How We Learn (29 page)

In a 2007 study, researchers at Harvard and McGill universities tested college students’ ability to discern an embedded hierarchy in what looked like
a simple game. The research team asked the students to study pairs of colored eggs, one pair at a time, on a computer screen. The eggs were ranked one over another. For example:

The students were split into two groups: one studied the eggs in the morning, one studied them in the evening. Both groups memorized the relative ranks of the pairs quickly and aced a test on them just afterward. But twelve hours later, the groups got another test, asking them to rank eggs they’d
not
seen directly compared. This is the “embedded” Grishilda-Thorian question, and the answer is not so obvious. If aqua trumps rainbow, does that mean it also trumps paisley? And what about coral? Does it rank third, or fourth? The students never got to see the entire ranking of all the eggs while studying, so it was hazy.

It was hazy, that is, until they slept on it.

The group that studied in the evening and took the test the next morning after a night’s sleep—the “sleep group,” as they were called—scored 93 percent on the most distantly related pair, i.e., the hardest question. The group that studied in the morning and took the test in the evening, without having slept—the “wake group”—scored 69 percent. A full twenty-four hours later, each student took the test yet again, and the sleep group’s advantage had increased on the most distantly related pairs. That’s a large difference on the hardest questions—35 percent, separating one kind of student from
another—but it’s not unusual in studies of sleep and learning. “We think what’s happening during sleep is that you open the aperture of memory and are able to see this bigger picture,” the study’s senior author, Matthew Walker, told me. “There is evidence, in fact, that REM is this creative memory domain when you build different associations, combine things in different ways and so on.”

In a game like this one, he and his coauthors argue, we are very good at building separate categories of associations (aqua over rainbow, paisley over coral), but the more obscure relationships
between
those categories are harder to sort out—until we sleep.

The investigation of sleep as consolidator of learning is still a work in progress. After scientists chasing Freud hit a wall in the 1960s, sleep research, like its nocturnal subjects, dropped off the deep end. The money tapered off. The window Eugene Aserinsky had opened, revealing REM sleep, seemed, for a time, to expose little more than another dark room. “You had this great excitement, basically followed by forty years of nothing; it was just horrible,” Robert Stickgold, a neuroscientist at Harvard, told me. But in the past two decades, dozens of studies like Walker’s have brightened the horizon, turning sleep into one of the most promising—and contentious—frontiers of learning science. The preponderance of evidence to date finds that sleep improves retention
and
comprehension of what was studied the day before, and not just for colored eggs. It works for vocabulary. Word pairs. Logical reasoning, similar to what’s taught in middle school math. Even the presentation you’ll be giving at work, or the exam that’s coming up at school. For all of these, you need to memorize the details of important points and to develop a mental map of how they fit together. The improvements tend to be striking, between 10 and 30 percent, and scientists don’t understand the dynamics of unconscious states well enough yet to explain why.

My own theory is that sleep amplifies many of the techniques we’ve discussed in this book. The spacing effect described in
chapter 4
, for instance, is especially strong with intervals of a day or two (plus
sleep). Philip Ballard’s “reminiscence”—that puzzling improvement in memory of “The Wreck of the Hesperus” poem described in
chapter 2
—crested in the first day or two. A good night’s sleep could surely loosen the “fixedness” that makes it hard to see a solution to the Pencil Problem, discussed in
chapter 6
, right away. The brain is likely doing many of the same things with information while asleep as it does while awake—or at least performing
complementary
functions.

The story hardly ends there, however.

Scientists have begun to study the effects of interrupting particular stages of sleep, like REM, to isolate the impact those stages have on learning specific skills or topics. Remember, sleep has five dimensions that we know of: REM, and the four stages surrounding it. Our brain waves have distinct patterns in each of those periods, suggesting that different mental dynamics are at work in each one. Could it be that each stage is specialized to consolidate a specific kind of skill, whether it’s a geometric proof, a writing assignment, or a tennis serve? Many scientists now suspect so, based on evidence that comes from both animals and humans. These findings have coalesced into a remarkable hypothesis, first described in 1995 by Italian scientists led by Antonio Giuditta at the University of
Naples Federico II. The idea has since been fleshed out by others, mostly Robert Stickgold at Harvard and Carlyle Smith of Trent University in Peterborough, Ontario, who have contributed enough experimental heft to make this model of sleep learning a full-grown theory, the most comprehensive explanation yet for how the different stages of sleep consolidate memory.

Technically, I suppose, we should call this idea the Giuditta-Smith-Stickgold Model of Learning Consolidation. I prefer to call it, simply, the Night Shift Theory. The lights go out, and basic maintenance is done. Here’s what the Night Shift Theory says happens overnight, during each stage:

Stage 1:
This one is a scratch. It’s impossible to deprive people of
Stage 1 light sleep, if they’re going to sleep at all. Its role in consolidating memories is hard to isolate, though it’s often laced with REM-like periods.

REM:
These storms of neural firing appear to aid pattern recognition, as in the colored egg experiment, as well as creative problem solving and perceiving relationships that weren’t apparent during the day, as in a difficult calculus problem. It likely plays the largest role, of all the stages, in aiding percolation. People still get these benefits from sleep sans REM—just not to the same degree. REM is also involved in interpreting emotionally charged memories. “We believe that it’s during REM that the brain strips away the visceral feeling experienced at the time an emotional memory is formed,” Matthew Walker, the Berkeley brain scientist who coauthored the colored egg study, told me, “but holds on to the actual information, the details, the where and when of what happened.” That panic you felt the last time you opened a geometry exam? It’s better to have that feeling “stripped”—or at least reduced—so you can recall what the panic-inducing problems actually were. Walker describes REM as “a nighttime therapy session.”

Stage 2:
This is the motor memory specialist. In a series of little-known studies, Carlyle Smith trained people in what he calls the “rotor task.” This is a hand-eye coordination exercise in which people have to use their nonwriting hand to chase a moving spotlight across a computer screen using a joystick. It’s easy enough to improve and people generally do—but not as quickly if they’re deprived of Stage 2 sleep. “Stage 2 seems to be the single most critical stage for motor learning,” Smith told me. “When we deprive people of Stage 2, we don’t see that same level of improvement, and we believe the findings extend to all types of motor learning, whether it’s music or athletics and possibly mechanical skills.”

Stages 3 and 4:
These two are usually lumped together in learning research as slow-wave or deep sleep. This is prime retention territory. Starve people of deep slumber, and it doesn’t just dim their beauty;
they don’t get the full benefit of sleep-aided recall of newly learned facts, studied vocabulary, names, dates, and formulas. “We have a lot of evidence that slow-wave is important for declarative memory consolidation, and that this doesn’t happen as much in REM,” Stickgold told me.

To put all this in some perspective, let’s dial up the sleep architecture graph once more.

The first thing to note about this diagram is that it traces the architecture for a person who, in this case, goes to sleep at 11
P.M.
and wakes up at 7
A.M.
The architecture looks roughly the same for everyone, though, no matter what time he or she regularly goes to bed and wakes up. In an important sense, getting the usual doses of all five stages is the meaning of a full night’s sleep. Each stage somehow complements the others’ work. Where it really gets interesting is when we alter our usual sleep schedule to prepare for some performance, whether a speech, a tryout, or an exam.

Notice, for example, that the longest stretch of Stage 2 sleep is just before waking. Cut that short and you miss out on the period when your brain is consolidating a skateboarding move, a difficult piano fingering, or your jump shot. “The implication is that if you are preparing for a performance—a music recital, say—it’s better to stay up late than get up early,” Smith told me. “These coaches that have athletes or other performers up at five o’clock in the morning, I think that’s crazy.”

The same logic applies to REM. The largest dose is in the early morning, between those chunks of Stage 2. If you’re prepping for a math or chemistry test, an exam that’s going to strain your ability to detect patterns, better to stay up late and, if possible, hit the snooze button in the morning. Let the cock crow till he’s hoarse.

Deep sleep, on the other hand, pools in the front half of a typical night’s slumber, as you can see from the diagram. That’s the slow wavelength you want when preparing for a test of retention, like new vocabulary, or filling in the periodic table. Arrange your studying so that you hit the sack at your regular time, get a strong dose of the deep stuff—and roll out of bed early for a quick review before dawn.

All of this is to say that if you’re going to burn the candle, it helps to have some idea of which end to burn.

Here’s the best part: You may not have to burn it at all.

Napping is sleep, too. In a series of experiments over the past decade, Sara Mednick of the University of California, San Diego, has found that naps of an hour to an hour and half often contain slow-wave
deep sleep and REM. People who study in the morning—whether it’s words or pattern recognition games, straight retention or comprehension of deeper structure—do about 30 percent better on an evening test if they’ve had an hour-long nap than if they haven’t. “It’s changed the way I work, doing these studies,” Mednick told me. “It’s changed the way I live. With naps of an hour to an hour and half, we’ve found in some experiments that you get close to the same benefits in learning consolidation that you would from a full eighthour night’s sleep.”

• • •

Learning is hard. Thinking is hard. It’s as exhausting, though in a different way, as physical labor and wears most of us down at a similar rate. Yes, some people can spend fourteen hours a day doing grueling mental work and then relax by solving puzzles or attending poetry readings by some Eastern European exile. Good for them.
Me, I fall more squarely in the Michael Gazzaniga camp of learning. Gazzaniga, the neuroscientist who discovered the right brain/left brain specialization we explored in
chapter 1
, worked long days and nights in the lab at Caltech on his landmark studies. “We had all these people at Caltech back then who became big names—Richard Feynman, Roger Sperry, Murray Gell-Mann, Sidney Coleman—but we weren’t working all the time,” Gazzaniga told me. “We weren’t intellectuals in the sense that we were going out to see people lecturing or cultural events in the evening. That was martini time.”

And we’re almost there.

Let’s return to Jerome Siegel’s theory of sleep, the one we described at the beginning of the chapter. He argues that sleep evolved to keep us safe when the hunting and gathering was scarce or too risky. We are awake when the foraging is good, when socializing in the group is important, and asleep when there’s no percentage in pursuing any of the above, when the costs are too high. Sleep occupies so much time because it’s so central to immediate, day-to-day survival.