I haven't been myself since I started sleeping six hours per night. That was seven years ago. Turns out some 16 percent of Americans share my routine. That's 48 million people engaged in a perpetual pillow fight that gradually diminishes their productivity.

We are all, like Lili von Shtupp in "Blazing Saddles," tie-udd.

So says new research published earlier this year in Science Translational Medicine. Over the course of several weeks, it turns out, sleeping fewer than six hours a night takes a scientifically noticeable toll on the human mind—a toll that is merely masked, rather than cured, by the occasional 10-hour extended slumberfest.

As the researchers put it:

It is common for individuals to have relatively long sleep bouts on weekends or holidays but short sleep episodes on work or school days. Under such conditions, chronically sleep-restricted individuals may have a false sense of recovery from their previous sleep debt as a result of performing well for the first several hours of a usual waking day.

To conduct their study, a group of scientists led by Daniel A. Cohen placed nine people on a rigid sleep cycle over three weeks. Each period of roughly 33 waking hours was followed by 10 hours of sleep. The routine averaged out to 5.6 hours of sleep per day during the course of the study.

Two hours after they awoke, those in the experiment took the psychomotor vigilance test, a standard measure of attention. They repeated the test every four hours until it was time to hit the sack once more.

The study was designed, first, to track how much chronic sleep deprivation drains the mind, and second, to see whether it can be restored by the occasional binge of rest. Fresh after 10 hours sleep, the subjects indeed performed better on their first attention test of the day. As Cohen told Harvard magazine:

"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 into the second and third weeks of the study, test scores began to decline throughout the 33-hour waking period. One good night's rest, it seems, was able to temporarily erase the effects of prolonged sleep loss, even into the third week of the study. Still, throughout the day, the test scores reflected the true shortcomings of a brain "preloaded with fatigue." As Cohen and his colleagues conclude:

Data from this experiment reveal that individuals can develop a chronic sleep debt in the face of apparent full recovery from acute sleep loss.

Perhaps a short siesta is all that's needed to rouse us from our somnambulant existence. A few years back two Australian psychologists tried to identify the ideal nap length, in terms of refreshing the mind (pdf here). The researchers restricted test subjects to five hours sleep—from 2 to 7 a.m.—then, at 3 in the afternoon, had them to nap for various lengths of time. Three hours of testing followed the respite.

The nap strengths broke down like this:

  • 5-minute naps were no better than no nap at all;
  • 10-minute naps produced immediate improvement in fatigue, vigor, and cognitive performance that lasted up to 2.5 hours;
  • 20-minute naps showed improvements that lasted roughly 2 hours, though these benefits failed to emerge until 35 minutes post-nap;
  • 30-minute naps produced high levels of performance—up to roughly 2.5 hours—but not before test subjects shook "a period of impaired alertness" after waking.

The psychologists conclude, in the journal Sleep:

Overall, the 10-minute nap was the most effective afternoon nap duration (of those investigated) for improving alertness and performance following mild nocturnal sleep restriction.

Now, those fortunate enough to be able to nap for 90 minutes a day might actually be sharpening their minds in the process. Recent research, presented at a AAAS meeting in Februrary and reported by Scientific American, found that when people snoozed for an hour and a half, their brains shifted memories from a short-term home, in the hippocampus, to a more permanent storage area. This transition, in effect, clears the cache of our short-term memories.

The problem, of course, for many humans as well as the Headcase, is finding that extra 80 minutes to sleep during the day. After all, if we Six Hour Sleepers could become Almost-Eight Hour Sleepers, we wouldn't be in this fix. But hey, the world needs dreamers.


For another way to restore attention, see my post on nature.

For a different kind of sleep, see a brief old article of mine on hover beds.

HTs to Barker and Cardiff Garcia, who filled in for the Headcase here and here.

Follow me on twitter: e_jaffe

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