You wake up, go to the kitchen and pour juice on your cereal and milk in your glass. You're not alone: New research suggests many people are as mentally impaired when they wake up as if they were drunk -- even if they got a full night's sleep.
Sleep inertia, that groggy, disoriented feeling that that comes with waking up, has been well documented by researchers, who say it can last a few minutes or in some cases, up to two hours. For the first time, a study has measured how sleep inertia impairs cognitive abilities, said University of Colorado researcher Kenneth Wright. "We wanted to know, how bad is this?"
His study found that volunteers performed much worse on a series of tests immediately after waking than when they had gone without sleep for 24 hours.
When volunteers stayed up for 24 hours, they scored about 80 per cent as high as they normally did on tests that assessed short-term memory, counting skills, and the ability to add two numbers.
Their score was even lower immediately after they were woken up after eight hours sleep. They performed only 65 per cent as well as they normally did.
An earlier study on sleep deprivation found that not sleeping for 24 hours leaves people as mentally impaired as if they had a blood alcohol level of .08 per cent. It appears sleep inertia may be worse.
"For a short period, at least, the effects of sleep inertia may be as bad or worse than being legally drunk," said Dr. Wright.
Sleep inertia is worse if someone is sleep deprived, and if someone is woken out of deep sleep, which tends to occur earlier in the night.
The study could be important for medical residents and interns in hospitals who may work 80 hours or more a week and catch naps when they can, said Dr. Wright.
They may be prone to errors when performing the math required to calculate the dosage of medicine a patient requires, he said. He is not suggesting they forgo naps, which may be essential to combat sleep deprivation. But he said they should wait for their mental fog to lift before making key decisions.
The work also has implications for firefighters, who may have to drive an emergency vehicle shortly after being suddenly woken up, and for commercial truck drivers, who can pull over for a nap in their cab.
It also might explain why people can make poor decisions when they are woken up to face an emergency at home. If a person is awoken suddenly by a fire alarm, sleep inertia may keep them in bed when they should be getting out of the house.
There were only nine men in Dr. Wright's study, published today by the Journal of the American Medical Association. That is small sample size, but adequate to study a phenomenon that has been as well documented as sleep inertia, he said.
Thomas Balkin, a researcher at the Walter Reed Army Institute of Research in Washington, has found a biological basis for early-morning grogginess. He scanned people's brains as they woke up, and found the prefrontal cortex, believed to be responsible for problem solving and complex thought, takes longer to become active following sleep than other areas of the brain. Blood flow increases to other areas of the brain first.
More work is needed to find out how much individual variation there is in sleep inertia, because some people obviously have more trouble waking up then others. Some people are only disoriented for a few minutes after waking. Others can still feel thick-headed for two hours afterward, and find themselves doing stupid things, like trying to shave with the wrong side of the razor.
Caffeine can help, said Dr. Wright.
"Sleep inertia is the prime reason people reach for that cup of coffee."
