Erin O’Donnell in Harvard Magazine:
it’s a time-honored practice among medical residents, cramming undergrads, and anyone else burning the candle at both ends: get very little sleep for days, maybe even pull an all-nighter, and then crash for an extra-long night of shut-eye to catch up.
Ten hours of sleep at once may indeed recharge us, and allow us to perform well for several hours after waking, according to research recently published inScience Translational Medicine. But “the brain literally keeps track of how long we’ve been asleep and awake—for weeks,” says Harvard Medical School (HMS) neurology instructor Daniel A. Cohen, M.D., lead author of the study. And that means that the bigger our aggregate sleep deficit, the faster our performance deteriorates, even after a good night’s rest.
Cohen and his coauthors monitored nine young men and women who spent three weeks on a challenging schedule: awake for 33 hours, asleep for 10—the equivalent of 5.6 hours of sleep a day. (This approximates the schedule of a medical resident, but many of us live under similar conditions; the National Sleep Foundation reports that 16 percent of Americans sleep six or fewer hours a night.) When the study participants were awake, they took a computer-based test of reaction time and sustained attention every four hours.
The researchers were surprised to discover just how much an extended rest boosted test performance. “Even though people were staying awake for almost 33 hours, when they had the opportunity to sleep for 10 hours, their performance shortly after waking was back to normal,” Cohen says. “The really interesting finding here is that there’s a short-term aspect of sleep loss that can be made up relatively quickly, within a long night.”
But the days and weeks of lost sleep eventually took their toll. The investigators knew from previous research that people awake for 24 hours straight display reaction times comparable to those of people who are legally drunk. Cohen’s new study reveals that those who pull an all-nighter on top of two or three weeks of chronic sleep loss reach that level of severe impairment faster—after just 18 hours awake.