Additional questionnaires
itchiness
At the end of each session participants were asked to indicate the perceived intensity of stimulation (1–10; very low-very intense). They also completed a side-effects questionnaire which required participants to report the presence and intensity of a list of typical side-effects (e.g., itchiness, burning, iron taste, etc.). This questionnaire also asked participants to estimate when stimulation began, how long it lasted and whether they felt it impacted their performance on the word recall task. These questions were used to determine the effectiveness of sham stimulation.