scholarly journals Effects of transcranial alternating-current stimulation to secondary motor areas on cortical oscillations in stroke patients

2019 ◽  
Author(s):  
Lutz A. Krawinkel ◽  
Marlene Bönstrup ◽  
Jan F. Feldheim ◽  
Robert Schulz ◽  
Winifried Backhaus ◽  
...  
Keyword(s):  
Phase Locking ◽  
Premotor Cortex ◽  
Alternating Current ◽  
Oscillatory Activity ◽  
Stroke Patients ◽  
Cortical Oscillations ◽  
Motor Network ◽  
Transcranial Alternating Current Stimulation ◽  
Phase Locking Value ◽  
Motor Areas

AbstractBackgroundThere is growing evidence that secondary motor areas are relevant for recovery after motor stroke. Communication among brain areas occurs via synchronization of oscillatory activity which can potentially be modulated via transcranial alternating-current stimulation (tACS).HypothesisWe hypothesized that tACS to secondary motor areas of the stroke-lesioned hemisphere leads to modulation of task-related connectivity among primary and secondary motor areas, reflected in metrics of EEG coupling in the frequency domain.MethodsWe applied focal tACS at 1mA peak-to-peak intensity to ipsilesional ventral premotor cortex (PMv) and supplementary motor area (SMA) in chronic stroke patients while they moved their impaired hand. To probe effects of stimulation on cortical oscillations, several task-related EEG-based connectivity metrics (coherence, imaginary coherence, phase-locking value, mutual information) were assessed before and after each stimulation.ResultsOverall, we found significant but weak modulations of the motor network by tACS. Stimulation of PMv reduced task-related coupling between (i) both primary motor cortices (M1) (coherence, −0.0514±0.0665 (mean±SD, active stimulation) vs. 0.0085±0.0888 (sham), p=0.0029) and (ii) between ipsilesional M1 and contralesional PMv (coherence, - 0.0386±0.0703 vs. 0.0226±0.0694, p=0.0283; phase-locking value, −0.0363±0.0581 vs. 0.0036±0.0497, p=0.0097) compared with sham stimulation.ConclusionsIn this exploratory analysis, tACS to the ipsilesional PMv induced a weak decrease of task-related connectivity between ipsilesional M1 and contralesional M1 and PMv. As an excess of interhemispheric coupling is under discussion as maladaptive phenomenon of motor reorganization after stroke (e.g., bimodal balance-recovery model), tACS-induced reduction of coupling might be an interesting approach to assist re-normalization of the post-stroke motor network.

scholarly journals Alpha oscillatory activity causally linked to working memory retention: insights from online phase-locking closed-loop transcranial alternating current stimulation (tACS)

2021 ◽  
Author(s):  
Xueli Chen ◽  
Ru Ma ◽  
Wei Zhang ◽  
Qianying Wu ◽  
Ajiguli Yimiti ◽  
...  
Keyword(s):  
Working Memory ◽  
Closed Loop ◽  
Phase Locking ◽  
Alternating Current ◽  
Causal Link ◽  
Oscillatory Activity ◽  
Memory Retention ◽  
Alpha Oscillations ◽  
Transcranial Alternating Current Stimulation ◽  
Retention Intervals

Although previous studies have reported correlations between alpha oscillations and the "retention" sub-process of working memory (WM), no direct causal evidence has been established in human neuroscience. Here, we developed an online phase-locking closed-loop transcranial alternating current stimulation (tACS) system capable of precisely controlling the phase difference between tACS and concurrent endogenous oscillations. This system permits both up- and down-regulation of brain oscillations at the target stimulation frequency, and is here applied to empirically demonstrate that parietal alpha oscillations causally relate to WM retention. Our experimental design included both in-phase and anti-phase alpha-tACS applied to 39 participants during the retention intervals of a modified Sternberg paradigm. Compared to in-phase alpha-tACS, anti-phase alpha-tACS decreased both WM performance and alpha activity. Moreover, the in-phase tACS-induced changes in WM performance were positively correlated with alpha oscillatory activity. These findings strongly support a causal link between alpha oscillations and WM retention, and illustrate the broad application prospects of phase-locking tACS.

scholarly journals The role of alpha oscillations in a premotor-cerebellar loop in modulation of motor learning: insights from transcranial alternating current stimulation

2020 ◽  
Author(s):  
Christine Schubert ◽  
Alhuda Dabbagh ◽  
Joseph Classen ◽  
Ulrike M. Krämer ◽  
Elinor Tzvi
Keyword(s):  
Motor Learning ◽  
Sequence Learning ◽  
Premotor Cortex ◽  
Alternating Current ◽  
Oscillatory Activity ◽  
Motor Sequence Learning ◽  
Motor Sequence ◽  
Alpha Oscillations ◽  
Transcranial Alternating Current Stimulation

AbstractAlpha oscillations (8-13 Hz) have been shown to play an important role in dynamic neural processes underlying learning and memory. The goal of this study was to scrutinize the role of α oscillations in communication within a network implicated in motor sequence learning. To this end, we conducted two experiments using the serial reaction time task. In the first experiment, we explored changes in α power and cross-channel α coherence. We found a gradual decrease in learning-related α power over left premotor cortex (PMC), somatosensory cortex (S1) and tempo-parietal junction (TPJ). Alpha coherence between left PMC/S1 and right cerebellar crus I was reduced for sequence learning, possibly reflecting a functional decoupling in a motor-cerebellar loop during the motor learning process. In the second experiment in a different cohort, we applied 10Hz transcranial alternating current stimulation (tACS), a method shown to entrain local oscillatory activity, to left M1 (lM1) and right cerebellum (rCB) during sequence learning. We observed learning deficits during rCB tACS compared to sham, but not during lM1 tACS. In addition, learning-related α power following rCB tACS was increased in left PMC, possibly reflecting a decrease in neural activity. Importantly, learning-specific coherence between left PMC and right cerebellar lobule VIIb was enhanced following rCB tACS. These findings suggest that interactions within a premotor-cerebellar loop, which are underlying motor sequence learning, are mediated by α oscillations. We show that they can be modulated through external entrainment of cerebellar oscillations, which then modulates motor cortical α and interferes with sequence learning.

scholarly journals Conducting double-blind placebo-controlled clinical trials of transcranial alternating current stimulation (tACS)

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Flavio Frohlich ◽  
Justin Riddle
Keyword(s):  
Rational Design ◽  
Target Identification ◽  
Alternating Current ◽  
Sine Wave ◽  
Brain Network ◽  
Double Blind ◽  
Double Blind Placebo ◽  
Cortical Oscillations ◽  
Transcranial Alternating Current Stimulation ◽  
Therapeutic Platform

AbstractMany psychiatric and neurological illnesses can be conceptualized as oscillopathies defined as pathological changes in brain network oscillations. We previously proposed the application of rational design for the development of non-invasive brain stimulation for the modulation and restoration of cortical oscillations as a network therapeutic. Here, we show how transcranial alternating current stimulation (tACS), which applies a weak sine-wave electric current to the scalp, may serve as a therapeutic platform for the treatment of CNS illnesses. Recently, an initial series of double-blind, placebo-controlled treatment trials of tACS have been published. Here, we first map out the conceptual underpinnings of such trials with focus on target identification, engagement, and validation. Then, we discuss practical aspects that need to be considered for successful trial execution, with particular regards to ensuring successful study blind. Finally, we briefly review the few published double-blind tACS trials and conclude with a proposed roadmap to move the field forward with the goal of moving from pilot trials to convincing efficacy studies of tACS.

scholarly journals Perception of Rhythmic Speech Is Modulated by Focal Bilateral Transcranial Alternating Current Stimulation

2020 ◽  
Vol 32 (2) ◽  
pp. 226-240 ◽  
Author(s):  
Benedikt Zoefel ◽  
Isobella Allard ◽  
Megha Anil ◽  
Matthew H. Davis
Keyword(s):  
Speech Perception ◽  
Speech Processing ◽  
Alternating Current ◽  
Stream Segregation ◽  
Causal Role ◽  
Oscillatory Activity ◽  
Transcranial Alternating Current Stimulation ◽  
Neural Entrainment ◽  
Actual Speech

Several recent studies have used transcranial alternating current stimulation (tACS) to demonstrate a causal role of neural oscillatory activity in speech processing. In particular, it has been shown that the ability to understand speech in a multi-speaker scenario or background noise depends on the timing of speech presentation relative to simultaneously applied tACS. However, it is possible that tACS did not change actual speech perception but rather auditory stream segregation. In this study, we tested whether the phase relation between tACS and the rhythm of degraded words, presented in silence, modulates word report accuracy. We found strong evidence for a tACS-induced modulation of speech perception, but only if the stimulation was applied bilaterally using ring electrodes (not for unilateral left hemisphere stimulation with square electrodes). These results were only obtained when data were analyzed using a statistical approach that was identified as optimal in a previous simulation study. The effect was driven by a phasic disruption of word report scores. Our results suggest a causal role of neural entrainment for speech perception and emphasize the importance of optimizing stimulation protocols and statistical approaches for brain stimulation research.

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

2018 ◽  
Author(s):  
Florian H. Kasten ◽  
Burkhard Maess ◽  
Christoph S. Herrmann
Keyword(s):  
Mental Rotation ◽  
Spatial Filtering ◽  
Alternating Current ◽  
Mental Rotation Task ◽  
Oscillatory Activity ◽  
Control Analysis ◽  
Alpha Band ◽  
Oscillatory Dynamics ◽  
Continuous Application ◽  
Transcranial Alternating Current Stimulation

AbstractNon-invasive approaches to modulate oscillatory activity in the brain receive growing popularity in the scientific community. Transcranial alternating current stimulation (tACS) has been shown to modulate neural oscillations in a frequency specific manner. Due to a massive stimulation artifact at the targeted frequency, only little is known about effects of tACS during stimulation. I.e. it remains unclear how the continuous application of tACS affects event-related oscillations during cognitive tasks. Depending on whether tACS merely affects pre‐ or post-stimulus oscillations or both, stimulation can alter patterns of event-related oscillatory dynamics in various directions or may not affect them at all. Thus, knowledge about these directions is crucial to plan, predict and understand outcomes of solely behavioral tACS experiments. Here, a recently proposed procedure to suppress tACS artifacts by projecting MEG data into source space using spatial filtering was utilized to recover event-related power modulations in the alpha band during a mental rotation task. MEG of twenty-five volunteers was continuously recorded. After 10 minutes of baseline measurement, they received either 20 minutes of tACS at individual alpha frequency or sham stimulation. Another 40 minutes of MEG were acquired thereafter. Data were projected into source space and carefully examined for residual artifacts. Results revealed strong facilitation of event-related power modulations in the alpha band during tACS application. Data provide first direct evidence, that tACS does not counteract top-down suppression of intrinsic oscillations, but rather enhances pre-existent power modulations within the range of the individual alpha (=stimulation) frequency.SignificanceTranscranial alternating current stimulation (tACS) is increasingly used in cognitive neuroscience to study the causal role of brain oscillations and cognition. However, online effects of tACS so far largely remain a ‘black box’ due to an intense electromagnetic artifact encountered during stimulation. The current study is the first to employ a spatial filtering approach to recover and systematically study event-related oscillatory dynamics during tACS, which can potentially be altered in various directions. TACS facilitated pre-existing patterns of oscillatory dynamics during the employed mental rotation task, but does not counteract or overwrite them. In addition, control analysis and a measure to quantify tACS artifact suppression are provided that can enrich future studies investigating tACS online effects.

scholarly journals The hidden state-dependency of transcranial alternating current stimulation (tACS)

2020 ◽  
Author(s):  
Florian H. Kasten ◽  
Christoph S. Herrmann
Keyword(s):  
Markov Models ◽  
Alternating Current ◽  
Oscillatory Activity ◽  
Brain Disorders ◽  
State Dependency ◽  
Non Invasive ◽  
Transcranial Alternating Current Stimulation ◽  
Brain States ◽  
Invasive Techniques ◽  
The Brain

AbstractNon-invasive techniques to electrically stimulate the brain such as transcranial direct and alternating current stimulation (tDCS/tACS) are increasingly used in human neuroscience and offer potential new avenues to treat brain disorders. However, their often weak and variable effects have also raised concerns in the scientific community. A possible factor influencing the efficacy of these methods is the dependence on brain-states. Here, we utilized Hidden Markov Models (HMM) to decompose concurrent tACS-magnetoencephalography data into transient brain-states with distinct spatial, spectral and connectivity profiles. We found that out of four spontaneous brain-states only one was susceptible to tACS. No or only marginal effects were found in the remaining states. TACS did not influence the time spent in each state. Our results suggest, that tACS effects may be mediated by a hidden, spontaneous state-dependency and provide novel insights to the changes in oscillatory activity underlying aftereffects of tACS.

scholarly journals Local network-level integration mediates effects of transcranial Alternating Current Stimulation

2017 ◽  
Author(s):  
Marco Fuscà ◽  
Philipp Ruhnau ◽  
Toralf Neuling ◽  
Nathan Weisz
Keyword(s):  
Occipital Cortex ◽  
Alternating Current ◽  
Functional Network ◽  
Local Network ◽  
Oscillatory Activity ◽  
Alpha Power ◽  
State Dependency ◽  
External Stimulation ◽  
Posterior Cingulate ◽  
Transcranial Alternating Current Stimulation

AbstractTranscranial alternating current stimulation (tACS) has been proposed as a tool to draw causal inferences on the role of oscillatory activity in cognitive functioning and has the potential to induce long-term changes in cerebral networks. However, the mechanisms of action of tACS are not yet clear, though previous modeling works have suggested that variability may be mediated by local and network-level brain states. We used magnetoencephalography (MEG) to record brain activity from 17 healthy participants as they kept their eyes open (EO) or closed (EC) while being stimulated either with sham, weak, or strong alpha-tACS using a montage commonly assumed to target occipital areas. We reconstructed the activity of sources in all stimulation conditions by means of beamforming. The analysis of resting-state data revealed an interaction of the external stimulation with the endogenous alpha power difference between EO and EC in the posterior cingulate. This region is remote from occipital cortex, which showed strongest EC vs. EO alpha modulation, thus suggesting state-dependency long-range effects of tACS. In a follow-up analysis of this online-tACS effect, we find evidence that this dependency effect could be mediated by functional network changes: connection strength from the precuneus, a region adjusting for a measure of network integration in the two states (EC vs. EO during no-tACS), was significantly correlated with the state-dependency effect in the posterior cingulate (during tACS). No analogous correlation could be found for alpha power modulations in occipital cortex. Altogether, this is the first strong evidence to illustrate how functional network architectures can shape tACS effects.

scholarly journals Multivariate pattern analysis reveals location specific aftereffects of 10Hz motor cortex transcranial alternating current stimulation

2021 ◽  
Author(s):  
Elinor Tzvi ◽  
Jalal Alizadeh ◽  
Christine Schubert ◽  
Joseph Classen
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Pattern Analysis ◽  
Premotor Cortex ◽  
Alternating Current ◽  
Eeg Signal ◽  
Multivariate Pattern Analysis ◽  
Eeg Signals ◽  
Transcranial Alternating Current Stimulation ◽  
Multivariate Pattern

Background: Transcranial alternating current stimulation (tACS) may induce frequency-specific aftereffects on brain oscillations in the stimulated location, which could serve as evidence for region-specific neuroplasticity. Aftereffects of tACS on the motor system remain unknown. Objective: To find evidence for aftereffects in short EEG segments following tACS to two critical nodes of the motor network, namely, left motor cortex (lMC) and right cerebellum (rCB). We hypothesized that aftereffects of lMC will be stronger in and around lMC compared to both active stimulation of rCB, as well as inactive (sham) control conditions. Methods: To this end, we employed multivariate pattern analysis (MVPA), and trained a classifier to distinguish between EEG signals following each of the three stimulation protocols. This method accounts for the multitude facets of the EEG signal and thus is more sensitive to subtle modulation of the EEG signal. Results: EEG signals in both theta (θ, 4-8Hz) and alpha (α, 8-13Hz) were better classified to lMC-tACS compared to rCB-tACS/sham, in and around lMC-tACS stimulation locations (electrodes FC3 and CP3). This effect was associated with a decrease in power following tACS. Source reconstruction revealed significant differences in premotor cortex but not in primary motor cortex as the computational model suggested. Correlation between classification accuracies in θ and α in lMC-tACS was stronger compared to rCB-tACS/sham, suggesting cross-frequency effects of tACS. Nonetheless, θ/α phase-coupling did not differ between stimulation protocols. Conclusions: Successful classification of EEG signals to left motor cortex using MVPA revealed focal tACS aftereffects on the motor cortex, indicative of region-specific neuroplasticity.

scholarly journals Phase-specific manipulation of neural oscillatory activity by transcranial alternating current stimulation

2019 ◽  
Author(s):  
Marina Fiene ◽  
Bettina C. Schwab ◽  
Jonas Misselhorn ◽  
Christoph S. Herrmann ◽  
Till R. Schneider ◽  
...  
Keyword(s):  
Phase Shift ◽  
Occipital Cortex ◽  
Alternating Current ◽  
Oscillatory Activity ◽  
Optimal Timing ◽  
Healthy Human ◽  
Oscillatory Phase ◽  
Transcranial Alternating Current Stimulation ◽  
Onset Delays ◽  
Human Participants

AbstractBackgroundOscillatory phase has been proposed as a key parameter defining the spatiotemporal structure of neural activity. To enhance our understanding of brain rhythms and improve clinical outcomes in pathological conditions, phase-specific modulation of oscillations by transcranial alternating current stimulation (tACS) emerged as a promising approach. However, the effectiveness of tACS in humans is still critically debated.ObjectiveHere, we investigated the phase-specificity of tACS effects on visually evoked steady state responses (SSRs) in 24 healthy human participants of either sex.MethodsTo this end, we used an intermittent electrical stimulation protocol and assessed the influence of tACS on SSR amplitude in the interval immediately following tACS.ResultsWe observed that the phase shift between flicker and tACS modulates evoked SSR amplitudes. The tACS effect size was dependent on the strength of flicker-evoked oscillatory activity, with larger effects in participants showing weaker locking of neural responses to flicker phase. Neural sources of phase-specific effects were localized in the parieto-occipital cortex within flicker-entrained regions. Importantly, the optimal phase shift between flicker and tACS associated with strongest SSRs was correlated with cortical SSR onset delays over the visual cortex.ConclusionsOverall, our data provide electrophysiological evidence for phase-specific modulations of oscillatory activity by tACS in humans. As the optimal timing of tACS application was dependent on neural conduction times as measured by SSR onset delays, data suggest that the interaction between tACS effect and SSR was cortical in nature. These findings corroborate the physiological efficacy of tACS and highlight its potential for controlled modulations of brain signals.

Sign in / Sign up

Export Citation Format

Share Document