P284 Bilateral effects of unilateral anodal tDCS on motor cortex plasticity and the cross-transfer of strength

Abstract

Introduction Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that utilizes weak direct currents to induce polarity-dependent modulation of corticospinal excitability. The cross-transfer of strength following unilateral training may be modulated by increased corticospinal excitability of the ipsilateral primary motor cortex (iM1). Although tDCS exerts a modulatory effect over the stimulation region, several studies have also demonstrated that distal areas of the brain connected to the region of stimulation may also be affected. However, no studies have investigated the effect of unilateral anodal-tDCS (a-tDCS) on the contralateral unstimulated hemisphere and whether this increases or decreases bilateral M1 activity and its subsequent effects on motor performance. Objectives : We examined the bilateral effect of unilateral a-tDCS applied to either the iM1 or contralateral M1 prior to a single bout of unilateral strength training on corticospinal excitability, inhibition, and the cross-transfer of strength. Materials and methods In a randomized cross-over design, changes in strength, corticospinal excitability and inhibition of the untrained arm, were analysed in 13 participants in both left and right M1. Participants were exposed to 20 min of anodal and sham tDCS in a contralateral (anode over the left M1) or ipsilateral (anode over right M1) arrangement, followed by an acute bout of strength training of the right biceps. Results Both contralateral and ipsilateral a-tDCS and strength training of the right biceps, increased strength of left untrained biceps by 10% and 12% compared to 3% following sham tDCS. TMS revealed that both arrangements of a-tDCS in combination with strength training, increased corticospinal excitability and decreased silent period duration in both hemispheres, however these changes were greater in the left hemisphere compared to sham tDCS and training ( P Conclusion The findings show that a-tDCS in both contralateral and ipsilateral arrangements in combination with an acute bout of strength training induces bilateral corticospinal plasticity and increases the cross-transfer of strength.