KELLY MCEVERS, HOST:
A night without sleep leaves most of us feeling a little flat or sluggish. Now scientists have found a biological explanation. NPR's Jon Hamilton reports on evidence that when brain cells are deprived of sleep, they slow down.
JON HAMILTON, BYLINE: When you see something unexpected, your brain tries to respond quickly.
ITZHAK FRIED: You can imagine yourself driving a car and suddenly somebody jumps in front of the car at night.
HAMILTON: Itzhak Fried is a brain researcher at the University of California, Los Angeles. He says there's lots of evidence that sleepy drivers take longer to hit the brakes. But Fried wanted to know why, so he and a team of researchers studied how certain brain cells respond to information coming from the eyes.
FRIED: We saw the very neurons, you know, which are responsible for the way that you process the world in front of you on the highway or on the job or in any situation.
HAMILTON: The team was able to study these neurons in a dozen people with severe epilepsy. These people often spend a week or more with tiny wires in their brains to help doctors figure out the source of their seizures. And this allowed the scientists to monitor the bursts of electrical activity produced by specific brain cells as patients looked at images of faces, places and animals. Then, Fried says, four of the participants were kept awake all night and given the image test again. This time, Fried says, there was a clear difference.
FRIED: The neurons, the nerve cells, are responding slower, the responses are diminished, and they are smeared over longer periods of time.
HAMILTON: In other words, each cell took longer to produce the electrical bursts it uses to communicate with other cells and the signal was weaker. What's more, the brain cells tended to show this sluggish behavior just before a participant had a mental lapse while trying to classify an image. The finding appears in this week's edition of the journal Nature Medicine, and it's made Fried think differently about his own sleepless nights. He says he's a bit horrified by the long shifts he spent treating patients during his training as a neurosurgeon.
FRIED: I remember with some horror, you know, the kind of hours that we were subject to.
HAMILTON: Since then, training programs have imposed limits on the hours doctors can work. Fried says that's probably a good thing for patients. He also says he's working to get more rest than he used to.
FRIED: I'm trying to impose the lesson that I learned from my research on myself as well.
HAMILTON: One night at a time. Jon Hamilton, NPR News.
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