Research highlight

Sleep on it

Nature Neuroscience

January 19, 2009

Selectively disrupting a stage of sleep known as slow-wave sleep results in worse memory and reduced hippocampal activation in the brain during memory encoding, finds a study online this week in Nature Neuroscience.

A period of sleep between training and later retesting is known to benefit performance on some tasks, including memory tasks. Ysbrand Van Der Werf and colleagues suggest that the kind of sleep may be as important as the amount of sleep.

While people slept, the authors recorded the brain’s surface electrical activity via electroencephalograms (EEGs). When the EEGs were consistent with a sleep stage known as slow-wave sleep, a beeping sound was automatically set off. Slow-wave sleep is state of deeper sleep, so although the beep did not awaken the people taking part in this study, they slid out of slow-wave sleep into a different, shallower sleep stage.

Although the total amount of sleep that these people got was unchanged, they later did worse on a test where they had to remember scenes, compared to people who had slept normally. When the group of people with disrupted sleep was later scanned in a fMRI scanner as they viewed scenes they had to remember, they had reduced activity in a part of the brain known as the hippocampus. This area has previously been shown to be important for memorizing and recalling things.

These results suggest that hippocampus-dependent memory is particularly affected by shallow sleep.

doi: 10.1038/nn.2253

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