P 88. Unilateral and bilateral tDCS of the human motor cortex does not differentially modulate motor function in healthy adults

Abstract

Introduction Transcranial direct current stimulation (tDCS) is a non-invasive technique that modulates the excitability of neurons within the primary motor cortex (M1). Neuronal excitability is modified by the application of direct currents in a polarity specific manner, with anodal-tDCS increasing excitability and cathodal decreasing excitability. Recently it has been shown that bilateral tDCS significantly modulates cortical excitability when compared to unilateral anodal stimulation. However, the effects of different tDCS montages on modulating motor performance are unclear. Further, it remains unclear if changes in motor performance following tDCS outlast the period of stimulation. Objective To determine whether unilateral or bilateral tDCS differentially modulates motor performance of the non-dominant hand in healthy participants. A secondary objective was to further elucidate the mechanisms underlying any potential aftereffects on motor performance following unilateral and bilateral tDCS. Methods Using a randomized, counter-balanced, cross-over design, with a one-week wash-out period, 9 participants (5 female and 4 male, age range 22–45 years) were exposed to 13 min of sham, unilateral or bilateral tDCS applied at 1.0 mA. In all tDCS conditions, the anode was placed over the “hot spot” of the non-dominant extensor carpi radialis longus muscle (ECRL) as determined by transcranial magnetic stimulation (TMS). The applied current was induced by a saline-soaked pair of surface sponge electrodes (25 cm2) delivered by a NeuroConn DC stimulator. TMS was used to measure M1 excitability and short-interval intracortical inhibition (SICI) of the non-dominant contralateral ECRL at baseline, immediately post, 30 and at 60 min following cessation of tDCS. We evaluated motor function at each of these time points in all conditions by having participants complete a Purdue peg board test. Results Both unilateral and bilateral tDCS facilitated motor performance immediately following tDCS (7 & 4% respectively), 30 min (13 & 6%) and 60 min post (21 & 9%)(all p Conclusion Our findings show that both unilateral and bilateral tDCS modulated motor performance for up to 60 min following the removal of tDCS, but the different types of tDCS electrode montages did not differentially modulate motor task performance of the non-dominant hand or indices of cortical plasticity. We have also shown that tDCS (unilateral and bilateral) modulates both cortical excitability and inhibition that outlasts the period of stimulation. Together, these results indicate that tDCS induces behavioral changes in the non-dominant hand as a consequence of mechanisms associated with long-term potentiation.