Sleeping Like a Baby, Learning at Warp Speed

March 22, 2013, 8:45 p.m. ET

Sleeping Like a Baby, Learning at Warp Speed

By ALISON GOPNIK

Babies and children sleep a lot—12 hours a day or so to our eight. But why would children spend half their lives in a state of blind, deaf paralysis punctuated by insane hallucinations? Why, in fact, do all higher animals surrender their hard-won survival abilities for part of each day?

Children themselves can be baffled and indignant about the way that sleep robs them of consciousness. We weary grown-ups may welcome a little oblivion, but at nap time, toddlers will rage and rage against the dying of the light.

Part of the answer is that sleep helps us to learn. It may just be too hard for a brain to take in the flood of new experiences and make sense of them at the same time. Instead, our brains look at the world for a while and then shut out new input and sort through what they have seen.

Children learn in a particularly profound way. Some remarkable experiments show that even tiny babies can take in a complex statistical pattern of data and figure out the rules and principles that explain the pattern. Sleep seems to play an especially important role in this kind of learning.

In 2006, Rebecca Gómez and her colleagues at the University of Arizona taught 15-month-old babies a made-up language. The babies listened to 240 “sentences” made of nonsense words, like “Pel hiftam jic” or “Pel lago jic.” Like real sentences, these sentences followed rules. If “pel” was the first word, for instance, “jic” would always be the third one.

Half the babies heard the sentences just before they had a nap, and the other half heard them just after they woke up, and they then stayed awake.

Four hours later, the experimenters tested whether the babies had learned the “first and third” rule by seeing how long the babies listened to brand-new sentences. Some of the new sentences followed exactly the same rule as the sentences that the babies had heard earlier. Some also followed a “first and third” rule that used different nonsense words.

Remarkably, the babies who had stayed awake had learned the specific rules behind the sentences they heard four hours before—like the rule about “pel” and “jic.” Even more remarkably, the babies who had slept after the instruction seemed to learn the more abstract principle that the first and third words were important, no matter what those words actually were.

Just this month, a paper by Ines Wilhelm at the University of Tübingen and colleagues showed that older children also learn in their sleep. In fact, they learn better than grown-ups. They showed 8-to-11-year-olds and adults a grid of eight lights that lit up over and over in a particular sequence. Half the participants saw the lights before bedtime, half saw them in the morning. After 10 to 12 hours, the experimenters asked the participants to describe the sequence. The children and adults who had stayed awake got about half the transitions right, and the adults who had slept were only a little better. But the children who had slept were almost perfect—they learned substantially better than either group of adults.

There was another twist. While the participants slept, they wore an electronic cap to measure brain activity. The children had much more “slow-wave sleep” than the adults—that’s an especially deep, dreamless kind of sleep. And both children and adults who had more slow-wave sleep learned better.

Children may sleep so much because they have so much to learn (though toddlers may find that scant consolation for the dreaded bedtime). It’s paradoxical to try to get children to learn by making them wake up early to get to school and then stay up late to finish their homework.

Colin Powell reportedly said that on the eve of the Iraq war he was sleeping like a baby—he woke up every two hours screaming. But really sleeping like a baby might make us all smarter.