Missing out on sleep pretty much guarantees feeling crummy the next day. But it can also lead to dangerous or even disastrous decision-making. Sleep-deprived operators failed to prevent the Chernobyl nuclear power plant meltdown and the Exxon Valdez oil spill.
And during the Civil War, some historians think that Confederate Gen. Stonewall Jackson's confused command during the battles of June 1862 was due to sleep deprivation.
When we lose sleep, it seems we lose our ability to think on our feet — to take in new information and adjust our behavior, according to a study published in the June issue of the journal Sleep.
Researchers at Washington State University figured this out by rounding up 26 volunteers. Half went without any sleep for two days, while the other half slept normal hours. Over the course of a week, the scientists tested everyone's ability to complete decision-making tests.
In one test, the volunteers had to click a button when they saw certain numbers and hold back when they saw others. Then the rule was switched.
The well-rested group did better on this task in general. But when the rule was reversed, none of the sleep-deprived volunteers were able to get the right answer — even after 40 tries.
"It wasn't just that sleep-deprived people were slower to recover," says Paul Whitney, a psychologist at the university who led the study. "Their ability to take in new information and adjust was completely devastated."
Whitney says sleep scientists still don't understand why this happens. But it looks like the lack of sleep may be dulling the nervous system's response to new information. They found this out by hooking up the volunteers to electrodes that tracked their bodies' response to stimuli.
"Normally, the machine will pick up when people have a strong negative or positive response to something," Whitney says. "And we found that for the sleep-deprived group, the machine wasn't picking up much. Their reactions were completely blunted," Whitney says.
Sleep loss didn't affect all types of thinking. Everyone did pretty well on tasks that tested short-term memory, though the well-rested people did slightly better.
Since we can function fairly well in some aspects without sleep, people often don't realize just how much sleep deprivation can impair them, Whitney says.
If you can, he says, avoid making any high-stakes decisions when you're short of sleep, he says. And if you don't have a choice, take some extra time to make sure you're considering all the factors.
"The implication here is you should know that the most likely error you'll make when you haven't slept is that you're not going to second-guess yourself as much as you probably should," he says.
Of course, this is only a preliminary study — it's one of the first to test how sleep affects high-level decision-making. And while the study subjects were up for two consecutive days, in real-world situations people are more likely to get inadequate sleep over a long period of time, rather than no sleep over a short period.
Previous studies have shown that the effects of chronic sleep loss are similar to the acute sleep deprivation the subjects of this study experienced, Whitney says.
"It's hard to simulate in a lab the kind of decision-making that is predictive of what happens in a natural, real-world situation," says Charles Czeisler, head of the Division of Sleep and Circadian Disorders at Brigham and Women's Hospital and chairman of the board of the National Sleep Foundation, who wasn't involved in the recent research. "But this study does a really good job of getting at that."
It scientifically proves what we've known for a while — in high-stakes situations, sleep loss can be disastrous. "There have been many situations throughout history, particularly in military battles, where very highly capable individuals made mistakes when they were exhausted," Czeisler says. "This shows that when we practice disaster preparedness, we should think about how are we're going to rotate command-and-control."
And sleep is important even when you're not making life-or-death decisions, he adds. "People are increasingly burning the candle at both ends. And that's really not a good idea. It can even be dangerous."