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Exercise Affects How the Teen Brain Encodes Memories

TeenBasketball; credit: John "K", http://creativecommons.org/licenses/by-sa/2.0/deed.en

More and more research suggests that exercise is good for the aging brain. Researchers are also now working to understand how exercise affects the brains and behaviors of adolescents. A new study shows that while exercise does not improve teenagers’ performance on certain memory tasks, it does affect how their brains adapt to perform the tasks.

“Given the tremendous amount of remodeling that goes on during adolescence, the brain may be especially sensitive to experiences, both good and bad,” says Dr. Megan Herting of Children’s Hospital Los Angeles and the University of Southern California. “As a society we have become increasingly less physically active, and while it has been shown that exercise is good for the aging brain, less research has examined how exercise influences the healthy developing brain.”

Herting, working with Dr. Bonnie Nagel of the Oregon Health & Science University, decided to test verbal memory performance in high- versus low-fit male teens. In the study, high-fit teens participated in 10 or more hours of aerobic exercise a week, while low-fit teens only exercised less than an hour per week.

The researchers showed the participants pairs of words in an fMRI scanner, asking them to both remember the pairing and to subjectively decide if they thought the words “fit” together or not to help promote verbal processing. After seeing all of the word pairs, a brief delay of 20 minutes occurred before the participants viewed the word pairs again on a computer and had to match the words that had been presented together. The researchers recorded brain activity during this task to assess differences in how the teens learned the pairs.

Surprisingly, the researchers did not find that higher-fit teens performed better on the memory task than the lower-fit participants, as reported in the Journal of Cognitive Neuroscience. “While we did not see differences in verbal memory-performance between the high and low-fit teens, we did see brain differences,” Herting says.

When we make a new memory, we use the prefrontal cortex and hippocampus and then simultaneously deactivate other areas of the brain that usually serve as our “default network.” In the high-fit teens, the brain behaved as expected, recruiting resources from the hippocampus and lessening activity from the default network. But in the low-fit teens, the default network activity did not reduce as much as expected and even more resources came from the hippocampus to correctly remember the word pairings.

Herting says that these differences may suggest that that the low-fit youth brains adapt in order to perform similarly to their peers. “It is also known that higher-fit elderly seem to have greater memory and less age-related brain changes than low-fit elderly,” she says. “So perhaps in adolescence, the exercise-related changes do not influence memory behavior as the brain is still young and healthy and can compensate, but the benefits of exercise during adolescence may contribute to better cognitive and brain reserves later on during the aging process.”

Herting says that more research is necessary to understand how these exercise-related brain differences influence other types of cognitive tasks and how they may represent behavioral differences over time. Also, the results so far are correlational only, so further work would require teens to participate in an exercise intervention study to establish a cause and effect.

“Therefore, it remains to be determined what optimal exercise dose is required to lead to memory-related brain changes in youth,” Herting says. “Nonetheless, our research highlights that aerobic fitness during this developmental period relates to brain activity, suggesting it is important to conduct future studies to determine just how exercise may contribute to healthy brain development.”

–Lisa M.P. Munoz

Differences in Brain Activity during a Verbal Associative Memory Encoding Task in High- and Low-fit Adolescents, Megan M. Herting and Bonnie J. Nagel, Journal of Cognitive Neuroscience, published online December 18, 2012.

Media contact: Lisa M.P. Munoz, CNS Public Information Officer, cns.publicaffairs@gmail.com

 

 

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