A two-step approach could be considered, that might include, first, a traditional group comparison of a group of children with ADHD to a group of control children to find brain connections that are atypical in the disorder. This approach may identify connections that are on average atypical in ADHD, even if the effects are not detectible or expected in all ADHD subjects (Nigg et al., 2005; Sonuga-Barke et al., 2003). However, this approach would also not clarify to what component of the disorder an atypical connection is related. Therefore, this conventional approach could then be followed, as a second step, by a dimensional method that would identify how those brain connections relate to specific endophenotypes even if they are not atypical in all subjects with the disease. In this sense, one might be able to identify neural circuits related to the etiology of relatively homogeneous component behaviors. In this report we apply this multi-level approach to elucidate the mechanisms of atypical reward processing in ADHD. The described approach does not rely on DSM-IV defined subgroups; instead, it focuses on a narrower behavioral domain central to ADHD – reward valuation (Sagvolden et al., 2005).
