Recovering Brain Dynamics During Concurrent tACS-M/EEG: An Overview of Analysis Approaches and Their Methodological and Interpretational Pitfalls

Kasten, Florian H.; Herrmann, Christoph S.

doi:10.1007/s10548-019-00727-7

Cited by 53 publications

(47 citation statements)

References 38 publications

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“…It is thus crucial to validate that tACS effects can be reliably induced in less controlled environments outside the laboratory and to find out which environmental conditions may determine stimulation success. While the assessment of online effects of tACS on EEG oscillations remains a major challenge due to a massive stimulation artefact introduced to electrophysiological recordings-see [114] for a review-the study of stimulation aftereffects in the EEG still provides the most direct evidence for tACS efficacy in naturalistic, or real-life, experiments. In addition, EEG-guided tACS parameter selection may be useful to increase the effects of stimulation.…”

Section: Discussionmentioning

confidence: 99%

The Modulation of Cognitive Performance with Transcranial Alternating Current Stimulation: A Systematic Review of Frequency-Specific Effects

et al. 2020

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Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation technique that allows the manipulation of intrinsic brain oscillations. Numerous studies have applied tACS in the laboratory to enhance cognitive performance. With this systematic review, we aim to provide an overview of frequency-specific tACS effects on a range of cognitive functions in healthy adults. This may help to transfer stimulation protocols to real-world applications. We conducted a systematic literature search on PubMed and Cochrane databases and considered tACS studies in healthy adults (age > 18 years) that focused on cognitive performance. The search yielded n = 109 studies, of which n = 57 met the inclusion criteria. The results indicate that theta-tACS was beneficial for several cognitive functions, including working memory, executive functions, and declarative memory. Gamma-tACS enhanced performance in both auditory and visual perception but it did not change performance in tasks of executive functions. For attention, the results were less consistent but point to an improvement in performance with alpha- or gamma-tACS. We discuss these findings and point to important considerations that would precede a transfer to real-world applications.

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Section: Discussionmentioning

confidence: 99%

The Modulation of Cognitive Performance with Transcranial Alternating Current Stimulation: A Systematic Review of Frequency-Specific Effects

et al. 2020

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“…However, we do not have direct insights to what extent tACS has induced lateralized power changes in the targeted frequency bands due to technical limitations of our EEG system. Assessing effects of tACS on electrophysiological measures imposes a major challenge, as EEG signals are massively contaminated by a strong electromagnetic artifact that cannot be reliably removed up to this point 22 . Given recent successful attempts to uncover online effects of tACS on event-related oscillations 29 , 46 , future studies may be able to directly observe effects of lateralized α- and γ-tACS on (event-related) inter-hemispheric α-/γ-power asymmetry.…”

Section: Discussionmentioning

confidence: 99%

“…The hybrid electrical stimulation/EEG device allows for time-efficient application of multiple stimulation and EEG electrodes and flexible remote control over stimulation signals. However, due to insufficient dynamic range of the EEG system, the large stimulation artifact resulted in saturation of the EEG signals precluding any analysis of EEG signals during stimulation 22 . We further refrained from analyzing task related EEG due to the low spatial sampling available from the system (4-channels).…”

Section: Methodsmentioning

confidence: 99%

“…This way, tACS allows to modulate brain oscillations in a frequency specific manner. Although direct insight into stimulation effects on brain activity in humans are rare due to a massive stimulation artifact introduced to electrophysiological recordings 22 , elevated power in the stimulated frequency band has been repeatedly observed in EEG recordings after stimulation 23 – 27 . Other studies applied stimulation at frequencies antagonistically coupled to the target oscillation in order to reduce its power.…”

Section: Introductionmentioning

confidence: 99%

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Hemisphere-specific, differential effects of lateralized, occipital–parietal α- versus γ-tACS on endogenous but not exogenous visual-spatial attention

Kasten

Wendeln

Stecher

et al. 2020

Sci Rep

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Orienting spatial attention has been associated with interhemispheric asymmetry of power in the α- and γ-band. Specifically, increased α-power has been linked to the inhibition of unattended sensory streams (e.g. the unattended visual field), while increased γ-power is associated with active sensory processing. Here, we aimed to differentially modulate endogenous and exogenous visual-spatial attention using transcranial alternating current stimulation (tACS). In a single-blind, within-subject design, participants performed several blocks of a spatial cueing task comprised of endogenous and exogenous cues while receiving lateralized α- or γ-tACS or no stimulation over left or right occipital-parietal areas. We found a significant, differential effect of α- and γ-tACS on endogenous (top-down) spatial attention but not on exogenous (bottom-up) attention. The effect was specific to tACS applied to the left hemisphere and driven by a modulation of attentional disengagement and re-orientation as measured during invalid trials. Our results indicate a causal role of α-/γ-oscillations for top-down (endogenous) attention. They may further suggest a left hemispheric dominance in controlling interhemispheric α-/γ-power asymmetry. The absence of an effect on exogenous attention may be indicative of a differential role of α-/γ-oscillations during different attention types or spatially distinct attentional subsystems.

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“…These residuals likely originate from non-linear modulations of the tACS artifact elicited by physiological processes in the human body (Noury et al, 2016;Noury and Siegel, 2018), which also have to be taken into account in EEG recordings. The issue of tACS artifact correction in MEG data is discussed elsewhere (Neuling et al, 2015;Noury et al, 2016;Neuling et al, 2017;Noury and Siegel, 2018;Kasten and Herrmann, 2019) and will not be further addressed in this article.…”

Section: Introductionmentioning

confidence: 99%

Signal-Space Projection Suppresses the tACS Artifact in EEG Recordings

Vosskuhl

Mutanen

Neuling

et al. 2020

Front. Hum. Neurosci.

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BackgroundTo probe the functional role of brain oscillations, transcranial alternating current stimulation (tACS) has proven to be a useful neuroscientific tool. Because of the excessive tACS-caused artifact at the stimulation frequency in electroencephalography (EEG) signals, tACS + EEG studies have been mostly limited to compare brain activity between recordings before and after concurrent tACS. Critically, attempts to suppress the artifact in the data cannot assure that the entire artifact is removed while brain activity is preserved. The current study aims to evaluate the feasibility of specific artifact correction techniques to clean tACS-contaminated EEG data.New MethodIn the first experiment, we used a phantom head to have full control over the signal to be analyzed. Driving pre-recorded human brain-oscillation signals through a dipolar current source within the phantom, we simultaneously applied tACS and compared the performance of different artifact-correction techniques: sine subtraction, template subtraction, and signal-space projection (SSP). In the second experiment, we combined tACS and EEG on one human subject to demonstrate the best-performing data-correction approach in a proof of principle.ResultsThe tACS artifact was highly attenuated by SSP in the phantom and the human EEG; thus, we were able to recover the amplitude and phase of the oscillatory activity. In the human experiment, event-related desynchronization could be restored after correcting the artifact.Comparison With Existing MethodsThe best results were achieved with SSP, which outperformed sine subtraction and template subtraction.ConclusionOur results demonstrate the feasibility of SSP by applying it to a phantom measurement with pre-recorded signal and one human tACS + EEG dataset. For a full validation of SSP, more data are needed.

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Recovering Brain Dynamics During Concurrent tACS-M/EEG: An Overview of Analysis Approaches and Their Methodological and Interpretational Pitfalls

Cited by 53 publications

References 38 publications

The Modulation of Cognitive Performance with Transcranial Alternating Current Stimulation: A Systematic Review of Frequency-Specific Effects

The Modulation of Cognitive Performance with Transcranial Alternating Current Stimulation: A Systematic Review of Frequency-Specific Effects

Hemisphere-specific, differential effects of lateralized, occipital–parietal α- versus γ-tACS on endogenous but not exogenous visual-spatial attention

Signal-Space Projection Suppresses the tACS Artifact in EEG Recordings

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