Think Smart: A Neuroscientist's Prescription for Improving Your Brain's Performance (6 page)

Although I’m somewhere in the middle of the exercise continuum, I freely admit that evidence exists favoring the view that maximal brain benefits can come only from prolonged and highly effortful exercise such as long-distance marathons or triathlons. It’s correctly pointed out that such challenges increase not only cardiovascular fitness, but also strengthen cognitive and psychological traits like focus and endurance.

The Japanese novelist Haruki Murakami captures this link between extreme physical effort and mental endurance: “You’ve got to have physical strength and endurance to be able to spend a year writing a novel and then another year rewriting it again ten or fifteen times. Stamina and concentration are two sides of the same coin. I sit at my desk and write every day, no matter what, whether I like it or not, whether it’s painful or enjoyable. I do this day after day, and eventually—it’s the same as running—I get to that spot where I know it’s been what I’ve been looking for all along. You need physical strength for something like that. . . . It’s like passing through a wall. You just slip through.”

Some experts claim that for walking or running exercises to be beneficial they must involve long distances. Certainly from the evolutionary point of view, that might make sense: although humans are slow runners compared with other animal species, we excel at endurance running and can outrun most other animals over long distances. But does this necessarily suggest that we will gain the most brain benefits by long-distance running? Since at this point nobody can answer that question for certain, the choice is an individual one. (As mentioned earlier, I’m persuaded by Kramer’s findings of the benefits of a forty-five-minute walk three times a week.)

So should you follow a similar take-it-to-the-limit philosophy of exercise, or are the forty-five-minute walks three times a week sufficient? On this point, you will have to decide for yourself the level of exercise intensity you wish to pursue. One word of caution: If you’ve been physically inactive most of your life and now wish to engage in highly strenuous physical exercise, you should first undergo a physical exam and cardiac stress test, then decide about your goals. Murakami took up exercise primarily to improve his mental stamina. You may desire simply to lose weight, increase your energy, and improve your overall health. To accomplish this you don’t have to participate in triathlons. But whatever your motivation, you can be confident that exercise of any intensity will improve your overall brain health.

After nutrition and exercise comes the third basic component of the brain health troika: sleep.

In our hard-driving 24/7 culture, sleep gets little respect. Many of us consider it a useless though unavoidable “downtime” that cuts into our productivity. That sentiment at least partially explains why, on the average, people are sleeping forty-five minutes less today than their ancestors only twenty-five years ago. Yet sleep isn’t something that we can simply do away with.

I remember that the hardest part of my medical school and internship training was the need to balance high performance with insufficient sleep. After a day spent in a busy clinic, I worked for much of that evening and into the early hours of the next morning in the emergency room. After perhaps two hours of sleep, from four a.m. to six a.m., I had to be ready to put in another full day on the wards working with patients. Only at the end of that stint was I free to “crash” until the next morning, when I started another thirty-six-hour sleep-deprived endurance contest. I continued that every-other-night schedule for a whole year during my internship.

Fortunately, working despite severe sleep deprivation is now a thing of the past for doctors-in-training. Today they work much more sensible hours, and for good reason. If we’re sufficiently sleep deprived, our judgment and performance are seriously affected; if we’re sleepy enough, for instance, our driving skills approach those of individuals observed with alcoholic intoxication.

At the other extreme, the more we sleep (up to a point, of course) the better we perform: high-achieving students usually sleep more than their less successful counterparts, according to studies correlating sleep and student grades. But how much sleep do we actually need for our brain to function at its best? And why does our cognitive performance deteriorate so dramatically when we don’t get enough of it?

I posed these questions to sleep researcher Clifford Saper of Harvard University. “Think of the brain in terms of the lowly tomato,” he told me. “Tomatoes grow in the summer by carrying out photosynthesis during the day and storing the energy derived from that process. At night they use that stored energy for growth. A similar process occurs in the brain. During the day it takes in a tremendous amount of energy in the form of information. In order to store that information the brain has to make long-term changes in its structure at the level of synapses. To do that, it uses the same cell-to-cell signaling systems that it used during the day to store the information in the first place. At night the brain, like the tomato, uses its stored energy for growth, making the necessary structural changes for information storage.”

Thus, contrary to popular opinion, the brain doesn’t “turn off ” during sleep. The sleeping brain has distinct activity patterns and electrical signatures consisting of the periodic repetition of four basic phases. Rapid eye movement sleep (REM, also known as dream sleep, since this is the phase when dreams occur) is characterized by brain waves that most resemble those found during wakefulness. The other three phases, collectively referred to as non-REM (NREM) sleep, display electrically distinctive substages of sleep that regularly alternate with one another about every ninety minutes during the night.

During REM sleep the brain makes those structural changes mentioned by Saper. Further, during REM the brain is reusing some of the same synapses used while awake. This explains why most of our dreams relate to events, situations, and concerns that happened during the previous day.

A sleep experiment carried out several years ago provides a neat proof of the association of daytime events and nighttime dreams. It involved people who had spent many hours during the previous day playing Tetris. That night they dreamed of falling shapes—suggesting that the brain synapses that had been used for Tetris were more easily activated during sleep, hence the dreams of falling shapes. Other synapses that hadn’t been involved in Tetris remained deactivated during sleep.

A similar process takes place during learning and the establishment of memories. During sleep the brain “replays” the same pattern of activity that occurred when something was learned during the previous day. Thus a PET scan “snapshot” of the brain’s activation patterns taken during daytime learning is virtually identical to the PET “snapshot” of activity later that night. In one famous experiment illustrating this, Pierre Macquet of the University of Liège, Belgium, monitored brain activity in men playing a virtual reality game in which they learned to wend their way through a virtual town. The same regions of the brain (the hippocampus) that were activated when the men visually explored the virtual town also activated that night during slow wave sleep.

Furthermore, the more a person learns during the day, the greater the amount of replay during the night, according to a study of computer video game players. At night, when the game players were asleep, the same memory encoding vigorously came online—the identical finding in the Macquet study. “How strongly the hippocampus came back online at night predicted how much better the players would be the next day,” says Matthew Walker, director of the sleep and imaging laboratory at Beth Deaconess Medical Center in Boston. “The more the brain learns, the more it demands from sleep at night.” Walker’s comments provide a partial explanation for the finding, mentioned earlier, that high-achieving students require more sleep than their less studious counterparts.

For learning to take place, a certain amount of time must pass in order for “consolidation” to take place. “Consolidation goes beyond simply stabilizing or fixating memories—it enhances them as well,” according to Walker. In addition, the timing of these two processes differs.

Consolidation occurs whether we’re awake or asleep. Enhancement, in contrast, occurs primarily if not exclusively during sleep. “This ‘off-line’ effect during sleep can produce additional learning,” says Walker.

Walker’s research suggests a strategy for taking advantage of the distinction between consolidation and enhancement: since sleep-induced enhancement involves improving upon what you have learned while awake, you should schedule periods of sleep between practice sessions. That way you benefit from the fact that sleep restores, refreshes, and enhances the local brain circuits mentioned by Saper that are involved in skill learning.

To get a feeling for how all this works, think back to when you learned a new tennis stroke. Initially your performance improved as a result of repeated repetition. But if you continued beyond a certain point, additional practice led to deterioration in your performance (the “overpractice” effect known to every athlete). It’s speculated that the performance deterioration reflects a selective fatigue of those brain regions used during learning that new stroke.

What is the proper response to that predictable sequence of improvement followed by a falloff in performance? Stop practicing at the first sign of deterioration in your performance and don’t return to tennis practice until after a night’s sleep. Thanks to the consolidation-enhancement nexus, you’ll wake the next morning with the relevant brain circuits refreshed. As a result, your performance will incorporate all of the things you learned during your practice session the day before.

In general, you can expect a selective enhancement for your weakest areas of tennis or golf performance if you get in a night’s sleep before taking your next lesson. This holds true for any activity requiring the learning and repetition of skilled muscular movements. For reasons that aren’t entirely clear, sleep serves to improve one’s overall performance by selectively enhancing those areas that are most in need of improvement.

Getting a good night’s sleep increases efficiency and helps you perform at your best. In one experiment confirming this, a night’s sleep restored accuracy and speed to the peak level achieved during the initial learning phase in a simple typing task.

“A key role of sleep in learning and memory is to restore the local brain circuits participating in the learning of a skill, thereby maximizing the benefits of presleep training,” Walker told me. In short, if you learn something while awake, you can increase your chances of remembering it by “sleeping on it.”

Here’s one more important detail about consolidation and memory: The initial period of memory consolidation occurs within the first six hours after learning. In practical terms, if you try to learn a second unrelated skill during that period, you will interfere with what you just learned during your initial effort. This is especially true in physical activities (motor programs, as neuroscientists refer to them). So after the completion of a tennis lesson you should not follow that up during those crucial six hours with instruction in golf or any other motor skill lest learning that second activity interfere with your memory consolidation for the tennis. Researchers discovered this principle from an experiment during which subjects learned a series of finger movements followed by an immediate follow-up session in which the participants learned the reverse sequence. When taken in succession, learning that second sequence impaired the performance for the first sequence. But the two sequences were equally well retained if several hours of sleep separated learning the two skills.

So if you want a selective improvement in your weakest areas of tennis or golf, remember the six-hour consolidation rule and make certain you get in a night’s sleep between lessons. This holds true as well for any activity requiring the learning and repetition of skilled muscular movements. Although no one knows exactly why, sleep improves one’s overall performance by selectively enhancing those areas that are most in need of improvement.

If your sleep is disrupted, your recall for what you’ve learned declines, your memory returns to a labile, easily modified state, and consolidation doesn’t take place. Sleep researcher Robert Strecker of Harvard University described for me his experiment that led to this conclusion.

Strecker placed rats in a water maze—the equivalent of a rat swimming pool filled with murky water concealing a small platform hidden beneath the surface. Since rats aren’t long-distance swimmers, they need to find the platform as quickly as possible and climb up on it. Once having learned the location of the platform, rats tend to remember it and swim quickly to the platform when placed back in the water. Sleep-deprived rats that had been purposely woken up periodically during the night before the water maze test took longer than well-rested rats to find the platform.

“This suggests that sleep fragmentation resulting from periodic awakenings affects the hippocampus, the area responsible for storing spatial maps in the brain,” Stecker says.

At the molecular level, sleep deprivation leads to the accumulation of stress hormones in the hippocampus, which in turn stunts the growth of cells that establish new memories. Moreover, this effect of sleep fragmentation is difficult to reverse. Even after being allowed to sleep undisturbed the following night, the rat’s memory for the platform location remained impaired.

Except in nightmares, sleep fragmentation in our own species doesn’t involve desperate searches for platforms hidden beneath murky water. Rather, our sleep fragmentation involves bouts of insomnia, defined as one or more of the following symptoms for at least a week: taking more than an hour to fall asleep; wakefulness for over half an hour during the night; failure to feel refreshed and rested upon awakening. This combination of symptoms is common. Sleep specialists estimate that 70 million Americans suffer from insomnia.