does the longer application of anodal-transcranial direct current stimulation increase corticomotor excitability further? a pilot study

introduction: anodal transcranial direct current stimulation (a-tdcs) of the primary motor cortex (m1) has been shown to be effective in increasing corticomotor excitability. 　methods: we investigated whether longer applications of a-tdcs coincide with greater increases in corticomotor excitability compared to shorter application of a-tdcs. ten right-handed healthy participants received one session of a-tdcs (1ma current) with shorter (10 min) and longer (10+10 min) stimulation durations applied to the left m1 of extensor carpi radialis muscle (ecr). corticomotor excitability following application of a-tdcs was assessed at rest with transcranial magnetic stimulation (tms) elicited motor evoked potentials (mep) and compared with baseline data for each participant. 　results: mep amplitudes were increased following 10 min of a-tdcs by 67% (p = 0.001) with a further increase (32%) after the second 10 min of a-tdcs (p = 0.005). mep amplitudes remained elevated at 15 min post stimulation compared to baseline values by 65% (p = 0.02). 　discussion: the results demonstrate that longer application of a-tdcs within the recommended safety limits, increases corticomotor excitability with after effects of up to 15 minutes post stimulation.