Consequently, tDCS might, in this case, induce plasticity of non-task-related synapses, which might reduce or abolish learning-related performance improvements. Application of tDCS before motor learning will, however, result in already stimulation-induced plasticity before performance, which might lead to mixed effects on different synapses, including homeostatic processes. The mechanism might be conjoint activation of task-relevant neurons via task performance and tDCS, if applied simultaneously, which will make it easier for the respective neuronal connections to cross the threshold for plasticity induction. Thus, task-related LTP-like plasticity in combination with tDCS may play a critical role during motor learning for performance improvement. When the effect of anodal and cathodal tDCS on motor performance was tested by applying stimulation either during or before task performance, faster learning was found by anodal tDCS only when stimulation was applied during task performance (Stagg et al., 2011). Indeed, LTP-like plasticity-inducing tDCS improved motor learning when stimulation was applied during task performance (Nitsche, Schauenburg, et al., 2003 Savic & Meier, 2016). TDCS-generated neuroplasticity is thought to enhance learning-related plasticity (LTP) when task performance and stimulation are conducted simultaneously. In accordance, in a motor set-shifting task, in which one of two motor responses was correct in each trial, cathodal tDCS conducted before performance slowed motor RTs (Leite et al., 2011). However, for relatively simple RT tasks, tDCS applied before performance may also induce functional alterations (Devanathan & Madhavan, 2016 MГјller, Orosz, Treszl, Schmid, Sperner, 2008). TDCS influences both motor learning (Nitsche, Schauenburg, et al., 2003 Savic & Meier, 2016) and performance of simple motor and cognitive tasks (NozariВё Woodard, & Thompson-Schill, 2014) when stimulation is applied during task execution. Since the neurophysiological effects of motor cortex tDCS can remain for a considerable period after stimulation (Nitsche & Paulus, 2000, 2001), also the impact on motor performance might outlast the stimulation itself. The functional effects of tDCS on motor performance and coordination so far have been tested primarily during stimulation (Cuypers et al., 2013 Foerster et al., 2013 Leenus, Cuypers, Vanvlijmen, & Meesen, 2015 Nitsche, Schauenburg, et al., 2003 Pavlova, Kuo, Nitsche, & Borg, 2014) or immediately thereafter (Drummond, Hayduk-Costa, Leguerrier, & Carlsen, 2017 Leite, Carvalho, Fregni, & GonГ§alves, 2011). These findings suggest that the motor cortex excitability changes induced by tDCS can improve motor responses, and these effects critically depend on the time interval between stimulation and task performance. Performance 60 min after anodal tDCS was not significantly different throughout the entire task. Performance 30 min after anodal tDCS was improved only in the last block of the reaction-time task.

Performance zero min after anodal tDCS was improved during the whole course of the task. The aim of this study was to compare the effects of a single session of anodal tDCS (1.5 mA, for 15 min) applied over the left primary motor cortex (M1) versus sham stimulation on performance of a go/no-go simple reaction-time task carried out at three different time points after tDCS-namely, 0, 30, or 60 min after stimulation. The timing of tDCS relative to task performance could determine the efficacy of tDCS to modulate performance. Specifically, tDCS applied over the motor cortex is considered to improve reaction time in simple and complex tasks. Anodal transcranial direct current stimulation (tDCS) induces long-term potentiation-like plasticity, which is associated with long-lasting effects on different cognitive, emotional, and motor performances.

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