A new study shows that nine and 10-year-old kids who are more aerobically fit have more fibrous and compact white-matter tracts in their brains than kids who are less fit.
According to researchers, white matter describes the bundles of axons that carry nerve signals from one region of the brain to another. More compact white matter is associated with faster and more efficient nerve activity, the researchers explain.
“Previous studies suggest that children with higher levels of aerobic fitness show greater brain volumes in gray-matter brain regions important for memory and learning,” said University of Illinois postdoctoral researcher Laura Chaddock-Heyman, Ph.D.
She conducted the study with kinesiology and community health professor Dr. Charles Hillman and psychology professor and Beckman Institute director Dr. Arthur Kramer.
“Now for the first time we explored how aerobic fitness relates to white matter in children’s brains,” she said.
The team used diffusion tensor imaging (DTI) — also called diffusion MRI — to look at five white-matter tracts in the brains of 24 children. DTI analyzes water diffusion into tissues. Less water diffusion in white matter means the tissue is more fibrous and compact, both desirable traits, according to the scientists.
The researchers noted they controlled for several variables, such as social and economic status, the timing of puberty, IQ, or a diagnosis of ADHD or other learning disabilities, that might have contributed to the differences in the brain.
The analysis revealed significant fitness-related differences in the integrity of several white-matter tracts in the brain, including the corpus callosum, which connects the brain’s left and right hemispheres; the superior longitudinal fasciculus, a pair of structures that connect the frontal and parietal lobes; and the superior corona radiata, which connect the cerebral cortex to the brain stem.
“All of these tracts have been found to play a role in attention and memory,” Chaddock-Heyman said.
To take the findings further, the team is now two years into a five-year randomized, controlled trial to determine whether white-matter tract integrity improves in children who begin a new physical fitness routine and maintain it over time. The researchers are looking for changes in aerobic fitness, brain structure and function, and genetic regulation.
“Prior work from our laboratories has demonstrated both short- and long-term differences in the relation of aerobic fitness to brain health and cognition,” Hillman said. “However, our current randomized, controlled trial should provide the most comprehensive assessment of this relationship to date.”
“The new findings add to the evidence that aerobic exercise changes the brain in ways that improve cognitive function,” Chaddock-Heyman said.
“This study extends our previous work and suggests that white-matter structure may be one additional mechanism by which higher-fit children outperform their lower-fit peers on cognitive tasks and in the classroom,” she said.
The study was published in the open-access journal Frontiers in Human Neuroscience.