CHICAGO – Children with attention-deficit/hyperactivity disorder use different neural pathways for visual working memory than do children without the disorder, according to one of the first neuroimaging studies of the inattention component of the disorder.
The findings reveal a disruption of normal functional connectivity in visual attention-related tasks in children with attention-deficit/hyperactivity disorder (ADHD), reported Xiaobo Li, Ph.D., of the Albert Einstein College of Medicine in New York.
Dr. Xiaobo Li
The study points to the potential future use of functional magnetic resonance imaging (fMRI) as a diagnostic tool for the brain disorder, which affects an estimated 5%-8% of school-age children, she said.
Current diagnostic techniques for ADHD rely primarily on behavioral assessments of hyperactivity and impulsivity, and neuroimaging studies to date also have tended to focus on these behavioral components, Dr. Li said in a press briefing at the annual meeting of the Radiological Society of North America. The neurobiological foundation of inattention has not been well studied, but it deserves attention because it is an equally important component of the condition, she said.
Most of the neuroimaging studies of impulsivity and hyperactivity in ADHD have indicated a disruption in the connection between the frontal and striatal cortices, "but this is not enough for a conclusion of ADHD," Dr. Li said.
In the current study, 18 nonmedicated children with combined-type ADHD and 18 healthy children matched for age (range, 9-14 years), IQ, and other variables completed two 5-minute visual attention tasks. Subjects were shown a set of numbers, followed by a series of additional number sets. They were asked to indicate with a handheld device whether each set did or did not match the original digit sequence.
Brain activation and post-hoc functional connectivity were assessed with fMRI scans during the task. Researchers analyzed 16 brain regions showing the most significant levels of activity. They looked at the averages for each group and generated a between-group comparison.
Compared with the control group, children with ADHD showed abnormal activity in several regions of the brain involved in the processing of visual working memory information, Dr. Li reported.
Specifically, the investigators found increased involvement of the anterior cingulate cortex and decreased and disrupted functional connectivity between the frontal lobe and the parietal lobe in children with ADHD.
The findings also suggest that functional differences in the bilateral middle temporal gyri may be associated with the psychopathology of ADHD.
These functional differences may stem from impairments in the white matter pathways involved in visual attention information processing, Dr. Li said.
ADHD "is a brain disorder, so we should use brain markers as more accurate diagnostic criteria," she stated. "Before we truly understand the foundations of each component, we can’t develop very reliable diagnostic criteria. But with this study, we are working on that."
Dr. Li had no financial disclosures related to this study.