Is Hyperactivity in Children With Attention Deficit/Hyperactivity Disorder (ADHD) a Functional Response to Demands on Specific Executive Functions or Cognitive Demands in General?

Objective: Hyperactivity is a core and impairing deficit in the clinical model of attention-deficit/hyperactivity disorder (ADHD). However, the extent to which hyperactivity in ADHD is evoked by cognitively challenging tasks in general or by demands on specific executive functions remains unclear. Method: A clinically evaluated and carefully phenotyped community-referred sample of 184 children ages 8-13 (M = 10.40, SD = 1.50; 61 girls) with ADHD (n = 119) and without ADHD (neurotypical children and children with psychiatric disorders other than ADHD) were administered multiple, counterbalanced executive (working memory, inhibitory control, set shifting) and nonexecutive tests. Objective measures of gross motor movement (hyperactivity) were obtained using actigraphy. Results: Using bifactor s-1 modeling, results indicate that children with ADHD demonstrate moderately elevated levels of motor movement relative to non-ADHD children. Additionally, findings indicated that hyperactivity in ADHD reflects the outcome of at least two similarly important factors: (a) a baseline level of elevated motor movement that is independent of environmental demands on their executive and nonexecutive cognitive abilities (d = 0.72); and (b) additional elevations attributable to demands placed on specific executive functions, with working memory and inhibition demands evoking similarly large, differential increases in movement for children with ADHD above and beyond their elevated baselines (Delta d = 0.80). Conclusions: These findings suggests that executive function demands exacerbate, but do not fully explain, hyperactivity in ADHD, and/or there are at least two pathways to hyperactivity in ADHD-hyperactivity caused by environmental demands that challenge their underdeveloped executive functions, and hyperactivity caused by one or more other factors that need future research to identify.