Newfound Ways Exercise Keeps the Brain Healthy and Strong

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New research fills a knowledge gap related to physical activity, lifestyle habits, cognition, and brain tissue microstructure in older adults. These findings (Dawe et al., 2021) were published on July 7 in the peer-reviewed journal PLoS ONE.

"The association between physical activity and cognition in older adults is partially accounted for by MRI-based signatures of brain tissue microstructure," the authors explain in their paper's abstract.

For this study, neuroscientists conducted postmortem MRI brain scans of 318 older adults who'd worn fitness trackers and undergone detailed cognitive and motor testing during their lifetime as part of the Rush University Memory and Aging Project. The average age of participants at death was 91.1 years. Postmortem MRI provides a novel window into the neurobiology of cognitive decline (or lack thereof) in later life.

Following death, the researchers used magnetic resonance imaging scans to quantify the health and integrity of brain tissue microstructure. Their postmortem analysis combined with in vivo testing unearths noteworthy links between daily physical activity levels, brain tissue microstructure, and global cognition.

Daily Physical Activity, Higher Fitness Levels, and White Matter Integrity Often Go Hand in Hand

White matter tracts form neural pathways that connect different regions of gray matter throughout the brain. Notably, the researchers identified two brain signatures that appear to mediate the association between physical activity and cognition in older adults related to these white matter pathways.

One of these brain signatures "spanned periventricular white matter and hippocampus, while the other encompassed white matter of the occipital lobe." According to the authors, "this mediation remained evident after controlling for motor abilities and neurodegenerative and vascular brain pathologies."

Previous research in animals and humans has linked better white matter integrity with regular aerobic exercise and higher levels of cardiorespiratory fitness. Human studies have also identified a correlation between white matter microstructure integrity and better cognitive functioning (Roberts, Anderson, & Husain, 2011). On the flip side, white matter abnormalities or altered tract-specific white matter microstructure are linked to poorer cognitive performance (Cremers et al., 2016).

Another study published earlier this year (Reber et al., 2021) found that neurosurgery patients with brain lesions involving densely connected white matter hubs experienced more significant impairment to their cognitive performance than patients with brain lesions involving gray matter regions. (See "The Brain's White Matter Hubs Take Center Stage.")

Maintaining White Matter Integrity via Physical Activity May Help to Offset Age-Related Cognitive Decline

Accumulating evidence suggests that in addition to slowing down gray matter atrophy and the loss of brain volume due to age-related shrinkage, regular physical activity may also help to maintain white matter microstructure integrity as we age.

"[Our] analyses are consistent with the notion that brain tissue microstructure, as quantified by postmortem MRI, partially mediates the association between higher levels of physical activity and better cognitive function," Dawe et al. conclude. "In particular, the current findings indicate that a more active lifestyle in older adults may confer cognitive benefits in part through a neurobiological pathway involving brain tissue microstructure that can be quantified and visualized using MRI."

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That said, like most MRI-based brain imaging studies, the latest (2021) paper on "physical activity, brain tissue microstructure, and cognition in older adults" has limitations. Although this study advances our understanding of how "brain tissue microstructure mediates the relation between physical activity and cognition in old age," the researchers acknowledge that more research is needed to "elucidate the molecular mechanisms underlying this pathway."

In terms of future research, the authors note that their recent findings "may help to direct future studies focused on specific brain regions to elucidate the molecular mechanisms underlying this pathway, thereby catalyzing further drug discovery for maintaining cognition."