3-year brain lag found in ADHD kids
They can catch up to their peers, says a reassuring study.
Published November 13, 2007
The brains of children with attention deficit hyperactivity disorder develop more slowly than those of other children but eventually catch up, according to a government study published Monday that suggests ADHD might be a transient condition, at least for some people.
Using advanced imaging techniques, scientists found that the cortices of children with ADHD reach peak thickness an average of three years later than children without the disorder.
The cortex is involved in decision-making and supports the ability to focus attention, remember things moment to moment and suppress inappropriate actions - functions often deficient in children with ADHD.
Dr. Philip Shaw of the National Institute of Mental Health said that although brain development was slower among children with ADHD, it followed a normal pattern, which should reassure parents.
Shaw, lead author of the report published in Proceedings of the National Academy of Sciences, said the results could help explain why many children with ADHD appear to grow out of the disorder and become less impulsive and fidgety as they mature.
"There has been a debate about whether ADHD is a delay or deviance from normal brain development," he said. "This study comes down strongly in favor of delay."
About 4.4-million school-age children in the United States, or 3 percent to 5 percent, have ADHD, which can lead to poor school performance and behavior problems. Half of children diagnosed with the disorder are treated with stimulants, such as Ritalin, or other medicines.
Researchers used magnetic resonance imaging equipment to scan the brains of 223 children and adolescents with ADHD and 223 youngsters without the disorder. The scans were repeated two, three or four or more times at three-year intervals.
Scientists focused on the cortex, which becomes thicker as the brain builds new connections to process all the things children are learning - a key milestone in brain development. They measured cortical thickness at 40,000 points on each scan, creating a detailed map of brain development in the two groups.
In general, they found that the parts of the cortex involved in sensory and motor processing reached peak thickness earlier than the areas responsible for decision-making and other higher-order functions.
In children with ADHD, developmental lags were most pronounced in the prefrontal cortex, which supports attention and working memory, among other things. Half of the cortical points in ADHD children reached peak thickness at an average age of 10.5, contrasted with 7.5 in children without the disorder.
The primary motor cortex reached peak thickness at age 7.4 in children with ADHD, about five months earlier than in normal children, researchers found. Shaw said it was possible that the early maturation of the primary motor cortex contributed to the fidgety behavior characteristic of ADHD.
The study, which focused on one aspect of brain development, did not explain why some people continue to experience ADHD symptoms as adults.
Dr. Bradley S. Peterson of Columbia University , who was not connected to the study, said that although the brains of children with ADHD reached the appropriate thickness, there was no way of knowing from the study whether individual cells were normal.
"Billions of cells make up brain tissue, and we cannot measure all the cells and all the connections between the cells," he said. "Subtle deficits could easily remain."
In addition, he said, the study did not examine the process of cortical thinning that takes place in late adolescence - a second developmental milestone in which unneeded connections are pruned to shape the adult brain.
Government researchers plan to continue tracking some study participants through adulthood, Shaw said.
"We have not captured this later transition," he said. "It is possible some people never quite get there and that is what accounts for the persistent" ADHD.
Hope for unruly kindergartners
In another study that may ease fears about young children with behavioral problems, an international team of researchers analyzed measures of social and intellectual development from more than 16,000 children and found that disruptive or antisocial behaviors in kindergarten did not correlate with academic success at the end of elementary school.
Kindergartners who interrupted the teacher, defied instructions and even picked fights were performing as well in reading and math as well-behaved children of the same abilities when they both reached fifth grade, the study found.
Other researchers cautioned that the findings, reported today in the journal Developmental Psychology, did not imply that emotional problems were trivial or could not derail academic success in the years before or after elementary school.
New York Times