title: Unihemispheric concurrent dual-site cathodal transcranial direct current stimulation: the effects on corticospinal excitability.
abstract: We aimed to assess the effects of concurrent cathodal transcranial direct current stimulation (c-tDCS) of two targets in a hemisphere, termed unihemispheric concurrent dual-site cathodal tDCS (c-tDCSUHCDS ), on the size of M1 corticospinal excitability and its lasting effect. Secondary aims were to identify the mechanisms behind the efficacy of c-tDCSUHCDS and to evaluate the side effects of this new technique. Twelve healthy volunteers received 20 min c-tDCS under five conditions in a random order: M1 c-tDCS, c-tDCSUHCDS of M1-dorsolateral prefrontal cortex (DLPFC), M1-primary sensory cortex (S1), M1-primary visual cortex (V1) and sham. The M1 corticospinal excitability of the first dorsal interossei muscle was assessed before, immediately after, and 30 min, 60 min and 24 h after the interventions. Short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) were also assessed, using a paired-pulse paradigm. Compared to conventional M1 c-tDCS, corticospinal excitability significantly increased following c-tDCSUHCDS of M1-DLPFC and M1-V1 for up to 24 h (P = 0.001). Significant increases in ICF were observed following c-tDCSUHCDS of M1-DLPFC (P = 0.005) and M1-V1 (P = 0.002). Compared to baseline values, ICF and SICI increased significantly at T60 (P < 0.001) and T24 h (P < 0.001) following the concurrent c-tDCS of M1 and V1. Sham c-tDCSUHCDS did not induce any significant alteration. The corticospinal excitability increase was mainly accompanied by ICF increase, which indirectly indicates the activity of glutamergic mechanisms. The findings may help us to more fully understand the brain function and develop future motor learning studies. No significant excitability change induced by sham c-tDCSUHCDS suggests that there is no placebo effect associated with this new tDCS technique.
authors.affiliation: Department of Physiotherapy, School of Primary Health Care, Faculty of Medicine, Nursing and Health Sciences, Monash University, Building B, Frankston 3199, Melbourne, Vic., Australia.
authors.forename: Bita
authors.initials: B
authors.lastname: Vaseghi
authors.affiliation: Department of Medicine, Royal Melbourne Hospital, The University of Melbourne, Melbourne, Vic., Australia.
authors.forename: Maryam
authors.initials: M
authors.lastname: Zoghi
authors.affiliation: Department of Physiotherapy, School of Primary Health Care, Faculty of Medicine, Nursing and Health Sciences, Monash University, Building B, Frankston 3199, Melbourne, Vic., Australia.
authors.forename: Shapour
authors.initials: S
authors.lastname: Jaberzadeh
mesh_terms: D000328:Adult; D002540:Cerebral Cortex / Q000502:physiology*; D005260:Female; D007839:Functional Laterality; D006801:Humans; D008297:Male; D011712:Pyramidal Tracts / Q000502:physiology*; D065908:Transcranial Direct Current Stimulation / Q000009:adverse effects*
keywords: corticospinal excitability; functional connectivity; human; lasting effect; primary motor cortex; unihemispheric dual-site cathodal transcranial direct current stimulation