Original articlesEffect of methylphenidate on executive functioning in adults with attention-deficit/hyperactivity disorder: Normalization of behavior but not related brain activity
Section snippets
Participants
The initial subject sample consisted of 13 men diagnosed with ADHD, combined type (American Psychiatric Association 1994), and a group of 11 healthy normal control (NC) subjects matched for age, gender, and general intelligence (Table 1). Two of the ADHD men in the unmedicated condition did not participate in the medicated condition, and brain positron emission tomography (PET) data from one of the ADHD participants in the off-medication condition was incomplete. Therefore, the final ADHD
MPH effects on ADHD symptoms and PASAT performance
The mean daily dose of MPH was 19 mg (SD = 9.07) administered over a mean of 2.9 (SD = .74) divided doses per day. Methylphenidate pharmacotherapy was statistically effective in reducing ADHD symptoms as measured by the CGI and self and other’s ratings on the Adult ADHD DSM-IV Rating Scale (Table 2). Methylphenidate improved PASAT performance accuracy of 82% (SD = 12.90) at baseline to 89% (SD = 6.15) at end point (t = 2.73, df = 9, p = .02). The NC group performed significantly better on the
Discussion
Similar to Mehta et al (2000), we found that MPH administration reduced EF-related activity in the PFC. We speculate that reductions in rCBF in the PFC are due to the release of dopamine by MPH in the PFC that, in turn, act on dopamine D1 and D2 receptors. Increases in dopamine have been shown to cause reductions in the firing activity of PFC neurons (Isacson et al 2004; Parfitt et al 1990; Zhou and Hablitz 1999). Dopamine, acting through D1 receptors, appears to inhibit local excitatory
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