Duration but not intensity influences transcranial direct current stimulation (tDCS) after-effects on cortical excitability

Recent studies have shown heterogeneous results regarding the influence of intensity and duration of motor transcranial direct current stimulation (tDCS) on cortical excitability. In this pilot crossover study including 14 healthy participants, we compared the effects of a single session of anodal-tDCS set with two commonly used durations (20 and 30 minutes) and intensities (1 and 2 mA) on short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF). Regardless of the current intensity, 20 minutes of tDCS increased SICI (3 ms inter-stimulus interval ISI) and decreased ICF (7 ms ISI); 30 minutes of tDCS did not affect cortical excitability.