Effects of Methylphenidate on Cognitive Functions in Boys With Attention Deficit Hyperactivity Disorder: Does Baseline Performance Matter?

Objective: Although attention deficit hyperactivity disorder (ADHD) is associated with cognitive deficits, there is considerable heterogeneity and only a minority of individuals with the disorder demonstrate a deficit in any cognitive domain. Recent studies indicate that the relationships between ADHD symptoms and cognition are complex with a dissociation between medication responses across these two domains. Method: We examined whether methylphenidate (MPH) differentially impacts on cognition in those with and without pretreatment cognitive deficits in a 4-week randomized controlled crossover of high (0.6 mg/kg/dose) and low (0.3 mg/kg/dose) dose MPH and placebo in 75 medication-naive boys with ADHD. Cognition was assessed using tasks from the Cambridge Neuropsychological Test Automated Battery (CANTAB). Confirmatory factor analysis (CFA) was used to form latent cognitive factors of executive functioning, visual memory, and reaction time, as well as a general cognition factor. Results: Compared to placebo, both high and low MPH doses significantly improved performance on pattern recognition (PR), spatial recognition (SR), and simple reaction time. The low, but not the high, dose improved performance on the Stockings of Cambridge (SOC) and delayed matching-to-sample tasks. Both doses also significantly improved performance on the executive functioning, visual memory, reaction time skills, and general cognitive latent variables. There were however no differences in the effects of MPH on cognition between those with and without a baseline cognitive deficit, for either the observed task values or the latent cognitive factor scores. Conclusions: We conclude that MPH can enhance executive functioning, visual memory, reaction time, and general cognitive function in boys with ADHD. These improvements are not dependent on baseline cognitive performance. What is the public health significance of this article? As medication effects on cognition are independent of baseline performance and of the effects on symptoms clinicians should assess and monitor both cognitive and symptom outcomes when treating ADHD.