Modulation of corticospinal excitability and inhibition of the contralateral M1 during and after ipsilateral anodal tDCS

BackgroundTranscranial direct current stimulation (TDCS) targeting the primary motor hand area (M1-HAND) may induce lasting shifts in corticospinal excitability, but after-effects show substantial inter-individual variability. Functional magnetic resonance imaging (fMRI) can probe after-effects of TDCS on regional neural activity on a whole-brain level.ObjectiveUsing a double-blinded cross-over design, we investigated whether the individual change in corticospinal excitability after TDCS of M1-HAND is associated with changes in task-related regional activity in cortical motor areas.MethodsSeventeen healthy volunteers (10 women) received 20 min of real (0.75 mA) or sham TDCS on separate days in randomized order. Real and sham TDCS used the classic bipolar set-up with the anode placed over right M1-HAND. Before and after each TDCS session, we recorded motor evoked potentials (MEP) from the relaxed left first dorsal interosseus muscle after single-pulse transcranial magnetic stimulation(TMS) of left M1-HAND and performed whole-brain fMRI at 3 Tesla while participants completed a visuomotor tracking task with their left hand. We also assessed the difference in MEP latency when applying anterior-posterior and latero-medial TMS pulses to the precentral hand knob (AP-LM MEP latency).ResultsReal TDCS had no consistent aftereffects on mean MEP amplitude, task-related activity or motor performance. Individual changes in MEP amplitude, measured directly after real TDCS showed a positive linear relationship with individual changes in task-related activity in the supplementary motor area and AP-LM MEP latency.ConclusionFunctional aftereffects of classical bipolar anodal TDCS of M1-HAND on the motor system vary substantially across individuals. Physiological features upstream from the primary motor cortex may determine how anodal TDCS changes corticospinal excitability.

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Preconditioning cathodal transcranial direct current stimulation facilitates the neuroplastic effect of subsequent anodal transcranial direct current stimulation applied during cycling in young adults

10.1101/653634 ◽

2019 ◽

Author(s):

Maryam Pourmajidian ◽

Benedikt Lauber ◽

Simranjit K Sidhu

Keyword(s):

Direct Current ◽

Transcranial Direct Current Stimulation ◽

Motor Evoked Potentials ◽

Corticospinal Excitability ◽

Anodal Tdcs ◽

Double Blind ◽

Cycling Exercise ◽

Direct Current Stimulation ◽

Post Test ◽

Double Blind Design

AbstractThe study aimed to examine the effect of a priming cathodal transcranial direct current stimulation (ctDCS) before subsequent anodal-tDCS (atDCS) was applied during low workload cycling exercise on the corticospinal responses in young healthy individuals. Eleven young subjects participated in two sessions receiving either priming ctDCS or sham stimulation, followed by atDCS while cycling (i.e. ctDCS-atDCS, sham-atDCS) at 1.2 times their body weight (84 ± 20 W) in a counterbalanced double-blind design. Corticospinal excitability was measured with motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation with the intensity set to produce an MEP amplitude of 1 mV in a resting hand muscle at baseline (PRE), following priming tDCS (POST-PRIMING) and post atDCS combined with cycling exercise (POST-TEST). There was a significant interaction between time and intervention (P < 0.01) on MEPs. MEPs increased from PRE (1.0 ± 0.06 mV) to POST-TEST (1.3 ± 0.06 mV) during ctDCS-atDCS (P < 0.001) but did not change across time during sham-atDCS (1.0 ± 0.06 mV, P > 0.7). Furthermore, MEPs were higher in ctDCS-atDCS compared to sham-atDCS (P < 0.01) at both POST-PRIMING (ctDCS-atDCS: 1.1 ± 0.06, sham-atDCS: 1.0 ± 0.06) and POST-TEST (ctDCS-atDCS: 1.3 ± 0.06, sham-atDCS: 1.0 ± 0.06). These outcomes demonstrate that cathodal tDCS priming can enhance corticospinal excitability following anodal tDCS applied in combination with cycling exercise. The findings have implications for the application of tDCS in combination with cycling exercise in rehabilitation and sporting contexts.

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tDCS Anodal tDCS increases bilateral corticospinal excitability irrespective of hemispheric dominance

The Journal of Science and Medicine ◽

10.37714/josam.v2i2.40 ◽

2020 ◽

Vol 2 (2) ◽

pp. 1-17

Author(s):

Simin Rahman ◽

Ummutal Siddique ◽

Ashlyn Frazer ◽

Alan Pearce ◽

Dawson Kidgell

Keyword(s):

Primary Motor Cortex ◽

Corticospinal Excitability ◽

Hemispheric Dominance ◽

Anodal Tdcs ◽

Medical Practitioners ◽

Non Invasive ◽

Design Changes ◽

Bilateral Effects ◽

The Brain ◽

Stimulation Technique

Background: Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that utilizes weak direct currents to induce polarity-dependent modulation of corticospinal excitability. Although tDCS exerts a modulatory effect over the stimulation region, several studies have also demonstrated that distal areas of the brain connected to the region of stimulation may also be affected, as well as the contralateral hemisphere. Objective: We examined the effect of a single session of anodal tDCS on corticospinal excitability and inhibition of both the stimulated and non-stimulated hemisphere and examined the influence of these responses by the brain-derived neurotrophic factor (BDNF) polymorphism. Methods: In a randomized cross-over design, changes in corticospinal excitability and inhibition of the stimulated and non-stimulated hemispheres were analysed in 13 participants in both the dominant and non-dominant primary motor cortex (M1). Participants were exposed to 20 min of anodal and sham tDCS and also undertook a blood sample for BDNF genotyping. Results: TMS revealed a bilateral increase in corticospinal excitability irrespective of which hemisphere (dominant vs non-dominant) was stimulated (all P < 0.05). Furthermore, the induction of corticospinal excitability was influenced by the BDNF polymorphism. Conclusion: This finding shows that anodal tDCS induces bilateral effects in corticospinal excitability irrespective of hemispheric dominance. This finding provides scientists and medical practitioners with a greater understanding as to how this technique may be used as a therapeutic tool for clinical populations.

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Determination of anodal tDCS intensity threshold for reversal of corticospinal excitability: an investigation for induction of counter-regulatory mechanisms

Scientific Reports ◽

10.1038/s41598-020-72909-4 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Maryam Hassanzahraee ◽

Michael A. Nitsche ◽

Maryam Zoghi ◽

Shapour Jaberzadeh

Keyword(s):

Primary Motor Cortex ◽

Motor Evoked Potentials ◽

Single Pulse ◽

Random Order ◽

Corticospinal Excitability ◽

Regulatory Mechanisms ◽

Anodal Tdcs ◽

Post Intervention ◽

Stimulation Intensity ◽

Intensity Threshold

Abstract Transcranial direct current stimulation is applied to modulate activity, and excitability of the brain. Basically, LTP-like plasticity is induced when anodal tDCS (a-tDCS) is applied over the primary motor cortex. However, it has been shown that specific parameters of a-tDCS can induce a plasticity reversal. We aimed to systematically assess the intensity threshold for reversal of the direction of plasticity induced by a-tDCS, monitored by corticospinal excitability (CSE), and explored mechanisms regulating this reversal. Fifteen healthy participants received a-tDCS in pseudo-random order for 26 min with four intensities of 0.3, 0.7, 1, and 1.5 mA. To measure CSE changes, single-pulse TMS was applied over the left M1, and motor evoked potentials of a contralateral hand muscle were recorded prior to a-tDCS, immediately and 30-min post-intervention. Paired-pulse TMS was used to evaluate intracortical excitation and inhibition. CSE increased significantly following a-tDCS with an intensity of 0.7 mA; however, the expected effect decreased and even reversed at intensities of 1 and 1.5 mA. ICF was significantly increased while SICI and LICI decreased at 0.7 mA. On the other hand, a significant decrease of ICF, but SICI and LICI enhancement was observed at intensities of 1, and 1.5 mA. The present findings show an intensity threshold of ≥ 1 mA for 26 min a-tDCS to reverse LTP- into LTD-like plasticity. It is suggested that increasing stimulation intensity, with constant stimulation duration, activates counter-regulatory mechanisms to prevent excessive brain excitation. Therefore, stimulation intensity and plasticity induced by a-tDCS might non-linearly correlate in scenarios with prolonged stimulation duration.

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No effect of tDCS of the primary motor cortex on isometric exercise performance or perceived fatigue

10.31236/osf.io/xs69q ◽

2019 ◽

Author(s):

James Graeme Wrightson ◽

Rosemary Twomey ◽

Guillaume Y. Millet

Keyword(s):

Motor Cortex ◽

Exercise Performance ◽

Primary Motor Cortex ◽

Isometric Exercise ◽

Knee Extension ◽

Corticospinal Excitability ◽

Knee Extensors ◽

Anodal Tdcs ◽

Isometric Knee Extension ◽

Before And After

Introduction: Anodal transcranial direct current stimulation (tDCS) of the primary motor cortex has been reported to improve isometric exercise performance without changing corticospinal excitability. One possible cause for this may be the previous use of relatively high (2 mA) current intensities, which have inconsistent effects on corticospinal excitability. The present pre-registered study aimed to replicate previously reported ergogenic effects of 2 mA tDCS, and examine whether 1 mA anodal tDCS both improved isometric exercise performance and perceived fatigue, and more reliably altered corticospinal excitability. Methods: On three separate occasions, participants performed a sustained submaximal isometric knee extension until failure after receiving either 1 mA, 2mA or sham anodal tDCS. Corticospinal excitability of the knee extensors was measured using transcranial magnetic stimulation immediately before and after tDCS. Rating of fatigue was recorded throughout the isometric exercise.Results: Neither 1 nor 2 mA tDCS improved exercise performance, or reduced perceived fatigue, compared to sham stimulation. There was also no effect of tDCS on the corticospinal excitability of the knee extensors.Discussion: We found no effect of tDCS on either exercise performance, perceived fatigue or corticospinal excitability. This study adds to the growing body of literature which has failed to find an ergogenic effect of tDCS. Large preregistered replications of previously reported effects are now required before tDCS can be considered an effective method to improve exercise performance.

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