AUTHOR=Vaseghi Bita , Zoghi Maryam , Jaberzadeh Shapour 

TITLE=The effects of anodal-tDCS on corticospinal excitability enhancement and its after-effects: conventional vs. unihemispheric concurrent dual-site stimulation

JOURNAL=Frontiers in Human Neuroscience

VOLUME=9

YEAR=2015

URL=https://www.frontiersin.org/journals/human-neuroscience/articles/10.3389/fnhum.2015.00533

DOI=10.3389/fnhum.2015.00533

ISSN=1662-5161

ABSTRACT=<p>Previous researchers have approved the ability of anodal transcranial direct current stimulation (a-tDCS) of the primary motor cortex (M1) to enhance corticospinal excitability (CSE). The primary aim of the current study was to investigate the effect of concurrent stimulation of M1 and a functionally connected cortical site of M1 on CSE modulation. This new technique is called unihemispheric concurrent dual-site a-tDCS (a-tDCS<sub>UHCDS</sub>). The secondary aim was to investigate the mechanisms underlying the efficacy of this new approach in healthy individuals. In a randomized crossover study, 12 healthy right-handed volunteers received a-tDCS under five conditions: a-tDCS of M1, a-tDCS<sub>UHCDS</sub> of M1-dorsolateral prefrontal cortex (DLPFC), a-tDCS<sub>UHCDS</sub> of M1-primary sensory cortex (S1), a-tDCS<sub>UHCDS</sub> of M1-primary visual cortex (V1), and sham a-tDCS<sub>UHCDS</sub>. Peak-to-peak amplitude of transcranial magnetic stimulation (TMS) induced MEPs, short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were assessed before and four times after each condition. A-tDCS<sub>UHCDS</sub> conditions induced larger MEPs than conventional a-tDCS. The level of M1 CSE was significantly higher following a-tDCS<sub>UHCDS</sub> of M1-DLPFC than other a-tDCS<sub>UHCDS</sub> conditions (<italic>p</italic> &lt; 0.001), and lasted for over 24 h. The paired-pulse TMS results after a-tDCS of M1-DLPFC showed significant facilitatory increase and inhibitory change. A-tDCS<sub>UHCDS</sub> of M1-DLPFC increases M1 CSE twofold that of conventional a-tDCS. A-tDCS<sub>UHCDS</sub> of M1-DLPFC enhances the activity of glutamergic mechanisms for at least 24 h. Such long-lasting M1 CSE enhancement induced by a-tDCS<sub>UHCDS</sub> of M1-DLPFC could be a valuable finding in clinical scenarios such as learning, motor performance, or pain management. The present study has been registered on the Australian New Zealand Clinical Trial at <ext-link ext-link-type="uri" xlink:href="http://www.anzctr.org.au/" xmlns:xlink="http://www.w3.org/1999/xlink">http://www.anzctr.org.au/</ext-link> with registry number of ACTRN12614000817640.</p>