The Impact of Stimulant Medication on the Relation Between Working Memory and Activity Level in ADHD.

There is a positive association between heightened activity levels and improved working memory performance (WM) in individuals with Attention-Deficit/Hyperactivity Disorder (ADHD). Recent research suggests that stimulant medications may have a simultaneous positive impact on WM and motor skills. Yet, it is unclear the specific connection between movement, WM, and stimulant use. We examined how visuospatial (VS) and phonological (PH) WM performance varied with children's stimulant medication usage and naturally occurring activity level. In a repeated measures design, children with ADHD (n = 43; 7-12 years old) completed WM tasks while wearing actigraphy watches to monitor activity level on and off stimulant medication. Significant large sized main effects were observed for medication condition on PH (p < .05, η_p² = .14) and VS (p < .001, η_p² = .30) WM. Activity level also had significant medium sized main effects on PH (p < .01, η_p² = .09) and VS (p < .005, η_p² = .10) WM. There was a significant medium sized interaction for VS WM (p < .005, η_p² = .11), indicating that the effect of medication on performance was greatest in the highest activity level category. The findings suggest that a combination of stimulant medication and an "optimal" level of movement may be most effective for improving VS WM.