Abstract
This study examined the effects of methylphenidate (MPH) on reaction time (RT) variability in children with attention deficit hyperactivity disorder (ADHD). Using a broad battery of computerized tasks, and both conventional and ex-Gaussian indicators of RT variability, in addition to within-task manipulations of incentive and event rate (ER), this study comprehensively examined the breadth, specificity, and possible moderators of effects of MPH on RT variability. A total of 93 children with ADHD completed a 4-week within-subject, randomized, double-blind, placebo-controlled crossover trial of MPH to identify an optimal dosage. Children were then randomly assigned to receive either their optimal MPH dose or placebo after which they completed five neuropsychological tasks, each allowing trial-by-trial assessment of RTs. Stimulant effects on RT variability were observed on both measures of the total RT distribution (ie, coefficient of variation) as well as on an ex-Gaussian measure examining the exponential portion of the RT distribution (ie, τ). There was minimal, if any, effect of MPH on performance accuracy or RT speed. Within-task incentive and ER manipulations did not appreciably affect stimulant effects across the tasks. The pattern of significant and pervasive effects of MPH on RT variability, and few effects of MPH on accuracy and RT speed suggest that MPH primarily affects RT variability. Given the magnitude and breadth of effects of MPH on RT variability as well as the apparent specificity of these effects of MPH on RT variability indicators, future research should focus on neurophysiological correlates of effects of MPH on RT variability in an effort to better define MPH pharmacodynamics.
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Acknowledgements
Funding for this study was provided by NIH (R01MH074770). This research was also supported by a Mid-Career Investigator Award in Patient-Oriented Research (PI: Epstein; K24 MH064478) and two Mentored Patient-Oriented Research Career Development Awards from the National Institute of Mental Health (PIs: Brinkman & Froehlich; K23 MH083881 & K23 MH083027).
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Dr Epstein receives funding from Eli Lilly and Company as an investigative site for a pharmaceutical trial. Eli Lilly and Company market atomoxetine, a drug used to treat ADHD. The authors declare no other conflict of interest.
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Epstein, J., Brinkman, W., Froehlich, T. et al. Effects of Stimulant Medication, Incentives, and Event Rate on Reaction Time Variability in Children With ADHD. Neuropsychopharmacol 36, 1060–1072 (2011). https://doi.org/10.1038/npp.2010.243
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DOI: https://doi.org/10.1038/npp.2010.243
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