SOCIETY FOR NEUROSCIENCE
Fall Meeting, Nov. 7-11
LOS ANGELES -- Scans of brain activity in adults with attention-deficit/hyperactivity disorder (ADHD) are significantly different from scans of adults without ADHD, yet few difference are noted between scans of these two groups once the ADHD patients begin to take the drug Ritalin (methylphenidate), report researchers from Emory University at this week's meeting of the Society for Neuroscience.
The study is the first to evaluate the role of Ritalin on working memory in persons with ADHD.
Brain activity was first recorded using positron emission tomography (PET) in 13 nonmedicated adults with and nine adults without ADHD while they performed a challenging auditory arithmetic task known as the PASAT (Paced Auditory Serial Addition Task). As expected, the persons with ADHD had more difficulty performing the task unmedicated. Researchers noted from the scans that cerebral blood flow was dysfunctional in the ADHD patients - that areas of their brains were over active in some areas and underactive in others during the task. Task-related neural activity among men with ADHD was not noted in the frontal region, an area traditionally associated with working memory, as it was in the normal control subjects, but rather appeared in the PET images to be most concentrated in the brain's cerebellum and basal ganglia, areas associated with more basic motor functioning and attention. But when researchers repeated the test on the same group of adults with ADHD while they were treated with Ritalin (methylphenidate) and compared PET scans to those of the nonpatients, the brain images were remarkably similar, with the exception of the absence of frontal activations in the ADHD group.
"Medication decreased activation, particularly in the cerebellum and basal ganglia while increasing activation in novel areas," reports first author Julie Schweitzer, Ph.D., of Emory, referring to the "inappropriate" brain regions called upon to help solve the task in the unmedicated subjects. "Methylphenidate may improve working memory by decreasing activation in competing regions that are unnecessary for task demands and by recruiting new compensatory regions."
Dr. Schweitzer showed in a previous PET and regional cerebral blood flow (rCBF) study (Schweitzer et al., 1997) a dysfunction in the same right frontal medial region in patients with ADHD when asked to perform a working memory task.
Working memory is a fairly new term that replaces and expands upon the concept of short-term memory. Researchers have theorized that working memory serves not only as temporary storage for new information, but also the active manipulation of this information. Part of the active process may involve inhibiting -- or forgetting -- certain knowledge.
Disruption of working memory may explain many of the everyday difficulties individuals with ADHD encounter, from coping with laborious reading to never remembering to complete one of multiple unfinished tasks, Dr. Schweitzer says. "These findings expand upon earlier data on AD/HD that suggested there was underactivity in AD/HD and show us that there are also areas that are overactive," says Dr. Schweitzer, who is assistant professor of Psychiatry and Behavioral Sciences at the Emory University School of Medicine. "These data provide us with novel clues in regard to developing more specific drug treatment for individuals with ADHD."
Other Emory collaborators on the study included Doug O. Lee, M.D.; Tim D. Ely, B.S.; Matt Ostrowitz; Russell B. Hanford, M.A.; and Scott T. Grafton, M.D.; John M. Hoffman, M.D., of the Department of Neurology and Emory PET Center and Clint D. Kilts, Ph.D., of the Department of Psychiatry and Behavioral Sciences. The study was supported by the National Institute of Mental Health. (Abstract 375.12)
Media Contacts: Sarah Goodwin, 404/727-3366, sgoodwi@emory.edu
Kathi Ovnic, 404/727-9371, covnic@emory.edu
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