Includes sections: the slumbering brain, food for thought, metaphysical fitness, keeping stress in check, stimulation throughout life
Each of us has just one brain, so probably the smartest single thing you can do in life is to treat your brain with care. What exactly does that mean? Although the development and organization of the brain are amazingly complex, taking care of it is really quite simple. The basics include sleeping well, eating well, staying fit, drinking in moderation, and taking routine precautions like fastening seat belts and wearing bicycle helmets.
Obviously, some brain-related problems—such as a head injury, stroke, a bout of depression, or anxiety—require the attention of a neurologist, psychiatrist, or other specialist. But there is still a lot you can do on your own to get the most out of your brain and, in so doing, the most out of life.
To illustrate the value of basic brain care and to show how researchers are continuing to probe and refine these principles, we describe several recent studies in this chapter. As we said earlier, however, neuroscience is a never-ending process of refining ideas. Some of the research we cite may still need to be replicated and analyzed. It is important to state, therefore, that these studies are far from the only ones that support this chapter’s basic advice. They are merely the latest investigations into the best way to take care of our brains.
The Slumbering Brain
Your parents probably told you about the benefits of a good night’s sleep—especially on nights when they wanted one themselves. But what does sleep actually do for us? Surprisingly, science cannot yet answer this question in full. We cannot say exactly why we sleep nor what happens during the different stages of sleep. One thing we know for sure is that sleep keeps us alive. If rats are deprived of sleep for a couple of weeks, their appetite drops off, their body temperature becomes unstable, and they die. Researchers are convinced that humans, too, cannot survive a prolonged stretch of sleep deprivation. Fortunately, this theory has never been put to an empirical test.
Rest must be at least a partial answer to the question of why we sleep, but again, scientific knowledge is spotty on this issue. It is true that some parts of the brain are relatively tranquil at night, but other parts keep busy, performing critical jobs while the rest of the body goes on break. A number of recent studies suggest that at night our brains process information received during the day. In particular, the brain “consolidates” learning and memory during sleep, especially during the rapid eye movement (REM), or dream, phases. (See more about sleep stages.)
Many researchers are now investigating sleep with the help of the latest technologies. In a study in 2000 at the University of California at San Diego, functional magnetic resonance imaging (fMRI) brain scans showed that sleep-deprived subjects performing verbal tasks had to work harder—and recruit different parts of the brain to help out—than well-rested subjects performing the same tasks. In another brain imaging study that same year, this one using positron-emission tomography (PET) scans, researchers at the University of Liège in Belgium found that people learning a task at a computer displayed the same pattern of neuronal firing in the brain as they did that night during REM sleep. The team concluded that some sort of mental training goes on in the REM sleep phase to solidify the memories we acquire during the day.
A third study in 2000, at the Harvard Medical School, illustrated the drawbacks of cutting sleep short. Undergraduate volunteers learned to pick out visual targets on a computer screen and were tested on that skill later in the day. They showed no gain in proficiency. The students took the same test the following day. Those who had had more than six hours of sleep found the targets more quickly than before, but those who had slept less showed no improvement. As one of the researchers described it, this was “one of those ‘your mother was right’ studies.” With any kind of learning, it is a good idea to sleep on it. Meanwhile, more studies are under way to explore the relationship between sleep and memory.
Food for Thought
For living, breathing, and thinking humans, just staying in place takes energy. Each of us needs energy, for example, to power our heart so that it can pump blood carrying oxygen and nutrients to the brain (among other spots in the body) to sustain the brain cells that keep our vital systems running. An active, learning human requires even more energy than a stationary one. Like any high-performance machine, the brain needs fuel, the higher quality the better. A good diet is essential for developing and maintaining a healthy nervous system—another thing your parents might have told you, although they probably put it in more general terms.
We all need protein to survive, but it is especially important for people undergoing rapid growth. For humans, the brain grows the most during the last several months in the womb and the first two years of life. In addition to protein, dietary fat is also critical for the formation of nerve and brain tissue during the first few years. Accordingly, parents and other caregivers should feed infants whole rather than skim milk, despite our national obsession with fat consumption. Undernourished babies can end up with lighter brains, with smaller brain cells that are fewer in number, with less extensive dendrite branching than average, and with less insulation of nerve fibers by the fatty coating called myelin—conditions that may be irreversible.
If taken by women of childbearing age before and during early pregnancy, the B vitamin folic acid can prevent birth defects of the brain and spine. Other B vitamins are required for the synthesis of neurotransmitters. Minerals such as iodine, iron, manganese, and zinc are also vital for the proper functioning of the nervous system, but they must be taken in the proper quantities: too much can be as bad as, or even worse than, too little.
Timing is significant in nutrition. Scientists have not worked out a precise feeding schedule that optimizes brain performance, but studies have demonstrated the importance of a good breakfast. Elementary school children, for example, improved their academic performance and had fewer behavioral problems after participating in a national school breakfast program, according to research at Massachusetts General Hospital and Harvard Medical School.
By now, it is common knowledge that a high cholesterol diet, rich in saturated fats, can contribute to the clogging of arteries. That condition may in turn lead to a stroke that kills brain cells, impairing speech and other brain functions. A healthy diet helps keep your cholesterol level down, but eating for health does not mean you have to cut fat from your diet altogether. Cholesterol, for example, comes in two varieties: low-density lipoproteins and high-density lipoproteins. The first clog the arteries with fatty buildup, while the second clear arteries of such deposits. In addition, one type of fat commonly found in fish (omega-3 fatty acids) is needed to keep the nervous system running smoothly. Because fish is such a rich source of these essential fatty acids, it is sometimes called brain food or, as described in one article, “Prozac of the sea.”
Although fats are a necessary part of sound nutrition, most Americans consume too much and would benefit from eating lower-fat foods. A recent study at Case Western Reserve University suggests that people with a genetic predisposition for Alzheimer’s disease, having a susceptibility gene called ApoE-4, should consider a low-fat diet loaded with fruits and vegetables. The study found that people with the ApoE-4 gene had eight times the risk of getting the disease if they ate a high-fat, as opposed to low-fat, diet. Though more research is necessary on this question, the prescribed diet already makes sense for most people on nutritional grounds.
As a general rule, good nutrition for the body is good nutrition for the brain. Be wary of diets and products advertised as “brain food,” which can throw off your nutritional balance. If you use common sense when it comes to diet, normally your brain will do just fine.
Special Diet for Epilepsy
Some doctors now recommend a special high-fat diet, in which most of the calories one gets each day come from things like butter and cream, for certain patients suffering from severe epilepsy. The idea behind this “ketogenic” diet is that some of the fats are digested and converted into “ketones” that enter the brain and act as a sedative, damping down electrical disturbances. Although the diet offers potential benefits for those who have frequent seizures, it can also have harmful side effects. People should not try this diet without strict medical supervision.
Working out does more than keep your muscles toned and your body trim; it can also keep your mind sharp. Although the mechanisms responsible for the benefits are not entirely clear, many studies are exploring how physical exercise helps the brain. The following is a sample of some promising experiments in this field.
One of the most straightforward benefits of exercise is that it promotes blood flow through the brain, supplying nerve cells with more oxygen and nutrients. Psychologists at the University of Illinois tested the benefits of exercise on three groups of laboratory rats. Two groups of rats were put on different exercise regimens, while the third remained sedentary. Autopsies revealed that the rats that exercised developed more capillaries around their neurons, which were capable of supplying their brains with more oxygen and nutrients.
A 1995 study at the University of California at Irvine concluded that the mental gains from exercise stem from more than just increased blood flow. Rats that exercised on treadmills had enhanced levels of brain-derived neurotrophic factor (BDNF), a “growth factor” or protein that sustains the function and survival of many types of neurons. The effect became more pronounced as the animals logged more miles; the animals that ran the farthest produced the most protein. The biggest increases in BDNF appeared in parts of the brain associated with memory and higher mental processing, including the hippocampus.
Many people consider exercise on a treadmill a mindless activity, but a 1999 study at the Salk Institute suggests otherwise. This project found that mice that exercised regularly on treadmills performed significantly better when tested in a maze than mice denied access to the treadmills. Postmortem exams indicated that the mice who ran also had twice as many hippocampal cells as those who did not. Furthermore, when physical exercise is combined with mental exercise, there may be different, even more direct benefits to the brain. As part of the University of Illinois study mentioned above, researchers sent a fourth group of rats through a daily obstacle course that demanded balance and manual dexterity. This group formed relatively few new blood vessels around their neurons but a significant number of new synapses connecting them.
Although findings from animal experiments cannot be directly translated to humans, some of the foregoing results appear to be borne out in human studies as well. In a University of Illinois study, researchers divided 100 sedentary adults, 60 to 75 years old, into two groups. One group walked vigorously three times a week; the other engaged in gentle stretch-and-tone exercises. Six months later, the walking group had quicker mental reaction times, performing “task switching” tests on a computer up to 25 percent faster than the stretch-and-tone crowd.
Regular aerobic exercise can also help you sleep better, especially if you do it three or more hours before bedtime, according to a 1997 study from the Stanford University School of Medicine. In addition, exercise can reduce stress, which takes its own toll on the brain.
Keeping Stress in Check
It’s hard to deny that we live in a stressful society. Many of us are busy from the instant we wake up to the moment we fall asleep, taking care of children, commuting to and from work, putting in a solid eight to twelve hours at the office, keeping up with our reading and e-mail and phone correspondence, and then having to confront 100-odd cable TV channels. The human response to stress—an increase in heart rate, blood pressure, breathing, metabolism, and blood flow to muscles—has evolved over millions of years and is responsible, in no small measure, for the survival of our species. It also contributes to peak performance under pressure—an asset to athletes, firefighters, and countless others. But the inappropriate activation of the stress response, in a world where people rarely face life-or-death situations, can eventually damage both the heart and the brain.
Researchers have examined how stress affects people in various ways. As one example, in a five-year study published in 1998, psychologists gave memory tests to people in their 70s and asked them to find their way through different mazes. The subjects who did the worst on the tests had the highest levels of cortisol, a stress hormone in the glucocorticoid family. Over the years these same people had lost the most brain cells from the hippocampus, a brain structure critical for memory.
Some studies imply that there is a link between a shrinking hippocampus and chronic exposure to glucocorticoids like cortisol. We see this most clearly in an extreme condition called Cushing’s syndrome, in which the adrenal glands release large quantities of glucocorticoids. This condition is accompanied by memory problems known as Cushingoid dementia. MRI brain scans performed at the University of Michigan showed that the hippocampus shrinks in Cushing’s patients. People who secreted the most glucocorticoids suffered the most serious memory problems and the worst hippocampal atrophy.
However, other studies question whether the glucocorticoids alone are responsible for the degeneration of hippocampal neurons. A 1999 study performed at the University of Washington exposed aging rats to elevated glucocorticoid concentrations for 12 months without increasing their exposure to stress. The average size of the hippocampus in these rats, as well as the number and density of neurons in that region, remained the same as in an unexposed control group. Hippocampal damage, the researchers concluded, must arise from other effects of stress, perhaps in conjunction with elevated glucocorticoid levels but not due only to them. These results hint that the organic effects of stress on the brain are complex and unlikely to yield to a simple remedy.
Unfortunately, stress is not the only thing we have to worry about. Research at Washington University School of Medicine in St. Louis shows that chronic depression can also harm the hippocampus. In a 1999 study, investigators scanned the brains of 48 women, ranging from age 23 to 86. In women who had a history of depression, the size of the hippocampus was 9 percent to 13 percent smaller. The hippocampal volumes were smaller in women who had been depressed more often, but age was not a factor. Glucocorticoids may be involved here, too, as depressed patients produce abnormally high quantities of this stress hormone.
Fortunately, there are techniques for managing stress. Physical conditioning can help by lowering your blood pressure and resting heart rate. Exercise—such as aerobic workouts and competitive sports—can also provide an outlet for relieving some of the stress and frustration that build up in a day. Some people achieve deep relaxation through contemplative activities like yoga and meditation, while others may prefer listening to Mozart or wild dancing. People who handle stress well generally have strong social ties with others. Whenever possible, they avoid putting themselves in situations in which they feel helpless, buffeted by forces beyond their control. However, when things don’t go their way, they try to take it in stride. (For more on the “mind-body connection,” see our section on the brain-body loop.)
Stimulation Throughout Life
Proper development of the brain requires stimulation through the different senses—touch, sight, sound, smell, and taste. The maturation of the nervous system, including the building and strengthening of connections among neurons, is shaped by stimulation of this sort and fine-tuned by years of experience. The importance of talking to children, exposing them to music and art, and keeping them involved in playful, creative activities as well as emotionally engaged, is clear. Despite all the marketing related to the “Mozart effect” and other forms of stimulation for young children, there is little hard evidence for the notion of achieving additional benefits—some kind of “mental bonus”—through superenriched environments and enhanced stimulation. In fact, overstimulating children can be counterproductive by causing stress.
Many researchers are now skeptical of the idea of a “critical window” of opportunity during the first three years of life. The brain is, without question, extremely malleable in the early years, but recent studies show that it does not become unbendable, or “hardwired,” at the end of childhood or even in adolescence. Indeed, the phenomenon of “neural plasticity”—the brain’s ability to generate new cells, forge new connections, and strengthen old ones—persists into adulthood. And we get the most from our brains by keeping them exercised, a strategy sometimes called “use it or lose it.”
A 1995 Harvard Medical School study of 1,192 people aged 70 to 79 found that intellectual vigor and physical fitness can both keep people mentally sharp and keep more brain cells alive. The researchers speculate that by having more brain cells “in reserve,” people may be able to stave off memory loss and dementia—conditions once considered almost inevitable by-products of old age. A steady dose of novel challenges and stimulating tasks, it appears, may be the ticket to cerebral fitness for both young and old.
Similar results have been found from studying the world’s oldest people, centenarians. In 1992 researchers at the Harvard Medical School launched the New England Centenarian Study (NECS) to systematically analyze all people 100 years old and over in an eight-town area around Boston to learn how they reached such advanced ages while avoiding the common age-related diseases. Several findings have emerged from this pioneering work.
Part of the reason many centenarians maintain a high cognitive level is that they keep their minds active in a variety of ways: they may continue to work, read challenging books, play bridge, or do crossword puzzles. Learning a foreign language promotes the growth of dendrites, forging new connections between neurons. Complex activities like music, painting, and dance, which involve different parts of the brain, can provide a “whole-brain workout,” the NECS authors conclude. By expanding neuronal networks, these people may build up a “functional reserve” that helps them compensate for changes associated with aging.
Healthy centenarians also keep physically active, as much as possible, and do not smoke. They avoid alcohol and drug abuse—practices that can lead to memory problems, dementia, and other forms of mental impairment. Not surprisingly, most have found ways to keep stress under control, either because of their innate dispositions or because of deliberate choices. One centenarian in the NECS study, after realizing that “worrying didn’t do any good,” decided to become a “fun guy” who wouldn’t worry about anything.
It is unrealistic to assume we can all become stress-resistant personalities by an act of will. Some people seem to be born with temperaments that make them more prone to anxiety than others. Nor can we all expect to live to 100. But by pursuing a healthy lifestyle as best we can, we can lead richer and fuller lives, while preserving the mental capacity to enjoy them.