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More Evidence That Sleep Enhances Memory and Learning

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Do you ever feel forgetful and a little sluggish of mind? Do you wish you could pick up new skills more quickly and easily? Here's a tip: You can boost your learning power by beefing up your sleep routine.

Researchers at Northwestern University are among the latest to demonstrate that memory and ability for a recently learned skill is enhanced and strengthened by sleep. This is just the latest in a series of recent breakthroughs that are providing us with a deeper understanding of how sleep functions in the brain to support learning and memory.

In this study, researchers had people learn how to play two separate musical melodies using visual symbols. After learning to play the two tunes, participants took a 90-minute nap. During the nap, researchers played only one of the melodies. They also monitored brain activity during the nap period, in order to present the music during slow-wave sleep. Slow-wave sleep is a deep, non-REM phase of sleep, also known as delta sleep or stage three sleep. This is a restorative stage of sleep that has been linked in other research with the creation and consolidation of memory.

What did researchers discover?

When asked to replay the two melodies after their naps, the participants were able to re-play the song they'd heard during sleep with greater accuracy than the song they hadn't been exposed to while sleeping. Researchers also found that EEG measurements of brain activity during slow-wave sleep correlated to the degree of improvement in memory -- an indication that researchers may have been able to measure the very brain activity that was helping strengthen memory.

The investigations into the relationships between sleep, learning, and memory are an exciting and very active area of scientific research. There have been a series of studies in recent months that show the advances made in our understanding of how sleep affects the brain and, in turn, our ability to learn new skills and to transfer that new learning into long-term memory:

  • I wrote about this study, which investigated the role that sleep plays in converting new learning into established memories. Researchers found that students who slept shortly after memorizing two different sets of word pairs had better recall of the information they'd learned than those who didn't sleep for several hours.
  • This study showed the effects of a sleep disorder on memory in children. Researchers studied 54 children with obstructive sleep apnea (yes, kids can have this kind of sleep disorder as well as adults!). The researchers examined whether sleep apnea could have a negative impact on visual memory. They found that children with obstructive sleep apnea had more difficulty with both short- and long-term memory recall than children without the sleep disorder.
  • The effect of sleep on memory appears to change as we age. This study included both younger and older adults in measuring the degree of memory consolidation during slow-wave sleep. They found that the strength of the positive effect of slow-wave sleep on memory appeared to diminish with age. Younger people received more of a measurable benefit -- a memory boost -- than older people did. The older participants didn't demonstrate the same improvements to memory that younger people did. But older people did exhibit a negative effect on memory when they were deprived of slow-wave sleep.
  • This latest study isn't the first time we've seen evidence that exposure to sound during deep sleep can influence and enhance memory. In this study, researchers taught participants to pair a particular image of an object with a particular location on a computer screen. Forty-five minutes after the learning exercise was complete, participants took a nap. During their nap, researchers played sounds associated with some of the objects they'd been working with earlier. The nappers were not aware they'd been exposed to these sounds. After waking, they were asked to perform the same exercise they'd learned earlier. Researchers found that people had better memory for the placement of objects that were linked to the sounds they'd heard during sleep.
  • And it's not just sound that can penetrate deep sleep to enhance memory -- this research showed how exposure to smell could help consolidate memory during sleep. Participants learned a memory game that involved memorizing the location of card pairs on a computer screen. While learning, they were exposed to the scent of roses. Thirty minutes after completing the exercise, they slept, and were exposed to the rose scent again during slow-wave sleep. People scored substantially higher when tested for memory recall after sleep-time exposure to the smell than when they slept without any exposure to the smell, or when they were given the scent again before they went to sleep.

This is fascinating stuff for any of us interested in the science of sleep and the science of the brain. But it's also important information for everybody, science-buff or not: Getting regular, restful, and plentiful sleep makes our minds -- and our memories -- work better.

Sweet Dreams,
Michael J. Breus, PhD
The Sleep Doctor™
www.thesleepdoctor.com

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