at stimulation sites (C3 and C4 electrodes). Overall, the present results fail to provide evidence that bilateral tACS with high current density applied over sensorimotor regions at 10 and 20 Hz reliably modulates offline brain oscillation power at the stimulation site. These results may have implications for the design and implementation of future protocols aiming to induce sustained changes in brain activity, including in clinical populations.
Highlights
The endogenous oscillations of the brain are associated with specific cognitive functions and are believed to play an important role in regimenting communication between cortical and subcortical a reas[1,2]
The goal of the present study was to determine whether transcranial alternating current stimulation (tACS) applied at fixed frequencies of 10 Hz and 20 Hz over sensorimotor areas can induce oscillatory aftereffects in the stimulated areas
Bayesian analyses further support the absence of effects on alpha and beta power post-tACS
Summary
The endogenous oscillations of the brain are associated with specific cognitive functions and are believed to play an important role in regimenting communication between cortical and subcortical a reas[1,2]. Considering their putative association with various cognitive states and pathophysiological d isorders[3,4], there is high interest in modulating these oscillations non-invasively. Studies using transcranial magnetic stimulation (TMS) have shown frequency-specific tACS effects on corticospinal e xcitability[9,10,11]. Whereas some studies have reported offline effects of alpha or beta tACS on corticospinal excitability[11,37,38], most studies have shown no aftereffects[19,39,40,41,42,43] or mixed results[21,44,45]
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