The study adds to growing evidence that one of the best ways to protect our minds may be to get our bodies moving.
Exercise appears to be key to maintaining and even improving our thinking skills as we age, said J. Carson Smith, a professor of kinesiology at the University of Maryland at College Park who led the study.
How older brains can change with exercise
As most of us know from painful experience, mental agility often stutters as we get older, starting in early middle age and accelerating from there. Do we have increasing difficulty remembering names or where we parked the car or if we took a vitamin this morning or was it yesterday?
Brain scans and other research suggest this decline occurs in part because brain structure and function can wear out over time. Neurons weaken or die, and the connections between individual neurons, as well as between larger networks of cells within the brain, wither.
Scientists have naturally wondered whether we can slow or reverse this fall in our brain function. To investigate this pressing question, Smith and his colleagues recruited 33 volunteers in their 70s and 80s, about half of whom suffered from mild cognitive impairment, a loss of thinking skills that often precedes Alzheimer\’s disease.
Everyone was asked to 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 silent during a functional MRI scan that pinpointed electrical activity in many parts of their brains.
Afterwards, half of the volunteers, including some with mild cognitive impairment, started exercising, visiting a supervised gym four times a week to walk briskly for about 30 minutes. The others remained inactive.
After four months, everyone repeated the original tests.
But their results diverged. Users, even those with mild cognitive impairment, scored better on cognitive tests, particularly on the story repeat version. Sedentary volunteers do not.
Most intriguingly, the athletes\’ brains had changed. Prior to the study, brain scans of older volunteers had shown mostly weak or scattered connections between and within major brain networks.
Our brains work best when various 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 brain connections were stronger than before, with cells and entire networks lighting up at once, a common hallmark of better thinking.
What can we learn from the brains of mice
To better understand exactly how exercise can change our brains as we age, however, neuroscientists had to turn to mice.
Researchers have long known that mammalian brains, including ours, create a few new neurons in adulthood, a process called neurogenesis.
Neurogenesis is important for brain health and appears to be boosted by exercise. In studies, when mice run, they pump out twice to three times as many new neurons as sedentary animals.
But those neurons aren\’t useful if they don\’t survive and integrate into larger brain networks. In one study, published in eNeuro in May, researchers let a group of young adult mice run wild while others stood still, and then injected all of the animals\’ brains with a safe, modified virus designed to infect newly formed neurons. born and marked with a phosphorescent jellyfish dye.
Then, for six months, the runners ran and the participants sat, after which the researchers added a different substance to the mouse brain, designed to glue onto the light cells those created when the animals were young and started running or not and work finds its way into their wiring, the snaking dendrites that connect neurons to each other and to more distant parts of the brain.
Using the substance as a marker, the researchers could trace each of these cellular connections.
And they found that the exercising mice had not only created more neurons when they started running than the sedentary animals, but now, as the mice approached retirement age (in rodent terms), those same cells were wired into more complex and extensive way in animal brain networks.
The runners\’ neurons were better wired than the sedentary animals\’ neurons.
What does this mean for younger brains
What does this research mean for the rest of us, who may not be old people or rats yet?
I think that should be encouraging, especially for people who may be concerned that their brains are starting to get dull, Smith said. In his study, even once-sedentary older people with worrying signs of cognitive decline improved their brain connections and thinking with just a few hours of walking a week.
But the findings also suggest that starting to exercise while you\’re young might be even wiser. The young mice that ran around probably built a cognitive pool of healthy neurons and connections, more so than among the inactive animals, which served them well as they aged, said Henriette van Praag, associate professor of biomedical sciences at Florida Atlantic University and senior author of the mouse study.
Better yet, start and don\’t stop.
Given the state of the science, I\’d say it\’s probably a good idea to pursue physical activity in your youth and continue it through middle age and even into old age, said Russell Swerdlow, professor of neurology and director of the Alzheimer\’s Disease Research Center at the US. \’University of Kansas, which was not involved in the new studies.
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