Functional imaging studies of attention-deficit hyperactivity disorder (ADHD) tend to follow a dimensional rather than a categorical approach and focus on a combination of behavioral- and circuit-specific paradigms to elucidate neural abnormalities specific to behavioral subtypes. A much needed approach is the application of methods designed to examine functional interactions between various brain regions such as prefrontal cortex, caudate nuclei, putamen and globus pallidus to delineate more closely the neural circuits underlying the psychopathology. The authors hypothesized that ADHD is a progressive neurodevelopmental disorder in which the initial deficit is at the site of dopaminergic cell bodies. A step in investigating ADHD using neuroimaging involves the use of cognitive/behavioral activation tasks that place demands on the neurobiochemical systems that are putatively dysfunctional in ADHD. Continuous performance tasks (CPTs) are used frequently in research to assess deficits in sustained attention in individuals with ADHD.