Anodal Transcranial Direct Current Stimulation (tDCS) Over the Primary Motor Cortex (M1) Enhances Motor Response Inhibition and Visual Recognition Memory

BACKGROUND Transcranial direct current stimulation (tDCS) is a non-invasive brain modulatory technique that can boost cognitive processes and alter performance in cognitive tasks. The effect of anodal-tDCS on cognitive functions following a single session has been repeatedly reported. However, results are varied, mixed, and confounded by several factors, including differences in tDCS current intensity and sham conditions used. Therefore, we assessed the effect of a single session of anodal-tDCS over the primary motor cortex (M1) on cognitive functions, particularly response inhibitory control and visual recognition memory, in healthy adults. MATERIAL AND METHODS Thirty healthy male subjects participated in a randomized, double-blind, sham-controlled tDCS study (2 mA, for 20 min). In the sham stimulation, subjects received the same intensity (2 mA, for 30 s, ramped up, then ramped down). We assessed the cognitive functions response inhibitory control and visual recognition memory using the stop signal task (SST) and pattern recognition memory (PRM) task before and after the stimulation. RESULTS There was a statistically significant difference in cognitive function as assessed by the stop signal task go trial (SST) (P=0.019) and SST correct response time on go trials (P=0.04) after real stimulation only. There was no significant effect observed in sham condition. CONCLUSIONS The findings suggest that anodal-tDCS applied over M1 improves inhibitory control and visual recognition memory compared to sham stimulation. Thus, application of anodal-tDCS to the M1, as an integral node in inhibitory motor control, might be a promising adjuvant therapeutic intervention for modulation of motor response inhibition.