【英语语言学习】睡眠与健康

Sleep. It's something we spend about a third of our lives doing, but do any of us really understand what it's all about?

Two thousand years ago, Galen, one of the most prominent medical researchers of the ancient world, proposed that while we're awake, our brain's motive¹ force, its juice, would flow out to all the other parts of the body, animating² them but leaving the brain all dried up, and he thought that when we sleep, all this moisture that filled the rest of the body would come rushing back, rehydrating the brain and refreshing³ the mind. Now, that sounds completely ridiculous to us now, but Galen was simply trying to explain something about sleep that we all deal with every day. See, we all know based on our own experience that when you sleep, it clears your mind, and when you don't sleep, it leaves your mind murky⁴. But while we know a great deal more about sleep now than when Galen was around, we still haven't understood why it is that sleep, of all of our activities, has this incredible restorative function for the mind.

So today I want to tell you about some recent research that may shed new light on this question. We've found that sleep may actually be a kind of elegant design solution to some of the brain's most basic needs, a unique way that the brain meets the high demands and the narrow margins⁵ that set it apart from all the other organs of the body.

So almost all the biology that we observe can be thought of as a series of problems and their corresponding solutions, and the first problem that every organ must solve is a continuous supply of nutrients⁷ to fuel all those cells of the body. In the brain, that is especially critical; its intense electrical activity uses up a quarter of the body's entire energy supply, even though the brain accounts for only about two percent of the body's mass. So the circulatory system solves the nutrient⁶ delivery problem by sending blood vessels⁸ to supply nutrients and oxygen to every corner of our body.

You can actually see it in this video here. Here, we're imaging blood vessels in the brain of a living mouse. The blood vessels form a complex network that fills the entire brain volume. They start at the surface of the brain, and then they dive down into the tissue itself, and as they spread out, they supply nutrients and oxygen to each and every cell in the brain.

Now, just as every cell requires nutrients to fuel it, every cell also produces waste as a byproduct, and the clearance⁹ of that waste is the second basic problem that each organ has to solve. This diagram shows the body's lymphatic system, which has evolved to meet this need. It's a second parallel network of vessels that extends throughout the body. It takes up proteins and other waste from the spaces between the cells, it collects them, and then dumps them into the blood so they can be disposed of.

But if you look really closely at this diagram, you'll see something that doesn't make a lot of sense. So if we were to zoom¹⁰ into this guy's head, one of the things that you would see there is that there are no lymphatic vessels in the brain. But that doesn't make a lot of sense, does it? I mean, the brain is this intensely active organ that produces a correspondingly large amount of waste that must be efficiently¹¹ cleared. And yet, it lacks lymphatic vessels, which means that the approach that the rest of the body takes to clearing away its waste won't work in the brain.

So how, then, does the brain solve its waste clearance problem? Well, that seemingly mundane¹² question is where our group first jumped into this story, and what we found as we dove down into the brain, down among the neurons and the blood vessels, was that the brain's solution to the problem of waste clearance, it was really unexpected. It was ingenious, but it was also beautiful. Let me tell you about what we found.

So the brain has this large pool of clean, clear fluid called cerebrospinal fluid. We call it the CSF. The CSF fills the space that surrounds the brain, and wastes from inside the brain make their way out to the CSF, which gets dumped, along with the waste, into the blood. So in that way, it sounds a lot like the lymphatic system, doesn't it? But what's interesting is that the fluid and the waste from inside the brain, they don't just percolate¹³ their way randomly¹⁴ out to these pools of CSF. Instead, there is a specialized¹⁵ network of plumbing¹⁶ that organizes and facilitates this process. You can see that in these videos. Here, we're again imaging into the brain of living mice. The frame on your left shows what's happening at the brain's surface, and the frame on your right shows what's happening down below the surface of the brain within the tissue itself. We've labeled the blood vessels in red, and the CSF that's surrounding the brain will be in green. Now, what was surprising to us was that the fluid on the outside of the brain, it didn't stay on the outside. Instead, the CSF was pumped back into and through the brain along the outsides of the blood vessels, and as it flushed down into the brain along the outsides of these vessels, it was actually helping¹⁷ to clear away, to clean the waste from the spaces between the brain's cells.

If you think about it, using the outsides of these blood vessels like this is a really clever design solution, because the brain is enclosed in a rigid¹⁸ skull¹⁹ and it's packed full of cells, so there is no extra space inside it for a whole second set of vessels like the lymphatic system. Yet the blood vessels, they extend from the surface of the brain down to reach every single cell in the brain, which means that fluid that's traveling along the outsides of these vessels can gain easy access to the entire brain's volume, so it's actually this really clever way to repurpose one set of vessels, the blood vessels, to take over and replace the function of a second set of vessels, the lymphatic vessels, to make it so you don't need them. And what's amazing is that no other organ takes quite this approach to clearing away the waste from between its cells. This is a solution that is entirely²⁰ unique to the brain.

But our most surprising finding was that all of this, everything I just told you about, with all this fluid rushing through the brain, it's only happening in the sleeping brain. Here, the video on the left shows how much of the CSF is moving through the brain of a living mouse while it's awake. It's almost nothing. Yet in the same animal, if we wait just a little while until it's gone to sleep, what we see is that the CSF is rushing through the brain, and we discovered that at the same time when the brain goes to sleep, the brain cells themselves seem to shrink, opening up spaces in between them, allowing fluid to rush through and allowing waste to be cleared out.

So it seems that Galen may actually have been sort of on the right track when he wrote about fluid rushing through the brain when sleep came on. Our own research, now it's 2,000 years later, suggests that what's happening is that when the brain is awake and is at its most busy, it puts off clearing away the waste from the spaces between its cells until later, and then, when it goes to sleep and doesn't have to be as busy, it shifts into a kind of cleaning mode to clear away the waste from the spaces between its cells, the waste that's accumulated throughout the day. So it's actually a little bit like how you or I, we put off our household chores during the work week when we don't have time to get to it, and then we play catch up on all the cleaning that we have to do when the weekend rolls around.

Now, I've just talked a lot about waste clearance, but I haven't been very specific about the kinds of waste that the brain needs to be clearing during sleep in order to stay healthy. The waste product that these recent studies focused most on is amyloid-beta, which is a protein that's made in the brain all the time. My brain's making amyloid-beta right now, and so is yours. But in patients with Alzheimer's disease, amyloid-beta builds up and aggregates²¹ in the spaces between the brain's cells, instead of being cleared away like it's supposed to be, and it's this buildup of amyloid-beta that's thought to be one of the key steps in the development of that terrible disease. So we measured how fast amyloid-beta is cleared from the brain when it's awake versus²² when it's asleep, and we found that indeed, the clearance of amyloid-beta is much more rapid from the sleeping brain.

So if sleep, then, is part of the brain's solution to the problem of waste clearance, then this may dramatically change how we think about the relationship between sleep, amyloid-beta, and Alzheimer's disease. A series of recent clinical studies suggest that among patients who haven't yet developed Alzheimer's disease, worsening sleep quality and sleep duration are associated with a greater amount of amyloid-beta building up in the brain, and while it's important to point out that these studies don't prove that lack of sleep or poor sleep cause Alzheimer's disease, they do suggest that the failure of the brain to keep its house clean by clearing away waste like amyloid-beta may contribute to the development of conditions like Alzheimer's.

So what this new research tells us, then, is that the one thing that all of you already knew about sleep, that even Galen understood about sleep, that it refreshes and clears the mind, may actually be a big part of what sleep is all about. See, you and I, we go to sleep every single night, but our brains, they never rest. While our body is still and our mind is off walking in dreams somewhere, the elegant machinery²³ of the brain is quietly hard at work cleaning and maintaining this unimaginably complex machine.

Like our housework, it's a dirty and a thankless job, but it's also important. In your house, if you stop cleaning your kitchen for a month, your home will become completely unlivable very quickly. But in the brain, the consequences of falling behind may be much greater than the embarrassment²⁴ of dirty countertops, because when it comes to cleaning the brain, it is the very health and function of the mind and the body that's at stake, which is why understanding these very basic housekeeping functions of the brain today may be critical for preventing and treating diseases of the mind tomorrow.

Thank you.

1 motive   

n.动机，目的；adv.发动的，运动的

参考例句：

• The police could not find a motive for the murder.警察不能找到谋杀的动机。
• He had some motive in telling this fable.他讲这寓言故事是有用意的。

2 animating   

v.使有生气( animate的现在分词 )；驱动；使栩栩如生地动作；赋予…以生命

参考例句：

• Nature has her animating spirit as well as man who is nature's child. 大自然就象它的孩子――人类一样，有活生生的灵魂。 来自辞典例句
• They were doubtlessly the animating principle of many hours that superficially seemed vacant. 在表面看来无所事事的许多时刻中，它们无疑是活跃的因素。 来自辞典例句

3 refreshing   

adj.使精神振作的，使人清爽的，使人喜欢的

参考例句：

• I find it'so refreshing to work with young people in this department.我发现和这一部门的青年一起工作令人精神振奋。
• The water was cold and wonderfully refreshing.水很涼，特别解乏提神。

4 murky   

adj.黑暗的，朦胧的；adv.阴暗地，混浊地；n.阴暗；昏暗

参考例句：

• She threw it into the river's murky depths.她把它扔进了混浊的河水深处。
• She had a decidedly murky past.她的历史背景令人捉摸不透。

5 margins   

边( margin的名词复数 )； 利润； 页边空白； 差数

参考例句：

• They have always had to make do with relatively small profit margins. 他们不得不经常设法应付较少的利润额。
• To create more space between the navigation items, add left and right margins to the links. 在每个项目间留更多的空隙，加左或者右的margins来定义链接。

6 nutrient   

adj.营养的，滋养的；n.营养物，营养品

参考例句：

• Magnesium is the nutrient element in plant growth.镁是植物生长的营养要素。
• The roots transmit moisture and nutrient to the trunk and branches.根将水分和养料输送到干和枝。

7 nutrients   

n.（食品或化学品）营养物，营养品( nutrient的名词复数 )

参考例句：

• a lack of essential nutrients 基本营养的缺乏
• Nutrients are absorbed into the bloodstream. 营养素被吸收进血液。 来自《简明英汉词典》

8 vessels   

n.血管( vessel的名词复数 )；船；容器；（具有特殊品质或接受特殊品质的）人

参考例句：

• The river is navigable by vessels of up to 90 tons. 90 吨以下的船只可以从这条河通过。 来自《简明英汉词典》
• All modern vessels of any size are fitted with radar installations. 所有现代化船只都有雷达装置。 来自《现代汉英综合大词典》

9 clearance   

n.净空；许可(证)；清算；清除，清理

参考例句：

• There was a clearance of only ten centimetres between the two walls.两堵墙之间只有十厘米的空隙。
• The ship sailed as soon as it got clearance. 那艘船一办好离港手续立刻启航了。

10 zoom   

n.急速上升；v.突然扩大，急速上升

参考例句：

• The airplane's zoom carried it above the clouds.飞机的陡直上升使它飞到云层之上。
• I live near an airport and the zoom of passing planes can be heard night and day.我住在一个飞机场附近，昼夜都能听到飞机飞过的嗡嗡声。

11 efficiently   

adv.高效率地，有能力地

参考例句：

• The worker oils the machine to operate it more efficiently.工人给机器上油以使机器运转更有效。
• Local authorities have to learn to allocate resources efficiently.地方政府必须学会有效地分配资源。

12 mundane   

adj.平凡的；尘世的；宇宙的

参考例句：

• I hope I can get an interesting job and not something mundane.我希望我可以得到的是一份有趣的工作，而不是一份平凡无奇的。
• I find it humorous sometimes that even the most mundane occurrences can have an impact on our awareness.我发现生活有时挺诙谐的，即使是最平凡的事情也能影响我们的感知。

13 percolate   

v.过滤，渗透

参考例句：

• The rain will percolate through the soil.雨水渗入土中。
• New fashions took a long time to percolate down.新时尚要很长时间才能在大众中流行起来。

14 randomly   

adv.随便地，未加计划地

参考例句：

• Within the hot gas chamber, molecules are moving randomly in all directions. 在灼热的气体燃烧室内，分子在各个方向上作无规运动。 来自辞典例句
• Transformed cells are loosely attached, rounded and randomly oriented. 转化细胞则不大贴壁、圆缩并呈杂乱分布。 来自辞典例句

15 specialized   

adj.专门的，专业化的

参考例句：

• There are many specialized agencies in the United Nations.联合国有许多专门机构。
• These tools are very specialized.这些是专用工具。

16 plumbing   

n.水管装置；水暖工的工作；管道工程v.用铅锤测量（plumb的现在分词）；探究

参考例句：

• She spent her life plumbing the mysteries of the human psyche. 她毕生探索人类心灵的奥秘。
• They're going to have to put in new plumbing. 他们将需要安装新的水管。 来自《简明英汉词典》

17 helping   

n.食物的一份&adj.帮助人的，辅助的

参考例句：

• The poor children regularly pony up for a second helping of my hamburger. 那些可怜的孩子们总是要求我把我的汉堡包再给他们一份。
• By doing this, they may at times be helping to restore competition. 这样一来, 他在某些时候,有助于竞争的加强。

18 rigid   

adj.严格的，死板的；刚硬的，僵硬的

参考例句：

• She became as rigid as adamant.她变得如顽石般的固执。
• The examination was so rigid that nearly all aspirants were ruled out.考试很严，几乎所有的考生都被淘汰了。

19 skull   

n.头骨；颅骨

参考例句：

• The skull bones fuse between the ages of fifteen and twenty-five.头骨在15至25岁之间长合。
• He fell out of the window and cracked his skull.他从窗子摔了出去，跌裂了颅骨。

20 entirely   

ad.全部地，完整地；完全地，彻底地

参考例句：

• The fire was entirely caused by their neglect of duty. 那场火灾完全是由于他们失职而引起的。
• His life was entirely given up to the educational work. 他的一生统统献给了教育工作。

21 aggregates   

数( aggregate的名词复数 )； 总计； 骨料； 集料（可成混凝土或修路等用的）

参考例句：

• Snowflakes are loose aggregates of ice crystals. 雪花是冰晶的松散凝结。
• Our airplanes based in Europe should be included in the aggregates. 我们驻欧飞机应包括在总数内。

22 versus   

prep.以…为对手，对；与…相比之下

参考例句：

• The big match tonight is England versus Spain.今晚的大赛是英格兰对西班牙。
• The most exciting game was Harvard versus Yale.最富紧张刺激的球赛是哈佛队对耶鲁队。

23 machinery   

n.(总称)机械，机器；机构

参考例句：

• Has the machinery been put up ready for the broadcast?广播器材安装完毕了吗？
• Machinery ought to be well maintained all the time.机器应该随时注意维护。

24 embarrassment   

n.尴尬；使人为难的人(事物)；障碍；窘迫

参考例句：

• She could have died away with embarrassment.她窘迫得要死。
• Coughing at a concert can be a real embarrassment.在音乐会上咳嗽真会使人难堪。