Attention Deficit Hyperactivity Disorder

Although the longitudinal course of this condition and its prevalence in adulthood have been sources of controversy, a growing literature has documented the persistence of ADHD into adulthood, with about two-thirds of ADHD children continuing to experience impairing symptoms of the disorder though adulthood. Over time, symptoms of hyperactivity and impulsivity are more likely to diminish compared with symptoms of inattention.

Prevalence studies from North America, Europe, and Asia show that ADHD affects about 5 percent of the population. The impact of the disorder on society, in terms of financial cost, stress to families, and disruption in schools and workplaces, is enormous. Although current treatments for the disorder are not 100 percent effective, clinical trials have shown that stimulant medications, such as methylphenidate and amphetamine, relieve symptoms and lessen adverse outcomes, while showing few adverse side effects. Because these medicines increase the availability of the neurotransmitter dopamine in the brain, dysregulation of dopamine systems has been a primary candidate for the pathophysiology of ADHD. But drugs like desipramine and alomoxeline, which have their effects on other brain systems, also exert strong anti-ADHD effects. This suggests that dysregulation of dopamine systems cannot completely explain the pathophysiology of ADHD.

Neuropsychological and neuroimaging studies provide converging evidence for the hypothesis that brain dysfunction causes the symptoms of ADHD. Neuropsychological tests show many ADHD patients to have deficits in the executive functions needed for organizing, planning, sequencing, and inhibiting behaviors. These performance deficits are similar to, albeit milder than, the deficits seen among patients with frontal lobe disorders. Several structural and functional neuroimaging studies implicate networks of regions throughout the brain, not just in the frontal lobes.