How siestas help memory 午睡怎样增进记忆力

How siestas help memory
午睡怎样增进记忆力

Sleepy heads
昏昏欲睡的大脑

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

Researchers say an afternoon nap prepares the brain to learn

研究者认为午睡可以让头脑更清醒，学习更高效

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.

疯狗和英国人——正如这首歌唱到的那样——正午时分顶着太阳外出。而英国人的直系后裔——美国公司的惯例会让你朝九晚五地呆在办公室里，甚至更长时间。但是世界上大部分人还是更喜欢来个午觉。一份提交到在圣迭戈举行的AAAS科学年会的报告中说：这么做是正确的。有午睡习惯的人很少有死于心脏类疾病的——这个已成定论。现在，马修·沃克和他在加利福尼亚大学伯克利分校的同事发现这些人很可能记忆力也会比其他人好。沃克博士发现，午餐之后打个小盹会让头脑更清醒，学习更高效。

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.

人们早已知道睡眠能够巩固已建立的记忆。沃克正在试图扩展这一认识，他的办法是观察睡眠在大脑记忆形成的初始阶段扮演的角色。他的兴趣点在一种叫做“事件记忆”的记忆上，这种记忆与时间、地点和次数相关联。和这种记忆相反的是“程序记忆”，是记住那种完成机械任务所需的技能，例如开车。他和他的团队想验证的理论是：一个人随着清醒状态的加深，其形成新的“事件记忆”的能力就会减弱；还有，睡觉因此就能恢复大脑高效学习的能力。

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.

他们找来39个人来参加两个时间段的学习——一个在中午，一个在晚上6点。在每段时间的学习中，参与者都要努力去记住并且回忆100组图片和名字的组合。在第一个时间段的学习过后，参与者被任意安排到两组：一组是“受控制组”——必须一直保持清醒；一组是“打盹儿组”——有100分钟的睡觉时间，期间全程监控。

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.

从头到尾一直保持清醒的那群人的学习效果变差了。而那些小睡的人则相反——他们提高了学习能力，在晚上的表现要优于中午。这些发现表明睡觉加强了短期记忆，而且为吸收新信息铺平了道路。

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.

人们都知道知识性的记忆会被存在一个叫作“海马”的区域，该结构位于大脑中心。但是这些记忆并不会在那里停留很长时间，而是会被发送到前额皮质以备长期储存。测量脑电活动的脑电图显示，这种记忆转移的能力和一种叫作“第二阶段非REM睡眠”的特定状态的睡眠有关。

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.

理想的小睡遵循一个90-100分钟的周期。头30分钟是浅睡，帮助改善运动功能。然后是30分钟的第二阶段睡眠，在此期间，“海马”得到唤起。之后，小睡的60到90分钟之间是“快速眼动睡眠”，或被叫作REM，期间会有梦境发生。研究表明，在这段时间，大脑将刚刚从海马里“下载”来的新记忆和那些已存记忆建立了联系——从而使新体验与更广阔的背景相关联。

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.

沃克博士说，小睡的好处非常大，甚至抵得过一整夜的睡眠。但是他也建议白天的小睡不应睡得太晚，否则会影响夜间的睡眠。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状态被称作“睡眠惰性”，发生在大脑从深睡中醒来之时，这个时候，脑细胞仍然在慢节奏律动，大脑温度低，血流速度缓慢。位于圣迭戈的加利福尼亚大学的萨拉·麦德尼克说，没有午睡习惯的人和有规律午睡的人比起来更容易发生这种情形。这可能是因为那些醒来容易头脑晕沉的人平时很少午睡的原因。但是，也许只有多多午睡，才能少少头晕。熟能生巧嘛！万事同理。

译者：eastx
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