"A fundamental objective of neuroscience research is to understand how the human brain develops," explains lead investigator Bradley L. Schlaggar, M.D., Ph.D., instructor of neurology and pediatrics. "We need such knowledge to understand how normal brains develop and to learn what goes wrong in pediatric neurology-related disorders. Only then can we develop clinical interventions to treat these children."
Most studies of this kind are unable to distinguish whether variations between age groups reflect developmental differences or whether they simply reflect the fact that children don't perform as well overall as their adult counterparts. Schlaggar, working with Steven E. Petersen, Ph.D., the James S. McDonnell Professor of Cognitive Neuroscience, and members of Petersen's laboratory, employed several strategies to address this problem.
They tested 19 children aged seven to 10 on single-word processing tasks, which require participants to say a word in response to a written word (for example, antonyms). Functional magnetic brain imaging (fMRI) scans from these tasks were compared with images from 22 adults (an average of 25 years old) who had completed similar tasks. FMRI images reveal which brain regions are actively involved in different tasks. The study highlighted two brain regions in left frontal and left extrastriate cortex, which are known to play a key role in language processing and are believed to undergo substantial development between childhood and adulthood.
Normally during an fMRI study, participants repeat a task several times and the results from the entire set of repetitions are averaged together to produce an image. Schlaggar, however, evaluated each repetition individually using an approach called event-related analysis. This technique minimizes the amount that head movements cloud the images, thereby making verbal responses feasible. With a verbal response, the researchers could analyze both reaction time and accuracy, and could ensure that the children and adults were in fact performing the task as instructed.
The researchers identified six subregions within the left frontal and extrastriate cortex in child and adult participants. These six regions - four in the frontal cortex and two in the extrastriate cortex - were examined more carefully to answer the most critical question: Are there differences due to brain maturation or are any of the differences simply the result of slower and less accurate performance by children?
To answer this key question, they divided the participants into two categories: The "matched" category contained performance data that was similar for both groups; the "non-matched" group contained data where adults and children clearly performed differently.
Of the six regions examined, two - one in the frontal cortex, one in the extrastriate cortex - revealed differences in brain activity in both the matched and unmatched groups, indicating an age-related effect rather than a performance-related effect. The extrastriate region was more active in children than adults, whereas the frontal region was active in adults and not in children.
According to Schlaggar, there are two important lessons from these results. First, children do appear to use their brains differently than adults when successfully performing identical language tasks. Second, although multiple regions appeared to be differentially active when comparing adults and children, many of those differences were due to performance discrepancies, not age-related maturation.
"Our results show that comparing two groups with functional neuroimaging data may be misleading if one does not control for performance differences between the groups," says Schlaggar. "Our results strongly suggest that, during these tasks, functional neuroanatomy is still developing during early school years. When we study the functional neuroanatomy of children who have brain pathology, it's important to keep in mind this developmental context."
Schlaggar BL, Brown TT, Lugar HM, Visscher KM, Miezin FM, Petersen SE. Functional neuroanatomical differences between adults and school-age children in the processing of single words. Science, 296, pg. 1476-9, May 24, 2002.
Funding from the National Institutes of Health and the McDonnell Center for Higher Brain Function supported this research.
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