Sleeping In Space

In general, they found, longer naps were better. No surprise there. But they also found that some cognitive functions benefited more from napping than others:

Shuttle pilots need to be mentally sharp to operate controls like these

"To our amazement, working memory performance benefited from the naps, [but] vigilance and basic alertness did not benefit very much," says Dinges.

"Working memory," he explains, "involves focusing attention on one task while holding other tasks in memory ... and is a fundamental ability critical to performing complex work [like piloting a spaceship]. A poor working memory could result in errors."

For vigilance and alertness, which involve the ability to maintain sustained attention and to notice important details, they found that the total amount of sleep during 24 hours remained the most important factor.

Another interesting finding was that naps didn't work as well for volunteers on a nocturnal schedule. Sleep schedules for some of Dinges' subjects were flipped, so that anchor sleep occurred when their bodies thought it was daytime. The nap, then, fell in the middle of biological nighttime. This simulated what might happen when an astronaut's biological clock is out of sync with the mission schedule.

These out-of-sync volunteers had a very hard time waking from naps, and the grogginess of sleep inertia lasted for up to an hour. Some sleep inertia did occur after naps on a normal schedule too, notes Dinges, but the inertia after a nighttime nap was much more severe.

The ultimate goal, says Dinges, is to tie all these data together into a mathematical model of naps. Such a model, written as a computer program, could prescribe effective naps compatible with the scheduling demands of a mission. Not only astronauts would benefit from such a program, but also doctors, pilots, firefighters … the list goes on.

Such a program is still in the future. Meanwhile, Dinges notes another finding of their study: Naps are a short-term fix, offering only temporary boosts in mental acuity. "They cannot replace adequate recovery sleep over many days," he says.

In the end, there's no substitute for 8 sweet hours of shut-eye.