tDCS Anodal tDCS increases bilateral corticospinal excitability irrespective of hemispheric dominance

Background: 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. 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, as well as the contralateral hemisphere. Objective: We examined the effect of a single session of anodal tDCS on corticospinal excitability and inhibition of both the stimulated and non-stimulated hemisphere and examined the influence of these responses by the brain-derived neurotrophic factor (BDNF) polymorphism. Methods: In a randomized cross-over design, changes in corticospinal excitability and inhibition of the stimulated and non-stimulated hemispheres were analysed in 13 participants in both the dominant and non-dominant primary motor cortex (M1). Participants were exposed to 20 min of anodal and sham tDCS and also undertook a blood sample for BDNF genotyping. Results: TMS revealed a bilateral increase in corticospinal excitability irrespective of which hemisphere (dominant vs non-dominant) was stimulated (all P < 0.05). Furthermore, the induction of corticospinal excitability was influenced by the BDNF polymorphism. Conclusion: This finding shows that anodal tDCS induces bilateral effects in corticospinal excitability irrespective of hemispheric dominance. This finding provides scientists and medical practitioners with a greater understanding as to how this technique may be used as a therapeutic tool for clinical populations.