Friday, August 13, 2010

Dealing with It: How the Brain Handles Sleep Loss

A new study from the Proceedings of the National Academy of Sciences, shows that the brain copes with short- and long-term sleep loss similarly.

The University of Wisconsin-Madison-based researchers found that five nights of restricted sleep affects the brain the same way as acute total sleep deprivation.

Dr. Chiara Cirelli noted in a press release that even mild sleep restriction for several nights can affect performance on cognitive tasks.

Recent studies found that five days with only four hours of sleep per night result in cognition problems that do not fully recover after one night of sleep, even if 10 hours in bed are allowed.

Cirelli and her team kept rats awake 20 hours a day over five days while continuously recording the animals' brain waves with a sophisticated EEG as they were asleep and awake. The EEGs measured slow wave activity (SWA). It is the best marker of an individual's need to sleep as well as the intensity of sleep that follows wakefulness.

In general, the longer awake, the higher is SWA in the subsequent sleep. Cirelli explained that the researchers knew that this was true after short-term sleep deprivation. But this research indicated that same result for chronic sleep restriction.

According to the rat cumulative SWA measures, the sleep restriction produced intense recovery sleep following each wake cycle, with both longer and deeper sleep. The more effective the researchers were in keeping the animals awake during those 20 hours, the larger the sleep rebound they saw during the following four hours.

Even when the animals seemed awake and were moving around, heightened SWA was evident in their "wake" EEG.

"Monitoring SWA levels during waking time is very important in understanding the whole picture," she says. "High SWA levels during periods of both sleeping and waking signal that you need to go to sleep."

Researchers can use what they learn from short-term deprivation and apply it to long-term deprivation. This application is important, as more than 70 million Americans suffer from sleep disorders.

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