Effects of beta-tACS on corticospinal excitability: A meta-analysis

Wischnewski, Miles; Schutter, Dennis J.L.G.; Nitsche, Michael A.

doi:10.1016/j.brs.2019.07.023

Cited by 58 publications

(53 citation statements)

References 65 publications

(70 reference statements)

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“…It is also possible that the -alpha related pulsed facilitation of corticospinal excitability observed in this experiment only holds for the case of spontaneous -alpha oscillations at rest, whereas relative inhibition may be observable in MEP and SICI during -alpha de-and resynchronization in the context of motor tasks. Interestingly, such a state-dependent flip of effect direction has also been observed for TACS of the motor cortex at beta frequency (for a recent meta-analysis see Wischnewski et al, 2019), which paradoxically increased corticospinal excitability during rest (Feurra et al, 2011(Feurra et al, , 2013 but not during motor imagery (Feurra et al, 2013), while having the expected inhibitory or akinetic effect on motor performance (Pogosyan et al, 2009;Joundi et al, 2012). Then again, TACS at alpha frequency facilitated corticospinal excitability when applied during motor imagery rather than rest (Feurra et al, 2013).…”

Section: Potential Mechanisms Mediating -Alpha Related Pulsed Facilitmentioning

confidence: 69%

Pulsed Facilitation of Corticospinal Excitability by the Sensorimotor μ-Alpha Rhythm

et al. 2019

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Alpha oscillations (8 -14 Hz) are assumed to gate information flow in the brain by means of pulsed inhibition; that is, the phasic suppression of cortical excitability and information processing once per alpha cycle, resulting in stronger net suppression for larger alpha amplitudes due to the assumed amplitude asymmetry of the oscillation. While there is evidence for this hypothesis regarding occipital alpha oscillations, it is less clear for the central sensorimotor -alpha rhythm. Probing corticospinal excitability via transcranial magnetic stimulation (TMS) of the primary motor cortex and the measurement of motor evoked potentials (MEPs), we have previously demonstrated that corticospinal excitability is modulated by both amplitude and phase of the sensorimotor -alpha rhythm. However, the direction of this modulation, its proposed asymmetry, and its underlying mechanisms remained unclear. We therefore used real-time EEG-triggered single-and paired-pulse TMS in healthy humans of both sexes to assess corticospinal excitability and GABA-A-receptor mediated short-latency intracortical inhibition (SICI) at rest during spontaneous high amplitude -alpha waves at different phase angles (peaks, troughs, rising and falling flanks) and compared them to periods of low amplitude (desynchronized) -alpha. MEP amplitude was facilitated during troughs and rising flanks, but no phasic suppression was observed at any time, nor any modulation of SICI. These results are best compatible with sensorimotor -alpha reflecting asymmetric pulsed facilitation but not pulsed inhibition of motor cortical excitability. The asymmetric excitability with respect to rising and falling flanks of the -alpha cycle further reveals that voltage differences alone cannot explain the impact of phase.The pulsed inhibition hypothesis, which assumes that alpha oscillations actively inhibit neuronal processing in a phasic manner, is highly influential and has substantially shaped our understanding of these oscillations. However, some of its basic assumptions, in particular its asymmetry and inhibitory nature, have rarely been tested directly. Here, we explicitly investigated the asymmetry of modulation and its direction for the human sensorimotor -alpha rhythm. We found clear evidence of pulsed facilitation, but not inhibition, in the human motor cortex, challenging the generalizability of the pulsed inhibition hypothesis and advising caution when interpreting sensorimotor -alpha changes in the sensorimotor system. This study also demonstrates how specific assumptions about the neurophysiological underpinnings of cortical oscillations can be experimentally tested noninvasively in humans.

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Section: Potential Mechanisms Mediating -Alpha Related Pulsed Facilitmentioning

confidence: 69%

Pulsed Facilitation of Corticospinal Excitability by the Sensorimotor μ-Alpha Rhythm

et al. 2019

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“…Additional factors may influence the effect of 20 Hz tACS, such as intensity, phase and duration of stimulation, electrode montage, and activation during stimulation. For example, a recent meta-analysis on the effects of beta tACS showed that only intensities above 1 mA are able to introduce excitatory effects on MCE [25].…”

Section: Neural Plasticitymentioning

confidence: 99%

“…Regarding 20 Hz, previous results are heterogeneous with some studies showing an inhibitory effect in adults (for review, see [25]); therefore, this too is treated as an exploratory hypothesis.…”

Section: Introductionmentioning

confidence: 99%

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The Effects of 1 mA tACS and tRNS on Children/Adolescents and Adults: Investigating Age and Sensitivity to Sham Stimulation

et al. 2020

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The aim of this study was to investigate the effect of transcranial random noise (tRNS) and transcranial alternating current (tACS) stimulation on motor cortex excitability in healthy children and adolescents. Additionally, based on our recent results on the individual response to sham in adults, we explored this effect in the pediatric population. We included 15 children and adolescents (10–16 years) and 28 adults (20–30 years). Participants were stimulated four times with 20 Hz and 140 Hz tACS, tRNS, and sham stimulation (1 mA) for 10 minutes over the left M1HAND. Single-pulse MEPs (motor evoked potential), short-interval intracortical inhibition, and facilitation were measured by TMS before and after stimulation (baseline, 0, 30, 60 minutes). We also investigated aspects of tolerability. According to the individual MEPs response immediately after sham stimulation compared to baseline (Wilcoxon signed-rank test), subjects were regarded as responders or nonresponders to sham. We did not find a significant age effect. Regardless of age, 140 Hz tACS led to increased excitability. Incidence and intensity of side effects did not differ between age groups or type of stimulation. Analyses on responders and nonresponders to sham stimulation showed effects of 140 Hz, 20 Hz tACS, and tRNS on single-pulse MEPs only for nonresponders. In this study, children and adolescents responded to 1 mA tRNS and tACS comparably to adults regarding the modulation of motor cortex excitability. This study contributes to the findings that noninvasive brain stimulation is well tolerated in children and adolescents including tACS, which has not been studied before. Finally, our study supports a modulating role of sensitivity to sham stimulation on responsiveness to a broader stimulation and age range.

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“…For example, the after-effects of alpha tACS are thought to rely on plasticity-related changes evoked by spike-timing dependent plasticity (STDP) (Zaehle et al, 2010). While it has been shown that beta and gamma tACS can affect cortical excitability and inhibition (Heise et al, 2016; Nowak et al, 2018; Wischnewski et al, 2019b), the after-effects on spectral power are unknown. Ideally one would be able to assess changes in oscillatory activity during tACS, however it remains unresolved whether the tACS artifact can be proficiently removed from concurrent magneto- and electroencephalography (M/EEG) recordings (Neuling et al, 2017; Noury & Siegel, 2018).…”

Section: Introductionmentioning

confidence: 99%

Effects of beta- and gamma-band rhythmic stimulation on motor inhibition

Leunissen

Heise

et al. 2020

Preprint

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Voluntary movements are accompanied by an increase in gamma-band oscillatory activity (60-100Hz) and a strong desynchronization of beta-band activity (13-30Hz) in the motor system at both the cortical and subcortical level. Conversely, successful motor inhibition is associated with increased beta power in a fronto-basal-ganglia network. Intriguingly, gamma activity also increases in response to a stop-signal. In this study, we used transcranial alternating current stimulation to drive beta and gamma oscillations to investigate whether these frequencies are causally related to motor inhibition. We found that 20Hz stimulation targeted at the pre-supplementary motor area enhanced inhibition and increased beta oscillatory activity around the time of the stop-signal in trials directly following stimulation. In contrast, 70Hz stimulation seemed to slow down the braking process, and predominantly affected go task performance. These results demonstrate that the effects of tACS are state-dependent and that especially fronto-central beta activity is a functional marker for successful motor inhibition.

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Effects of beta-tACS on corticospinal excitability: A meta-analysis

Cited by 58 publications

References 65 publications

Pulsed Facilitation of Corticospinal Excitability by the Sensorimotor μ-Alpha Rhythm

Pulsed Facilitation of Corticospinal Excitability by the Sensorimotor μ-Alpha Rhythm

The Effects of 1 mA tACS and tRNS on Children/Adolescents and Adults: Investigating Age and Sensitivity to Sham Stimulation

Effects of beta- and gamma-band rhythmic stimulation on motor inhibition

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