The study adds to a growing body of evidence that one of the best ways to protect our minds may be to move our bodies.
“Exercise appears to be key” to maintaining and even improving our thinking ability as we age, said J. Carson Smith, a professor of kinesiology at the University of Maryland in College Park, who led the study.
How aging brains can be changed by exercise
As many of us know from sad experience, mental agility often stutters as we age, starting in early middle age and accelerating from there. We have increasing problems remembering our names or where we parked our car or did we take our vitamin this morning or was it yesterday?
Brain scans and other research suggest that this decline occurs in part because brain structure and function can deteriorate over time. Neurons weaken or die, and connections between individual neurons, as well as between wider networks of cells within the brain, disappear.
Scientists naturally wondered if we could slow or reverse this decline in our brain function. To investigate this pressing question, Smith and his colleagues hired 33 volunteers in their 70s and 80s, about half of whom lived mild cognitive impairmentloss of thinking ability that often precedes Alzheimer’s disease.
Everyone was asked complete a series of physiological and mental tests. In one, researchers read a short story aloud and asked volunteers to tell it. In another, volunteers lay quietly during a functional MRI scan that pinpointed electrical activity in many parts of their brains.
After that, half of the volunteers, including some with mild cognitive impairment, began exercising, visiting a supervised gym four times a week to walk briskly for about 30 minutes. The others remained inactive.
After four months, they all repeated the original tests.
But their results differed. Exercisers, even those with mild cognitive impairment, scored better on cognitive tests, particularly the story repetition version. The volunteers who were sitting did not.
Even more intriguingly, the exercisers’ brains changed. Before the study, brain scans of older volunteers showed mostly weak or discontinuous connections between and within major brain networks.
Our brains work best when different, distinct networks interact and connect, facilitating complex thinking and memory formation. This process can be seen in action on brain scans, when connected brain networks light up in tandem, like synchronized Christmas lights.
After four months of exercise, scans showed that the brain’s connections were stronger than before, with cells and entire networks lighting up at the same time, a common feature of better thinking.
What we can learn from mouse brains
However, to better understand how exercise can change our brains as we age, neuroscientists had to turn to mice.
Researchers have known for some time that mammalian brains, including ours, create some new neurons in adulthood, a process called neurogenesis.
Neurogenesis is important for brain health and happens to be enhanced by exercise. IN studieswhen mice run, they pump out two or three times as many new neurons as sedentary animals.
But these neurons are not useful unless they survive and integrate into wider brain networks. In the study, which was published in May in eNeurthe researchers let one group of young adult mice run while the others remained still, then injected the brains of all the animals with a safe, modified virus designed to infect newborn neurons and label them with phosphorescent dye from jellyfish.
Then, for six months, the runners ran while the keepers sat, after which the researchers added a different substance to the mouse brains, designed to shine on the light-emitting cells—those created when the animals were young and either just starting to run or not—and work its way through their wiring, winding dendrites that connect neurons to each other and to more distant parts of the brain.
Using the substance as a marker, the researchers were able to track the connection of each of these cells.
And they found that the exercising mice not only created more neurons when they first started running than the sedentary animals, but now, as the mice approached retirement age (in rodent terms), those same cells were more complex and more extensively connected with the brain network of animals.
The runners’ neurons were better connected than those of the sedentary animals.
What this means for young brains
What does this research mean for the rest of us, who may not yet be old men or mice?
“I think that should be encouraging,” especially for people who may be worried that their brains are starting to go numb, Smith said. In his study, even elderly people who were once sedentary with signs of worsening cognitive decline improved their brain connections and thinking with just a few hours of walking a week.
But the results also suggest it may be wiser to start exercising while you’re young. Young mice that ran likely built up a “cognitive reserve” of healthy neurons and connections, more so than among inactive animals, that served them well as they aged, said Henriette van Praag, associate professor of biomedical sciences at Florida Atlantic University and senior author of the study. about mice.
Better yet, start and don’t stop.
“Given the state of the science, I would say it’s probably a good idea to engage in physical activity during youth, and continue into middle and even old age,” said Russell Swerdlow, professor of neurology and director of Alzheimer’s disease at the University of Kansas. Center for Disease Research, which was not involved in the new studies.
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