After the sixth night at the lab, participants were woken up after eight hours of sleep. Immediately, they took an adding test.
There was no hemming and hawing, no dawdling over coffee or the newspaper. Instead, the day started abruptly, with the math test starting within seconds of waking.
Participants fumbled and stumbled through the test, performing much worse than usual. After about 20 minutes to an hour, their performance was closer to normal.
Then, participants were kept up for 26 hours straight at the lab. Right afterward, they took another addition test. Math scores were better after the all-nighter than immediately after eight hours of sleep.
"These were very healthy people who had performed the test hundreds of times, making the results even more profound," Wright says in the news release.
Grogginess Like Drunkenness
Other researchers have equated sleep inertia, or morning grogginess, to being drunk, write Wright and colleagues.
Many people can delay mental challenges for a few minutes while their brains get up to speed. But some people, like doctors, soldiers, and emergency workers, have to be ready to go at a moment's notice, Wright's team notes.
The adding test challenged short-term memory, counting skills, and speedy thinking. The brain's prefrontal cortex handles those skills, along with problem solving, complex thinking, and emotions.
In short, workers who must be at the top of their game at the drop of a hat can't afford a groggy prefrontal cortex.
Give Me a Moment ... or More?
Sleep inertia doesn't last long, with "severe" performance problems lasting three minutes, write the researchers.
They note that in other studies, "severe" performance problems have lasted up to 10 minutes, with detectable glitches present for at least two hours after waking.
Their study was small, and people don't normally do math first thing in the morning, so the researchers call for more studies of sleep inertia.
The goal: Learn how bad it really is and how to handle those morning moments when duty calls but the brain can't quite keep up.