Neuroscientists have long known that shut-eye helps consolidate memories in adults. Napping may play an equally crucial role in infants and young children.
(13 Jan 2022) Dozing in a bassinet, a newborn baby wears a stretchy cap fitted with more than 100 soft electrodes. A low beep sounds, and she squints. Nearby, scientists watch jagged lines moving across a computer screen, recording electrical activity in the infant’s brain. The scientists want to know what’s going on in there — and that tiny squinting action suggests that the baby has been learning while she sleeps.
A newborn’s job is to learn about and adapt to everything in their environment, says William Fifer, a developmental neuroscientist at Columbia University Irving Medical Center in New York. Yet newborns spend some 70 percent of their time asleep. So Fifer and developmental psychologist Amanda Tarullo, now at Boston University, decided to see if they could catch learning in action while babies slumber.
Infants just one or two days old, the researchers found, can learn that a tone predicts a gentle puff of air — such that, eventually, the infants blink after hearing the tone alone, much as Pavlov’s famous dogs drooled in response to certain sounds that initially had been followed by food.
In adults, the importance of sleep for learning has been well established through decades of research. But much less is known about how sleep and learning interact in newborns, let alone how that relationship changes as infants grow into toddlers and preschoolers.
Naps are especially puzzling. Studies suggests they’re crucial to early learning, but most kids naturally stop napping between the ages of three and five. No one knows why, but a cadre of researchers is on the case. Their emerging understanding of the tangled relationship between napping and learning may eventually help parents, preschools and policymakers make decisions that improve kids’ health and learning.
Sleeping on it
Sleep in infants and young children looks very different than it does in adults, and sleep patterns change dramatically as kids develop. Newborns sleep some 16 to 18 hours a day. At first, they sleep randomly throughout the day, but by about six months their inner clocks sync up with the day-night cycle. By about 12 months, infants snooze mostly at night, with a couple daytime naps. By around two years, most kiddos are down to one nap a day.
Research suggests that napping plays an important role in many important things infants learn. “Sleep is crucial for earliest word learning,” says Manuela Friedrich, a neuroscientist at Humboldt University of Berlin. In a 2015 study, Friedrich’s team showed this by presenting 90 infants ages nine to 16 months with images of unknown objects — things that looked like dumbbells or Tinkertoys, for instance.
While viewing each image, the children heard the object’s name — a made-up word, such as “bofel” or “zuser” — and electroencephalogram (EEG) recordings captured their brains’ responses. An hour or two later, the researchers tested the infants’ recollection by showing the images again, either paired with the object’s name they had heard before or a different made-up word. Because the infants were too young to rattle off the objects’ names, the researchers examined the EEG recordings for evidence that they’d made the connection. Previous research had identified certain features of an EEG trace — like a voltage blip at a particular time — that appear when people hear something unexpected. In Friedrich’s study, the presence of a blip would show that an infant was surprised to hear the object paired with the “wrong” word, indicating that the baby had earlier learned a word-object association.
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