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Jogging with brain

health-and-fitness Updated: Apr 22, 2012 01:28 IST
Highlight Story

The value of mental-training games may be speculative, but there is another, easy-to-achieve, scientifically proven way to make yourself smarter. Go for a walk or a swim. For more than a decade, neuroscientists and physiologists have been gathering evidence of the beneficial relationship between exercise and brainpower. But the newest findings make it clear that this isn’t just a relationship; it is the relationship. Using sophisticated technologies to examine the workings of individual neurons — and the makeup of brain matter itself — scientists in just the past few months have discovered that exercise appears to build a brain that resists physical shrinkage and enhance cognitive flexibility. Exercise, the latest neuroscience suggests, does more to bolster thinking than thinking does.

The most persuasive evidence comes from several new studies of lab animals living in busy, exciting cages. It has long been known that so-called “enriched” environments — homes filled with toys and engaging, novel tasks — lead to improvements in the brainpower of lab animals. Last year, researchers at the Beckman Institute for Advanced Science and Technology at the University of Illinois, put four groups of mice into four distinct living arrangements.

Of mice and men

One group lived in a world of sensual and gustatory plenty, dining on nuts, fruits and cheeses, all of it washed down with variously flavoured waters. Neon-hued balls, plastic tunnels, nibble-able blocks, mirrors and seesaws filled other parts of the cage. Group 2 had access to all of these pleasures, plus they had small disc-shaped running wheels in their cages. A third group’s cages held no embellishments, and they received standard, dull kibble. And the fourth group’s homes contained the running wheels but no other toys or treats.

All the animals completed a series of cognitive tests at the start of the study. Then they ran, played or, if their environment was unenriched, lolled about in their cages for several months.

At the end of the study, Rhodes’s team found that the toys and tastes, no matter how stimulating, had not improved the animals’ brains. “Only one thing had mattered,” Rhodes says, “and that’s whether they had a running wheel.” Animals that exercised, whether or not they had any other enrichments in their cages, had healthier brains and performed significantly better on cognitive tests than the other mice. Animals that didn’t run, no matter how enriched their world was otherwise, did not become smarter.

Builds to last longer

Why would exercise build brainpower in ways that thinking might not? The brain, like all muscles and organs, is a tissue, and its function declines with underuse and age. Beginning in our late 20s, most of us will lose about 1% annually of the volume of the hippocampus, a key portion of the brain related to memory and certain types of learning.

Exercise though seems to slow or reverse the brain’s physical decay, much as it does with muscles. Although scientists thought until recently that humans were born with a certain number of brain cells and would never generate more, they now know better. In the 1990s, using a technique that marks newborn cells, researchers determined during autopsies that adult human brains contained quite a few new neurons. Fresh cells were especially prevalent in the hippocampus, indicating that neurogenesis — or the creation of new brain cells — was primarily occurring there. Even more heartening, scientists found that exercise jump-starts neurogenesis. Mice and rats that ran for a few weeks generally had about twice as many new neurons in their hippocampi as sedentary animals. Their brains, like other muscles, were bulking up.

But it was the ineffable effect that exercise had on the functioning of the newly formed neurons that was most startling. Brain cells can improve intellect only if they join the existing neural network, and many do not, instead rattling aimlessly around in the brain for a while before dying.

One way to pull neurons into the network, however, is to learn something. In a 2007 study, new brain cells in mice became looped into the animals’ neural networks if the mice learned to navigate a water maze, a task that is cognitively but not physically taxing. But these brain cells were very limited in what they could do. When the researchers studied brain activity afterward, they found that the newly wired cells fired only when the animals navigated the maze again, not when they practiced other cognitive tasks. The learning encoded in those cells did not transfer to other types of rodent thinking.

Exercise, on the other hand, seems to make neurons nimble. When researchers in a separate study had mice run, the animals’ brains readily wired many new neurons into the neural network. But those neurons didn’t fire later only during running. They also lighted up when the animals practiced cognitive skills, like exploring unfamiliar environments. In the mice, running, unlike learning, had created brain cells that could multitask.

Wired for thought

Just how exercise remakes minds on a molecular level is not yet fully understood, but research suggests that exercise prompts increases in something called brain-derived neurotropic factor (BDNF), a substance that strengthens cells and axons, fortifies the connections among neurons and sparks neurogenesis. After workouts, most people display higher BDNF. levels in their bloodstreams.

Whether any type of exercise will produce these desirable effects is another unanswered and intriguing issue. A limited number of studies in the past have found cognitive benefits among older people who lifted weights for a year and did not otherwise exercise. But most studies to date, and all animal experiments, have involved running or other aerobic activities.

Whatever the activity, though, an emerging message from the most recent science is that exercise needn’t be exhausting to be effective for the brain. When a group of 120 older men and women were assigned to walking or stretching programs for a major 2011 study, the walkers wound up with larger hippocampi after a year. Meanwhile, the stretchers lost volume to normal atrophy. The walkers also displayed higher levels of BDNF in their bloodstreams than the stretching group and performed better on cognitive tests.

In effect, the researchers concluded, the walkers had regained two years or more of hippocampal youth. Sixty-five-year-olds had achieved the brains of 63-year-olds simply by walking, which is encouraging news for anyone worried that what we’re all facing as we move into our later years is a life of slow (or not so slow) mental decline.

The New York Times