Memory: Forgetting Is the New Normal

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This could be a boon to middle-agers whose concentration is slipping, since studies show just how vital paying attention can be to forming memories. In one study, neuroscientist Dr. Adam Gazzaley of the University of California, San Francisco, recruited two groups of subjects--one ages 19 to 30 and the other 60 to 77--and scanned their brains while they were looking at pictures of human faces, then again when they were viewing landscapes. This allowed him to map out where in the brain they were taking in these images. Then he put the volunteers back in the scanner and told them that he was going to show them four pictures simultaneously--two of faces, two of scenery--and that he wanted them to focus only on the faces. When the younger volunteers did this, they showed increased activity in the part of the brain that deals with facial recognition and decreased activity in the part that processes landscapes. Not so the older participants; they couldn't shut out the scenery and focus on just one thing. Says Gazzaley: "They are overwhelmed by interference."

In a related study, psychologist Susan De Santi of NYU's Center for Brain Health studied subjects who had been diagnosed with mild cognitive impairment (MCI), a condition that can be transitory but one that also often segues to Alzheimer's. Two years later, some did develop the disease, but in others the symptoms faded. What De Santi found was that younger subjects who had no trouble paying attention saw their conditions improve.

"MCI is memory problems combined with problems in some other cognitive domain, like verbal fluency or spatial reasoning," De Santi says. "Seventy-one percent of those who had memory problems plus some other problem ended up getting sick with Alzheimer's, but only 8% of people who had only memory problems got sick."

Something else is going on as we get older that also impairs memory: our brains are making fewer neurons. Until a decade ago, the common assumption was that we were born with a fixed number of brain cells that die off as we age, making us, well, dimmer. That, however, is not the case. It is now known that the brain continues to produce neurons throughout the life cycle, but only in two places: the olfactory bulb and the hippocampus. And not just anywhere in the hippocampus but in the dentate gyrus, the very node that Small has identified as the site of impairment in normal memory loss. So why should memory fade at all? The answer may come from the gym.

A decade ago, when neuroscientist Fred Gage of the Salk Institute made the discovery that the adult brain continues to regenerate, the brains in question belonged to mice. Some of the mice had been sedentary, others had been exercising, and the ones that logged the most miles on their wheels produced many more new neurons than did the sedentary ones.

Now it turns out that the same appears to be true for humans. In a paper published last spring, a team led by Gage, Small and Richard Sloan, a psychologist at Columbia University, revealed that after pounding the treadmill four times a week for an hour for 12 weeks, a group of previously inactive men and women, ages 21 to 45, showed substantial increases in cerebral blood volume (CBV)--a proxy for neurogenesis because where there are more cells, there are more blood vessels.

Not only did the CBV profile of the human exercisers mirror that of the mice, but the people who exercised more did better on a slew of memory tests. Other evidence backs this up. In a study of "previously sedentary" older subjects by psychologist Arthur Kramer at the University of Illinois and others at Israel's Bar-Ilan University, investigators found that those who engaged in aerobic exercise did better cognitively than those who stretched and toned but never got their heart rates pumping. What's more, subsequent imaging showed that aerobic exercise "increased brain volume in regions associated with age-related decline in both structure and cognition."

Meanwhile, researchers from the Karolinska Institute in Stockholm who have been following over 1,500 people for more than 35 years found a significantly lower rate of dementia, including Alzheimer's, in those who exercised. Another study, this one of 2,000 elderly men living in Hawaii, showed that those who walked two miles or more a day were half as likely to develop dementia as those who walked a quarter-mile or less.

Cerebral blood volume is not the only thing responsible for this brain-boosting. Also at work is the fact that exercise increases what's known as brain-derived neurotrophic factor (BDNF), a protein that stimulates the birth of new brain cells and then helps them differentiate and connect. BDNF also enhances neural plasticity, the process by which the brain changes in response to learning. In diseases like Alzheimer's, depression, Parkinson's and dementia, BDNF levels are low. In people who exercise, BDNF levels rise.

But physical activity isn't all there is to improving your memory. There's also what you eat. Take blueberries. According to Jim Joseph, a neuroscientist with the U.S. Department of Agriculture in Boston, blueberries seem to have nearly magical powers: they zap free radicals (highly reactive atoms that can damage tissue), reverse aging, enhance cognition and--and this is the kicker--cause new neurons to grow. If you're a rat.

In one of his animal studies, Joseph and his associates developed a series of motor-skills tests that they called the Rat Olympics. Rats had to walk balance beams and stay upright during a log-rolling task. Those raised on special blueberry rat chow did significantly better than those that were not, leading Joseph to conclude that "blueberries were actually able to reverse motor deficits in these aging animals." More remarkably, when mice that had been genetically altered to express Alzheimer's were put on the blueberry diet, they did not experience memory loss. Joseph's research has shown some similar benefits from walnuts, which contain alpha-linolenic acid, an essential omega-3 fatty acid.