A 2007 study by Stewart H. Mostofsky and colleagues in the journal Human Brain Mapping revealed an association between ADHD and three physical characteristics of the brain: decrease in the cortical volume, decrease in surface area of the brain, and folding throughout the brain. As reported in the November 23, 2007, press release ''Research Identifies New Features of Brain Structure That May Lead to ADHD,'' the researchers, who are from the Kennedy Krieger Institute in Baltimore, studied children ages 8 to 12. Twenty-one children diagnosed with ADHD were compared to a control group of thirty-five. The developing children were matched typically in age and gender. The study found children with ADHD showed decreased total brain volume and decreased volume throughout the cortex of the brain or outer gray matter regions comprise of neurons. They also found that this reduction in cortical volume may be attributed to decreased folding in the cortex, suggesting that folding is the key brain feature associated with ADHD. This study is the first to examine cortical folding and ADHD and suggests that biological causes may begin early in development, during gestation through infancy.

Prior studies that have been conducted have examined the brains of children with ADHD with imaging studies that measure the size and volume of various brain regions. However, this study used computer-generated images or brain maps for each subject that allowed them to measure and examine additional important structural features, including surface area and thickness, and to following activity throughout the brain, as well as within specific regions. These areas of the frontal lobe of the brain are associated with control of attention and behavior.

Cortical folding appears to be an important element in the development of ADHD. Results of the study found that children with ADHD showed a greater than 7 percent reduction in total cerebral volume (TCV) compared to the control group of typically developing children. In addition, children with ADHD showed reduced cortical volumes and surface area of the brain compared to typically developing children, with a reduction of more than 8 percent in each brain hemisphere. Because the study looked beyond volume, additional measures of brain structure revealed that children with ADHD showed a significant decrease in cortical folding across the entire cerebral cortex, even after accounting for the decrease in TCV. Because no significant difference was found in the thickness of the brain, the results indicated that cortical folding is an important factor to the reduced cortical volume observed in ADHD. Cortical folding begins in early development of the fetus at about 16 weeks' gestation and reaches its peak at about 18 months of age. It is then followed by a gradual leveling out to adult levels at about 23 years of age. During development when the brain can no longer expand because of the size of the skill, the only way to increase in surface area is if the cortex becomes more folded. Thus, cortical folding is critical to increasing the structural and functional capacity of the brain.

A 2007 report by Shaw et al. in the Proceedings of the National Academy of Sciences USA found that crucial parts of brains of children with ADHD develop more slowly than other youngster's brains. Earlier studies of brain imaging research missed this happening. According to Dr. Shaw, National Institute of Mental Health, the lag can be as much as 3 years in brain regions that suppress inappropriate actions and thoughts, focus attention, and assist in remembering things from moment to moment. The study did find a normal pattern of cortex maturation, although it was delayed in children with ADHD. This could explain why many youths eventually seem to grow out of the disorder. However, some children do not appear to grow out of the disorder, and researchers are working to determine the differences between those that have a good outcome and those who do not.

As an organ, the brain is very complex in its functioning. Although scientists are hard at work trying to identify how basic structure affects function, conclusions are still sketchy. Exploring the deep mysteries of the inner space of the brain is still as much of a challenge as studying the unknowns of outer space.

Bibliography:

1) Barkley, Russell. 2006. Attention-deficit hyperactive disorder: A handbook for diagnosis and treatment. 3rd ed. New York: Guilford Press

2) Brown, Thomas E. 2005. Attention deficit disorder: The unfocused mind in children and adults. New Haven: Yale University Press

3) Levy, R., and Goldman-Rakic, P. S. 1999. Association of storage and processing functions in the dorsolateral prefrontal cortext of the nonhuman primate. Journal of Neuroscience, 19:5149-58

4) Ornstein, Robert. 1997. The right mind: Making sense of hemispheres. New York: Harcourt Brace; Piano, Marina. 2003. Scientists Use MRIs to study ADHD, depression in children. San Antonio Express-News (Texas), May 19:F1

5) Shaw, Philip et al. 2007. Attention-deficit/hyperactivity disorder is characterized by a delay in cortical maturation. Proceedings of the National Academy of Sciences USA 104:19649-54

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