Event-related electrical stimulation of motor cortices enhances performance in a hand-tapping task

Introduction: Transcranial electrical stimulation (TES) for about 20 min, has resulted in the majority of observed effects in related TES research. While this duration of stimulation has been recognised as safe for human use, some researchers incorporated an alternative method of administration incorpo- rating less than 3 minutes of stimulation, to investigate whether it still produces significant results. It has been shown that short duration stimulation significantly improved verbal memory performance on a word recognition task, in which less than 2 s of anodal stimulation administered per trial was sufficient. Methods: This study sought to investigate whether stimulation locked to Events (‘Event-related’ stimulation) was effective for the improvement of other types of memory, such as procedural motor memory. To test this, response times (RTs) for an implicit sequence- learning hand-tapping task using anodal tDCS over the primary motor cortex (PMC) were compared across Event-related, Constant, and Sham conditions (n ¼ 15 per condition). Participants were asked to tap the buttons on a response box with six buttons as soon as a cue light lit up in the button. Results: Differences in the slopes of RTs over blocks of trials were fitted with an exponential decay function, which revealed a sig- nificant difference in the exponential decay variable, comparing Event-related and Sham conditions (p ¼ 0.042). Discussions: These results show that Event-related stimulation was effective for the improvement of procedural motor memory as compared to Sham. The results of this is another evidence of effectiveness of short duration of stimulation and highlight the importance of synchronisation of stimulation with the ongoing task.