2018.6.24翻译材料：我们为何会做梦？

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Why do we sleep? And when we sleep, why do we dream? Do our nocturnal visions serve any fundamental biological purpose? Despite the fact that we spend about a third of our lives asleep and perhaps a sixth dreaming, scientists can offer no clear answer to these questions after many decades of global research.

我们为什么睡觉？当我们睡觉时，我们为什么做梦？我们的夜间幻像服务于任何根本的生理目的吗？尽管我们花大约三分之一的生命时光睡觉，也许六分之一的生命时光做梦，但在经过几十年的全球研究后，科学家们对于这些问题仍无法给出明确的答案。

“The short answer is that we don’t know why we sleep,” admits Yuval Nir, who runs a sleep laboratory at Tel Aviv University. “It is not what the public wants to hear but as a scientist I have to say it.” Vladyslav Vyazovskiy, a neuroscientist at Oxford university, agrees: “Surprisingly, the function of sleep remains elusive.”

“简短的回答是我们不知道我们为什么睡觉，”特拉维夫大学(Tel Aviv University)睡眠实验室主管尤瓦尔•尼尔(Yuval Nir)表示，“这不是公众希望听到的，但作为科学家我不得不这么说。”牛津大学(Oxford university)神经学家弗拉迪斯拉夫•维亚佐夫斯基(Vladyslav Vyazovskiy)对此表示同意：“奇怪的是，睡眠的功能仍难以捉摸。”

We do know that without it we would suffer the consequences. “Sleep is undoubtedly an essential life-support system,” says Matthew Walker of the University of California, Berkeley, and author of the bestselling Why We Sleep. All animals with nervous systems sleep. Sleep deprivation causes disease and in extreme cases may be fatal.

我们确实知道，如果没有睡眠，我们会遭受不好的后果。加州大学伯克利分校(University of California, Berkeley)、畅销书《我们为什么睡觉》(Why We Sleep)的作者马修•沃克(Matthew Walker)表示：“睡眠无疑是不可或缺的生命支持系统。”有神经系统的所有动物都睡觉。剥夺睡眠会导致疾病，在极端情况下可能是致命的。

Dreaming is more of a mystery, says Nir. “And dreams feed into even bigger questions, such as why we are conscious and why we experience anything at all, which science has not begun to answer.”

尼尔表示，做梦更是一个谜。“而且梦衍生出更大的问题，例如我们为什么有意识，我们为什么会有任何体验，科学还没有开始回答这些问题。”

Scientists used to associate dreaming solely with REM (rapid eye movement) sleep. It has recently become clear, however, that it also occurs in non-REM sleep — complicating the search for answers. “Dreams in non-REM sleep tend to be more static and often feature a recurring thought, like worrying about failure to study for an exam,” explains Nir. “In REM sleep, they are more active and visual.”

过去，科学家把做梦单纯与快速眼动睡眠期(REM)联系在一起。然而，近来变得明显的是，梦也出现在非快速眼动睡眠期中，这让搜寻答案的努力复杂化。“非快速眼动睡眠期的梦往往比较静止，经常是反复出现的想法，例如担心考试不及格，”尼尔解释道，“在快速眼动睡眠期，梦境更积极和可视。”

The desire to understand our dreams is as old as dreams themselves. In ancient times, many leaders saw immense significance in their content, using it to guide their decision-making. Religions have sought divine revelations in dreams. Freudian and Jungian psychoanalysts see dreams as an important window into the mind; the symbolic dream images that Carl Jung listed in the early 20th century are still used by practitioners today.

“解梦”的愿望与梦本身一样古老。在古代，很多领袖看到了梦境内容的巨大重要性，用它来指导决策。宗教一直在梦境中寻找圣贤的启示。心理分析学家弗洛伊德(Freudian)和荣格(Jungian)把梦视为思想的重要窗户；卡尔•荣格(Carl Jung)在20世纪初列出的象征性梦境图像仍然被当今的从业者使用。

At the other extreme, some researchers see dreaming as a meaningless “epiphenomenon” — an incidental byproduct of the neural information processing that takes place during sleep, particularly during the REM phases. In this view, dreams are no more useful than the waste heat emitted by a lightbulb whose sole purpose is to illuminate.

在另一个极端，一些研究人员把做梦视为毫无意义的“附带现象”，是在睡眠期间（特别是在快速眼动睡眠期）发生的神经信息处理的意外副产品。根据这种观点，梦与灯泡发光时发出的热量一样毫无用处，灯泡的唯一功用是发光。

But most sleep scientists believe that the emotions and narratives conjured up in our dreams do have a function beyond the neural data-­processing that produces them. “There are good sets of evidence to support two functional benefits of dreaming,” says Walker. “One is problem solving and creativity. The other is emotional therapy.”

但多数睡眠科学家认为，梦中出现的情绪和叙事确实具备一种在产生这些情绪的神经数据处理以外的功能。“有很多证据支持梦的两个功能性好处，”加州大学伯克利分校的沃克表示，“一个是解决问题和创造性。另一个是情绪治疗。”

One type of experiment, pioneered by Harvard University, sets volunteers a difficult problem, such as solving a virtual-reality puzzle, and then lets them sleep before tackling it. Participants who report dreams related to the puzzle achieve better results than those who do not. There is also evidence that dreaming helps people to resolve painful emotional experiences.

哈佛大学(Harvard University)首创的一类实验给志愿者提出一个难题，例如解决一个虚拟现实难题，然后让他们在解决问题前睡一觉。报告做梦与难题相关的参与者，取得了比没有做这种梦的人更好的结果。还有证据显示，做梦会帮助人们化解痛苦的情绪体验。

Each of us varies in how much of our dreams we remember on waking. But the benefits of dreams do not depend on our remembering them, says Russell Foster, neuroscience professor at Oxford. “I don’t think dreams are important in our conscious decision-making, because we forget so much of them,” he says. If the content of dreams was directly useful in waking life, the theory goes, evolution would have given us better memories for them.

我们每个人在醒来后对于梦的记忆量各有不同。但牛津大学的神经科学教授罗素•福斯特(Russell Foster)表示，梦的好处不取决于我们是否记得它们。他表示：“我不认为，梦在我们有意识的决策中会发挥重要作用，因为梦里的很多内容我们都忘记了。”按照这种理论，如果梦的内容对于醒着的生活直接有用的话，进化会让我们更好地记住梦。

There are many famous examples of literature, art, music and scientific ideas inspired by dreams, though some may have been embellished. Scholars, for example, have challenged the veracity of the best-known instance from science — the 19th-century chemist August Kekulé coming up with the ring structure of the compound benzene after dreaming of snakes swallowing their tails. Amid all the uncertainty, however, sleep researchers are confident of one thing, Foster says: “There are people who are utterly convinced that dreams can predict the future. But they have no predictive power at all.”

有很多著名的例子表明文学、艺术、音乐和科学理念是由梦带来灵感的，尽管其中一些可能有吹嘘成分。例如，学者们挑战了科学界最知名案例的真实性，19世纪化学家奥古斯特•凯库勒(August Kekulé)号称在梦到蛇吞下自己的尾巴后，提出了化学元素苯的环状结构。然而，在所有这些不确定性中，睡眠研究人员对一件事有把握。福斯特表示：“一些人完全相信，梦可以预测未来。但其实它们根本没有什么预测能力。”

Dreams may remain mysterious, but plausible answers are emerging about some of our multiple biological reasons for sleeping. The ancient origins of sleep lie in the circadian pattern of activity and rest that governs most forms of life on earth. The profound changes in light, temperature and food availability that take place over 24 hours led species to evolve features specialised for optimal performance under either diurnal or nocturnal conditions, but not both.

梦可能仍是一个谜，但对于睡眠的一些生理原因，可信的答案正在出现。睡眠的古老源头在于活动与休息的昼夜节奏模式，它控制着地球上的多数生命形式。24小时内出现的光照、温度和食物可获得性的深刻变化，让物种进化为两类：一类在日间表现最优，另一类在夜间表现最优。

As animals evolved to move around during the day, feeding and procreating, natural selection simultaneously favoured night-time inactivity to keep them out of the way of predators, pathogens and accidental injury. Conversely, nocturnal creatures developed an urge to rest out of harm’s way in daytime conditions. “Species are adapted to a particular temporal niche just as they are to a physical niche,” Foster says. “Activity at the wrong time often means death.”

随着动物进化为在白天四处活动、进食和生育，自然选择同时倾向于让它们在夜间不活动，以避免受到天敌、病原体和意外伤害的侵害。相反，夜行动物在进化过程中形成了在日间休息以避免吃亏的本能。“物种适应了特别的时间上的生态位，就像他们适应了物理上的生态位一样，”福斯特表示，“在错误的时间活动经常意味着死亡。”

Once a circadian cycle had been established, evolution drove further specialisation, so that essential biological housekeeping functions take place during the animal’s downtime, when the brain is not swamped with incoming sensory information and the body is not devoted to energy-intensive activity.

一旦形成了一个昼夜周期，进化就推动了进一步分工，使得基本的生物管家功能发生在动物的休息时段——这时大脑没有被输入的感官信息淹没，身体也没有投入到能量密集型活动。

All animals have a powerful drive to sleep, which eventually becomes irresistible. “This can be described mathematically as the interaction between two fundamental processes,” says Vyazovskiy. “One is sleep pressure, which builds up from the time you wake and then reduces as you sleep. The other is the circadian process, which keeps track of time and tells the brain when it should be awake.”

所有动物都有强大的睡眠驱动力，这种驱动力最终是不可抗拒的。“这在数学上可以被描述为两个基本过程之间的相互作用，”牛津大学的维亚佐夫斯基说，“一种是睡眠压力，它从你醒来的时候开始逐渐变大，然后在你睡觉的时候变小。另一个是昼夜节律过程，它能记录时间，并告诉大脑什么时候应该醒来。”

The verified record for staying awake without stimulants is held by Randy Gardner, a Californian high-school student who fended off sleep for just over 11 days in 1964, closely monitored by scientists. Such an experiment would be regarded as unethical today, because of the known risk to health of extreme sleep deprivation.

得到证实的无刺激情况下清醒时间纪录保持者是加州高中生兰迪•加德纳(Randy Gardner)——1964年，在科学家们的密切监测下，他在11天多一点时间里没有睡眠。此类实验在今天将被认为是不道德的，因为极度缺乏睡眠具有已知的健康风险。

Two very different housekeeping functions are known to operate in the sleeping brain. The more prosaic — discovered in 2012 at the University of Rochester in the US — is a waste-disposal mechanism that clears the brain of toxic proteins and other cellular rubbish arising from cerebral activity. The glymphatic system, as it is known, pumps cerebrospinal fluid through the brain and flushes waste back into the body’s main circulatory system, which takes it into the liver for eventual disposal.

目前已经知道的是，两种不同的管家功能在睡眠中的大脑运行。比较平常的一种功能——这是2012年由美国罗彻斯特大学(University of Rochester)发现的——是一种排毒机制，它能清除大脑活动中产生的有毒蛋白质和其他细胞垃圾。脑部类淋巴系统(glymphatic system)把脑脊液泵入大脑，然后将废物冲刷回人体的主要循环系统，由其把废物送入肝脏进行最终处理。

Brain cells called glia contract by as much as 60 per cent during sleep, leaving more space between them for the cerebrospinal fluid to wash through. Walker invites us to “think of the buildings of a large city physically shrinking at night, allowing municipal cleaning crews easy access to pick up garbage strewn in the streets, followed by a good pressure-jet treatment of every nook and cranny”.

在睡眠过程中，被称为神经胶质(glia)的大脑细胞体积收缩至多60%，在彼此间留下更大空间，让脑脊液畅通无阻地冲刷而过。沃克邀请我们“想象一个大城市里的建筑物在夜间体积会缩小，让市政清洁人员很容易收集散落在街道上的垃圾，然后对每个角落和缝隙进行一次彻底的高压喷水冲洗”。

The existence of the glymphatic system may help to explain the observation that inadequate sleep increases the risk of suffering Alzheimer’s disease, Walker says. It gives less time for toxic molecules involved in the disease, such as amyloid and tau proteins, to be cleared from the brain.

沃克表示，脑部类淋巴系统的存在，可能有助于解释为什么睡眠不足会增加患阿尔兹海默症(Alzheimer’s disease)的风险。睡眠不足意味着，可从大脑中排走与这种疾病相关的有毒分子（例如淀粉样蛋白和Tau蛋白）的时间较短。

Another key operation that takes place during sleep is information-processing and memory consolidation — neural activity whose details remain elusive despite many years of scientific study. The two broad categories of sleep that roll through the brain in slow waves during the night, REM and non-REM, both play a role in a complex data-processing dance.

睡眠时运行的另一项关键功能是信息处理和记忆巩固——尽管经过了多年科学研究，但这种神经活动的具体机制仍然难以捉摸。在夜间以慢波形式发生在大脑中的两大类睡眠——快速眼动睡眠期和非快速眼动睡眠期——都在复杂的数据处理“舞蹈”中发挥作用。

A good example of the theories being put forward to make sense of the emerging evidence was published this month by Penny Lewis, a psychology professor at Cardiff University, with international colleagues in the journal Trends in Cognitive Sciences. Their model proposes that the brain organises information into a useful framework during non-REM sleep, while REM helps us to see beyond that framework and make unexpected connections between memories.

最近，卡迪夫大学(Cardiff University)心理学教授佩妮•刘易斯(Penny Lewis)跟国际同僚在《认知科学趋势》(Trends in Cognitive Sciences)期刊上发表论文，提出了解释最新证据的理论。他们的模型提出，在非快速眼动睡眠期间，大脑将信息组织到一个有用的框架，而快速眼动睡眠帮助我们超越这个框架，在记忆之间建立起意想不到的联系。

In non-REM sleep, memories captured by the brain’s hippocampus are replayed there and in the cortex. As we detect similarities between them, the information is laid down in the cortex within a framework based on thematic links. During REM, the cortex is no longer synchronised with the hippocampus and is free to replay the stored information in different combinations. This is facilitated by special brain waves that appear to activate areas of the cortex almost randomly.

在非快速眼动睡眠期间，被大脑海马体捕获的记忆在那里和大脑皮层中重放。当我们检测到它们之间的相似性时，信息就会按照一个基于主题链接的框架被放置在大脑皮层中。在快速眼动睡眠期间，大脑皮层不再与海马体同步，而是可以自由地以不同组合形式重放所储存信息。这是由特殊的脑电波所促成的，这些脑电波似乎在近乎随机地激活大脑皮层的各个区域。

To illustrate the idea, Lewis gives an example similar to Kekulé’s benzene dream. In 1911, the physicist Ernest Rutherford proposed a structure for atoms, with tiny electrons in orbit around a relatively large nucleus, which was based on planets orbiting the sun. According to Lewis’s theory, Rutherford might have replayed his recent thinking about atoms during REM sleep along with a randomly activated memory of the solar system, enabling him to make a mental connection between them. Unlike Kekulé, he need not have remembered a dream to make the connection.

为了说明这个想法，刘易斯举了一个类似凯库勒的苯梦的例子。1911年，物理学家欧内斯特•卢瑟福(Ernest Rutherford)提出了一种原子结构：像行星围绕太阳转动那样，微小的电子在轨道上围绕着一个相对较大的原子核转动。根据刘易斯的理论，也许是在快速眼动睡眠期，卢瑟福重放了他对原子的思考，以及有关太阳系的随机记忆，这使他能够在两者之间建立起心理联系。跟凯库勒不同的是，他不需要记住一个梦境来建立联系。

But Lewis admits: “We have been very careful not to talk about dreaming in our paper. Indeed, I tend to stay away from dreaming, because it is hard to do scientific work on it.” Unfortunately for those eager to unlock the mysteries of their dreams, many neuroscientists and psychologists today agree.

但刘易斯承认：“我们在论文中一直非常小心，没有谈及做梦。事实上，我倾向于远离做梦，因为我们很难对做梦展开科学研究。”对于那些渴望解锁自己梦境秘密的人，遗憾的是，当今许多神经科学家和心理学家都同意这一观点。