Effect of Low-Intensity Transcranial Magnetic Stimulation on Response Inhibition of Adult ADHD

Introduction: Response inhibition is an impaired cognitive function in ADHD individuals. This primary deficit during cancelation of an intended movement is observed even in the minimal demanding cognitive tasks. Studies have shown that transcranial magnetic stimulation (TMS) specially on dorsolateral prefrontal cortex (DLPFC) can improve the response inhibition. Nevertheless, the TMS has a low spatial resolution and its effect may not be observed in a single-session intervention. Studies showed that low-intensity TMS has higher spatial resolution. Therefore, in this study we aimed to evaluate effectiveness of this method for intervention of response inhibition in ADHD individuals. Methods: In a double-blind paradigm, performance of the adult ADHDs while executing a Stroop color and word test (SCWT) were measured during a sham or a real stimulation of the DLPFC. Subsequently, response inhibitions of the participants were measured before and after the stimulation. Number of correct, wrong and missed answers to 96 computerized trials, and response times of the answers were measured. In addition, changes in electro-cortical activities during the rest phase before and after the stimulation were also evaluated. Results: After checking for data normality, paired t-tests between behavioral data showed that low-intensity magnetic stimulation of the DLPFC can improve response inhibition (reduce errors) even in a single-session intervention of ADHD individuals. Having said that, the answering times did not change significantly. The behavioral changes were associated with significant changes in power of EEG in delta and beta frequency bands at the frontal areas. Conclusion: The proposed stimulation protocol with low-intensity TMS had a fair effect on the response inhibition in adult ADHDs. Therefore, it potentially could be suggested as a treatment protocol on the response inhibition in ADHD individuals.