Sounds During Sleep May Help You Remember
You may not be able to learn a foreign language in your sleep, but you can strengthen certain memories, according to a study in the journal Science.
The study, led by researchers at Northwestern University, found that hearing certain sounds during a nap helped people remember information associated with those sounds once they woke up.
"They were a little bit better, a little more accurate," says John Rudoy, a graduate student at Northwestern and the study's lead author.
The study builds on decades of research suggesting that sleep is a time when the brain processes things it has learned, Rudoy says.
"When you take a nap or have a full night's sleep after learning something, you're actually better at it the morning after," he says.
Memorizing Images
Rudoy and a team of researchers thought it might be possible to influence which memories the brain strengthened during sleep. So they recruited a dozen volunteers and taught them to play a special game on the computer.
The game involved studying 50 images, one at a time, accompanied by appropriate sound cues. The image of a cat was accompanied by a meow, while the image of a breaking wine glass featured the sound of breaking glass.
Each image was assigned to a specific location on the screen. The cat might always appear in the lower left, for example, while a train might always show up in the top right.
After some practice, the volunteers took a test that showed they had become pretty good at remembering the location associated with each image.
Then they took a nap.
Sleep Sounds
Once brain monitors showed that a person was deeply asleep, the scientists began to play the sound cues for some, but not all, of the images.
After the volunteers woke up, they took the test again. And they were better at remembering the correct location for the images associated with sounds they heard in their sleep, Rudoy says.
The volunteers didn't remember which sounds they'd heard while asleep, Rudoy says. But apparently, some part of their brain could.
"It got in there somehow and seemed to strengthen the particular memories that were associated with those sound cues," Rudoy says.
Better Performance
The effect was pretty modest. And the result doesn't suggest the brain can learn something completely new during sleep, Rudoy says.
Even so, it's still a pretty startling finding, says James McGaugh, a neurobiology professor and memory expert at the University of California, Irvine.
"What it suggests is that there is a way to provide additional information during sleep that will strengthen memories that had been previously formed," he says
Consolidation
In the past few decades, much of the research on sleep and memory has focused on a process called consolidation, in which some of the things we learn gradually become integrated into the networks in our brain.
Studies have suggested that a lot of consolidation goes on during REM sleep, which is when we dream. But the new study looked at deep sleep, about which much less is known.
Also, the new study found that hearing sound cues while awake did not have the same effect as hearing them while asleep.
McGaugh says he finds that puzzling, and says the results do not fit neatly into what's known about memory consolidation during sleep.
But he adds that the findings are "provocative and interesting," and bound to lead to more studies on ways to influence memories while we sleep.
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ROBERT SIEGEL, host:
From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.
MELISSA BLOCK, host:
And I'm Melissa Block.
It's a tempting idea: Learn something while you sleep, such as a foreign language or math.
(Soundbite of recording)
Unidentified Man: You are about to learn your timetables, which is so very easy because you are such an intelligent person.
BLOCK: Well, while learn-while-you-sleep programs like that one might claim to be successful, there is not much evidence that sort of thing works. But as NPR's Jon Hamilton reports, a new study in the journal Science suggests it may be possible to bolster memories of things you've already learned while you nap.
JON HAMILTON: Just to be clear, scientists do not believe you'll ever be able to learn Urdu while snoozing.
Mr. JOHN RUDOY (Researcher, Cognitive Neuroscience, Northwestern University): I still wouldn't buy any of those things that you see on late-night TV.
HAMILTON: John Rudoy is a researcher at Northwestern University. He says the new study builds on decades of research showing that sleep helps the brain processes memories.
Mr. RUDOY: When you take a nap or have a full night's sleep after learning something, you're actually better at it the morning after.
HAMILTON: Rudoy and his colleagues thought it might be possible to get a sleeping brain to focus on strengthening specific memories. So they got a dozen volunteers to look at a series of 50 different photos flashed one at a time on a computer screen.
Mr. RUDOY: A tea kettle was one. A cat was another one. A train was one.
HAMILTON: Each of the 50 photos appeared in a unique location on the screen. The cat was in one spot, the tea kettle in another and each image had a very brief sound cue.
(Soundbite of cat meow)
(Soundbite of train engine)
(Soundbite of tea kettle whistle)
HAMILTON: The goal was to learn the proper location for each imagine. After a few practice rounds, the volunteers took a test and scored pretty well. Then they took a nap. Once a volunteer was deeply asleep, the scientists played a series of sound cues for some, but not all of the images.
(Soundbite of sound cues)
HAMILTON: Rudoy says after the volunteers woke up, they took the test again.
Mr. RUDOY: And it turns out that they were a little bit better, a little bit more accurate at placing the photographs that had been cued while they were asleep than they were at placing the photographs that had not been cued while they were asleep.
HAMILTON: Rudoy says the volunteers didn't remember what they'd heard while they slept, but apparently their brains did.
Mr. RUDOY: It got in somehow and seemed to strengthen the particular memories that were associated with those sound cues.
HAMILTON: The effect was pretty modest. And the result didn't suggest that you can learn something completely new during sleep. But James McGaugh, a memory expert at the University of California, Irvine, says it's still a pretty startling finding.
Professor JAMES MCGAUGH (Memory Expert, University of California, Irvine): What it suggests is that there's a way of providing additional information during sleep that will strengthen memories that have been previously formed.
HAMILTON: McGaugh says most research on sleep and memory has focused on a process called consolidation. That's how the networks in our brain gradually integrate stuff that seems important. Studies have suggested that consolidation takes place during REM sleep, which is when we dream. But this study played sounds for people who were in so-called slow wave or deep sleep. And McGaugh says he's puzzled by one of the results - the finding that hearing sound cues while awake did not provide the same memory benefit as hearing them while asleep.
Prof. MCGAUGH: Is this interesting and is it provocative? Yes. Does it fit into the standard sleep consolidation literature? No. It doesn't fit neatly and nicely into that. It's something new.
HAMILTON: And still unproved. But it could mean the sounds we hear during sleep do somehow affect our brains.
Jon Hamilton, NPR News. Transcript provided by NPR, Copyright National Public Radio.
