METHYLPHENIDATE SLOWS RIGHT-HEMISPHERE PROCESSING IN CHILDREN WITH ATTENTION-DEFICIT HYPERACTIVITY DISORDER/

To examine the effects and particularly, any potential detrimental eff ects of methylphenidate on right hemisphere processing in children wit h attention-deficit/hyperactivity disorder (ADHD), the performance of 26 children (aged 8-15 years) with ADHD was compared under methylpheni date and placebo on various cognitive tasks in a double-blind within-s ubjects design. Results indicated that reaction times on a tachistosco pic task were slower on methylphenidate for stimuli that produced a le ft visual field advantage (reflecting better right hemisphere function ing) but not for stimuli that produced a right visual field advantage (reflecting better left hemisphere functioning) off for bilateral stim uli. It is argued that methylphenidate induces a slower response on ta sks involving right hemisphere processing, resulting in slower reactio n times and unchanged accuracy rates. Findings on two tasks that more closely reflect classroom-type tasks revealed an improvement in perfor mance on methylphenidate, suggesting that any stimulant-induced benefi ts on learning style may have overcome detrimental effects on unilater al processing. These findings may help understand the complex, diverse , and sometimes unpredictable effects of psychostimulants on cognitive functioning that are observed clinically in individuals treated for A DHD.