several times a day in a therapeutic context, and the outcome measure is usually therapeutic response as measured by the Clinical Global Impression-Severity scale (CGI-S; Guy 1976) and the ADHD Rating Scale-IV (ARS; DuPaul et al. 1998). In both studies of healthy adults and studies of children diagnosed with ADHD, neuroimaging has also been used to examine variation in brain responses to acute amphetamine and methylphenidate administration. These include techniques such as single photon emission computerized tomography (SPECT), functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) to assess the binding of specific ligands (Warwick 2004; Cabeza and Nyberg 2000).
