Alpha Power Increase After Transcranial Alternating Current Stimulation at Alpha Frequency (α-tACS) Reflects Plastic Changes Rather Than Entrainment

There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

Abstract

Background

Periodic stimulation of occipital areas using transcranial alternating current stimulation (tACS) at alpha ( α) frequency (8–12 Hz) enhances electroencephalographic (EEG) α-oscillation long after tACS-offset. Two mechanisms have been suggested to underlie these changes in oscillatory EEG activity: tACS-induced entrainment of brain oscillations and/or tACS-induced changes in oscillatory circuits by spike-timing dependent plasticity.

Objective

We tested to what extent plasticity can account for tACS-aftereffects when controlling for entrainment “echoes.” To this end, we used a novel, intermittent tACS protocol and investigated the strength of the aftereffect as a function of phase continuity between successive tACS episodes, as well as the match between stimulation frequency and endogenous α-frequency.

Methods

12 healthy participants were stimulated at around individual α-frequency for 11–15 min in four sessions using intermittent tACS or sham. Successive tACS events were either phase-continuous or phase-discontinuous, and either 3 or 8 s long. EEG α-phase and power changes were compared after and between episodes of α-tACS across conditions and against sham.

Results

α-aftereffects were successfully replicated after intermittent stimulation using 8-s but not 3-s trains. These aftereffects did not reveal any of the characteristics of entrainment echoes in that they were independent of tACS phase-continuity and showed neither prolonged phase alignment nor frequency synchronization to the exact stimulation frequency.

Conclusion

Our results indicate that plasticity mechanisms are sufficient to explain α-aftereffects in response to α-tACS, and inform models of tACS-induced plasticity in oscillatory circuits. Modifying brain oscillations with tACS holds promise for clinical applications in disorders involving abnormal neural synchrony.

Highlights

•

Intermittent periodic stimulation of occipital areas with alpha-tACS enhances offline EEG alpha power.
•

Alpha-aftereffects cannot be explained by neuronal entrainment but are more likely due to plastic changes.
•

We propose a physiological constraint to a recent model of tACS-induced spike-timing dependent plasticity.

Related collections

Most cited references 66

Record: found
Abstract: found
Article: not found

Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation.

M A Nitsche, W Paulus (2000)

In this paper we demonstrate in the intact human the possibility of a non-invasive modulation of motor cortex excitability by the application of weak direct current through the scalp. Excitability changes of up to 40 %, revealed by transcranial magnetic stimulation, were accomplished and lasted for several minutes after the end of current stimulation. Excitation could be achieved selectively by anodal stimulation, and inhibition by cathodal stimulation. By varying the current intensity and duration, the strength and duration of the after-effects could be controlled. The effects were probably induced by modification of membrane polarisation. Functional alterations related to post-tetanic potentiation, short-term potentiation and processes similar to postexcitatory central inhibition are the likely candidates for the excitability changes after the end of stimulation. Transcranial electrical stimulation using weak current may thus be a promising tool to modulate cerebral excitability in a non-invasive, painless, reversible, selective and focal way.

0 comments Cited 786 times – based on 0 reviews      Review now

Record: found
Abstract: found
Article: not found

Physiological basis of transcranial direct current stimulation.

Charlotte Stagg, Michael Nitsche (2011)

Since the rediscovery of transcranial direct current stimulation (tDCS) about 10 years ago, interest in tDCS has grown exponentially. A noninvasive stimulation technique that induces robust excitability changes within the stimulated cortex, tDCS is increasingly being used in proof-of-principle and stage IIa clinical trials in a wide range of neurological and psychiatric disorders. Alongside these clinical studies, detailed work has been performed to elucidate the mechanisms underlying the observed effects. In this review, the authors bring together the results from these pharmacological, neurophysiological, and imaging studies to describe their current knowledge of the physiological effects of tDCS. In addition, the theoretical framework for how tDCS affects motor learning is proposed.

0 comments Cited 634 times – based on 0 reviews      Review now

Record: found
Abstract: found
Article: not found

Spike timing-dependent plasticity: a Hebbian learning rule.

Natalia Caporale, Yang Dan (2008)

Spike timing-dependent plasticity (STDP) as a Hebbian synaptic learning rule has been demonstrated in various neural circuits over a wide spectrum of species, from insects to humans. The dependence of synaptic modification on the order of pre- and postsynaptic spiking within a critical window of tens of milliseconds has profound functional implications. Over the past decade, significant progress has been made in understanding the cellular mechanisms of STDP at both excitatory and inhibitory synapses and of the associated changes in neuronal excitability and synaptic integration. Beyond the basic asymmetric window, recent studies have also revealed several layers of complexity in STDP, including its dependence on dendritic location, the nonlinear integration of synaptic modification induced by complex spike trains, and the modulation of STDP by inhibitory and neuromodulatory inputs. Finally, the functional consequences of STDP have been examined directly in an increasing number of neural circuits in vivo.

0 comments Cited 504 times – based on 0 reviews      Review now

All references

Author and article information

Contributors

Alexandra Vossen

Gregor Thut

Journal

Journal ID (nlm-ta): Brain Stimul

Journal ID (iso-abbrev): Brain Stimul

Title: Brain Stimulation

Publisher: Elsevier

ISSN (Print): 1935-861X

Publication date PMC-release: 1 May 2015

Publication date (Print): May-Jun 2015

Volume: 8

Issue: 3

Pages: 499-508

Affiliations

[a ]School of Psychology, University of Glasgow, 58 Hillhead Street, Glasgow G12 8QB, United Kingdom

[b ]Institute of Neuroscience and Psychology, University of Glasgow, 58 Hillhead Street, Glasgow G12 8QB, United Kingdom

Author notes

[∗ ]Corresponding author. Tel.: +44 (0)141 330 5151. a.vossen.1@ 123456research.gla.ac.uk

[∗∗ ]Corresponding author. Tel.: +44 (0)141 330 3395. Gregor.Thut@ 123456glasgow.ac.uk

Article

Publisher ID: S1935-861X(14)00436-7

DOI: 10.1016/j.brs.2014.12.004

PMC ID: 4464304

PubMed ID: 25648377

SO-VID: 2e3be6de-d227-4d8c-afab-8fbae6d5e062

License:

This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

History

Date received : 4 September 2014

Date revision received : 3 December 2014

Date accepted : 14 December 2014

Comments

Comment on this article

Cited by 220

See all cited by

Most referenced authors 961

See all reference authors

- Version 1