BACKGROUND: Attention deficit/hyperactivity disorder (ADHD) is one of the most impairing neurodevelopmental disorders of childhood with a worldwide prevalence of 5.3% in children. It is featured by the presence of a persistent pattern of inattention and/or hyperactivity-impulsivity that profoundly affects or reduces the quality of social, academic, and occupational achievements. Influential models of ADHD mainly focus on a deficit in inhibitory control that leads to executive dysfunctions, associated to neural alteration in the prefrontal areas, the striatum, and the cerebellum. Although ADHD can be effectively treated with psychostimulants, a significant proportion of patients discontinue treatment because of adverse events or insufficient improvement of symptoms. In addition, cognitive abilities that are frequently impaired in ADHD are not directly targeted by medication. Therefore, additional treatment options, especially to improve cognitive abilities, are needed. Because of its relatively easy application and well-established safety, non-invasive brain stimulation, such as transcranial direct current stimulation (tDCS), is a promising additional treatment option for children with ADHD. To date, only eight studies have submitted children with ADHD to a maximal of 5 daily sessions. The fact that the technology is inexpensive, and has the potential of being used as a portable device at home by patients, further renders tDCS an attractive tool to explore in treatment in children with neuropsychological disorders, including ADHD. Further, functional near infrared spectroscopy (fNIRS), a non-invasive, compact, unrestrictive, and accessible functional neuroimaging modality has demonstrated its potential in the clinical diagnosis of ADHD children. Since fNIRS visualizes the neural attention and inhibition processes in children with ADHD while they perform tasks online, this technique may have great potential in recording neural changes by tDCS.

OBJECTIVES: The investigators aim to explore the acute and long-term effect of 20 daily sessions of home-based tDCS while doing homework. Our primary objectives seek to determine if tDCS improves: 1) ADHD symptoms, 2) executive function and/or inhibitory processes in children with tDCS. Our secondary aims look at 1) depressive and anxiety symptoms in children with ADHD and 2) the safety and feasibility of home-based tDCS in children with ADHD, and 3) evaluate the mechanisms through which tDCS could be therapeutic using fNIRS that reveals neuroplastic changes successfully.

METHODS: 75 children with ADHD will be submitted to a home-based active or sham fixed-dose tDCS (20 minutes of 1 mA) in a 1:1:1 double-blind, sham-controlled, randomized, parallel-group scheme. Children will be randomly assigned to receiving either 1) active tDCS of anodal left DLPFC and cathodal vertex, 2) active tDCS of anodal right IFG and cathodal posterior to left mastoid or 3) sham tDCS. Stimulation sessions will occur daily, Monday through Friday, for 20 days over a 4-week period. To determine the acute and longterm efficacy of home-based tDCS, children, parents, and teachers will be asked to weekly fill in questionnaires and/or perform tasks online on the weekend from their home. 1) ADHD symptoms will be evaluated using ADHD, DBD and VAS scales. Executive function and inhibitory processes will be determined by a change in I) Visual Search Task, II) Stroop Task, III) Go/No Go Task, IV) Stop Signal Task. 2) Depression/anxiety symptoms will be assessed using HADS and IDS-C scales. Safety and feasibility of home-based tDCS will be assessed using VAS scales and an adverse events questionnaire. Lastly, a change in oxygenated hemoglobin and deoxygenated hemoglobin will help elucidate the mechanisms of tDCS on ADHD. After the tDCS intervention, children will be asked to stay medication-free for as long as they can until study completion for maximal 1-month-post tDCS. All children will be evaluated in person at baseline (visit 1), immediately after the 4-week-treatment (visit 2), and a last visit within 1 month after treatment (visit 3). During these three visits, brain activation patterns of the children will be assessed online using fNIRS while performing the four behavioral tasks.

CONCLUSION: This study will be the first to increase the number of daily sessions of tDCS from 5 to 20 in children with ADHD, making it more than 5 times more likely to increase the response rate to tDCS. Knowledge gained by non-invasive brain stimulation (NIBS) research in children with ADHD might be translatable into an alternative effective treatment, reduce side-effects, and advance the development of closed-loop neuromodulation in ADHD in general. Additionally, no home-based remote tDCS study has ever been conducted in children. Demonstrating its potential will not only offer a more feasible alternative to daily laboratory visits or clinical consultations but may also reduce patient and clinic costs. Lastly, this study will be the first combining fNIRS and tDCS in order to elucidate the acute and longterm mechanisms of effective tDCS intervention in children with ADHD.