How siestas help memory
午睡怎樣增進記憶力

Sleepy heads
昏昏欲睡的大腦

Feb 25th 2010 | SAN DIEGO | From The Economist print edition

Researchers say an afternoon nap prepares the brain to learn

研究者認為午睡可以讓頭腦更清醒，學習更高效

MAD dogs and Englishmen, so the song has it, go out in the midday sun. And the business practices of England’s lineal descendant, America, will have you in the office from nine in the morning to five in the evening, if not longer. Much of the world, though, prefers to take a siesta. And research presented to the AAAS meeting in San Diego suggests it may be right to do so. It has already been established that those who siesta are less likely to die of heart disease. Now, Matthew Walker and his colleagues at the University of California, Berkeley, have found that they probably have better memory, too. A post-prandial snooze, Dr Walker has discovered, sets the brain up for learning.

瘋狗和英國人——正如這首歌唱到的那樣——正午時分頂著太陽外出。而英國人的直系后裔——美國公司的慣例會讓你朝九晚五地呆在辦公室里，甚至更長時 間。但是世界上大部分人還是更喜歡來個午覺。一份提交到在圣迭戈舉行的AAAS科學年會的報告中說：這么做是正確的。有午睡習慣的人很少有死于心臟類疾病 的——這個已成定論?，F(xiàn)在，馬修·沃克和他在加利福尼亞大學伯克利分校的同事發(fā)現(xiàn)這些人很可能記憶力也會比其他人好。沃克博士發(fā)現(xiàn)，午餐之后打個小盹會讓 頭腦更清醒，學習更高效。

The role of sleep in consolidating memories that have already been created has been understood for some time. Dr Walker has been trying to extend this understanding by looking at sleep’s role in preparing the brain for the formation of memories in the first place. He was particularly interested in a type of memory called episodic memory, which relates to specific events, places and times. This contrasts with procedural memory, of the skills required to perform some sort of mechanical task, such as driving. The theory he and his team wanted to test was that the ability to form new episodic memories deteriorates with accrued wakefulness, and that sleep thus restores the brain’s capacity for efficient learning.

人們早已知道睡眠能夠鞏固已建立的記憶。沃克正在試圖擴展這一認識，他的辦法是觀察睡眠在大腦記憶形成的初始階段扮演的角色。他的興趣點在一種叫做 “事件記憶”的記憶上，這種記憶與時間、地點和次數(shù)相關(guān)聯(lián)。和這種記憶相反的是“程序記憶”，是記住那種完成機械任務所需的技能，例如開車。他和他的團隊 想驗證的理論是：一個人隨著清醒狀態(tài)的加深，其形成新的“事件記憶”的能力就會減弱；還有，睡覺因此就能恢復大腦高效學習的能力。

They asked a group of 39 people to take part in two learning sessions, one at noon and one at 6pm. On each occasion the participants tried to memorise and recall 100 combinations of pictures and names. After the first session they were assigned randomly to either a control group, which remained awake, or a nap group, which had 100 minutes of monitored sleep.

他們找來39個人來參加兩個時間段的學習——一個在中午，一個在晚上6點。在每段時間的學習中，參與者都要努力去記住并且回憶100組圖片和名字的 組合。在第一個時間段的學習過后，參與者被任意安排到兩組：一組是“受控制組”——必須一直保持清醒；一組是“打盹兒組”——有100分鐘的睡覺時間，期 間全程監(jiān)控。

Those who remained awake throughout the day became worse at learning. Those who napped, by contrast, actually improved their capacity to learn, doing better in the evening than they had at noon. These findings suggest that sleep is clearing the brain’s short-term memory and making way for new information.

從頭到尾一直保持清醒的那群人的學習效果變差了。而那些小睡的人則相反——他們提高了學習能力，在晚上的表現(xiàn)要優(yōu)于中午。這些發(fā)現(xiàn)表明睡覺加強了短 期記憶，而且為吸收新信息鋪平了道路。

It is already well known that fact-based memories are stored temporarily in an area called the hippocampus, a structure in the centre of the brain. But they do not stay there long. Instead, they are sent to the prefrontal cortex for longer-term storage. Electroencephalograms, which measure electrical activity in the brain, have shown that this memory-refreshing capacity is related to a specific type of sleep called Stage 2 non-REM sleep.

人們都知道知識性的記憶會被存在一個叫作“海馬”的區(qū)域，該結(jié)構(gòu)位于大腦中心。但是這些記憶并不會在那里停留很長時間，而是會被發(fā)送到前額皮質(zhì)以備 長期儲存。測量腦電活動的腦電圖顯示，這種記憶轉(zhuǎn)移的能力和一種叫作“第二階段非REM睡眠”的特定狀態(tài)的睡眠有關(guān)。

The ideal nap, then, follows a cycle of between 90 and 100 minutes. The first 30 minutes is a light sleep that helps improve motor performance. Then comes 30 minutes of stage 2 sleep, which refreshes the hippocampus. After this, between 60 and 90 minutes into the nap, comes rapid-eye-movement, or REM, sleep, during which dreaming happens. This, research suggests, is the time when the brain makes connections between the new memories that have just been “downloaded” from the hippocampus and those that already exist—thus making new experiences relevant in a wider context.

理想的小睡遵循一個90-100分鐘的周期。頭30分鐘是淺睡，幫助改善運動功能。然后是30分鐘的第二階段睡眠，在此期間，“海馬”得到喚起。之 后，小睡的60到90分鐘之間是“快速眼動睡眠”，或被叫作REM，期間會有夢境發(fā)生。研究表明，在這段時間，大腦將剛剛從海馬里“下載”來的新記憶和那 些已存記憶建立了聯(lián)系——從而使新體驗與更廣闊的背景相關(guān)聯(lián)。

The benefits to memory of a nap, says Dr Walker, are so great that they can equal an entire night’s sleep. He warns, however, that napping must not be done too late in the day or it will interfere with night-time sleep. Moreover, not everyone awakens refreshed from a siesta.

沃克博士說，小睡的好處非常大，甚至抵得過一整夜的睡眠。但是他也建議白天的小睡不應睡得太晚，否則會影響夜間的睡眠。除此之外，也并不是所有人都 能在午睡之后精神充沛的。

The grogginess that results from an unrefreshing siesta is termed “sleep inertia”. This happens when the brain is woken from a deep sleep with its cells still firing at a slow rhythm and its temperature and blood flow decreased. Sara Mednick, from the University of California, San Diego, suggests that non-habitual nappers suffer from this more often than those who siesta regularly. It may be that those who have a tendency to wake up groggy are choosing not to siesta in the first place. Perhaps, though, as in so many things, it is practice that makes perfect.

因午睡而引起的不清醒狀態(tài)被稱作“睡眠惰性”，發(fā)生在大腦從深睡中醒來之時，這個時候，腦細胞仍然在慢節(jié)奏律動，大腦溫度低，血流速度緩慢。位于圣 迭戈的加利福尼亞大學的薩拉·麥德尼克說，沒有午睡習慣的人和有規(guī)律午睡的人比起來更容易發(fā)生這種情形。這可能是因為那些醒來容易頭腦暈沉的人平時很少午 睡的原因。但是，也許只有多多午睡，才能少少頭暈。熟能生巧嘛！萬事同理。

譯者：eastx