The Role of Inhibitory Control and Executive Functioning in Hyperactivity/ADHD

Abstract: This thesis examined inhibition, executive functioning and their possible relation to childhood problems of hyperactivity and inattention, in its clinical form referred to as Attention Deficit Hyper-activity Disorder (ADHD). Concurrent as well as longitudinal relations were of interest, and both clinical and non-clinical samples were studied. Study I demonstrated concurrent relations between executive inhibition and both hyperactivity and conduct problems in preschool. However, the relation between inhibition and conduct problems could be attributed to the large overlap between hyperactivity and conduct problems.In Study II, linear relations were found between executive inhibition and hyperactivity, whereas inhibition to the unfamiliar was related to hyperactivity, social initiative, as well as social anxiety. Non-linear analyses showed that children with high levels of both types of inhibition were at risk for developing low social initiative and social anxiety, whereas children with low levels of inhibition were at risk for developing hyperactivity, but at the same time protected from social anxiety. In Study III, executive inhibition was longitudinally related to ADHD symptoms in both school and at home for boys, but only in the school context for girls. Executive inhibition was also related to more general executive functioning deficits, and concurrent relations were found between executive functioning and ADHD symptoms, although in both cases only for boys. Inhibition and executive functioning made independent contributions to the understanding of ADHD symptoms for boys, and together explained about half the variance in inattention problems. In Study IV, group differences were found between ADHD children and controls for both inhibition and various other executive function measures. These measures also discriminated well between groups. The best model, which included measures tapping inhibition, working memory and emotion regulation, classified 86% of the children correctly. In summary, the results of the present thesis were mostly supportive of Barkley’s hybrid model of ADHD, although it should be noted that the question of whether inhibition should be regarded as primary to other executive functions requires further investigation.