Neuromodulation as way to affect ADHD related symptoms. A tDCS study

Introduction: ADHD is characterized by symptoms such as inattentiveness, hyperactivity, and impulsivity. Individuals with ADHD also experience increased levels of aggression and anger as a result of lack of emotion modulation (Oliver, Han, Bos & Backs, 2015). Individuals with ADHD often rely on medication to modulate these symptoms, but it is not always an effective course of treatment (Wehmeier, Schacht & Barkley, 2010). This study aimed at exploring the effects of tDCS on negative emotion regulation as it pertains to ADHD related symptoms, which could potentially provide support for the use of the tDCS as an alternative treatment for ADHD. The Ultimatum Game has been used to explore the divide between a participant's desire for fairness and personal gain (Iannello, Colombo & Antonietti, 2014). It has also been used to explore the impact of emotion on decision making (Riepl, Mussel, Osinsky, & Hewig, 2016). In the present study an unfairly biased version of the game was used to elicit negative emotions: regardless of the strategy used the participants were getting constant negative feedbacks. Methods: Sixty-six participants (age range 18-27; Mean = 22.03; SD = 1.42) were involved in the study. Participants were asked to complete three inventories: the Preference for Intuition and Deliberation scale, the Dickman Impulsivity Inventory, and the ADHD Self-Report Scale. After this first phase, they completed two emotion inventories; the Geneva Emotion Wheel and the Self-Assessment Manikin. Participants were then linked to the tDCS equipment - and randomly assigned to one of the three experimental conditions: right DLPFC cathodal stimulation and left DLPFC anodal stimulation, right DLPFC anodal stimulation and left DLPFC cathodal stimulation and sham condition. Stimulation was set at 1.5 mA for 20 minutes. After 5 minutes, participants were presented with a computerized version of the Ultimatum Game, They played with four fictional participants (described as more or less likely to accept unfair offers), and after each round, they received negative feedback. Following the Ultimatum Game, participants completed the GEW and SAM a second time. Results: Results highlighted a significant main effect of tDCS condition in modulating emotional responses - the effect was mediated by the score on the ADHS Self-Report Scale and was stronger for negative emotions. The stimulation did not affect the way participants played the Ultimatum Game. Conclusion: Consequences for future use of a tDSC based protocol to treat ADHD patients are critically discussed.