Children appear to approach adult levels of performance on many basic cognitive and motor skills by age 11 or 12, according to a new study coordinated by the National Institutes of Health (NIH).
The NIH Magnetic Resonance Imaging (MRI) Study of Normal Brain Development is tracking brain and behavioral development in about 500 healthy American children, from birth to age 18. A report published online today by the Journal of the International Neuropsychological Society contains the first glimpse of behavioral data - covering IQ, motor dexterity, language, computation, and social skills - collected from children ages 6 to 18.
The study "will provide researchers with a reference point for how the normal brain develops, so that they can better understand what goes wrong in children who have brain abnormalities caused by genetic disease, prenatal exposure to alcohol or drugs, or other factors," said lead author Deborah Waber, Ph.D., an Associate Professor of Psychiatry at Children's Hospital Boston and Harvard Medical School.
Some of the behavioral data validate trends seen in other studies; for example, they show that family income has an impact on a child's IQ and social behaviors. But the lack of evidence for dramatic cognitive growth during adolescence was a surprise.
The long-term goal of the study team is to link these behavioral data to MRI scans of the children's brains. Together, the two data sets will allow researchers to view how the brain grows and reorganizes itself throughout childhood, and to explore the meaning of the structural changes they see.
"This study will provide a comprehensive database for clinicians and scientists alike," said NIH Director Elias A. Zerhouni, M.D. "A neurologist who notices something unusual in a child's MRI could use the database to help determine if the anomaly is within the normal range of variation, or if it is cause for concern. A researcher studying an environmental toxin or genetic disease that affects brain development could use the database to help determine where and when development has strayed from its normal course."
The study was launched in 1999 in a joint effort by the National Institute of Neurological Disorders and Stroke (NINDS), the National Institute of Child Health and Human Development (NICHD), the National Institute on Drug Abuse (NIDA), and the National Institute of Mental Health (NIMH). The NIH Blueprint for Neuroscience Research, an initiative that combines resources from those Institutes and other NIH components, recently provided additional funding so that the study team could collect brain scans by diffusion tensor imaging (DTI), a kind of MRI. While conventional MRI allows clinicians and researchers to visualize different parts of the brain, DTI allows them to see the networks of fibers that connect these parts.
To peer into the normal developing brain, the investigators sought children from diverse geographic, socioeconomic and ethnic backgrounds. They recruited children from six sites across the U.S.: Children's Hospital in Boston; Children's Hospital Medical Center in Cincinnati; Children's Hospital in Philadelphia; University of California at Los Angeles; University of Texas, Houston; and Washington University, St. Louis. They also shaped the demographics of the study group - in terms of family income and ethnicity - to resemble the demographics of the U.S. population, based on census data from 2000. Finally, they used questionnaires to exclude children who had any signs or known risk of serious neurological or psychiatric disorders.
Recruitment and screening were handled by a Clinical Coordinating Center at Washington University. A Data Coordinating Center at the Montreal Neurological Institute at McGill University in Quebec is overseeing the imaging arm of the study and building the database of brain-behavior information.
Though no child will be observed for the entire 18-year developmental span covered by the study, each one will be evaluated for several months to several years, depending on their age. Children under age 6 at the time of recruitment are expected to go through dramatic, rapid developmental changes, and are being evaluated at short intervals. A total of 385 children have been recruited within the 6-18 age range, and are being evaluated at three time points - at the beginning, middle and end of a four-year period.
Today's publication summarizes the results of psychological tests conducted at the first time point. The tests measure a broad spectrum of abilities, from fine motor control, to social skills, to aspects of intelligence, such as the ability to explain verbal concepts or solve visual puzzles.
Children from low income families performed somewhat more poorly on IQ and achievement tests and displayed more behavioral problems compared to children from middle and higher income families. They did not differ, however, on many other measures of basic cognitive functions, like memory and verbal fluency, or on most measures of social adjustment. A relatively larger percentage of low income children were excluded by the study's rigorous selection criteria, but the healthy low income children who did participate performed above published norms for their demographic. This suggests that in previous studies, general health disparities might have inflated the cognitive gap between low and high income children, Dr. Waber said.
There were hints of much-cited differences in verbal and spatial ability between boys and girls, but these differences were not as sharp as those described in previous reports. In fact, there were no sex differences in verbal fluency. There were also no differences in calculation ability, suggesting that boys and girls have an equal aptitude for math.
Regardless of income or sex, children appeared to improve rapidly on many tasks between ages 6 and 10, with much less dramatic cognitive growth in adolescence. This result fits with previous research suggesting that in adolescence, there is a shift toward integrating what one knows rather than learning new basic skills. Dr. Waber cautions, however, that these data provide "snapshots" of development in different children at different time points, rather than following each child over a series of time points.
"We don't know whether every child's performance slows during adolescence, or whether some children continue to improve, while others do not," Dr. Waber said. "It's also possible that our standard tests don't measure what really changes in adolescence. As we follow these children over time, we will have a better understanding of what's happening."