The contribution of drug effects to the understanding of child psychiatric disorders.

The paper is part of a special section on 'psychopharmacotherapy in children'. Drugs not only help to treat symptoms successfully but may also help researchers and clinicians to gain a better understanding of the pathophysiology underlying these disturbances. This is exemplified in three child psychiatric disorders that exhibit disturbances in motor activity as a prominent symptom. These are general motor restlessness (ADHD), tic-disorder (sudden circumscribed motor actions) and stuttering (non-fluent speech). There is evidence that clinically useful drugs increase the cortical-subcortical interaction and tuning mechanisms providing the patients with a better self-regulation related to the motor performance.