Experimental neuropsychological testing of attentional and executive functions in the evaluation of pharmacological treatment responses to methylphenidate in patients with adult ADHD

In the present study, a combined task-switching and oddball paradigm was used to investigate the effects of pharmacological treatment with methylphenidate on attentional and executive functions in 20 adult patients suffering from attention-deficit hyperactivity disorder (ADHD). Patients performed two variants of a task-switching paradigm, in which geometric objects had to be classified according to either color or shape. In the first variant, response conflicts were induced by the occurrence of incongruency in the irrelevant stimulus dimension. Furthermore, rare oddballs were introduced in the currently irrelevant stimulus dimension in order to provoke sensory orienting reactions. In the second variant, the cue-target-interval (CTI) was systematically varied in order to assess the ability of the patients to actively prepare for task switches in advance. Treatment with methylphenidate led to significantly decreased error rates and reaction times in virtually all task conditions indicating a general positive effect on impulsive behavior of ADHD patients. The findings demonstrate the capability of experimental neuropsychological testing to objectify both attentional and executive dysfunctions and treatment effects in ADHD patients.