Originally Released: November 12, 1999
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Adults with attention deficit hyperactivity disorder (ADHD) seem to use different parts of their brain when performing memory tasks than do people without the disorder, according to a study presented by a University of Maryland School of Medicine researcher at the Society for Neuroscience annual meeting on October 28, 1999.
The study was the first to use brain images obtained from Positron Emission Tomography (PET) to evaluate the relationship between brain activity and successful and unsuccessful working memory performance in patients with ADHD. The PET scan shows where there is increased and decreased blood flow in the brain in response to certain stimulation.
"Our findings indicate that regions of the brain that should be working during certain types of memory tasks are not working in ADHD patients. This may provide important clues about why our patients have difficulty," says Julie Schweitzer, Ph.D., assistant professor of psychiatry at the University of Maryland School of Medicine who recently joined the faculty from Emory University where the study was conducted.
"People with ADHD have significant problems with the type of memory we call working memory," says Dr. Schweitzer. "A greater understanding what parts of the brain are most utilized when people with ADHD perform difficult working memory tasks may lead to the development of more effective medications, as well as improve our understanding of how people compensate by using different brain regions when necessary."
Examples of working memory include taking notes in a classroom during a lecture or trying to remember a phone number someone has just given you while listening to that person give further instructions. An interesting aspect to the study is that the patients who said they experienced more severe symptoms from their ADHD actually did the worst on the working memory test.
The study included 12 adults with ADHD who were not on medication. They were compared to 11 healthy adults who made up a control group.
ADHD, which affects as many as five percent of children in the U.S., is considered the most common child psychiatric disorder and there is increasing recognition that for many, the disorder continues throughout their life.
During the tests in the healthy control group, increases in brain activity were found in parts of the brain typically associated with working memory and attention, such as the right medial frontal cortex, the anterior cingulate, the temporal gyrus, and the precuneus. The right frontal cortex is thought to be involved in retrieving the information and the anterior cingulate may help by suppressing unnecessary information.
Decreases in brain activity among the healthy control subjects were seen in many of the same areas when they skipped a question or gave a wrong answer. Control subjects appeared to use the hippocampus, another region often associated with memory, when the working memory question required more thought and when they were having difficulty answering the question.
Subjects with ADHD showed a very different pattern of blood flow in the brain while taking the test. Instead of having activity in the frontal regions, they had increased blood flow in the basal ganglia, especially when their answers were correct. The basal ganglia area is typically associated with response readiness and motor control.
ADHD subjects did show activations in the precuneus when answering correctly, suggesting that they were able to use the visual strategies that control subjects may also have used to help the recall the working memory questions.
The results of this study suggest that individuals with ADHD may be relying on less efficient regions in the brain to perform working memory tasks. Dr. Schweitzer is currently studying how methylphenidate, one of the most common treatments for ADHD, affects working memory and blood flow within different regions of the brain.
Dr. Schweitzer's Emory University collaborators on the study include Tim D. Ely, B.S., Cary Zink, B.S., Russell B. Hanford, M.A., and Clint Kilts, Ph.D. of the Department of Psychiatry and Behavioral Sciences, and Scott T. Grafton, M.D. of the Department of Neurology and Emory Center for PET, and John M. Hoffman, M.D., formerly of Emory and currently at the National Cancer Institute. The study was supported by the National Institute of Mental Health.
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