The body was designed to be pushed, and when we push our bodies, we push our brains, too. Learning and memory evolved in concert with the motor functions that allowed our ancestors to track down food. As far as our brains are concerned, if we’re not moving, there’s no real need to learn anything.
In researching exercise and attention deficit disorder (ADHD or ADD), we’ve learned that exercise improves learning on three levels: It optimizes your mindset, by improving alertness, attention, and motivation. It prepares and encourages nerve cells to bind to one another, which is the cellular basis for learning new information. And it spurs the development of new nerve cells from stem cells in the hippocampus, an area of the brain related to memory and learning.
Several progressive schools have experimented with exercise to find out if working out before class boosts a child’s reading ability and her performance in other subjects. Guess what? It does.
We know now that the brain is flexible, or plastic, in the parlance of neuroscientists — more Play-Doh than porcelain. It is an adaptable organ that can be molded by input in much the same way as a muscle can be sculpted by lifting barbells. The more you use it, the stronger and more flexible it becomes.
Far from being hardwired, as scientists once envisioned it, the ADHD brain is constantly being rewired. I’m here to teach you how to be your own electrician.
Exercise: A Drug for Your Brain?
It’s all about communication. The brain is made up of one hundred billion neurons of various types that chat with one another by way of hundreds of different chemicals, to govern our thoughts and actions. Each brain cell might receive input from a hundred thousand others before firing off its own signal. The junction between cell branches is the synapse, and this is where the rubber meets the road. The way it works is that an electrical signal shoots down the axon, the outgoing branch, until it reaches the synapse, where a neurotransmitter carries the message across the synaptic gap in chemical form. On the other side, at the dendrite, or the receiving branch, the neurotransmitter plugs into a receptor — like a key into a lock — and this opens ion channels in the cell membrane to turn the signal back into electricity.
About 80 percent of the signaling in the brain is carried out by two neurotransmitters that balance each other’s effect: Glutamate stirs up activity to begin the signaling cascade, and gamma aminobutyric acid (GABA) clamps down on activity. When glutamate delivers a signal between two neurons that haven’t spoken before, the activity primes the pump. The more often the connection is activated, the stronger the attraction becomes. As the saying goes, neurons that fire together wire together. Which makes glutamate a crucial ingredient in learning.
Psychiatry focuses more on a group of neurotransmitters that act as regulators — of the signaling process and of everything else the brain does. These are serotonin, norepinephrine, and dopamine. And although the neurons that produce them account for only one percent of the brain’s hundred billion cells, these neurotransmitters wield powerful influence. They might instruct a neuron to make more glutamate, or they might make the neuron more efficient or alter the sensitivity of its receptors. They can lower the “noise” in the brain, or, conversely, amplify those signals.
I tell people that going for a run is like taking a little bit of Prozac and a little bit of Ritalin because, like the drugs, exercise elevates these neurotransmitters. It’s a handy metaphor to get the point across, but the deeper explanation is that exercise balances neurotransmitters — along with the rest of the neurochemicals in the brain.
How the Brain Learns and Creates Memories
As fundamental as the neurotransmitters are, there’s another class of master molecules that, over the past 15 years, has dramatically changed our understanding of connections in the brain. I’m talking about a family of proteins referred to as “factors,” the most prominent of which is the brain-derived neurotrophic factor (BDNF). Whereas neurotransmitters carry out signaling, neurotrophins, such as BDNF, build and maintain the infrastructure itself.
Once it became clear to researchers that BDNF was present in the hippocampus, the area of the brain related to memory and learning, they set out to test whether it was a necessary ingredient in the process. Learning requires strengthening the affinity between neurons through a dynamic mechanism called long-term potentiation (LTP). When the brain is called on to take in information, the demand naturally causes activity between neurons. The more activity, the stronger the attraction becomes, and the easier it is for the signal to fire and make the connection.
Say you’re learning a French word. The first time you hear it, nerve cells recruited for a new circuit fire a glutamate signal between each other. If you never practice the word again, the attraction between the synapses involved diminishes, weakening the signal. You forget.
The discovery that astonished memory researchers — and earned Columbia University neuroscientist Eric Kandel a share of the 2000 Nobel Prize — is that repeated activation, or practice, causes the synapses themselves to swell and make stronger connections. A neuron is like a tree that, instead of leaves, has synapses along its dendritic branches. Eventually new branches sprout, providing more synapses to further solidify the connections. These changes are called synaptic plasticity, which is where BDNF takes center stage.
Early on, researchers found that if they sprinkled BDNF onto neurons in a petri dish, the cells automatically sprouted new branches, producing the same structural growth required for learning. I call BDNF Miracle-Gro for the brain. BDNF also binds to receptors at the synapse, unleashing the flow of ions to increase the voltage and immediately improve the signal strength. Inside the cell, BDNF activates genes that call for the production of more BDNF, as well as serotonin and proteins that build up the synapses. BDNF directs traffic and engineers the roads, as well. Overall, it improves the function of neurons, encourages their growth, and strengthens and protects them against the natural process of cell death
The More Your Body Exercises, the Better Your Brain Functions
So how does the brain amp up its supply of BDNF? Exercise. In 1995, I was doing research for my book, A User’s Guide to the Brain, when I came across a one-page article in the journal Nature about exercise and BDNF in mice. There was scarcely more than a column of text, yet it said everything. According to the study’s author, Carl Cotman, director of the Institute for Brain Aging and Dementia at the University of California-Irvine, exercise seemed to elevate Miracle-Gro, or BDNF, throughout the brain.
By showing that exercise sparks the master molecule of the learning process, BDNF, Cotman nailed down a biological connection between movement and cognitive function. He set up an experiment to measure the levels of BDNF in the brains of mice that work out.
Unlike humans, rodents seem to enjoy physical activity, and Cotman’s mice ran several kilometers a night. When their brains were injected with a molecule that binds to BDNF and scanned, not only did the scans of the running rodents show an increase in BDNF over controls, but the farther each mouse ran, the higher the levels were.
As the stories of BDNF and exercise developed together, it became clear that the molecule was important not merely for the survival of neurons but also for their growth (sprouting new branches) and, thus, for learning. Cotman showed that exercise helps the brain learn.
“One of the prominent features of exercise, which is sometimes not appreciated in studies, is an improvement in the rate of learning, and I think that’s a cool take-home message,” Cotman says. “Because it suggests that, if you’re in good shape, you may be able to learn and function more efficiently.”
Indeed, in a 2007 study, German researchers found that people learn vocabulary words 20 percent faster following exercise than they did before exercise, and that the rate of learning correlated directly with levels of BDNF. Along with that, people with a gene variation that robs them of sufficient BDNF levels are more likely to have learning deficiencies. Without the so-called Miracle-Gro, the brain closes itself to the world.
Which isn’t to say that going for a run will turn you into a genius. “You can’t just inject BDNF and be smarter,” Cotman points out. “With learning, you have to respond to something in a different way. But the something has to be there.” And without question, what that something is matters.
Discovering the Power to Change Your Brain
Scientists all the way back to Ramón y Cajal — who won the Nobel Prize in 1906 for proposing that the central nervous system was made up of individual neurons that communicate at what he termed “polarized junctions” — have theorized that learning involves changes at the synapses. Despite the accolades, most scientists didn’t buy it. It took psychologist Donald Hebb to stumble onto the first hint of evidence.
The lab rules were loose in those days, and, apparently, Hebb thought it would be fine if he brought home some lab rats as temporary pets for his children. The arrangement turned out to be mutually beneficial: When he returned the rats to the lab, Hebb noticed that, compared to their cage-bound peers, they excelled in learning tests. The novel experience of being handled and toyed with somehow improved their learning ability, which Hebb interpreted to mean that it changed their brains. In his acclaimed 1949 textbook, The Organization of Behavior: A Neuropsychological Theory, he described the phenomenon as “use-dependent plasticity.” The theory was that the synapses rearrange themselves under the stimulation of learning.
Hebb’s work ties in with exercise because physical activity counts as novel experience, at least as far as the brain is concerned. In the 1960s, a group of psychologists at Berkeley formalized an experimental model called “environmental enrichment” as a way to test use-dependent plasticity. Rather than take rodents home, the researchers outfitted their cages with toys, obstacles, hidden food, and running wheels. They also grouped the animals together, so they could socialize and play.
It wasn’t all peace and love, though, and eventually the rodents’ brains were dissected. Living in an environment with more sensory and social stimuli, the lab tests showed, altered the structure and function of the brain. The rats fared better on learning tasks, and their brains weighed more compared to those housed alone in bare cages.
In a seminal study, in the early 1970s, neuroscientist William Greenough used an electron microscope to show that environmental enrichment made the neurons sprout new dendrites. The branching caused by the environmental stimulation of learning, exercise, and social contact caused the synapses to form more connections, and those connections had thicker myelin sheaths.
Now we know that such growth requires BDNF. This remodeling of the synapses has a huge impact on the circuits’ capacity to process information, which is profoundly good news. What it means is that you have the power to change your brain. All you have to do is lace up your running shoes.
How to Grow and Nurture New Neurons
For the better part of the twentieth century, scientific dogma held that the brain was hardwired once it was fully developed in adolescence — meaning we’re born with all the neurons we’re going to get. We can only lose neurons as life goes on.
Guess what? Neurons do grow back — by the thousands — through a process called neurogenesis. They divide and propagate like cells in the rest of the body. Neurons are born as blank-slate stem cells, and they go through a developmental process in which they need to find something to do in order to survive. Most of them don’t. It takes about 28 days for a fledgling cell to plug into a network. If we don’t use the newborn neurons, we lose them. Exercise spawns neurons, and the environmental enrichment helps those cells survive.
The first solid link between neurogenesis and learning came from Fred Gage, a neuroscientist of the Salk Institute, and his colleague Henriette van Praag. They used a rodent-sized pool filled with opaque water to hide a platform just beneath the surface in one quadrant. Mice don’t like water, so the experiment was designed to test how well they remembered, from an earlier dip, the location of the platform — their escape route. When comparing inactive mice with others that hit the running wheel for four kilometers a night, the results showed that the runners remembered where to find safety more quickly. The sedentary ones floundered before figuring it out.
When the mice were dissected, the active mice had twice as many new stem cells in the hippocampus as the inactive ones. Speaking generally about what they found, Gage says: “There is a significant correlation between the total number of cells and [a mouse’s] ability to perform a complex task. And if you block neurogenesis, mice can’t recall information.”
Although all this research has been done in rodents, you can see how it might relate to those progressive schools that exercise students before class begins: Gym class provides the brain with the right tools to learn, and the stimulation in the kids’ classes encourages those newly developing cells to plug into the network, where they become valuable members of the signaling community. The neurons are given a mission. And it seems that cells spawned during exercise are better equipped to spark this process.
Anyone for a run?
John Ratey, M.D., is a member of the ADDitude ADHD Medical Review Panel.
Smart Exercises to Improve ADHD Brains
Excerpted from Spark (#CommissionsEarned), by JOHN J. RATEY, M.D., and Eric Hagerman. Copyright © 2008 by John J. Ratey, M.D. Reprinted by permission of Little, Brown and Company, New York, N.Y. All rights reserved.
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