Effect of anodal tDCS on cortical activation during response preparation and activation.
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AbstractThere is some evidence that anodal transcranial direct current stimulation (tDCS) of the primary motor cortex increases motor output induced by transcranial magnetic stimulation (TMS) and measured by functional motor tasks. In this study, we examine the effect of anodal tDCS of the primary motor cortex (M1) on response preparation and execution processes using a cued go/nogo paradigm with both directional and non-directional cues. Sixty right-handed adults (37 older, 23 younger) completed two experimental sessions in which they received either sham or anodal tDCS of M1 in a randomised double blind design. EEG was recorded from 64 scalp electrodes while participants completed the cued go/nogo task and analysed via a semi-automatic processing pipeline utilising Fieldtrip and EEGLab toolboxes. We used time frequency analysis across a power band spectrum from 2-30Hz, encompassing the upper delta, theta, alpha and beta frequencies. Here we focus on the 1500ms cue-to-target interval to assess the effect of stimulation on cue processing (within the range of the cue-locked P3) and response preparation (across the development of the CNV). Under sham stimulation, differences in preparation were evident between directional and non-directional cues in both alpha and beta frequency bands. Specifically, left and right directional cues showed greater centro-parietal activation over the contralateral scalp, whereas non-directional cues showed bilateral activation over central scalp. This same pattern was found after anodal tDCS of M1, consistent with the absence of any behavioural difference between active and sham stimulation conditions. This finding contributes converging evidence to the conclusion that anodal tDCS does not affect cortical activity related to response preparation.