A new study of 9- and 10-year-olds finds that those who are more
aerobically fit have more fibrous and compact white-matter tracts in the brain
than their peers who are less fit. "White matter" describes the
bundles of axons that carry nerve signals from one brain region to another.
More compact white matter is associated with faster and more efficient nerve
activity.
The team reports its findings in the open-access journal Frontiers in
Human Neuroscience.
"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, who conducted the study with kinesiology and community health professor Charles Hillman
and psychology professor and Beckman Institute director Arthur Kramer.
"Now for the first time we explored how aerobic fitness relates to white
matter in children's brains."
The team used diffusion tensor imaging (DTI, also called diffusion
MRI) to look at five white-matter tracts in the brains of the 24 participants.
This method analyzes water diffusion into tissues. For white matter, less water
diffusion means the tissue is more fibrous and compact, both desirable traits.
The researchers 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 reported fitness
differences in the brain.
The analysis revealed significant fitness-related differences in the
integrity of several white-matter tracts in the brain: 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.
The team did not test for cognitive differences in the children in
this study, but previous work has demonstrated a link between improved aerobic
fitness and gains in cognitive function on specific tasks and in academic
settings.
"Previous studies in our lab have reported a relationship between
fitness and white-matter integrity in older adults," Kramer said.
"Therefore, it appears that fitness may have beneficial effects on white
matter throughout the lifespan."
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.
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