Polarity Specific Effects of Transcranial Direct Current Stimulation on Interhemispheric Inhibition

Abstract

Transcranial direct current stimulation (tDCS) has been used as a useful interventional brain stimulation technique to improve unilateral upper-limb motor function in healthy humans, as well as in stroke patients. Although tDCS applications are supposed to modify the interhemispheric balance between the motor cortices, the tDCS after-effects on interhemispheric interactions are still poorly understood. To address this issue, we investigated the tDCS after-effects on interhemispheric inhibition (IHI) between the primary motor cortices (M1) in healthy humans. Three types of tDCS electrode montage were tested on separate days; anodal tDCS over the right M1, cathodal tDCS over the left M1, bilateral tDCS with anode over the right M1 and cathode over the left M1. Single-pulse and paired-pulse transcranial magnetic stimulations were given to the left M1 and right M1 before and after tDCS to assess the bilateral corticospinal excitabilities and mutual direction of IHI. Regardless of the electrode montages, corticospinal excitability was increased on the same side of anodal stimulation and decreased on the same side of cathodal stimulation. However, neither unilateral tDCS changed the corticospinal excitability at the unstimulated side. Unilateral anodal tDCS increased IHI from the facilitated side M1 to the unchanged side M1, but it did not change IHI in the other direction. Unilateral cathodal tDCS suppressed IHI both from the inhibited side M1 to the unchanged side M1 and from the unchanged side M1 to the inhibited side M1. Bilateral tDCS increased IHI from the facilitated side M1 to the inhibited side M1 and attenuated IHI in the opposite direction. Sham-tDCS affected neither corticospinal excitability nor IHI. These findings indicate that tDCS produced polarity-specific after-effects on the interhemispheric interactions between M1 and that those after-effects on interhemispheric interactions were mainly dependent on whether tDCS resulted in the facilitation or inhibition of the M1 sending interhemispheric volleys.

Applications of transcranial direct current stimulation in children and pediatrics

“…Cathodal ipsilateral stimulation might have improved performance by a reduction of interhemispheric inhibition. This effect of interhemispheric interaction on cortical excitability induced by motor cortex tDCS has also been described in adults (Tazoe et al, 2014). Taking into account the excitabilityenhancing effect of 1 mA cathodal tDCS in children in the study of Moliadze et al (2015a), it cannot be ruled out, however, that excitability-enhancing ipsilateral tDCS had a performance-improving effect.…”

Brain state and polarity dependent modulation of brain networks by transcranial direct current stimulation

“…Additionally, a small number of studies have found that anodal tDCS decreases local GABA concentration and increases local Glutamine concentration, whereas cathodal tDCS decreases local Glutamine concentration (Hunter et al, ; Kim, Stephenson, Morris, & Jackson, ; Stagg et al, ). These changes could underlie the observed, and differential, effects of tDCS on local excitatory and inhibitory circuits (Sasaki, Miyaguchi, Kotan, Kojima, & Kirimoto, ; Stagg & Nitsche, ; Tazoe, Endoh, Kitamura, & Ogata, ; Wiethoff, Hamada, & Rothwell, ). As local changes in the excitatory/inhibitory balance are thought to produce changes in large‐scale brain networks (Deco, Hagmann, Romani, Mantini, & Corbetta, ), this might provide a mechanism for the remote effects on network activity we observed.…”

Spasticity Management: The Current State of Transcranial Neuromodulation

“…This issue however, needs to be confirmed, given that only some studies have used high‐frequency rTMS because of the increased risk of seizure [32]. In addition, the comparison between anodal‐ and cathodal‐tDCS, both acting on IHI, yielded similar results [74]. The difference with rTMS findings may depend on the fact that tDCS has gross effects on brain excitability, and therefore it can less selectively shape IHI or finely modulate intracortical inhibitory and facilitatory networks (which in turn influence IHI) [75].…”