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 motive force, its juice, would flow out to all the other parts of the body, animating ['ænɪmeɪt] them but leaving the brain all dried up, and he thought that when we sleep, all this moisture ['mɒɪstʃə] that filled the rest of the body would come rushing back, rehydrating[,riːhaɪ'dreɪt] the brain and refreshing 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 murky ['mɜːkɪ]. 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 [rɪ'stɒrətɪv] 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 margins that set it apart from all the other organs of the body
所以今天，我想给大家讲一些近期的研究，这些研究可能会揭示这些问题。 我们发现，睡眠实际上可能是对大脑的一些最基本的要求的一种简洁的解决方案， 是大脑满足身体高需求的一种独特的方式。 这种独特的方式将它与我们身体其他器官区分开来。
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 nutrients 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 nutrient delivery problem by sending blood vessels to supply nutrients and oxygen to every corner of our body.
对大脑来说，这是至关重要的， 它巨大的脑电波活动用尽了身体整个能量供应的四分之一，但大脑仅占据了 人体重量的百分之二。所以这个循环系统通过血管的传输，将营养和氧气送到身体的每一个角落，解决我们身体所需的营养供应。
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 clearance of that waste is the second basic problem that each organ has to solve.
This diagram shows the body's lymphatic [lɪm'fætɪk] 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 zoom 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 efficiently 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 mundane['mʌndeɪn; mʌn'deɪn] 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.
那么，大脑是怎样清理垃圾的呢？ 那么，这个看上去普通的问题就是我们团队最初做这个项目的原因。 我们发现， 当我们深入到大脑中， 一直深入到神经元和血管， 去寻找大脑解决垃圾清理问题的机制时，得到的结果出乎我们的意料。我们发现的东西很特别，又很美丽。 我来说说我们发现的东西。
So the brain has this large pool of clean, clear fluid called cerebrospinal [,serɪbrə(ʊ)'spaɪn(ə)l]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.
我们的大脑有一个区域，里面装满了 干净透明的液体，那种液体叫做脑脊液，我们简称CSF。CSF填充了大脑周围的空间，来自大脑中的废物从大脑中出来，到达CSF中 ，CSF和废物一起卸下，进入血液。
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 percolate ['pɜːkəleɪt] their way randomly out to these pools of CSF. Instead, there is a specialized network of plumbing that organizes and facilitates this process.
照这样，听起来这就像一个 淋巴系统，不是吗？ 但有趣的是，从大脑中出来的液体和废物，它们不是随意地渗透到 CSF的区域中。相反，有一个专门的管道网络，来组织和促进这个过程。
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 helping to clear away, to clean the waste from the spaces between the brain's cells.
那么，让我们吃惊的是大脑外面的液体（脑脊液） 它们不在外面呆着。相反，CSF（脑脊液）沿着血管外壁，流回 大脑中，并且在它沿着这些血管 流向大脑的同时， 它还要忙着将废物从这些脑细胞的间隙中带走。
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 rigid skull [skʌl] 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 entirely 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.
但是，刚刚我所讲的这一切当中，最最让我们感到惊奇的是，大脑中所有这些液体的工作状态， 只出现在睡眠时的大脑中！ 看，左边的这个视频显示了在一只醒着的老鼠的大脑，有多少脑脊液在流动呢？—— 几乎没有。
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.
然后，在大脑要睡觉时，它不必那样紧张工作， 大脑就切换到了“清理模式”， 开始清理 脑细胞间隙之间已经积累了一天的废物。 所以这有点像我，或者你， 我们在工作日工作的时候没有时间做家务，于是将家务推迟了。等周末到了，我们就会把所有要做的家务都做好。
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 ['æmɪlɒɪd], 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.
到现在，我们已经说了很多关于废物清理的事，但是我还没有具体介绍废物的种类，那些为了保持我们健康， 大脑必须要清理的废物的种类。 近期的研究关注最多的废物是淀粉样β蛋白，这是一种大脑始终会产生的蛋白质。就在此刻，我的大脑就正在产生淀粉样β蛋白，你的也是。
But in patients with Alzheimer's [ˈaltshaɪmə] disease, amyloid-beta builds up and aggregates 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 versus when it's asleep, and we found that indeed, the clearance of amyloid-beta is much more rapid from the sleeping brain.
但是患有老年痴呆症的人，在他们脑细胞的间隙中淀粉样β蛋白生成、聚集，不能被及时清除。 淀粉样β蛋白的累积是形成这种疾病的关键。 所以我们测量了在清醒状态下和沉睡时大脑清理淀粉样β蛋白的速度，并进行对比。 我们发现，处于睡眠中的大脑淀粉样β蛋白的清除速率更快。
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.
那么，如果睡眠是大脑进行废物清理的 关键步骤， 那么这就会奇迹般地改变我们 对睡眠、淀粉样β蛋白和老年痴呆症的认识。 一系列临床试验证明，在那些老年痴呆症还不是很严重的患者中， 睡眠质量和时间的恶化是与大脑中淀粉样β蛋白的的集聚有着很大的关系的。
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.
然而，值得指出的是，这些研究没有证实睡眠的缺乏或者低质量的睡眠会引起老年痴呆症； 但明确指出如果大脑，不及时清理废物（如淀粉样β蛋白） 来维持它自身的清洁， 很可能会促进像老年痴呆症这样的病症的恶化。
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 machinery of the brain is quietly hard at work cleaning and maintaining this unimaginably complex machine.
那么，这个新的研究告诉我们， 也就是我现在要告诉你们每个人的。现在我们都知道， 即使伽林也都知道，关于睡眠最重要的一点大概就是睡觉会使我们的思维变得清醒。 那么，我们每晚都在睡觉， 但是我们的大脑却从未休息过。 虽然我们的身体看起来不动了， 但是我们的思维却在到处梦游。 大脑的这些组织 始终在辛苦地工作，来保持这个极其复杂的“机器” 的清洁。
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 embarrassment 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. (Applause)
但是如果换作大脑，拖延“不做家务”的后果将会比我们不清理厨房台面的后果要严重得多。 那是因为，对于大脑来说，不及时清理垃圾会危及我们思维、身体健康和功能。 今天我们大脑所做的这些基础的、家务一般的苦差事，可能对防治疗明天的精神疾病具有重要的意义。谢谢你们！