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睡不够8小时,你的大脑真会变慢

更新时间:2016-11-23 11:22:37 来源:纽约时报中文网 作者:佚名

How Little Sleep Can You Get Away With?
睡不够8小时,你的大脑真会变慢

We all know that we don’t get enough sleep. But how much sleep do we really need? Until about 15 years ago, one common theory was that if you slept at least four or five hours a night, your cognitive performance remained intact; your body simply adapted to less sleep. But that idea was based on studies in which researchers sent sleepy subjects home during the day — where they may have sneaked in naps and downed coffee.

我们都知道自己睡眠不足。但我们到底需要多少睡眠呢?直到大约15年前,市面上还广泛流传着这样一个理论:如果你每晚至少睡4个或者5个小时,那么你的认知表现就不会受到影响;你的身体会逐渐习惯较少的睡眠。但在为这种观点提供依据的一些研究中,研究人员曾在白天把困倦的受试者送回家,而后者有可能在家里偷偷地小睡或者猛灌咖啡。

Enter David Dinges, the head of the Sleep and Chronobiology Laboratory at the Hospital at University of Pennsylvania, who has the distinction of depriving more people of sleep than perhaps anyone in the world.

接着,宾夕法尼亚大学医院(Hospital at University of Pennsylvania)的睡眠与时间生物学实验室(Sleep and Chronobiology Laboratory)负责人大卫·丁格斯(David F. Dinges)出场了。丁格斯的经历十分独特:他剥夺过很多人的睡眠,就人数而言世界上大概无人能出其右。

In what was the longest sleep-restriction study of its kind, Dinges and his lead author, Hans Van Dongen, assigned dozens of subjects to three different groups for their 2003 study: some slept four hours, others six hours and others, for the lucky control group, eight hours — for two weeks in the lab.

为了撰写发表于2003年的一篇论文,丁格斯和论文第一作者汉斯·凡东恩(Hans Van Dongen)开展了一项睡眠限制研究——其历时之久一度堪称同类研究之最——把受试者分成三组:一些人睡4小时,另一些人睡6小时,其他人则被幸运地分进了对照组,睡8小时——他们在实验室里总共待了两个星期。

Every two hours during the day, the researchers tested the subjects’ ability to sustain attention with what’s known as the psychomotor vigilance task, or P.V.T., considered a gold standard of sleepiness measures. During the P.V.T., the men and women sat in front of computer screens for 10-minute periods, pressing the space bar as soon as they saw a flash of numbers at random intervals. Even a half-second response delay suggests a lapse into sleepiness, known as a microsleep.

白天,研究人员每隔两小时便会以所谓的精神运动警觉性任务(psychomotor vigilance task,简称PVT)测试受试者持续集中注意力的能力。PVT被视为衡量困倦程度的黄金标准。参与PVT的男男女女需在电脑屏幕前坐上10分钟,每当看到数字一闪而过,就要立刻按下空格键,而数字的间隔时间是不固定的。反应哪怕只滞后半秒,也意味着受试者昏昏欲睡,即进入了人们所说的微睡状态。

The P.V.T. is tedious but simple if you’ve been sleeping well. It measures the sustained attention that is vital for pilots, truck drivers, astronauts. Attention is also key for focusing during long meetings; for reading a paragraph just once, instead of five times; for driving a car. It takes the equivalent of only a two-second lapse for a driver to veer into oncoming traffic.

如果你的睡眠一直都很好,那么PVT就是一项乏味但却简单的任务。它衡量的是对飞行员、卡车司机和宇航员来说至关重要的持续性注意力。在参加冗长的会议时,一次性阅读一个段落,而非看上五遍时,以及开车时,注意力同样是保持专注的关键所在。一名司机大约只要走神两秒钟,就有可能冲入对向车流中。

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. What was interesting was that those in the four- and six-hour groups had P.V.T. results that declined steadily with almost each passing day. Though the four-hour subjects performed far worse, the six-hour group also consistently fell off-task. By the sixth day, 25 percent of the six-hour group was falling asleep at the computer. And at the end of the study, they were lapsing fives times as much as they did the first day.

在为期14天的研究中,每天睡8小时的人几乎没走过神,也没有出现认知能力下降的问题,这并不令人意外。有意思的是,睡4小时和6小时的那些人的PVT测试成绩几乎是逐日稳步下降。虽然睡4小时的受试者的表现要糟糕得多,但睡6个小时的受试者也常常开小差。到了第六天,睡6小时的那组人中有25%会在电脑前睡着。而在研究收尾阶段,他们走神的次数多达第一天的5倍。

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. The same was true for an addition-subtraction task that measures speed and accuracy. 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.

在对工作记忆的测试中——受试者必须记住一些数字和符号,并用一个替代另一个——睡6小时的受试者并未拿出更好的表现——在两周之内,其测试成绩稳步下降。在衡量速度和准确度的加减运算任务中,情况也是如此。总之,两周结束时,睡6小时的受试者的能力受到了影响,就像参加了丁格斯的另一项研究,整整24小时没有睡过觉的人一样——其认知能力跟那些在法律上会被认定为醉酒者的人差不多。

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. 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. Belenky’s nine-hour subjects performed much like Dinges’s eight-hour ones. But in the seven-hour group, their response time on the P.V.T. slowed and continued to do so for three days, before stabilizing at lower levels than when they started. Americans average 6.9 hours on weeknights, according to the National Sleep Foundation. Which means that, whether we like it or not, we are not thinking as clearly as we could be.

因此,对大多数人来说,保持8小时的睡眠是很理想的,睡6小时就不太好了。不过,如果我们折衷一下会怎么样呢?低于哪个阈值,认知功能就会出现衰退?丁格斯的研究进行期间,其同事、马里兰州银泉市沃尔特·里德陆军研究院(Walter Reed Army Institute of Research)神经科学部门时任负责人格雷戈里·贝伦基(Gregory Belenky),正在开展一项类似的研究。他有意把受试者的睡眠时间限定为奇数——3小时、5小时、7小时和9小时——因此,把这两项研究综合起来,就可以提供一幅更为全面的关于睡眠限制的图景。在贝伦基的研究中,睡9小时的受试者的表现,和丁格斯的研究中睡8小时的受试者非常相似。但睡7小时的受试者参与PVT时,其反映速度会下降,连续三天都是如此,然后就会稳定在低于初始速度的较低水平上。来自国家睡眠基金会(National Sleep Foundation)的数据显示,美国人在工作日的晚上平均睡6.9小时。这意味着不管我们喜不喜欢,我们平日的思维并不像我们所能达到的那样清晰。

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. They can do the job for only so long, however. 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. But you do in five to seven days. Unless you’re doing work that doesn’t require much thought, you are trading time awake at the expense of performance.”

当然了,我们的日常生活比睡眠实验室里的生活更刺激:我们会喝咖啡,会待在明亮的灯光下,会在办公室里忙于与人周旋,所有这些都是针对困倦的“反制手段”。不过,它们只能在有限的时间内起作用。正如目前身为华盛顿州立大学斯波坎分校(Washington State University, Spokane)睡眠与绩效研究中心(Sleep and Performance Research Center)主任贝伦基在谈及认知缺陷时对我说的:“你不会在第一天就发现它。但到了第五至七天你就会看到相关迹象。除非你做的工作不太需要思考,否则你就是在为了换取醒着的时间而牺牲工作绩效。”凡东恩也是该校的教授。

And it’s not clear that we can rely on weekends to make up for sleep deprivation. Dinges is now running a long-term sleep restriction and recovery study to see how many nights we need to erase our sleep debt. But past studies suggest that, at least in many cases, one night alone won’t do it.

此外,目前尚不清楚我们是否可以依靠周末来弥补缺失的睡眠。丁格斯正在开展一项长期的睡眠限制和恢复研究,旨在确定我们需要花多少个夜晚来还清睡眠方面的欠债。但以往的研究显示,至少在很多情况下,仅仅一个晚上是不够的。

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 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. (There is also a small percentage who require 9 or 10 hours.)

当然了,睡眠者的情况并非千篇一律:丁格斯发现,一些需要睡8小时的人如果度过了一个只睡4小时的夜晚,情况立刻就会变得很糟,而另外一些需要睡8小时的人在度过好几个只睡4小时的夜晚之后,表现才会变差。(但终究会变差。)有一小部分人——据他估计占总人口的比例约为5%,甚至更低——可以在只睡5小时,甚至更短时间的情况下维持其表现水准,研究人员认为这源于基因方面的差异。(还有一小部分人需要睡9个或10个小时。)

Still, while it’s tempting to believe we can train ourselves to be among the five-hour group — we can’t, Dinges says — or that we are naturally those five-hour sleepers, consider a key finding from Van Dongen and Dinges’s study: after just a few days, the four- and six-hour group reported that, yes, they were slightly sleepy. But they insisted they had adjusted to their new state. Even 14 days into the study, they said sleepiness was not affecting them. In fact, their performance had tanked. In other words, the sleep-deprived among us are lousy judges of our own sleep needs. We are not nearly as sharp as we think we are.

人们很容易就会认为,我们可以把自己训练成只需睡5小时的人——丁格斯说我们其实做不到——或者我们天生就是只需睡5小时的人,但还是该看看凡东恩和丁格斯的研究得出的一个关键结论吧:仅仅几天过后,睡4小时和6小时的人就会报告说,没错,他们感觉有点儿困倦。但他们坚称已经适应了自己的新状态。即便是参加研究已经有14天了,他们还是说困倦没对他们造成影响。事实上,他们的表现已然大打折扣。换句话说,我们当中的睡眠不足者难以精确判断自身的睡眠需求。我们远远不像自己所以为的那样敏锐。

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