While there is ample evidence of the beneficial effects of exercise on cognition in animal models, it has been unclear whether the same holds true for humans. The new study tested the hypothesis in monkeys and provides information that is more comparable to human physiology as a result.
The international team of researchers trained adult female cynomolgus monkeys to run on a human-sized treadmill at 80 percent of their individual maximal aerobic capacity for one hour each day, five days per week, for five months. Another group of monkeys remained sedentary, meaning they sat on the immobile treadmill, for a comparable time. Half of the runners went through a three-month sedentary period after the exercise period. In all groups, half of the monkeys were middle aged (10 to 12 years old) and the others were more mature (15 to 17 years old). Initially, the middle-aged monkeys were in better shape than their older counterparts, but with exercise, all the runners became more fit.
During the fifth week of exercise training, standardized cognitive testing was initiated and then performed five days per week until week 24. In a preliminary task, the monkeys learned that by lifting a cover off a small well in the testing tray, they could have the food reward that lay within it. In a spatial delay task, a researcher placed a food reward in one of two wells and covered both wells in full view of the monkey. A screen was lowered to block the animal's view for a second, and then raised again. If the monkey displaced the correct cover, she got the treat. After reliably succeeding at this task, monkeys that correctly moved the designated one of two different objects placed over side-by-side wells got the food reward that lay within it.
"Monkeys that exercised learned to remove the well covers twice as quickly as control animals," said senior author Judy L. Cameron, Ph.D., a psychiatry professor at Pitt School of Medicine. "Also, they were more engaged in the tasks and made more attempts to get the rewards, but they also made more mistakes."
Later in the testing period, learning rate and performance were similar among the groups, which could mean that practice at the task will eventually overshadow the impact of exercise on cognitive function.
When the researchers examined tissue samples from the brain's motor cortex, they found that mature monkeys that ran had greater vascular volume than middle-aged runners or sedentary animals. But those blood flow changes reversed in monkeys that were sedentary after exercising for five months.
"We found that monkeys who exercised regularly at an intensity that would improve fitness in middle-aged people learned to do tests of cognitive function faster and had greater blood volume in the brain's motor cortex than their sedentary counterparts," Dr. Cameron said. "This suggests people who exercise are getting similar benefits."
Citation: Rhyu et al., 'Effects of aerobic exercise training on cognitive function and cortical vascularity in monkeys' (In Press), Neuroscience, March 2010; doi:10.1016/j.neuroscience.2010.03.003