The Unique and Combined Effects of Reinforcement and Methylphenidate on Temporal Information Processing in Attention-Deficit/Hyperactivity DisorderLuman, Marjolein PhD*; Papanikolau, Alky MD†; Oosterlaan, Jaap PhD*Journal of Clinical Psychopharmacology: August 2015 - Volume 35 - Issue 4 - p 414–421 doi: 10.1097/JCP.0000000000000349 Original Contributions Buy Abstract Author InformationAuthors Article MetricsMetrics Temporal information processing and reward sensitivity are neurocognitive impairments key to attention-deficit/hyperactivity disorder (ADHD). The aim of this study was to examine the unique and combined impact of reinforcement and methylphenidate (MPH) on temporal information processing in children with ADHD. We predicted that both monetary reinforcement and MPH would ameliorate temporal information processing deficits in ADHD, and we expected that the combined effect of reinforcement and MPH would be most beneficial. Forty children (23 with ADHD and 27 typical controls, aged 8–12 y) performed a time production task under 3 conditions: reward, response cost, and feedback only. Children with ADHD also performed the task (in random order) with placebo, a low, a medium, and a high dose of MPH. Dependent variables were time production accuracy and variability. At baseline, children with ADHD displayed poor internal clock functioning compared with controls, as reflected by greater underestimations of the 1-second interval, and they showed poor motor output as reflected by increased timing variability. Reward and response cost improved motor output (timing variability), with similar effects for both groups. Methylphenidate increased performance (timing variability) compared with placebo, with a higher dose showing greater effects. Effect sizes of reinforcement and medication were medium to large. Contrary to expectations, MPH did not add to the reinforcement effect. The results of this study confirm the value of reward and response cost being similar to that of MPH to optimize (timing) performance of children with ADHD. From the *Department of Clinical Neuropsychology, VU University Amsterdam, Amsterdam; and †De Bascule, Academic Centre for Child and Adolescence Psychiatry, Duivendrecht, The Netherlands. Received May 5, 2014; accepted after revision April 14, 2015. Reprints: Marjolein Luman, PhD, Department of Clinical Neuropsychology, VU University Amsterdam, Van der Boechorststraat 1, 1081 BT Amsterdam, The Netherlands (e-mail: email@example.com). Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.