- Primary purpose: pathophysiology and basic science The aim of this study is to enlarge the knowledge of the mechanism action of long acting formulations of amphetamines and the neurobiological basis of stimulant action. Furthermore, this study aims to test the predictions of the State Regulation Deficit Model (SRD) for the effect of stimulant medication and presentation rate of stimuli on task performance of children with ADHD. The basic hypothesis is that performance of children with ADHD and the effect of stimulant medication will depend on task demands and the presentation rate of stimuli.