As Eyes Close, Brain Opens Up to New Lessons

By Benedict Carey

The task looks very simple. Study pairs of Easter eggs on a computer screen and memorize how the computer has arranged them: the aqua egg over the rainbow one, the paisley over the coral one – and there are just six eggs in all.

Most people can study these pairs for about 20 minutes and ace a test on them, even a day later. But they’re much less accurate in choosing between two eggs that have not been directly compared: Aqua trumped rainbow but does that mean it trumps paisley? It’s hazy.

It’s hazy, that is, until you sleep on it.

In a study published in May, researchers at Harvard and McGill Universities reported that students who slept after playing this game scored significantly higher on a retest than those who did not sleep. While asleep the participants apparently figured out what they didn’t while awake: the hierarchy that linked the pairs.

“We think what’s happening during sleep is that you open the aperture of memory and are able to see this bigger picture,” said the study’s senior author, Matthew Walker, a neuroscientist who is now at the University of California, Berkeley. He added that many such insights occurred “only when you enter this wonder-world of sleep.”

Scientists have been trying for more than 100 years to determine why people need sleep. They have not learned much more than what every new parent quickly finds out: sleep loss makes you more reckless, more emotionally fragile, less able to concentrate and almost certainly more vulnerable to infection. They know, too, that some people get by fine on as few as three hours a night, even less, and that there are some people who have stayed up for more than week without significant health problems.

Now, a small group of neuroscientists is arguing that at least one vital function of sleep is bound up with learning and memory. A cascade of new findings, in animals and humans, suggest that sleep plays a critical role in storing important memories and perhaps in seeing connections that were invisible during waking.

The theory is controversial, and some scientists insist that it’s still far from clear whether the sleeping brain can do anything with memories that the waking brain doesn’t also do, in moments of quiet contemplation.

Yet the new research underscores a vast transformation in the way scientists have come to understand the sleeping brain. Once seen as a blank screen, a metaphor for death, it has emerged as an active, purposeful machine, a secretive intelligence that comes out at night to play – and to work – during periods of dreaming and during the netherworld chasms known as deep sleep.

“To do science you have to have an idea, and for years no one had one; they saw sleep as nothing but an annihilation of consciousness,” said Dr. J. Allan Hobson, a psychiatry professor at Harvard. “Now we know different, and we’ve got some very good ideas about what’s going on.”

The evidence was there all along. Infants make sucking motions when asleep, and their closed eyelids quiver, as if the eyeballs beneath had a life of their own. But it wasn’t until the early 1950s, in a lab at the University of Chicago, that scientists recorded and identified what was happening. Dr. Eugene Aserinsky and his adviser, Dr. Nathaniel Kleitman, published a famous paper in the journal Science in 1953 on the odd, unconscious state rapid eye movement, or REM, sleep.

“This was really the beginning of modern sleep research, though you wouldn’t have known it at the time,” said Dr. William Dement, then a medical student in Dr. Kleitman’s lab and now a professor of psychiatry and sleep medicine at Stanford University. “It took years for people to realize what we had.”

Dr. Dement, infatuated with Freud’s theories about dreams, quickly threw himself into the study of REM. He found that it was universal and occurred periodically through the night, alternating with other states. He gave them names: Stages 3 and 4, or deep sleep, when electrical waves roll as slow as mid-ocean swells; Stage 2, an intermediate stage between REM and deep sleep; and Stage 1, light sleep.

But then sleep research, like its nocturnal subjects, dropped from REM excitement back into a void. “You had this great excitement, basically followed by 40 years of nothing; it was just horrible,” said Dr. Robert Stickgold, a cognitive neuroscientist at Harvard. “Just a period of darkness.”

But the field found new life in the last 10 years or so, turning its focus to a long-neglected area: learning and memory. Recent studies suggest that the stages of sleep seem to be specialized to handle specific types of information.

On a recent Monday afternoon in Dr. Stickgold’s lab at Beth Israel Deaconess Medical Center in Boston, a postdoctoral student, Matthew Tucker, was running a study of the effect of naps on memorized words.

“We are finding that if a person takes a nap that contains slow-wave sleep – deep sleep – that performance on declarative memory tasks, which require the memorization of fact-based information like word-pairs, is enhanced compared to a person who doesn’t take a nap,” Dr. Tucker said.

Healthy sleepers usually fall into deep sleep about 20 minutes. They might spend an hour or more in those lolling depths early in the night, and typically less time later on. When memorizing facts, in short, it may be wiser to go to bed early at night and arise early, than to stay awake until 2 a.m., the research suggests.

REM sleep, the bulk of which comes later in the night, seems important for pattern recognition – for learning grammar, for example, or to bird-watch, or play chess.

In one 2003 study, Sara Mednick, then at Harvard and now at the University of California, San Diego, led a team that had 73 people come into the lab at 9 a.m. and learn to discriminate between a variety of textured patterns. Some of the participants then took a nap of about an hour at 2 p.m. and the others did not.

When retested at 7 p.m. the rested group did slightly better. When tested again the next morning, after everyone had slept the night, the napping group scored much higher. The naps included both REM and deep sleep.

“We think that a nap that contains both these states does about the same for memory consolidation as a night’s sleep,” when it comes to pattern recognition learning, Dr. Mednick said.

Stage 2 sleep also affects people in ways scientists are just beginning to understand. Dr. Carlyle Smith of Trent University in Canada has found a strong association between the amount of Stage 2 sleep a person gets and the improvement in learning motor tasks.

Musicians, among others, have sensed this for ages. A piece that frustrates the fingers during evening practice often flows in the morning.

Dr. Smith said that people typically got most of their Stage 2 sleep in the second half of the night. “The implication of this is that if you are preparing for a performance, a music recital, say, or skating performance, it’s better to stay up late than get up really early,” he said. “These coaches that have athletes or other performers up at 5 o’clock in the morning, I think that’s just crazy.”

Subimal Datta, a neuroscientist at Boston University School of Medicine, has documented that during sleep the brain is awash in a chemical bath unlike any during waking. Even before REM is detectable, Dr. Datta said, a small pocket of cells in the brainstem spurs a surge in glutamate – an activating chemical – which leads to protein synthesis and other changes that support long-term memory storage.

“During waking we have a thousand things happening at once, the library is filling up, and we can’t possibly process it all,” Dr. Datta said. While awake the brain is also gathering lots of valuable information subconsciously, he said, without the person’s ever being aware of it.

“It’s during sleep that we have this special condition to clear away this overload, and these REM processes then help store what’s important,” Dr. Datta said.

Dreams still defy scientific measurement but they, too, have a place in the evolving theory of sleep-dependent learning.

It is likely during REM, some scientists argue, that the brain proceeds to mix, match and juggle the memory traces it has preserved, looking for hidden connections that help make sense of the world. It also might account for that golden gift often attributed to a night’s sleep: inspiration. It was reportedly during sleep that the Russian scientists Dmitri Mendeleev’s periodic table of the elements tumbled into place. Athletes, including the golfer Jack Nicklaus, have also talked about insight coming during sleep.

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This news report is recommended by our Psychology teacher.
It's about our memory, even our learning ability is close to sleep.
After reading this report, I realized that I should take sleep seriously. We shouldn't burn the midnight oil to study because without sleep, we won't figure out something that we didn't understand when we were awake.
Sleep is an amazing process for our brain to "put things in order". We should cherish our sleeping time because sleep is important to our learning.