Sleepless Nights Make for Grumpier Brains

Mind's emotion centers less controlled when weary, MRI study shows

MONDAY, Oct. 22, 2007 (HealthDay News) -- Ever get a little testy after a bad night's sleep? Scientists may now know why.

A new study finds that a lack of sleep causes the brain's emotional centers to dramatically overreact to negative experiences.

A shutdown of the prefrontal lobe -- a brain region that normally keeps emotions under control -- is the reason for heightened emotional response in sleep-deprived people, said the researchers from Harvard Medical School and the University of California, Berkeley.

Reporting in the Oct. 23 issue of the journal Current Biology, the team said its study is the first to determine, at the neural level, why lack of sleep can lead to emotionally irrational behavior and may help improve understanding of the link between sleep disruptions and psychiatric disorders.

"This adds to the critical list of sleep's benefits," Matthew Walker of the University of California, Berkeley, said in a prepared statement. "Sleep appears to restore our emotional brain circuits, and, in doing so, prepares us for the next day's challenges and social interactions. Most importantly, this study demonstrates the dangers of not sleeping enough. Sleep deprivation fractures the brain mechanisms that regulate key aspects of our mental health."

The study included 26 healthy people who were assigned to either a normal sleep group or to a sleep deprivation group, where they were kept awake for 35 hours. Afterwards, functional magnetic resonance imaging (fMRI) was used to measure the participants' brain activity.

"We had predicted a potential increase in the emotional reaction from the brain (in people deprived of sleep), but the size of the increase truly surprised us," Walker said. "The emotional centers of the brain were over 60 percent more reactive under conditions of sleep deprivation than in subjects who had obtained a normal night of sleep."

He said it's almost as though lack of sleep causes the brain to revert "back to a more primitive pattern of activity, becoming unable to put emotional experiences in context and produce controlled, appropriate responses."

More information

The National Sleep Foundation has more about how sleep works.

SOURCE: Cell Press, news release, Oct. 22, 2007
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