Attention Deficit Hyperactivity Disorder in children and adolescents : neuropsychological deficits and functional outcomes

Sammanfattning: This thesis investigated the role of neuropsychological functioning in ADHD and some of the major functional consequences of the disorder: academic achievement and peer problems. Study I used both a logistic regression and Venn diagrams to illustrate the neuropsychological heterogeneity of Attention Deficit Hyperactivity Disorder (ADHD) in a school-aged sample. More specifically, independent effects were observed for executive functioning, reaction time variability as well as for both positive and negative aspects of emotional functioning. There were no effects of gender, and group differences generally remained significant when controlling for either IQ, comorbid conduct problems or internalizing problems. Study II investigated neuropsychological heterogeneity in a preschool sample. Independent effects of executive functioning, delay aversion and emotional functioning were found. Like Study I, the results of Study II showed that the associations between neuropsychological deficits and ADHD generally remained after controlling for IQ and comorbid conduct problems. In Study III, the aim was to investigate how the multiple neuropsychological deficits can explain secondary impairments. The results showed that working memory and reaction time variability partially mediated the relation between ADHD and academic achievement, whereas regulation of anger partially mediated the relation between ADHD and peer problems. Neither gender nor comorbid Oppositional Defiant Disorder/Conduct Disorder (ODD/CD) moderated these findings. In Study IV, neuropsychological deficits were investigated in relation to both ADHD symptoms and functional impairments, but here with a longitudinal design covering a period from preschool to late adolescence. Results show that executive and attention-related functions were primarily related to symptoms of inattention, while emotional functioning was predictive of both symptom domains. Hence, early onset neuropsychological deficits are predictive of development of ADHD. With regard to the role of comorbid ODD/CD, relations to anger disappeared when controlling for symptoms of ODD/CD, but the effect of regulation of happiness/exuberance remained significant for hyperactivity/impulsivity and just missed significance for inattention. These results emphasize the need to also include positive emotions as a possible cause of ADHD symptoms. In summary, neuropsychological deficits should be considered important aspects to target in relation to ADHD as well as to academic achievement and peer problems. Several aspects of neuropsychological functioning are deficient in both preschool and school-aged children, but the relative impact of each specific deficit varies with age. Adding to previous research, this thesis suggests that deficient emotional functioning is an important pathway both to ADHD and associated peer problems. Furthermore, this thesis suggests that reaction time variability is not just strongly related to ADHD, but also to academic achievement.