STUDIES REVEAL EXERCISE, EVEN STARTED IN MIDDLE AGE, BENEFITS THE BRAIN
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NR-11-05 (11/14/05). For more information, please contact Sara Harris at (202) 462-6688 or sharris@sfn.org.
STUDIES REVEAL EXERCISE, EVEN STARTED IN MIDDLE AGE, BENEFITS THE BRAIN
WASHINGTON, DC, November 14, 2005 — The “use it or lose it” mantra most often employed to fight the effects of mental aging now has a new twist. In animal studies, scientists are discovering the benefits of physical exercise on memory function. New studies show that exercise throughout life stimulates spatial memory, and that the benefits can be obtained even if the exercise begins at middle age. And for the first time, researchers have found that exercise may reduce harmful effects of sleep apnea, a common breathing condition.
Research by Karyn M. Frick, PhD, of Yale University, and her colleagues supports the idea that a lack of cognitive and physical stimulation may contribute to age-related memory loss and that physical activity reverses the effects. The study is significant to the field of neuroscience because it provides a more complete understanding of how environmental factors influence cognition in aging, according to Frick. “Approximately 80 percent of adults will experience some degree of memory loss as they age,” she says. “It is important to understand why and how different types of memory are affected by the aging process.”
The results also provide clinically important insights that may lead to the development of behavioral approaches to treat age-related memory decline, she says. “The value of such behavioral treatments over drug treatments is underscored by rising medication costs and the risk of drug interactions with the many medications taken by the elderly.”
The study examined young (3 months), middle-aged (15 months), and aged (21 months) female mice to identify the types of memory that are improved by different forms of environmental enrichment and to establish whether these improvements vary by age. Mice received 24-hour exposure to cognitively stimulating toys alone, running wheels alone, or both toys and running wheels for four weeks prior to behavioral testing and then throughout testing.
These mice were compared to non-enriched animals. Spatial memory was tested in the Morris water maze. In this task, a mouse was placed in a large circular tank of water and made to swim until it found an invisible escape platform submerged just underneath the surface of the water. Without visual cues from the platform, the mice must navigate using a spatial map of the room that they create using landmark cues in the maze room in order to locate the escape platform.
Results indicate that spatial memory in the Morris water maze became progressively worse with age. In general, all enrichment treatments improved spatial memory, although the wheels alone and wheels-and-toys conditions were the most effective, especially in middle-aged mice. In aged mice, the wheels-and-toys treatment most consistently improved spatial memory. In the object recognition task, all treatments improved memory in young mice but did not affect memory in older mice.
As a next step, researchers plan to determine how the chemistry and structure of the brain is affected by different forms of environmental enrichment. “Our ultimate goal in this line of research,” says Frick, “is to determine the effects of enrichment on brain and behavior. If enrichment is shown to maintain cognitive and brain functions, it will serve as a successful alternative to drug treatments for the growing aging population.”
Another study by David S. Albeck, PhD, of the University of Colorado at Denver and Health Sciences Center, and his colleague found that rats that were allowed access to a running wheel for a six-month period performed significantly better when solving a maze than rats the same age that had no access to a running wheel but lived in standard rat laboratory housing conditions before testing.
“These findings are new and interesting,” says Albeck, “because they confirm what has been suggested in other studies on humans: that increased voluntary physical activity, compared to a sedentary lifestyle, has beneficial effects on cognition.”
To investigate whether or not long-term voluntary running, without other aspects of an enriched environment can improve Morris maze performance, the rats in Albeck’s study were allowed access to a running wheel starting at middle age and then continuously allowed access until they became elderly, at which time their memory was then tested. The rats were tested in four trials a day for 10 consecutive days. On the second and fourth days, the exercised rats reached the hidden platform significantly faster than the controls. Performance on days 1, 3, and 5–10 were not statistically different between the two groups. Swim speed did not significantly differ between the groups, except for the first day, in which the sedentary controls swam faster than the exercise group.
These findings suggest that long-term voluntary exercise produces beneficial effects on memory and that the exercise program does not have to begin while the animal is young,” says Albeck.
Other studies by Barry W. Row, PhD, of the University of Louisville, and his colleagues suggest that exercise may also benefit people suffering from sleep apnea. Sleep apnea is an increasingly common breathing disorder characterized by brief periods of interrupted breathing during sleep that induces significant cognitive and cardiovascular consequences in people. “Our studies represent the first evidence that mild physical activity reduces the oxidative stress associated with intermittent hypoxia (brief periods of low oxygen in the blood) from sleep apnea,” says Row.
Row’s laboratory has used a recently developed animal model to investigate the effects of exposure intermittent hypoxia on cognitive function by replicating the breathing patterns seen during sleep in patients. Studies have shown that exposure to intermittent hypoxia is associated with learning deficits in rodents and that these deficits are associated with injury in regions of the brain such as the hippocampus, which are important for learning and memory. Additionally, reports in the literature, as well as work by Row and other investigators at the University of Louisville, have indicated that chronic exposure to such brief periods of low oxygen are associated with substantial oxidative stress, inflammation, and neurodegeneration in the brains of rodents and that the increased oxidative stress and inflammation, at least in part, underlie much of the adverse consequences linked to intermittent hypoxia.
Although specific surgical therapies are often used to treat sleep apnea, says Row, his latest study shows that non-specific behavioral therapies can also be an important part of a treatment regimen, especially in mild to moderate cases. He points to weight loss, which has been shown to decrease the number of breathing pauses in obese patients with sleep apnea, and to increased physical activity, which has been shown to enhance levels of growth factors and is protective in models of neuronal injury and degeneration which are thought to share similar mechanisms with Row’s model.
“In the study,” says Row, “we found that moderate daily physical activity significantly attenuates the learning deficits and increased oxidative stress associated with exposure to brief repeated periods of low oxygen during sleep in rodents.”
Row and his colleagues plan to look next at the mechanisms whereby physical activity reduces the oxidative stress associated with intermittent hypoxia, such as through increased activity of natural anti-oxidant mechanisms, as well as the effect of physical activity on functional recovery after exposure to such brief periods of low oxygen concentrations.
