Heterogeneity in ADHD: neuropsychological pathways, comorbidity and symptom domains.

The aim of the present study was to investigate different neuropsychological impairments and comorbid behavioral problems in relation to symptoms of Attention-Deficit/Hyperactivity Disorder (ADHD), studying the independent effects of different functions as well as specific relations to symptoms of hyperactivity/impulsivity and inattention. A community-based sample of school children (n = 182; the higher end of the ADHD symptom range was oversampled) completed neuropsychological tasks designed to measure executive function (EF), state regulation and delay aversion. Behavioral symptoms were measured through parental and teacher ratings of the DSM-IV criteria for ADHD and Oppositional Defiant Disorder (ODD). Both categorical and dimensional analyses were used to acquire a deeper understanding of ADHD. The results supported the notion that EF and state regulation constitute independent pathways to ADHD, primarily to symptoms of inattention. In addition, the present study points to the importance of viewing ADHD as a heterogeneous condition also with regard to the differential impact of neuropsychological functioning and comorbidity on different ADHD symptom groups and the two ADHD symptom domains.