We've long known exercise has a wonderful effect on the brain. It makes you happier, evens your temperament and can even mitigate the painful withdrawal from heroin addiction. Now evidence suggests being active improves cognition and memory and could alleviate the symptoms of ADHD in kids.
In a series of studies, Dartmouth researchers discovered these benefits vary according to age, and a specific gene appears to determine the degree to which exercise helps. This raises the possibility that exercise could be a treatment for attention-deficit hyperactivity disorder.
David Bucci, an associate professor in the Department of Psychological and Brain Sciences, began his study of exercise and memory by looking at attention deficit hyperactivity disorder. ADHD is among the most common childhood disorders, and Bucci was dismayed by the frequency with which medication is administered as treatment. There had to be another way, he thought.
"My entry into this was simply trying to look at how exercise is modifying the brain," Bucci told Wired. "We tried to figure out if the cognitive stuff is a side effect of the mood effects."
Bucci had heard from colleagues at the University of Vermont that among kids with ADHD that were attending summer camp, those who participated in team sports tended to respond better to behavioral intervention than sedentary kids. Intrigued, he and a team of grad students decided to take a closer look.
Initial research suggested exercise helps reduce ADHD-like behavior in rats, with female rats seeing better improvement than male rats. The researchers also found exercise improves object memory — the kind of memory that is not linked to context or events. That's when you remember something, but can't remember when or where it happened.
From there, Bucci's team examined the mechanism through which exercise appears to improve learning and memory. It is called the brain derived neurotropic factor, or the BDNF protein, and it is involved in the growth of the developing brain. Researchers found the degree of BDNF expression in exercising rats correlated positively with improved memory. They also found exercise had a longer, and more pronounced, effect on learning and memory in juvenile rats compared to adults that performed the same amount of exercise.
"As a youngster, your brain is still developing," Bucci said. "One of the contributors to its development is this growth stuff. By exercising, you're taking advantage and capitalizing on this period of development and plasticity."
The next logical step was to see if the effects translated to humans when looking at the specific gene that encodes that same protein.
In research published in the journal Neuroscience, Bucci's team studied sedentary Dartmouth undergrads who couldn't or wouldn't exercise more than once every two weeks or so. They were divided into two groups, having one group exercise regularly on a treadmill and the other remain sedentary. A subset did not exercise until the day of testing to see if there were any acute effects. The subjects took memory tests before and after the study, with the goal of determining if students would perform better if they exercised. Turns out there is a specific gene that determines the extent to which exercise helps.
All genes have two copies, or alleles. In most people, the amino acid valine is present at the 66th amino acid position in the genetic code. But in some people, methionine has been substituted for valine in one or both alleles. This is the switch-up Bucci and his colleagues have pinpointed as one reason exercise provides better cognitive and memory improvements for some people but not others.
"The expectation was that exercise after four weeks could make you do better," said Bucci. "The most striking thing, however, was that this was only true with the people who had this growth factor. If you had some substitution you did not get the benefits — the activity of that growth factor seemed to have a big effect."
Knowing that, Bucci said, means doctors could look at a child's genotype and identify those kids with ADHD who might respond to exercise as a treatment.
"It shows that exercise can help functions other than learning and memory," he said.
