The effect of a skipped dose (placebo) of methylphenidate on the learning and retention of a motor skill in adolescents with Attention Deficit Hyperactivity Disorder

Individuals with Attention Deficit Hyperactivity Disorder (ADHD) have difficulties in achieving optimal performance in many everyday and academic tasks, deficits attributed to impaired skill acquisition and procedural memory consolidation. We tested the effect of a skipped dose of methylphenidate (MPH) on learning a movement sequence and its subsequent consolidation into procedural memory in adolescents with ADHD. A crossover double-blind design with placebo was used. Sixteen male adolescents, 16-18 years-old, with ADHD and taking MPH formulations on a daily basis, were trained on performing a 5-element sequence of finger-to-thumb opposition movements. Participants took part in two study conditions, 2 months apart. In each condition a different movement sequence was trained and tested. Participants trained on the task either with active medication or placebo on the day of training, crossed-over between study conditions. Learning effects, speed and accuracy, were assessed within-session, during a 24-h memory consolidation phase. Retention was tested by 2 weeks post-training. There were robust gains in performance both within-session and during the 24-h consolidation phase, in both conditions. However, the discontinuation of MPH on the day of training significantly reduced performance speed, with no loss of accuracy. By 2 weeks, post-training performance was comparable. Adolescents with ADHD who are treated daily but skip a dose of MPH show significant slowing of performance relative to their own performance on medication. However, on a background of daily treatment a skipped dose has no deleterious effect on memory consolidation and retention.