Effects of methylphenidate on functional magnetic resonance relaxometry of the cerebellar vermis in boys with ADHD.

OBJECTIVE The authors used functional magnetic resonance imaging (fMRI) to test the effects of methylphenidate on steady-state blood volume in the midline vermis of the cerebellum in boys with attention deficit hyperactivity disorder (ADHD). This region was selected as it has been observed to be significantly smaller in children with ADHD. Also, in preclinical studies, the vermis has been shown to modulate forebrain dopamine systems, to influence locomotor activity, and to contain a significant density of dopamine transporters. METHOD T(2) relaxometry was used to indirectly assess blood volume in the cerebellum (hemispheres and midline vermis) of 10 boys with ADHD who were administered placebo or one of three different doses of methylphenidate continuously for 1 week. T(2) relaxation time values are inversely proportional to local cerebral blood volume. After each week of treatment, and within 1-3 hours of the boys' afternoon dose, testing for drug efficacy was performed by using objective measures of activity. RESULTS Moderate and high doses of methylphenidate increased T(2) relaxation time in a rate-dependent manner-increasing T(2) relaxation time in the most active children with ADHD and reducing T(2) relaxation time in subjects with ADHD who were not objectively hyperactive. CONCLUSIONS This preliminary study supports a role for the vermis in ADHD and suggests that further research is needed to clarify the relationship between vermal size, vermal blood flow, stimulant response, and the developmental pathophysiology of ADHD.