Effects of Transcranial Alternating Current Stimulation and Neurofeedback on Alpha (EEG) Dynamics: A Review

Transcranial alternating current stimulation (tACS) and neurofeedback (NFB) are two different types of non-invasive neuromodulation techniques, which can modulate brain activity and improve brain functioning. In this review, we compared the current state of knowledge related to the mechanisms of tACS and NFB and their effects on electroencephalogram (EEG) activity (online period/stimulation period) and on aftereffects (offline period/post/stimulation period), including the duration of their persistence and potential behavioral benefits. Since alpha bandwidth has been broadly studied in NFB and in tACS research, the studies of NFB and tACS in modulating alpha bandwidth were selected for comparing the online and offline effects of these two neuromodulation techniques. The factors responsible for variability in the responsiveness of the modulated EEG activity by tACS and NFB were analyzed and compared too. Based on the current literature related to tACS and NFB, it can be concluded that tACS and NFB differ a lot in the mechanisms responsible for their effects on an online EEG activity but they possibly share the common universal mechanisms responsible for the induction of aftereffects in the targeted stimulated EEG band, namely Hebbian and homeostatic plasticity. Many studies of both neuromodulation techniques report the aftereffects connected to the behavioral benefits. The duration of persistence of aftereffects for NFB and tACS is comparable. In relation to the factors influencing responsiveness to tACS and NFB, significantly more types of factors were analyzed in the NFB studies compared to the tACS studies. Several common factors for both tACS and NFB have been already investigated. Based on these outcomes, we propose several new research directions regarding tACS and NFB.

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Effects of weak transcranial alternating current stimulation on brain activity—a review of known mechanisms from animal studies

Frontiers in Human Neuroscience ◽

10.3389/fnhum.2013.00687 ◽

2013 ◽

Vol 7 ◽

Cited By ~ 160

Author(s):

Davide Reato ◽

Asif Rahman ◽

Marom Bikson ◽

Lucas C. Parra

Keyword(s):

Animal Studies ◽

Brain Activity ◽

Alternating Current ◽

Transcranial Alternating Current Stimulation

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Endogenous and exogenous electric fields as modifiers of brain activity: rational design of noninvasive brain stimulation with transcranial alternating current stimulation

Dialogues in Clinical Neuroscience ◽

10.31887/dcns.2014.16.1/ffroehlich ◽

2014 ◽

Vol 16 (1) ◽

pp. 93-102 ◽

Cited By ~ 15

Keyword(s):

Electric Fields ◽

Brain Stimulation ◽

Rational Design ◽

Brain Activity ◽

Field Potential ◽

Alternating Current ◽

Noninvasive Brain Stimulation ◽

Starting Point ◽

Recent Developments ◽

Transcranial Alternating Current Stimulation

Synchronized neuronal activity in the cortex generates weak electric fields that are routinely measured in humans and animal models by electroencephalography and local field potential recordings. Traditionally, these endogenous electric fields have been considered to be an epiphenomenon of brain activity. Recent work has demonstrated that active cortical networks are surprisingly susceptible to weak perturbations of the membrane voltage of a large number of neurons by electric fields. Simultaneously, noninvasive brain stimulation with weak, exogenous electric fields (transcranial current stimulation, TCS) has undergone a renaissance due to the broad scope of its possible applications in modulating brain activity for cognitive enhancement and treatment of brain disorders. This review aims to interface the recent developments in the study of both endogenous and exogenous electric fields, with a particular focus on rhythmic stimulation for the modulation of cortical oscillations. The main goal is to provide a starting point for the use of rational design for the development of novel mechanism-based TCS therapeutics based on transcranial alternating current stimulation, for the treatment of psychiatric illnesses.

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Changes in TMS measures of cortical excitability induced by transcranial direct and alternating current stimulation

The Oxford Handbook of Transcranial Stimulation, Second Edition ◽

10.1093/oxfordhb/9780198832256.013.20 ◽

2021 ◽

Author(s):

Michael A. Nitsche ◽

Walter Paulus ◽

Gregor Thut

Keyword(s):

Brain Stimulation ◽

Cortical Excitability ◽

Brain Activity ◽

Alternating Current ◽

Transcranial Electrical Stimulation ◽

Electrical Currents ◽

After Effects ◽

Brain Physiology ◽

Transcranial Alternating Current Stimulation ◽

Oscillatory Brain Activity

Brain stimulation with weak electrical currents (transcranial electrical stimulation, tES) is known already for about 60 years as a technique to generate modifications of cortical excitability and activity. Originally established in animal models, it was developed as a noninvasive brain stimulation tool about 20 years ago for application in humans. Stimulation with direct currents (transcranial direct current stimulation, tDCS) induces acute cortical excitability alterations, as well as neuroplastic after-effects, whereas stimulation with alternating currents (transcranial alternating current stimulation, tACS) affects primarily oscillatory brain activity but has also been shown to induce neuroplasticity effects. Beyond their respective regional effects, both stimulation techniques have also an impact on cerebral networks. Transcranial magnetic stimulation (TMS) has been pivotal to helping reveal the physiological effects and mechanisms of action of both stimulation techniques for motor cortex application, but also for stimulation of other areas. This chapter will supply the reader with an overview about the effects of tES on human brain physiology, as revealed by TMS.

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Motor Learning Based on Oscillatory Brain Activity Using Transcranial Alternating Current Stimulation: A Review

Brain Sciences ◽

10.3390/brainsci11081095 ◽

2021 ◽

Vol 11 (8) ◽

pp. 1095

Author(s):

Naoyuki Takeuchi ◽

Shin-Ichi Izumi

Keyword(s):

Motor Learning ◽

Brain Activity ◽

Alternating Current ◽

Social Effects ◽

Motor Deficits ◽

Noninvasive Brain Stimulation ◽

Transcranial Alternating Current Stimulation ◽

Oscillatory Brain Activity ◽

Teaching Learning ◽

The Relationship

Developing effective tools and strategies to promote motor learning is a high-priority scientific and clinical goal. In particular, motor-related areas have been investigated as potential targets to facilitate motor learning by noninvasive brain stimulation (NIBS). In addition to shedding light on the relationship between motor function and oscillatory brain activity, transcranial alternating current stimulation (tACS), which can noninvasively entrain oscillatory brain activity and modulate oscillatory brain communication, has attracted attention as a possible technique to promote motor learning. This review focuses on the use of tACS to enhance motor learning through the manipulation of oscillatory brain activity and its potential clinical applications. We discuss a potential tACS–based approach to ameliorate motor deficits by correcting abnormal oscillatory brain activity and promoting appropriate oscillatory communication in patients after stroke or with Parkinson’s disease. Interpersonal tACS approaches to manipulate intra- and inter-brain communication may result in pro-social effects and could promote the teaching–learning process during rehabilitation sessions with a therapist. The approach of re-establishing oscillatory brain communication through tACS could be effective for motor recovery and might eventually drive the design of new neurorehabilitation approaches based on motor learning.

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

10.1101/2020.12.23.423984 ◽

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.

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Dose-Dependent Effects of Transcranial Alternating Current Stimulation on Spike Timing in Awake Nonhuman Primates

10.1101/696344 ◽

2019 ◽

Cited By ~ 6

Author(s):

Luke Johnson ◽

Ivan Alekseichuk ◽

Jordan Krieg ◽

Alex Doyle ◽

Ying Yu ◽

...

Keyword(s):

Electric Fields ◽

Nonhuman Primates ◽

Brain Activity ◽

Alternating Current ◽

Spike Timing ◽

Novel Treatments ◽

Dose Dependent Fashion ◽

Transcranial Alternating Current Stimulation ◽

Dose Dependent

ABSTRACTWeak extracellular electric fields can influence spike timing in neural networks. Approaches to impose such fields on the brain in a noninvasive manner have high potential for novel treatments of neurological and psychiatric disorders. One of these methods, transcranial alternating current stimulation (TACS), is hypothesized to affect spike timing and cause neural entrainment. However, the conditions under which these effects occur in-vivo are unknown. Here, we show that TACS modulates spike timing in awake nonhuman primates (NHPs) in a dose-dependent fashion. Recording single-unit activity from pre-and post-central gyrus regions in NHPs during TACS, we found that a larger population of neurons became entrained to the stimulation waveform for higher stimulation intensities. Performing a cluster analysis of changes in interspike intervals, we identified two main types of neural responses to TACS – increased burstiness and phase entrainment. Our results demonstrate the ability of TACS to affect spike-timing in the awake primate brain and identify fundamental neural mechanisms. Concurrent electric field recordings demonstrate that spike-timing changes occur with stimulation intensities readily achievable in humans. These results suggest that novel TACS protocols tailored to ongoing brain activity may be a potent tool to normalize spike-timing in maladaptive brain networks and neurological disease.

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Closed-Loop Transcranial Alternating Current Stimulation: Towards Personalized Non-invasive Brain Stimulation for the Treatment of Psychiatric Illnesses

Current Behavioral Neuroscience Reports ◽

10.1007/s40473-021-00227-8 ◽

2021 ◽

Author(s):

Flavio Frohlich ◽

Leah Townsend

Keyword(s):

Brain Stimulation ◽

Closed Loop ◽

Alternating Current ◽

Psychiatric Illnesses ◽

Non Invasive ◽

Transcranial Alternating Current Stimulation

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Closed-loop transcranial alternating current stimulation of slow oscillations

Current Directions in Biomedical Engineering ◽

10.1515/cdbme-2015-0022 ◽

2015 ◽

Vol 1 (1) ◽

pp. 85-88 ◽

Cited By ~ 7

Author(s):

Christian Wilde ◽

Ralf Bruder ◽

Sonja Binder ◽

Lisa Marshall ◽

Achim Schweikard

Keyword(s):

Closed Loop ◽

Alternating Current ◽

Electrical Measurements ◽

Slow Oscillations ◽

Non Invasive ◽

Transcranial Alternating Current Stimulation ◽

Novel Method ◽

Endogenous Activity ◽

Stimulation Of

AbstractTranscranial alternating current stimulation (tACS) is an emerging non-invasive tool for modulating brain oscillations. There is evidence that weak oscillatory electrical stimulation during sleep can entrain cortical slow oscillations to improve the memory consolidation in rodents and humans. Using a novel method and a custom built stimulation device, automatic stimulation of slow oscillations in-phase with the endogenous activity in a real-time closed-loop setup is possible. Preliminary data from neuroplasticity experiments show a high detection performance of the proposed method, electrical measurements demonstrate the outstanding quality of the presented stimulation device.

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