Validating a Sham Condition for Use in High Definition Transcranial Direct Current Stimulation

High Definition Transcranial Direct Current Stimulation (HD-tDCS) offers improved focality for targeting specific brain areas to modulate neural excitability, compared to conventional tDCS. HD-tDCS is associated with increased scalp sensation during stimulation, potentially rendering conventional tDCS sham methods ineffective due to lack of blinding. Here we report validation data on a novel method for modeling the sham condition in HD-tDCS studies. Thirty-one participants completed sensation ratings during 20 min of continuous active versus sham stimulation. Over half of the participants reported feeling the stimulation for the duration of the experiment. There were no statistically significant differences in sensation ratings between sham and active stimulation. Further, participants were unable to guess above chance level when they received sham stimulation.