Ten Minutes of α-tACS and Ambient Illumination Independently Modulate EEG α-Power

Abstract

Transcranial alternating current stimulation (tACS) sees increased use in neurosciences as a tool for the exploration of brain oscillations. It has been shown that tACS stimulation in specific frequency bands can result in aftereffects of modulated oscillatory brain activity that persist after the stimulation has ended. The general relationship between persistency of the effect and duration of stimulation is sparsely investigated but previous research has shown that the occurrence of tACS aftereffects depends on the brain state before and during stimulation. Early alpha neurofeedback research suggests that particularly in the alpha band the responsiveness to a manipulation depends on the ambient illumination during measurement. Therefore, in the present study we assessed the brain’s susceptibility to tACS at the individual alpha frequency during darkness compared to ambient illumination. We measured alpha power after 10 min of stimulation in 30 participants while they continuously performed a visual vigilance task. Our results show that immediately after stimulation, the alpha power in the illumination condition for both the stimulated and sham group has increased by only about 7%, compared to about 20% in both groups in the ‘dark’ condition. For the group that did not receive stimulation, the power in darkness remained stable after stimulation, whereas the power in light increased by an additional 10% during the next 30 min. For the group that did receive stimulation, alpha power during these 30 min increased by another 11% in light and 22% in darkness. Since alpha power already increased by about 10% without stimulation, the effect of illumination does not seem to have interacted with the effect of stimulation. Instead, both effects seem to have added up linearly. Although our findings do not show that illumination-induced differences in oscillatory activity influence the susceptibility toward tACS, they stress the importance of controlling for factors like ambient light that might add an independent increase or decrease to the power of brain oscillations during periods, where possible persistent effects of stimulation are explored.

Integrating electric field modelling and neuroimaging to explain inter-individual variability of tACS effects

“…To ensure that participants remained awake and attentive during the 40 min measurement, they performed a visual change detection task similar to previous studies 13,16,38,56 (Fig. 1b).…”

Facilitated event-related power-modulations during transcranial alternating current stimulation (tACS) revealed by concurrent tACS-MEG

“…Alpha power increases up to 300-400% 514 fall into a physiologically plausible range for spontaneous alpha power changes or tACS ef-515 fects, as they are observed i.e. in studies on tACS after-effects(Neuling et al, 2013; Kasten 516 and Herrmann, 2017;Stecher et al, 2017). The artifact-to-brain-signal-ratio might neverthe-517 less be a useful tool for future studies to assess whether a residual artifact falls within the 518 same order of magnitude as the brain signal of interest and could also be used to evaluate 519 and optimize the performance of artifact suppression approaches i.e.…”

Modulating Brain Rhythms of Pain using Transcranial Alternating Current Stimulation (tACS)? A Sham-controlled Study in Healthy Human Participants

“…The tonic pain stimulus we applied evokes strong decreases in alpha oscillations in early somatosensory areas [27,39], which, together with previous tACS studies, led us to target S1 alpha oscillations using tACS. However, neuronal entrainment by tACS depends on the amplitude of the targeted oscillations [37,41]. Consequently, tasks which strongly suppress oscillations might be less susceptible for modulations using tACS.…”