Stimulation artifact source separation (SASS) for assessing electric brain oscillations during transcranial alternating current stimulation (tACS)

Haslacher, David; Nasr, Khaled; Robinson, Stephen E.; Braun, Christoph; Soekadar, Surjo R.

doi:10.1016/j.neuroimage.2020.117571

Cited by 35 publications

(39 citation statements)

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“…The field of tACS research has benefitted greatly from amplitude-modulated tACS (Witkowski et al, 2016; Negahbani et al, 2018; Haslacher et al, 2021), where the carrier frequency (usually a very high frequency; e.g., 220 Hz) is purposely amplitude modulated at the frequency of physiological interest (e.g., 10 Hz). If the modulation frequency (envelope) can itself reliably entrain neural activity at that frequency, then the problem of nonlinear modulations will be shifted into the higher frequency domain, and will instead occur symmetrically around the carrier, and symmetrically around the carrier plus-and-minus the modulation frequency.…”

Section: Discussionmentioning

confidence: 99%

“…Many methods exist for recovering the M/EEG from artefacts of tACS (Herrmann and Strüber, 2017; Kasten and Herrmann, 2019), with varying degrees of complexity and success. These methods include spatial filtering (beamforming, Neuling et al, 2015; Noury et al, 2016; Witkowski et al, 2016; ‘SASS,’ Haslacher et al, 2021), temporal filtering (notch, Voss et al, 2014; Hampel, Santos Monteiro et al, 2015), variations of template subtraction (Voss et al, 2014; Kohli and Casson, 2015, 2019; Noury et al, 2016; Dowsett and Taylor, 2017; Guggenberger and Gharabaghi, 2018), principal component analysis (PCA, Kohli and Casson, 2015; Santos Monteiro et al, 2015), and a combination of the latter two (Helfrich et al, 2014; Noury et al, 2016). Universally, these approaches assume linear stimulation artefacts— either time-invariance (i.e., an artefact is a scaled version of itself from cycle to cycle) or sensor-invariance (i.e., artefacts are scaled versions of one another from sensor to sensor).…”

Section: Introductionmentioning

confidence: 99%

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A need for time-varying models to suppress artefacts of tACS in the M/EEG

Bland

2021

Preprint

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Rhythmic modulation of brain activity by transcranial alternating current stimulation (tACS) can entrain neural oscillations in a frequency- and phase-specific manner. However, large stimulation artefacts contaminate concurrent 'online' neuroimaging measures, including magneto- and electro-encephalography (M/EEG) — restricting most analyses to periods free from stimulation ('offline' aftereffects). While many published methods exist for removing artefacts of tACS from M/EEG recordings, they universally assume linear artefacts: either time-invariance (i.e., an artefact is a scaled version of itself from cycle to cycle) or sensor-invariance (i.e., artefacts are scaled versions of one another from sensor to sensor). However, heartbeat and respiration both nonlinearly modulate the amplitude and phase of these artefacts, predominantly via changes in scalp impedance. The spectral symmetry this introduces to the M/EEG spectra may lead to false-positive evidence for entrainment around the frequency of tACS, if not adequately suppressed. Good electrophysiological evidence for entrainment therefore requires that tACS artefacts are fully accounted for before comparing online spectra to a control (e.g., as might be observed during sham stimulation). Here I outline an approach to linearly solve templates for tACS artefacts, and demonstrate how event-locked perturbations to amplitude and phase can be introduced from simultaneous recordings of heartbeat and respiration — effectively forming time-varying models of tACS artefacts. These models are constructed for individual sensors, and can therefore be used in contexts with few EEG sensors and with no assumption of artefact collinearity. I also discuss the feasibility of this approach in the absence of simultaneous recordings of heartbeat and respiration traces.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A need for time-varying models to suppress artefacts of tACS in the M/EEG

Bland

2021

Preprint

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“…However, through computer simulation, Kasten found that even the weak nonlinearity of the stimulation and recording hardware also lead to disordered modulation of the frequency and its harmonics, and artifacts are still present in the stimulation process (Kasten et al, 2018). Therefore, in view of the artifacts still existing in AM-tACS, David successfully separated the stimulus artifacts in AM-tACS through a real-time compatible artifact suppression algorithm and verified it in seven healthy volunteers (Haslacher et al, 2020).…”

Section: Interference Modulation Electrical Stimulationmentioning

confidence: 92%

Improving the Effect of Transcranial Alternating Current Stimulation (tACS): A Systematic Review

Liu

Wang

2021

Front. Hum. Neurosci.

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With the development of electrical stimulation technology, traditional transcranial alternating current stimulation (tACS) technology has been found to have the drawback of not targeting a specific area accurately. Studies have shown that optimizing the number and position of electrodes during electrical stimulation has a very good effect on enhancing brain stimulation accuracy. At present, an increasing number of laboratories have begun to optimize tACS. However, there has been no study summarizing the optimization methods of tACS. Determining whether different optimization methods are effective and the optimization approach could provide information that could guide future tACS research. We describe the results of recent research on tACS optimization and integrate the optimization approaches of tACS in recent research. Optimization approaches can be classified into two groups: high-definition electrical stimulation and interference modulation electrical stimulation. The optimization methods can be divided into five categories: high-definition tACS, phase-shifted tACS, amplitude-modulated tACS, the temporally interfering (TI) method, and the intersectional short pulse (ISP) method. Finally, we summarize the latest research on hardware useful for tACS improvement and outline future directions.

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“…The copyright holder for this preprint this version posted April 13, 2021. ; https://doi.org/10.1101/2021.03.26.437107 doi: bioRxiv preprint Amplitude-modulated tACS (AM-tACS) was proposed as a promising way to allow for effective magnetoencephalography (MEG) or EEG signal reconstruction during electrical stimulation [62][63][64][65]. However, similar to TI stimulation, studies on AM-tACS have also mostly focused on simulations, and no systematic experimental test to validate the effectiveness of AM-tACS on humans has been performed.…”

Section: Ti Stimulation Is Effective In the Human Motor Cortexmentioning

confidence: 99%

High Gamma and Beta Temporal Interference Stimulation in the Human Motor Cortex Improves Motor Functions

Xia

2021

International Journal of Psychophysiology

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Background: Temporal interference (TI) stimulation is a new technique of noninvasive brain stimulation. Envelope-modulated waveforms with two high-frequency carriers can activate neurons in target brain regions without stimulating the overlying cortex, which has been validated in mouse brains. However, whether TI stimulation can work on the human brain has not been elucidate.Objective: To assess the effectiveness and safety aspect of the envelope-modulated waveform of TI stimulation on human primary motor cortex (M1).Methods: Participants attended three sessions of 30-min TI stimulation at 2 mA during a random reaction time task (RRTT) or a serial reaction time task (SRTT). Motor cortex excitability was measured before and after TI stimulation.Results: In the RRTT experiment, only 70 Hz TI stimulation had a promoting effect on the reaction time (RT) performance and excitability of the motor cortex compared to sham stimulation. Meanwhile, compared with the sham condition, only 20 Hz TI stimulation significantly facilitated motor learning in the SRTT experiment, which was significantly positively correlated with the increase in motor evoked potential. Conclusion:These results indicate that the envelope-modulated waveform of TI stimulation has a significant promoting effect on human motor functions, experimentally suggesting the effectiveness of TI stimulation in humans for the first time and pave the way for further explorations.

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Stimulation artifact source separation (SASS) for assessing electric brain oscillations during transcranial alternating current stimulation (tACS)

Cited by 35 publications

References 39 publications

A need for time-varying models to suppress artefacts of tACS in the M/EEG

A need for time-varying models to suppress artefacts of tACS in the M/EEG

Improving the Effect of Transcranial Alternating Current Stimulation (tACS): A Systematic Review

High Gamma and Beta Temporal Interference Stimulation in the Human Motor Cortex Improves Motor Functions

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