How catching up on sleep helps the brain: study

NEW YORK Wed Mar 11, 2009 4:53pm EDT

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NEW YORK (Reuters Health) - Lack of sleep can make us feel distracted, foggy and forgetful, and a new study helps explain why.

Working with mice, Dr. Robert W. Greene of University of Texas Southwestern Medical Center in Dallas and colleagues identified a key molecular mechanism that regulates the brain's ability to mentally compensate for sleep deprivation.

They found that a molecule called an adenosine receptor is required for sleep-deprived animals to attain adequate levels of slow-wave activity in the brain after a sleepless night. It is this increase in slow-wave activity during rebound sleep that helps restore normal memory and attention skills to the sleep-deprived, the researchers report in the Journal of Neuroscience.

When we miss a night of sleep, our bodies make up for it by going through a more intense bout of slow-wave activity the next night, Greene explained in an interview. Slow-wave activity occurs during non-REM sleep, and involves large parts of the brain going into a synchronized rhythm, or oscillation.

To investigate why slow-wave activity might be important, Greene and his team looked at rodents genetically engineered to be unable to pump up slow-wave activity in response to sleep deprivation. The animals lacked receptors for adenosine -- a key energy source for cells that is necessary for initiating slow-wave activity.

Both normal mice and the engineered mice performed equally well on tests measuring several aspects of brain function. Depriving the normal mice of sleep didn't affect how they fared on the tests. But when the engineered mice were sleep-deprived, their performance on tasks measuring "working" memory suffered.

"This memory is the kind of memory that you would use for example when you're multi-tasking; you have to keep something in mind when you're doing something else," Greene said. For example, if you're talking on the phone with someone who gives you a phone number, which you keep in your mind as you search for a pencil to write it down.

The current results, Greene noted, suggest that rebound, intense slow-wave activity is essential for restoring our ability to focus and pay attention. "Eventually you'll pay the piper if you don't get your slow-wave activity."

And users of sleeping pills should beware, Greene noted, because these drugs all inhibit slow-wave activity. "Even though you can get a long night's sleep, it might not be as effective as it needs to be."

SOURCE: The Journal of Neuroscience, February 4, 2009.

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