研究顯示 睡眠不足確實對大腦有很大影響

We all know that we don't get enough sleep. But how much sleep do we really need?

我們都知道自己睡眠不足。但是我們真正需要多少睡眠呢？

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.

直到大約15年前，有這樣一個理論：如果你每晚至少睡4或5小時，你的認知表現依然保持完好；而你的身體只是適應了較少的睡眠。

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.

但是那種觀點是基於這樣研究：研究人員在白天把睏倦的受試者送回家，而後者有可能在家裏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.

賓夕法尼亞大學醫院的睡眠與時間生物學實驗室的負責人大衛·丁格斯剝奪過很多人的睡眠，就人數而言世界上無人能比。

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.

爲了2003年的研究，丁格斯和第一作者漢斯.凡東恩開展了一項同類研究中最長的睡眠限制研究，他們把受試者分成三組：一些人睡4小時，另一些人睡6小時，其他人則被幸運地分進了對照組，睡8小時——他們在實驗室裏待了兩個星期。

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.

白天，研究人員每隔兩小時就會使用精神運動警覺性任務來測試受試者持續集中注意力的能力。PVT被視爲衡量睏倦程度的黃金標準。

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.

參與PVT的男女需在電腦屏幕前坐10分鐘，每當看到不定時閃現的數字時，就要立刻按下空格鍵。

Even a half-second response delay suggests a lapse into sleepiness, known as a microsleep.

就算只滯後半秒，也暗示着受試者陷入了睡眠之中，即微睡眠。

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.

如果你的睡眠一直都很好，那麼PVT就是一項乏味卻簡單的任務。它衡量的是對飛行員、卡車司機和宇航員來說至關重要的持續性注意力。

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.

在參加冗長的會議時、在一次性閱讀一個段落，而非看五遍時，以及開車時，注意力同樣是保持專注的關鍵所在。一名司機大約只要走神兩秒鐘，就有可能衝入迎面而來的車流中。

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.

在爲期14天的研究中，每天睡8小時的人幾乎沒走過神，也沒有出現認知能力下降的問題，這並不令人意外。有趣的是，睡4小時和6小時的那些人的PVT測試成績幾乎逐日穩步下降。

Though the four-hour subjects performed far worse, the six-hour group also consistently fell off-task.

雖然睡4小時的受試者的表現要差得多，但是睡6小時的受試者也常常分心。

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.

到了第六天，睡6小時的那組人中有25%會在電腦前睡着。而在研究的收尾階段，他們走神的次數達到第一天的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.

在對工作記憶的測試中，受試者必須記住一些數字和符號，並用一個代替另一個--睡6小時的受試者沒有更好的表現--而是在兩週之內穩步下降。

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

在測量速度和準確度的加減運算任務中，情況也是如此。

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.

總之，兩週結束時，睡6小時的受試者的能力被削弱了，就像丁格斯的另一項研究中整整24小時沒有睡過覺的人一樣--其認知能力跟那些在法律上會被認定爲醉酒的人差不多。

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.)

當然，睡眠者的情況並非千篇一律：丁格斯發現，一些需要睡8小時的人如果有一晚只睡4小時，情況立刻就會變得很糟，而另外一些需要睡8小時的人在好幾晚只睡4小時之後，表現纔會變差。（但終究會變差。）

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.)

有一小部分人--據他估計約爲5%，甚至更低--可以在只睡5小時，甚至更短時間的情況下維持其表現，研究人員認爲這是遺傳原因。（還有一小部分人需要睡9或10小時。）