What’s in a nap? For babies, it may make long-lasting memories

Laura Sanders is away on maternity leave. This week’s guest post is from Science News web producer/staff writer Ashley Yeager, who also runs the Science Ticker blog.

Who doesn’t love a nice, long nap? For me, they help me organize my thoughts, give me a quick energy boost and make me less cranky. Unsurprisingly, my 20-month-old niece — we’ll call her Baby D — enjoys taking naps too. (And, they make her less cranky too). She often nods off not long after watching videos showing her how to say words in sign language. It’s almost as if she knows she’ll better remember what she has seen if she sleeps.

While the timing of Baby D’s naps is probably coincidental, she may be on to something. Taking naps after learning seems to help babies less than a year old make new memories and keep them — for about a day, anyway.

That’s what researchers discovered when working with 6- to 12-month-old infants. The team knew that sleep helps adults make memories, create new insights into old problems and connect different kinds of information. Nodding off also helps pre-school and school-aged kids remember facts or events. And, napping after learning a new trick helps mice grow more connections among nerve cells.

But not much has been done to see what sleep does for the youngest human minds attempting to make memories. Two studies have shown that sleep helps infants understand new words and grammar. To expand on that work, scientists in the England and Germany studied what 6- to 12-month-olds seem to remember about puppets in 4- to 24-hour spurts. In their study, the scientists had the babies watch someone remove a mitten from a hand puppet, shake it and then put it back on the soft, fuzzy critter.

After seeing several takes of the puppet show, one group of babies took a long nap (sleeping more than 30 minutes) within a 4-hour window, while the other group of babies stayed awake or slept less than 30 minutes.

After four hours, the babies were shown the puppets again and given the go-ahead to touch them. Those who took long naps made more attempts to imitate the mitten grab-and-shake they had seen earlier than the babies who hadn’t nodded off for very long. When shown the puppets again 24 hours later, the nappers again attempted more grabs, shakes and returns of the puppets’ mittens than those who hadn’t slept after the puppet show.

The results, the authors argue, suggest that a long nap helped the babies later remember how to imitate what they saw. Naps help infants form long-term memories, the scientists write in the January 12 Proceedings of the National Academy of Sciences. They add that nodding off for a while after learning may safeguard a baby’s new memory against interference from other incoming information.

Watching Baby D learn sign language seems to support to the scientists’ idea. When she watches her signing video then takes a nap, she seems to have surges in the new hand motions she shows us the next day. It’s anecdotal evidence, I know. But it’s hard not to like the idea that her naps may help her make new memories.

It’s one I may have to sleep on to truly understand.