A sham controlled within-subjects study design will be conducted. Clinical eligibility screening will be completed at baseline. All participants will undergo an extensive neuropsychiatric evaluation in which developmental neuropsychiatrists and psychologists will evaluate the cognitive and the adaptive level, the severity of ADHD symptoms, and the presence of comorbid psychiatric disorders. After completing baseline assessment (T0), participants will be exposure to 3 conditions with an intersession-interval of 24h (T1, T2, T3): A) a single administration of 1 milliampere (mA) anodal tDCS session over the dorsolateral prefrontal cortex (DLPFC); B) a single administration of 1 mA sham tDCS session over the DLPFC; C) a single administration of immediate release MPH (Ritalin®), in accordance with the National Institute for Clinical Excellence (NICE) guidelines for ADHD (NICE, 2000). The order of the conditions will be counterbalanced across participants. After recruitment, the participants will be assigned to one of the 6 possible combinations of conditions (ABC, ACB, BAC, BCA, CBA, or CAB). The assignment will be according to a randomization order generated by a computer. The randomization information will be maintained by an independent researcher until data collection is completed. Participants will be tested on inhibitory control, by the Stop Signal Task (SST) and on working memory, by the N-Back Task, at baseline (T0), during tDCS administration (after 10 minutes of anodal and sham conditions) and after 1 hour of MPH administration. To verify that carry-over effects will not occur, the SST and the N-Back Task will be performed before each session (T1, T2, T3) and results will be compared with those obtained at baseline (T0). If the participant will not return to baseline level, another evaluation will be administered at least after two hours and, again, until participant's performance will return to baseline. Participants and parents will be blinded to tDCS conditions allocation. The tDCS will be carried out with a BrainStim stimulator.
The aim of this study is comparing the effects of non-pharmacological intervention (transcranial Direct Current Stimulation, tDCS) with those of drug (methylphenidate, MPH) administration in children and adolescents with ADHD.~The investigators hypothesized that tDCS would improve inhibitory control and visuo-spatial working memory as well as MPH.