"During a test of divided attention, Ritalin increased activation in the basal ganglia, a structure of the brain involved in cognition and behavior," said first author Keith Shafritz, former graduate student in the interdepartmental Neuroscience Program at Yale and now a research associate at Duke University Medical Center. "We saw this activation in children with ADHD and those with reading disorder."
The study used functional magnetic resonance imaging (fMRI) to analyze the effect of the drug on brain function. Researchers found that adolescents with ADHD or reading disorder who were on placebo (not medicated) had less activation of the basal ganglia than a group of healthy participants. When the same participants received Ritalin, the drug normalized the activation, which relates to the amount of blood flow to a specific brain region in response to a cognitive task.
ADHD is characterized by inattention, but previous neuroimaging studies have examined the brain dysfunction associated with impulsivity. "This is one of few studies that used a test for attention rather than a cognitive test for impulsivity," said Shafritz. "It is also the first study, using fMRI to find that the attention circuitry in the brain is directly affected by ADHD."
The 27 study participants, ages 14 to 18 with either ADHD or reading disorder, were randomly assigned to receive Ritalin first or placebo first and didn't know to which group they were assigned. While in the MRI, the participants were given auditory or visual performance tasks to decide whether they saw or heard a real English word or a nonsense word. Their results were compared to a group of 14 healthy adolescents who were not given Ritalin.
Although Ritalin did not affect performance, it altered the areas of the brain that were active during the simple performance of tasks. These results suggest that both ADHD and reading disorder are associated with dysfunction in the brain's attentional circuitry and that methylphenidate normalizes activation within this neural system.
Other authors on the study included Karen E. Marchione, John C. Gore, Sally E. Shaywitz, and Bennett A. Shaywitz.
Citation: American Journal of Psychiatry, Vol. 161 November 2004.