Research Update: ADHD

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July 28, 2008
Study Using Simple "Go/No-Go" Task Finds Brain Inactivity Characterizes ADHD

Kennedy Krieger Research Update: Dr. Stewart Mostofsky

Dr. Stewart Mostofsky and his colleagues recently published a paper in the Journal of Cognitive Neuroscience examining differences in brain activity in children with Attention Deficit Hyperactivity Disorder (ADHD) and typically developing (TD) children. Dr. Mostofsky and his research team at the Kennedy Krieger Institute used a classic "Go/No-go" task to study response inhibition, or the ability to stop oneself from engaging in unwanted or unnecessary actions. During the "Go/No-go" task, most (75%) of the stimuli were "Go" stimuli, which set up a predominant tendency for the children to respond. Therefore, when the "No-go" stimuli appeared, children had to rapidly switch their behavior from more "automatic" responding to more selective withholding of a response. The study found no significant differences in brain activity between the two groups for the more automatic "Go" events. In contrast, for the "No-go" events, children with ADHD showed less brain activation in regions known to be important for selecting and rapidly switching behavior.

Response inhibition is believed to be a core deficit in ADHD that contributes to the excessive impulsive, hyperactive and inattentive behavior that defines the disorder. In this study, researchers studied 25 children with ADHD and 25 TD children between the ages of 8 and 13 using functional magnetic resonance imaging (fMRI). Children were instructed to press a button with their finger as quickly as possible each time a green spaceship appeared ("Go") and not to press the button if a red spaceship appeared ("No-go").

Researchers only saw differences between the two groups when the children had to select not to respond, which required them to actively switch their behavior and use circuits in the brain critical for response selection. These findings suggest that abnormalities in circuits of the brain important for motor response selection contribute to problems in response inhibition in children with ADHD. Additionally, these findings support the growing awareness of ADHD-associated irregularities in regions important for the control of voluntary actions. Further research may indicate whether children with ADHD have less activity in specific regions of the brain because of decreased capacity within these regions and/or a lesser degree of functional activity. Understanding the brain activity that causes deficient response inhibition may provide critical information for future ADHD diagnosis, prognosis and treatment strategies.

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