either Ritalin first or placebo first, and neither the researchers nor the participants knew whether they were receiving Ritalin or placebo on a given day (a double-blind study). Due to ethical considerations of giving a stimulant medication to adolescents without ADHD, the comparison group did not go through the drug trial, and were instead tested in a single testing session. During the study, participants were scanned in an MRI machine while they completed auditory and visual performance tests. Words were projected onto a screen and presented through a set of headphones. The words were either real English words or pronounceable nonsense words. During tests of selective attention, participants were prompted to pay attention to only one of the two presented words and to determine whether that word was a real word or a nonsense word. During tests of divided attention, participants saw and heard a word simultaneously and then needed to determine whether both the words were real words or nonsense words. We found that the brain activation patterns were remarkably similar between the ADHD, reading disorder, and comparison groups, with one major exception. Part of the basal ganglia, a collection of structures deep within the brain that are known to help direct voluntary motor movements and coordinate behavioral actions, was less active in the ADHD and reading disorder participants when participants took the placebo. When given Ritalin, the activation in this structure increased and was equivalent to the activation in the comparison group. Interestingly, Ritalin did not affect performance on the task, nor did it
differentially affect the brain activation patterns of the ADHD and reading disorder groups. These results suggest that both ADHD and reading disorder are associated with dysfunction in the brain’s attentional and executive functioning circuitry and that Ritalin may act to normalize activity in this circuitry, especially within the basal ganglia. One of the most unexpected findings in the study was that the effects of Ritalin on brain activation appeared to be independent of psychiatric diagnosis. This may indicate that Ritalin has similar effects on brain function whether or not ADHD is present. In another study, we examined the brain basis of executive functioning in a group of children and their parents, in which both the children and parents had a diagnosis of ADHD (Epstein et al., 2007). The children and parents participated in a double-blind medication trial with Ritalin. As before, participants were randomly assigned to receive Ritalin first or placebo first, and then received the alternate medication on a second testing day. Participants were then scanned using fMRI while they completed a go/ no-go response inhibition test. During the task, English letters appeared one at a time on a computer screen, and participants were instructed to press a button for all letters except “X.” Results from the group of children and parents with ADHD were compared to results from a group of child-parent dyads with no history of psychiatric disorder or learning disability. This comparison group did not participate in the medication trial. We found that compared with the group without ADHD, children and their
“... Ritalin exerts its behavioral and cognitive effects by altering the function of the basal ganglia.’’
parents with ADHD showed reduced activation in the basal ganglia and in regions of the frontal lobe of the cerebral cortex (a part of the brain often described as the brain’s CEO). Interestingly, Ritalin increased activation in the basal ganglia for both the children and parents with ADHD. These results indicate that the brain structures implicated in ADHD may not change over the course of development. Further, the results lend additional support to the idea that Ritalin exerts its behavioral and cognitive effects by altering the function of the basal ganglia. In another line of research, my colleagues and I have been investigating the brain basis of executive functioning in autism. Although the most prominent symptoms of autism are impairments in social interaction and social communication, many individuals with autism also have repetitive, stereotyped
fall 2009
HOFSTRA horizons
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