Stecher, Heiko I. and Herrmann, Christoph S. (2018) Absence of alpha-tACS aftereffects in darkness reveals importance of taking derivations of stimulation frequency and individual slpha variability into account. Frontiers in psychology, 9 (984). ISSN 1664-1078

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Transcranial alternating current stimulation (tACS) has found widespread use as a basic tool in the exploration of the role of brain oscillations. Many studies have shown that frequency-specific tACS is able to not only alter cognitive processes during stimulation, but also cause specific physiological aftereffects visible in the electroencephalogram (EEG). The relationship between the emergence of these aftereffects and the necessary duration of stimulation is inconclusive. Our goal in this study was to narrow down the crucial length of tACS-blocks, by which aftereffects can be elicited. We stimulated participants with α-tACS in four blocks of 1-, 3-, 5-, and 10-min length, once in increasing and once in decreasing order. After each block, we measured the resting EEG for 10 min during a visual vigilance task. We could not find lasting enhancement of α-power following any stimulation block, when comparing the stimulated groups to the sham group. These findings offer no information regarding the crucial stimulation duration. In addition, this conflicts with previous findings, showing a power increase following 10 min of tACS in the alpha range. We performed additional explorative analyses, based on known confounds of (1) mismatches between stimulation frequency and individual alpha frequency and (2) abnormalities in baseline α-activity. The results of an ANCOVA suggested that both factor explain variance, but could not resolve how exactly both factors interfere with the stimulation effect. Employing a linear mixed model, we found a significant effect of stimulation following 10 min of α-tACS in the increasing sequence and a significant effect of the mismatch between stimulated frequency and individual alpha frequency. The implications of these findings for future research are discussed.

Item Type: Article
Additional Information: Publiziert mit Hilfe des DFG-geförderten Open Access-Publikationsfonds der Carl von Ossietzky Universität Oldenburg.
Uncontrolled Keywords: transcranial alternating current stimulation (tACS), EEG, aftereffect, alpha oscillations, replication, tES reliability
Subjects: Philosophy and psychology > Psychology
Divisions: Faculty of Medicine and Health Sciences > Department of Psychology
Date Deposited: 02 Aug 2018 07:49
Last Modified: 08 Aug 2018 10:10
URN: urn:nbn:de:gbv:715-oops-37553
DOI: 10.3389/fpsyg.2018.00984

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