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.

The present study investigated the relation between executive functioning and symptoms of Attention-Deficit/Hyperactivity Disorder (ADHD) and Oppositional Defiant Disorder (ODD) in children aged 4-6. A population-based sample ðn=201) was used and laboratory measures of inhibition, working memory and verbal fluency and teacher ratings of disruptive behaviour problems were collected. Both group differences and linear relations were studied and comorbidity was controlled for dimensionally. In both categorical and dimensional analyses, executive functioning was associated with symptoms of ADHD, but not with symptoms of ODD when controlling for comorbidity, and no significant interactive effects of ADHD and ODD symptoms were found. Effect sizes for significant effects were generally in the medium range. Regarding sex differences, the control for comorbid ODD symptoms appeared to affect the relation between ADHD symptoms and executive functioning somewhat more for girls compared with boys. In conclusion, poor executive functioning in preschool appears to be primarily related to symptoms of ADHD, whereas the relation to symptoms of ODD can be attributed to the large overlap between these two disruptive disorders.

The aim of the present study was to investigate the independent relations of DSM-IV-defined inattention and behaviors characteristic of sluggish cognitive tempo (SCT) to neuropsychological factors and problem behaviors often comorbid with attention deficit/hyperactivity disorder (ADHD). By controlling for symptoms of DSM-IV-defined inattention, unique relations to SCT could be ascertained. Additionally, interactive relations of DSM-IV-defined inattention and SCT were of interest. A community-based sample of school children (N = 209; the higher end of the ADHD-symptom range was oversampled) completed neuropsychological tasks designed to measure executive function (EF), sustained attention, and state regulation. Behavioral symptoms were measured using parental and teacher ratings of the DSM-IV criteria for ADHD and Oppositional Defiant Disorder (ODD). The results showed that these two domains of inattention, DSM-IV-defined inattention and SCT, have neuropsychological processes and comorbid behavioral problems in common. However, when controlling for the overlap, DSM-IV-defined inattention was uniquely related to EF and state regulation, while SCT was uniquely related to sustained attention. In addition, the results showed an interactive relation of DSM-IV-defined inattention and SCT to ODD. Findings from the present study support the notion that DSM-IV-defined inattention constitutes a somewhat heterogeneous condition. Such results can further our theoretical understanding of the neuropsychological impairments and comorbid behavioral problems associated with ADHD symptoms.

This longitudinal study investigated ADHD symptoms and EF impairments in terms of continuity and cross-domain associations, as well as their predictive relations to a range of socioemotional problem behaviors. We applied a factorial ANOVA design to study additive and interactive effects in a sample of non-clinical preschool children (N = 87) and complemented these analyses with group contrasts. The results showed that early ADHD symptoms and EF impairments acted as predictors of continuing problems within each domain. However, it was only ADHD symptoms that predicted other aspects of socioemotional functioning such as dysfunctional emotional regulation and lower levels of social competence. There was no indication of interactive effects on any measure. In conclusion, our results showed that both ADHD symptoms and impaired EF act as early predictors of problem behaviors, although it is clear that predictions based on ADHD symptoms encompass a wider range of problems in early school age children.

The aim of the present study was to investigate possible independent and combined effects of inhibitory control, delay aversion, and RT variability in relation to symptoms of hyperactivity/impulsivity and inattention. A community-based sample of school children (N = 111) completed neuropsychological tasks designed to measure inhibitory control, delay aversion, and RT variability. Behavioral symptoms were measured through parental and teacher ratings of the DSM-IV criteria for ADHD and ODD. The results showed that inhibitory control and RT variability were primarily related to symptoms of inattention rather than hyperactivity/impulsivity. Further, out of the three neuropsychological factors studied, only inhibitory control contributed uniquely to the variance of ADHD symptoms. However, significant interaction effects of delay aversion and RT variability on symptoms of both hyperactivity/impulsivity and inattention were found. This study shows the importance of searching for possible combined effects of neuropsychological factors to learn more about the different pathways that lead to ADHD symptoms in children.