June 14, 2010

Infants Can Learn When They’re Asleep

Photo of a woman and a sleeping baby

Newborn infants are capable of a simple form of learning while they’re asleep, according to a new study. The finding may lead to new ways of identifying infants at risk for certain developmental disorders.

Newborns spend most of their time sleeping. Since these infants need to learn so much about their new surroundings, scientists have long suspected they do some of their learning while asleep. Over the past several years, researchers have discovered that newborns can process some information from the outside world—for example, sounds of speech—while they're asleep. It wasn't known, however, whether they could learn about the relationships between events while asleep.

Dr. William Fifer and his colleagues at Columbia University set out to explore whether infants could learn from experience during sleep. Their work was funded by NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) and National Institute of Mental Health (NIMH).

The researchers used an electroencephalogram—a machine that records electrical activity in the brain—to measure the brain activity of sleeping infants. A video camera monitored the infant’s facial expressions. The researchers played a tone while a machine blew a faint puff of air at each sleeping infant's eyelids. In response to the air puff, the infants reflexively squeezed their closed lids tighter. The researchers repeated this 9 times, each time pairing the air puff with the tone. The tenth time, the researchers played the tone without the air puff.

The scientists reported in the June 1, 2010, edition of Proceedings of the National Academy of Sciences that most of the infants (24 of 26) would scrunch their faces in response to a tone that was not accompanied by an air puff after the sequence was repeated for about 20 minutes. Moreover, the electroencephalograms detected changes in brain wave activity that occurred simultaneously with the tone. The researchers interpret this as further evidence that the infants had learned to associate the tone with the air puff.

Infants in a control group, who were exposed to random, unpaired tones and air puffs, didn’t squeeze their eyelids in response to isolated tones.

The researchers say that this is the first study to demonstrate that newborn infants are capable of learning about relationships between stimuli while asleep. It’s still unknown whether this quality is unique to infants or could also occur in older children and adults. It’s possible that the ability might diminish with age.

The scientists note that this type of learning is controlled by the cerebellum, a region of the brain that’s been implicated in many developmental disorders. This noninvasive measure of cerebellar function in sleeping newborn infants might one day provide a means to screen for developmental conditions very early in life, Fifer says.

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