February 1st, 2011
05:00 PM ET
Here's another reason to get some good sleep in the week leading up to a major test or presentation: Sleep selectively enhances memories that you expect to need in the future, a new study suggests.
Researchers in Germany tested a group of 141 healthy adult participants on tasks involving recalling words, locating a two-dimensional object, and reproducing a sequence of finger taps. Their results are published in the Journal of Neuroscience.
They found that participants who knew they would be tested on these things later remembered them better than those who didn't know after a good night's sleep of about 7 to 8 hours. Participants who were not permitted to sleep did not show memory improvement, regardless of whether or not they thought there would be a test.
This research sheds light on the intricacies of how memory works while we sleep, said Michael Breus, sleep expert in Scottsdale, Arizona, and author of "Beauty Sleep." Breus, who was not involved in the study, praised the experimental design and noted that it looked at the effects of both declarative memory (recalling facts and events) and procedural memory (skill sets).
Some next steps would be to figure out exactly how long these memories last, and how accurate they are later, Breus said. The longer you have a memory, the less accurate it usually becomes. But if there is a lot of emotion attached to an event, it stays clearer longer. For instance, you probably remember the moment when you learned of the attacks on September 11, 2001, but maybe not what was happening when you ordered a pizza last month.
How it works
Memory first gets encoded while you're awake through a horseshoe-shaped brain region called the hippocampus, where it gets temporarily stored for up to about a day or two, said Jan Born, study co-author and researcher at the University of Lübeck in Germany. But you may forget that memory relatively quickly because you get exposed to other things that are similar to the original memory, and the new information tends to override old information.
During sleep, memories get consolidated and stored for the longer haul in the neocortex. Longterm memory storage can last from a day or to up to a lifetime.
That transfer of memories from short to long-term storage takes place during slow-wave sleep, a stage of deep sleep that cycles with rapid eye movement (REM). During this slow-wave sleep, there is no dreaming, and if you wake up during it, you feel especially groggy. A typical night's sleep begins with non-REM sleep - light followed by deep sleep - followed by an REM stage, and then the two cycle with each other.
There is, however, some controversy about the role of REM sleep in memory. Traditionally the view has been that slow-wave sleep is physically restorative - in other words, tissue repair and metabolism and weight changes occur during this phase of snoozing - and that REM sleep is physically restorative, Breus said. But so much happens during sleep that it's hard to pin down exactly which phase is responsible for what.
"This study does bring to light some new possibilities in that area," he said.
Even a nap helps
Many other studies have found that even a nap benefits the consolidation of memory. Interestingly, a 2010 study in Current Biology found that naps boost memory only if you dream, even though memory enhancement appears to occur during slow-wave, non-dreaming sleep stages.
But in preparation for a big exam, a single night of good sleep doesn't help as much as a week or so consistently, Born said.
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