Lack of Sleep Catching Up With Soldiers

April 9 -- American troops have been on the move day and night, across hundreds of miles of desert. When they do stop, they're often repairing equipment or under enemy fire.

The result: Many soldiers and marines are getting only two or fours hours of sleep a night. And it's taking its toll.

"Sometimes you might be cleaning your weapon, or talking to a friend and you just slowly doze off," said Pfc. Favio Mendez. "It just happens."

When troops do get a break, it can be in the midst of rain or sandstorms.

"It's pretty tough," said another U.S. soldier. "You know, there's not any tents, there's nothing out there to sleep on. So there's just sand everywhere, in our nose, in our face."

Col. Gregory Belenky, a physician and sleep expert at the Walter Reed Army Institute of Research in Silver Springs, Md., says sleep — not simple rest — is critically important for battlefield troops.

"The brain needs sleep," Belenky told ABCNEWS. "The rest of the body, the muscles, the other organs, can do with simple rest. The heart muscle never rests. But the brain needs sleep in an active state to recuperate."

Dangerous Effects

Most soldiers, like most everyone else, need about eight hours of sleep a night. Give them less, said Belenky, even an hour less each night, and you start to see an effect.

"The real issue is chronic sleep restriction: days, weeks, months, with little sleep, with less than optimum amounts of sleep," he said.

To demonstrate the effect of sleep deprivation, the Army took images of the brain with PET, or positron emission tomography. After 24 hours without sleep, they found brain activity decreased significantly in two distinct areas: the prefrontal cortex and the thalamus, the areas of the brain responsible for attention, planning and anticipation.

The research suggests sleep deprivation may cause some soldiers on the battlefield to become confused about where they are, and what they're doing; and about whether a target is friend or foe.