Attention-deficit/hyperactivity disorder (ADHD) is a prevalent and persistent psychiatric disorder, which emerges early in childhood (American Psychiatric Association, 2000). The disorder is estimated to affect about 5% of the population world-wide (Polanczyk et al., 2007), is associated with several comorbid disorders, has poor long-term outcomes, and remains a major public health concern (Rommelse et al., 2009). A primary concern is to better characterize neural mechanisms related to ADHD so as to guide our understanding of pathophysiology.
