Attention Deficit/Hyperactivity Disorder

This chapter reviews attention deficit/hyperactivity disorder (ADHD), with an emphasis on structural and functional magnetic resonance imaging studies that have illuminated its neurobiology. Although most studies have small to medium samples, the overall number has grown substantially, and the focus here is on quantitative meta-analyses. Cumulative evidence implicates frontoparietal, striatal, thalamic, and cerebellar involvement in ADHD, but accumulating interactions among the default network and top-down regulatory networks, and visual and sensorimotor cortex are increasingly implicated. This multiplicity of neural systems is unlikely to be involved in all patients with ADHD, but the relevant subsets in relation to individual symptom dimensions have not yet been identified. The challenge is to identify these in relation to replicated genetic risk markers, which need to be explored in animal models. In this way, the nosology and therapeutics of the near future will emerge, as encouraged by the Research Domains Criteria project.