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

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-tdcsuhcds). 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-tdcsuhcds of m1-dorsolateral prefrontal cortex (dlpfc),a-tdcsuhcds of m1-primary sensory cortex (s1),a-tdcsuhcds of m1-primary visual cortex (v1),and sham a-tdcsuhcds. 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-tdcsuhcds conditions induced larger meps than conventional a-tdcs. the level of m1 cse was significantly higher following a-tdcsuhcds of m1-dlpfc than other a-tdcsuhcds conditions (p < 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-tdcsuhcds of m1-dlpfc increases m1 cse twofold that of conventional a-tdcs. a-tdcsuhcds of m1-dlpfc enhances the activity of glutamergic mechanisms for at least 24 h. such long-lasting m1 cse enhancement induced by a-tdcsuhcdsof 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 http://www.anzctr.org.au/ with registry number of actrn12614000817640. © 2015 vaseghi,zoghi and jaberzadeh.