Comparison of high-definition and conventional tDCS on visuomotor sequence learning

Abstract

Introduction Conventional transcranial Direct Stimulation (tDCS) has the disadvantage of spreading the current beyond the underlying cortical targets. More recent High-Definition tDCS (HD) is known to increase the spatial focality of the current. While anodal stimulation is generally thought to enhance cortical excitability and cathodal to reduce excitability, polarity-specificity of tDCS effects have been observed not to follow a simple general rule. The impact of tDCS at a network-level of brain modulation appears as a critical factor to explain its behavioral effects. Here, we propose to compare the effect of conventional-tDCS and HD-tDCS on a sequence-learning task (Serial-Response-Time-Task, SRTT) involving a network of visual and motor brain regions. Method The study involved 10 healthy participants. The SRTT generates fast (when the sequence is predicted in advance) and slow (when not) reaction times (RTs). During the task, participants were blinded for four 2 mA tDCS configurations (types: conventional, HD; conditions: active, sham). The active electrode was visual-POz cathodal. Continuous-EEG was acquired during tDCS. Results We observed a significant tDCS type condition on trial-by-trial RTs (F(1.46529) = 68.17, P Conclusions Visuomotor sequence learning improvement caused by tDCS involves a specific shift from a slow to a fast mode of processing. The visual HD-tDCS is superior over conventional-tDCS on this improvement and may be due to a focusing effect of the stimulation to the motion-perception network involved in the task. This argues for a network-level of tDCS-induced neuroplasticity rather than a local-level effect. The results raise the possibility of the usefulness of HD-tDCS in neurorehabilitation strategies for visuomotor dysfunctions.