Working out on a treadmill isn't just good for the body, it's good for the brain, according to a new study, the latest to weigh in on the cognitive benefits of exercise.

Regular exercise speeds learning and improves blood flow to the brain in monkeys, the study found. The researchers suspect the same would hold true for humans.

While there is ample evidence of the beneficial effects of exercise on cognition in other animal models, such as the rat, it has been unclear whether the same holds true for people, said study researcher Judy Cameron, a psychiatry professor at Pitt School of Medicine. Testing the hypothesis in monkeys can provide information that is more comparable to human physiology.

For one, monkeys exercise like people, in that they love getting on a treadmill (well sort of like us), and they won't run all night as rats would do if provided with a running wheel, Cameron said.

"Second, monkeys, like people, have well-developed cerebral cortices and that is the part of the brain used in cognition. Rats have a much less developed cortex, so again monkeys are more analogous to people," Cameron told LiveScience.

Monkeys on treadmills

Cameron and colleagues 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 a week, for five months. This regimen is equivalent to what is recommended for improving the fitness of middle-aged people.

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, the monkeys completed cognitive tests in which they had to choose which covered objects contained a food reward underneath. Monkeys that exercised were twice as fast at this task as those who didn't exercise.

However, later in the testing period, learning rate and performance was similar among the groups, which could mean that practice at the task will eventually overshadow the impact of exercise on cognitive function, Cameron said.

Brain tissue samples revealed that mature monkeys that ran had a greater volume of blood vessels compared with middle-aged runners or sedentary animals. (These blood vessels deliver oxygen and nutrients to the brain.) But those blood flow changes reversed in monkeys that were sedentary after exercising for five months.

Brain workout

The results agree with previous studies in this area. A recent review highlighted that exercisers learn faster, remember more, think clearer and bounce back more easily from brain injuries, such as a stroke. Some of these brain benefits are thought to arise out of the mild stress that exercise induces, which triggers the brain to protect against neuron damage. 

In addition, it could just be an effect of blood flow. "Physical exercise increases blood flow to the brain," Cameron said. "Blood delivers nutrients and oxygen, and this may be a large part of why exercise increases cognitive function."

She suspects the benefits could be two-fold for humans. "The monkeys were more alert and engaged as well as improved cognitive function in the first task they were tested in," Cameron said. "We expect that people would show similar effects of exercise. In addition, if over time people are more alert and engaged it would be likely that they would learn more from that alone.

The results were published in the journal Neuroscience.