Sleep Strengthens Your Memory

Sleep not only protects memories from outside interferences, but also helps strengthen them, according to research presented at the American Academy of Neurology's 59th Annual Meeting in Boston.

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The study looked at memory recall with and without interference (competing information). Forty-eight people between the ages of 18 and 30 took part in the study. All had normal, healthy sleep routines and were not taking any medications. Participants were divided evenly into four groups--a wake group without interference, a wake group with interference, a sleep group without interference and a sleep group with interference. All groups were taught the same 20 pairs of words in the initial training session.

The wake groups were taught the word pairings at 9 a.m. and then tested on them at 9 p.m. after 12 hours awake. The sleep groups were taught the word pairs at 9 p.m. and tested on them at 9 a.m. after a night of sleep. Just prior to testing, the interference groups were given a second list of word pairs to remember. The first word in each pair was the same on both lists, but the second word was different, testing the brain's ability to handle competing information, known as interference. The interference groups were then tested on both lists.

The study found that people who slept after learning the information performed best, successfully recalling more words. Those in the sleep group without interference were able to recall 12 percent more word pairings from the first list than the wake group without interference. With interference, the recall rate was 44 percent higher for the sleep group.

"This is the first study to show that sleep protects memories from interference," said study author Jeffrey Ellenbogen, MD, with Harvard Medical School in Boston, MA, and Fellow of the American Academy of Neurology. "These results provide important insights into how the sleeping brain interacts with memories: it appears to strengthen them. Perhaps, then, sleep disorders might worsen memory problems seen in dementia."

Sleep Makes Your Memories Stronger, and Helps With Creativity

As humans, we spend about a third of our lives asleep. So there must be a point to it, right? Scientists have found that sleep helps consolidate memories, fixing them in the brain so we can retrieve them later. Now, new research is showing that sleep also seems to reorganize memories, picking out the emotional details and reconfiguring the memories to help you produce new and creative ideas, according to the authors of an article in Current Directions in Psychological Science.

"Sleep is making memories stronger," says Jessica D. Payne of the University of Notre Dame, who co-wrote the review with Elizabeth A. Kensinger of Boston College. "It also seems to be doing something which I think is so much more interesting, and that is reorganizing and restructuring memories."

Payne and Kensinger study what happens to memories during sleep, and they have found that a person tends to hang on to the most emotional part of a memory. For example, if someone is shown a scene with an emotional object, such as a wrecked car, in the foreground, they're more likely to remember the emotional object than, say, the palm trees in the background -- particularly if they're tested after a night of sleep. They have also measured brain activity during sleep and found that regions of the brain involved with emotion and memory consolidation are active.

"In our fast-paced society, one of the first things to go is our sleep," Payne says. "I think that's based on a profound misunderstanding that the sleeping brain isn't doing anything." The brain is busy. It's not just consolidating memories, it's organizing them and picking out the most salient information. She thinks this is what makes it possible for people to come up with creative, new ideas.

Payne has taken the research to heart. "I give myself an eight-hour sleep opportunity every night. I never used to do that -- until I started seeing my data," she says. People who say they'll sleep when they're dead are sacrificing their ability to have good thoughts now, she says. "We can get away with less sleep, but it has a profound effect on our cognitive abilities."

Brain Evaluates Information Based on Future Expectations, Study Suggests

After a good night's sleep, people remember information better when they know it will be useful in the future, according to a new study in the Feb. 2 issue of The Journal of Neuroscience. The findings suggest that the brain evaluates memories during sleep and preferentially retains the ones that are most relevant.

Humans take in large amounts of information every day. Most is encoded into memories by the brain and initially stored, but the majority of information is quickly forgotten. In this study, a team of researchers led by Jan Born, PhD, of the University of Lübeck in Germany set out to determine how the brain decides what to keep and what to forget.

"Our results show that memory consolidation during sleep indeed involves a basic selection process that determines which of the many pieces of the day's information is sent to long-term storage," Born said. "Our findings also indicate that information relevant for future demands is selected foremost for storage."

The researchers set up two experiments to test memory retrieval in a total of 191 volunteers. In the first experiment, people were asked to learn 40 pairs of words. Participants in the second experiment played a card game where they matched pictures of animals and objects -- similar to the game Concentration -- and also practiced sequences of finger taps.

In both groups, half the volunteers were told immediately following the tasks that they would be tested in 10 hours. In fact, all participants were later tested on how well they recalled their tasks.

Some, but not all, of the volunteers were allowed to sleep between the time they learned the tasks and the tests. As the authors expected, the people who slept performed better than those who didn't. But more importantly, only the people who slept and knew a test was coming had substantially improved memory recall.

The researchers also recorded electroencephalograms (EEG) from the individuals who were allowed to sleep. They found an increase in brain activity during deep or "slow wave" sleep when the volunteers knew they would be tested for memory recall.

"The more slow wave activity the sleeping participants had, the better their memory was during the recall test 10 hours later," Born said. Scientists have long thought that sleep is important in memory consolidation. The authors suggest that the brain's prefrontal cortex "tags" memories deemed relevant while awake and the hippocampus consolidates these memories during sleep.

Gilles Einstein, PhD, an expert in memory at Furman University, said the new findings help explain why you are more likely to remember a conversation about impending road construction than chitchat about yesterday's weather. "These results suggest that sleep is critical to this memory enhancement," said Einstein, who was unaffiliated with the study. "This benefit extends to both declarative memories (memory for a road detour) and procedural memories (memory for a new dance step)."

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