Sleep researchers are learning new
and surprising things about sleeping in space.
by Patrick L Barry and Dr Tony
Space travel is sleepless
Despite NASA recommendations
that astronauts sleep 8 hours a day, they usually don't. Strange
sights and sounds, the stress of riding a powerful rocket, the lack
of a normal day-night cycle - all these things tend to keep space
travellers awake. Studies show that astronauts typically sleep 0.5
to 2.5 hours less than they do on Earth.
Although many astronauts
report feeling fully rested after only six hours of sleep, the fact
is, sleeplessness can cause irritability, forgetfulness and fatigue - none
of which astronauts need to deal with while piloting complicated
'ships that hurtle through space at tens of thousands of miles per
The solution seems
simple: Take a nap.
sleep like this?
But naps are a double-edged
sword. Sometimes napping can leave you feeling even drowsier than
before. If your body enters a deep sleep, trying to wake after only
an hour or so can be very unpleasant, and you might remain groggy
for some time afterward. This is called "sleep inertia."
Why do naps sometimes
backfire? Researchers don't yet know the physical causes of sleep
inertia, but they would like to be able to predict, at least, when
it's going to strike. This could help doctors prescribe naps of
the right time and duration for drowsy people in high-risk professions.
nap was the goal of a recent series of experiments funded by NASA
in cooperation with the National Space Biomedical Research Institute.
In those experiments, led by David Dinges, a professor at the University
of Pennsylvania School of Medicine, 91 volunteers spent 10 days
living on one of 18 different sleep schedules, all in a laboratory
setting. The sleep schedules combined various amounts of "anchor
sleep," ranging from about 4 to 8 hours in length, with daily
naps of 0 to 2.5 hours.
To measure how effective
the naps were, the scientists gave the volunteers a battery of tests
probing memory, alertness, response time, and other cognitive skills
throughout the experiment. They also measured things like core body
temperature and hormone levels in blood and saliva, all of which
fluctuate in a natural daily cycle known as a person's "biological
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:
pilots need to be mentally sharp to operate controls like
"To our amazement,
working memory performance benefited from the naps, [but] vigilance
and basic alertness did not benefit very much," says Dinges.
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.
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.