Background: ADHD is a neurodevelopmental disorder associated with significant morbidity and mortality that affects 5% of children, adolescents and adults worldwide. Pharmacological and behavioral therapies exist, but critical symptoms such as dysexecutive deficits remain unaffected.
Objective: To assess the cognitive and physiological effects of transcranial Direct Current Stimulation (tDCS) in adult ADHD patients in order to understand (1) the role of dorsolateral prefrontal cortex (DLPFC) laterality in ADHD dysexecutive deficits, (2) the physiological dynamics sustaining the modulation of executive function by tDCS, and (3) the impact of baseline physiological state on tDCS modulation.
Methods: In a randomized, placebo-controlled, double-blind, cross-over study 40 adult ADHD patients performed three experimental sessions in which they received 30 minutes of 2mA tDCS stimulation targeting the left versus right DLPFC versus sham. Before and after each session, half of the participants completed the Flanker task (EFT) and the other half performed the Stop Signal Task (SST) while we assessed behavioral performance and EEG.
Results: Anodal tDCS to the left DLPFC modulated cognitive (reaction time) and physiological measures (P300) of cognitive control in the EFT in a state-dependent manner, but there were no significant effects in the Stop-Signal-Reaction-Time of the SST.
Conclusions: We describe procognitive effects in adult ADHD patients associated with the modulation of physiological signatures of cognitive control, linking target engagement with clinical benefit, providing mechanistic support for the state-dependent nature of tDCS, and providing empirical evidence of the value of the ERPs as cross-sectional biomarkers of cognitive performance.