Blinding of transcranial direct current stimulation is compromised in typically developing children compared to young adults.

Achieving successful blinding is a persistent challenge for clinical trials involving transcranial direct current stimulation. Studies involving populations with increased sensory sensitivity, such as children, could be at risk for increased bias from inadequate blinding due to unique sensation of stimulation relative to adults. The objectives of this study were 1) To examine differences in transcranial stimulation blinding between children and young adults and its relationship to sensory sensitivity. 2) To test the efficacy of an ActiSham protocol for participant blinding, compared to a traditional sham protocol. Typically developing right-handed children (N = 12, 5-14 yr) and young adults (N = 15, 15-25 yr) completed a single-session study to test transcranial stimulation blinding after three conditions counterbalanced across participants: Active, Sham and ActiSham. Stimulation was paired with a motor learning task to simulate a combinatory neurorehabilitation intervention. After each condition, participants reported if they received real or fake stimulation and their response confidence. To quantify sensory sensitivity, participants completed the Sensory Profile (second edition). Compared to a chance level, 1) children and young adults correctly identified Active stimulation, 2) children incorrectly identified Sham and ActiSham stimulation and 3) young adults identified Sham and ActiSham stimulation at chance-level. Blinding accuracy was not related to sensory sensitivity. Children report stimulation as real stimulation with higher confidence for almost all conditions, indicating unsuccessful blinding compared to young adults. Future studies should consider alternative sham protocols or methods to improve blinding in child participants.