Memories May Be Enhanced By Sleep, Study Shows

A new study suggests sleeping may enhance our memories.

November 19, 2009, 12:38 PM

Nov. 19, 2009— -- For time-starved Americans, few ideas are more appealing than that of learning while sleeping. Why simply doze for eight hours when you can be learning Spanish as well?

The problem, of course, is science, which discredited the idea back in the 1950s. While tapes and CDs for prospective sleep learners are available online, studies have shown that they won't be very effective.

"The research at the time said the only thing that it did was to keep you awake," explained James McGaugh, a professor of neurobiology and behavior at the University of California, Irvine.

But for those who want to get something done while recharging their batteries, a new study suggests you may be able to accomplish something while asleep.

"Our memory systems are still active while we're asleep. Memories can be strengthened while we're asleep," said John Rudoy, a doctoral student in neuroscience at Northwestern and author of a new study appearing in the journal Science.

For the study, individuals were shown 50 objects on a computer screen and asked to remember the location. As they were shown the objects were accompanied by a related sound (for example a "meow" sound with a cat picture). They were tested on their memory and then took a nap. Half of the sounds were played while subjects napped, with their brain activity monitored.

Upon awakening, those subjects were better able to match locations of the objects whose sounds they had heard while asleep. They performed only 3 percent worse than they had on the first test with objects they heard a sound for, while they performed 18 percent worse in trying to match the location of objects whose sound they did not hear.

That effect did not occur in a different set of subjects who did the same test but did not nap, instead hearing the sounds played while still awake.

Rudoy explained that while the research suggests strengthening memories, don't count on being able to learn calculus while catching Zs.

"We show that you can strengthen existing memories while you sleep, but you can't learn new things while you sleep," he said.

Taking Advantage of Extra Time

Since the researchers did not look at linguistic cues, the research does not mean you can benefit from playing a tape of terms you learned during the day.

Rudoy explained that it might mean someone studying while listening to music could benefit by having that same music played while they were asleep, but even that would require further study.

Another possible application, years down the line, would be helping patients with diseases caused by negative memories retain more positive ones instead.

"You could imagine playing sounds associated with the memories you want to keep…could possibly have the desired effect," said Rudoy. "It would be great if that would work that way but we're not sure."

McGaugh said the study was novel and interesting, but more research would be needed to understand why it happened, since the study also raised some questions.

"I don't think it solves all the questions," said McGaugh. "For example, why is it that doing it with subjects who are awake did not have the same effect? What is there about the failure of this treatment while awake? To me, it's extremely puzzling."

But he said not to discount sleep's value to a learner.

"In general, there's considerable evidence suggesting that sleep promotes the fixation of long-term memories of things that were learned before going to sleep," said McGaugh.

A Discarded Idea's Enduring Appeal

Sleep-learning was widely discredited in the 1950s, so the fact that CDs are available says something about the appeal of the idea.

"The information is just not processed that way while you're asleep," said Scott Lilienfeld, a professor of psychology at Emory University who discussed the myth in his new book, "50 Great Myths of Popular Psychology: Shattering Widespread Misconceptions about Human Behavior."

The problem with the original research that suggested the possibility of sleep learning was that researchers didn't do enough to make sure the subjects were actually asleep.

"When studies later controlled for that fact by making sure subjects were in fact asleep…whatever affects there were disappeared," said Lilienfeld. "It shows why good scientific control was important."

While he said studies like the Northwestern one are important, he does worry that it may be misused by a misunderstanding of the science.

"The danger of this kind of thing -- is that then advocates of sleep assisted learning can misuse them, lead the public to think they can learn new things while they're sound asleep," said Lilienfeld. "It does not say anything about learning new information -- it does not mean or imply that one can learn entirely new information during sleep, nor do the results bear on learning complex information, like entirely new words, let alone languages or concepts."

For someone thinking of buying any sleep-learning device, Rudoy had this advice: "If someone comes to you tomorrow and tries to sell you something, I would be skeptical," he said.