Cameron says she looked at exercise's effects on monkeys because it allowed her to rule out human and environmental factors like smoking, drinking and obesity as well as the effects of the varied amount exercise that people get in their daily lives. "What we wanted to do was design a fitness program for monkeys that would really be very much like a fitness program for middle-aged humans," says Cameron, "[one] that would be recommended for people that want to improve cardio-vascular health or lose weight. [With] monkeys, we can actually have them living in a very standard living situation. Then they exercise by a set amount on a treadmill every day. We actually use a treadmill very much like what a person would use and we can exactly quantitate how much exercise they're getting."
Cameron separated 24 monkeys into three different groups: a sedentary group, who just lived in their home environment and, each day, got on the treadmill that wouldn't turn on; a group that exercised for five months on a regimen similar to what a middle-aged person might undertake; and a group that ran for five months and then was sedentary for an additional three months. There were also two age groups within each of those groups— some that were young, and some that were "middle aged."
Cameron then tested the monkeys with some learning tasks, such as hiding treats and asking the monkeys to find them. The exercisers appeared more alert and engaged during the tests. "What we found was that the monkeys that exercised, both the young and the old monkeys did better in learning new cognitive tasks and they are more alert and more engaged," says Cameron. "We did not show that they were smarter. The animals that exercised, in the end, did just the same as animals that didn't exercise, that is, the same number of answers correct on the tests that we were giving. But I think an increase in engagement and alertness is a very positive thing."
Measuring the volume of small blood vessels, or capillaries, in the motor cortex region of the brain, Cameron also found that the "middle-aged" monkeys who ran on a treadmill one hour a day, five days a week for twenty weeks "had more blood vessel volume in the brain. So that would suggest that perhaps, one of the underlying causes of the change in mental function would be more blood flow to the brain." But blood vessel volume returned to pre-exercise levels in the group that were sedentary for three months after the regular exercise regimen.
Overall, Cameron found that "monkeys that exercise have an increase in their alertness in their engagement, in mental activities." She believes this translates to people. "I think it means exercise is good for blood flow to your brain. And blood carries all the nutrients you need for the brain to do its work. So it carries oxygen and metabolic nutrients. So we suspect that's a very good thing for brain function."