![]() (There is also a small percentage who require 9 or 10 hours.) (But deteriorate it will.) There is a small portion of the population - he estimates it at around 5 percent or even less - who, for what researchers think may be genetic reasons, can maintain their performance with five or fewer hours of sleep. Not every sleeper is the same, of course: Dinges has found that some people who need eight hours will immediately feel the wallop of one four-hour night, while other eight-hour sleepers can handle several four-hour nights before their performance deteriorates. But past studies suggest that, at least in many cases, one night alone won’t do it. Dinges is now running a long-term sleep restriction and recovery study to see how many nights we need to erase our sleep debt. Unless you’re doing work that doesn’t require much thought, you are trading time awake at the expense of performance.”Īnd it’s not clear that we can rely on weekends to make up for sleep deprivation. As Belenky, who now heads up the Sleep and Performance Research Center at Washington State University, Spokane, where Van Dongen is also a professor, told me about cognitive deficits: “You don’t see it the first day. ![]() They can do the job for only so long, however. Of course our lives are more stimulating than a sleep lab: we have coffee, bright lights, the social buzz of the office, all of which work as “countermeasures” to sleepiness. Which means that, whether we like it or not, we are not thinking as clearly as we could be. Americans average 6.9 hours on weeknights, according to the National Sleep Foundation. slowed and continued to do so for three days, before stabilizing at lower levels than when they started. But in the seven-hour group, their response time on the P.V.T. Belenky’s nine-hour subjects performed much like Dinges’s eight-hour ones. He purposely restricted his subjects to odd numbers of sleep hours - three, five, seven and nine hours - so that together the studies would offer a fuller picture of sleep-restriction. So, for most of us, eight hours of sleep is excellent and six hours is no good, but what about if we split the difference? What is the threshold below which cognitive function begins to flag? While Dinges’s study was under way, his colleague Gregory Belenky, then director of the division of neuroscience at the Walter Reed Army Institute of Research in Silver Spring, Md., was running a similar study. All told, by the end of two weeks, the six-hour sleepers were as impaired as those who, in another Dinges study, had been sleep-deprived for 24 hours straight - the cognitive equivalent of being legally drunk. ![]() ![]() The same was true for an addition-subtraction task that measures speed and accuracy. The six-hour subjects fared no better - steadily declining over the two weeks - on a test of working memory in which they had to remember numbers and symbols and substitute one for the other. And at the end of the study, they were lapsing fives times as much as they did the first day. By the sixth day, 25 percent of the six-hour group was falling asleep at the computer. Though the four-hour subjects performed far worse, the six-hour group also consistently fell off-task. results that declined steadily with almost each passing day. What was interesting was that those in the four- and six-hour groups had P.V.T. Not surprisingly, those who had eight hours of sleep hardly had any attention lapses and no cognitive declines over the 14 days of the study. ![]()
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