中英逐字稿：
00:04
睡眠 用掉我們生命整整 1/3 的時間。 但是有誰真正了解睡眠呢？
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?
00:12
兩千年前，蓋倫， 古代數一數二的醫學專家， 認為我們醒著的時候 大腦的動力—腦汁， 會流出腦外，流到全身各部位 活絡全身， 但是讓大腦枯竭。 蓋倫認為當我們睡著， 身體的汁液 會流灌回大腦， 重新濕潤大腦， 使大腦甦活。 現在我們覺得這個看法很荒唐， 但蓋倫只是想解釋睡眠現象， 是我們每天都在面對的。 我們憑經驗都知道 睡眠會清理我們的頭腦。 不睡覺， 頭腦會變得昏昏沉沉。 我們現在雖然更認識睡眠， 比蓋倫的時代更了解， 但是我們還是搞不懂 為什麼所有人體活動中， 睡眠獨具這種奇妙的修復大腦功能。
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 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 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. 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.
01:10
所以今天我要分享最新研究 提供的可能答案。 我們發現，睡眠可能是 一種精密的設計， 用來滿足大腦某些最基本的需求。 大腦用這種獨特的方式 來應付本身的高度需求和不容差錯， 這些特性使大腦和其他器官截然不同。
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.
01:33
我們觀察到的幾乎所有生物現象 都可以看成是一連串的問題 和相對的解決方法。 而所有器官都必須解決的頭號問題是 如何源源不絕的供應營養素 以提供身體細胞所需。 對大腦而言，這更是至關重要。 大腦密集強烈的電子活動 耗用全身能量的 1/4， 雖然大腦只占 全身質量的 2%。 循環系統 負責解決輸送營養的問題， 利用血管傳送營養素和氧氣 到全身每一個部位。
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.
02:11
你可以從這個影片看到 這是一隻活體老鼠的大腦血管影像。 這些血管形成複雜的網絡 充滿整個大腦， 從大腦的表層 一直深入到組織本身。 隨著血管延伸，供應營養素和氧氣 給大腦裡面每一個細胞。
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.
02:36
接著， 就像每個細胞都需要養分才能生存， 所有細胞也都會產生副產品—廢物。 要怎麼清理這些廢物 是每個器官都要解決的第二個問題。 這是人體的淋巴系統。 經過演化，現在負責清除身體的廢物。 淋巴系統是第二套循環系統， 網絡遍佈全身。 它會帶走細胞之間的蛋白質和其他廢物， 收集起來，排到血液裡， 藉此把廢物清除。
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 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.
03:10
可是如果你仔細看這張圖， 會發現很奇怪的地方。 我們如果把頭部放大來看， 你會發現 大腦裡面沒有淋巴管。 但是這樣不合理，對吧？ 大腦明明是非常活躍的器官， 每天製造非常大量的廢物， 必須有效地清除。 可是大腦卻沒有淋巴管， 這表示身體其他器官清理廢物的方法 並不適用於大腦。
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.
03:45
那麼，大腦究竟要怎麼解決 廢物清理的問題？ 這個看似很普通的問題 引發我們團隊開始深入研究。 我們發現， 當我們探進大腦的深層， 來到神經元和血管之間， 我們發現大腦清理廢物的方法 超乎我們的想像。 實在太天才了， 也非常美。 我來說明一下。
So how, then, does the brain solve its waste clearance problem? Well, that seemingly mundane 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.
04:18
大腦有一個很大的「水池」， 裡面充滿乾淨、透明的液體， 叫做「腦脊髓液」， 簡稱 CSF。 腦脊髓液充滿大腦周圍的空間， 廢物會從大腦裡面 排出到腦脊髓液， 然後跟著腦脊髓液一起流到血液裡。 原理聽起來有點像淋巴系統，對吧？ 但是特別的是， 大腦裡面的液體和廢物 並不是隨便滲透到腦脊髓液裡， 而是有一個專門的「打水系統」 來指揮、促進這個過程。 你可以從這些影片裡看到 這些也是活體老鼠大腦的影像。 左邊是大腦表層的活動， 右邊是大腦表層下面 組織裡面的活動。 我們把血管標成紅色， 大腦周圍的腦脊髓液會標綠色。 我們很驚訝地發現， 大腦周圍的腦脊髓液 沒有留在外面， 而是被打回大腦裡面，穿透進去， 發生在沿著血管外緣的地方。 當血管旁邊的腦脊髓液，沖進大腦裡， 其實是在幫忙清除 腦細胞間的空隙裡的廢物。 你仔細想，就會知道 像這樣利用血管外緣 是很聰明的設計。 因為大腦是包在堅硬的腦殼裡， 裡面裝滿了腦細胞， 沒辦法再塞進一整組 像淋巴系統那樣的管路。 而腦中的血管 從大腦的表面 一直擴散深入，到最裡面的每一個細胞。 這表示 這些沿著血管外緣跑的液體， 可以很容易跟著進到整顆大腦。 所以，就是透過這個聰明的設計 叫大腦血管多做一件事， 負責淋巴管該做的工作，取而代之， 這樣就不需要淋巴管了。 最奇妙的是， 身體其他器官，都沒有用這種方式 清除細胞之間的廢物。 這是大腦特有的方法。
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 percolate their way randomly out to these pools of CSF. Instead, there is a specialized network of plumbing 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 helping 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 rigid skull 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.
06:49
我們最驚人的發現是， 大腦這整個設計， 我剛才講的所有過程， 這些腦脊髓液滲透大腦 只發生在我們睡著的時候。 左邊的影片 可以看出有多少腦脊髓液流進大腦， 這是活體老鼠醒著時候的大腦。 幾乎沒有滲透。 但是同樣這隻老鼠， 如果我們等一下，等牠睡著， 就會看到腦脊髓液 大量湧進腦裡。 我們也發現 大腦睡著的同時， 腦細胞似乎會縮小， 使細胞之間的空隙變大， 開路讓液體流過 把廢物帶走。
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.
07:37
這麼說， 蓋倫很可能看出一些端倪， 他說腦汁會在人睡著時 沖進大腦。 我們的研究在蓋倫兩千年以後 發現， 大腦醒著 而且最忙的時候， 會把清理工作暫時擱著， 暫時先不管細胞間囤積的廢物。 等我們睡著了， 大腦比較沒那麼忙， 就會啟動清除模式 開始倒垃圾， 打掃細胞之間的空間， 清除堆積了一整天的廢物。 所以其實有點像你跟我 週間不打掃家裡， 因為太忙沒時間打掃。 堆積如山後，再來個大掃除， 利用週末打掃乾淨。
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.
08:27
我剛講了很多廢物清除， 但是還沒有說明 大腦要利用睡眠時，清除哪些廢物， 才能維繫健康。 近期研究關注的大腦廢物 是乙型澱粉樣蛋白。 這是大腦中不斷產生的一種蛋白質。 我的大腦正在產生乙型澱粉樣蛋白， 你的大腦也是。 但是阿茲海默症的病患， 乙型澱粉樣蛋白會不斷增加、聚集， 囤積在大腦細胞之間的空隙， 無法正常清除。 這種乙型澱粉樣蛋白的累積 被認為是發展阿茲海默症的 關鍵步驟之一。 於是我們測量大腦清除它的速度， 比較大腦清醒和睡著兩種狀況。 我們發現，果然， 乙型澱粉樣蛋白的清除， 在大腦睡覺時，比清醒時快很多。
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 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.
09:21
所以，睡眠就是 大腦用來清除廢物的方法。 那麼，這可能大大改變我們如何看待 睡眠、乙型澱粉樣蛋白， 和阿茲海默症的關係。 一連串的近期臨床研究指出， 未罹患阿茲海默症的病人當中， 睡眠品質變差，或者睡眠時間變少 都跟腦中囤積大量 乙型澱粉樣蛋白相關。 雖然我必須提醒大家， 這些研究並沒有證明 睡眠不足或不良會導致阿茲海默症， 但確實有發現， 大腦如果不能保持清潔、 清除乙型澱粉樣蛋白等各種廢物， 可能導致像阿茲海默症這樣的疾病。
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.
10:10
所以，這項新研究告訴我們的， 也就是各位都已經知道的 睡眠的作用。 連蓋倫都有發現的， 就是睡眠會更新、清理大腦這件事， 可能就是我們為什麼要睡覺的主因。 你跟我，我們每天晚上睡覺。 可是我們的大腦 從來不休息。 我們的身體躺著不動， 思緒飄去神遊夢境時， 大腦的精密儀器悄悄地努力工作 清潔、維修 這部複雜到難以想像的機器。 這就像清掃家裡一樣， 是份骯髒又沒人感激你的工作， 但是卻非常重要。 在你家，如果一個月不清掃廚房， 很快就會髒亂得住不下去。 但是在大腦裡， 積垢不除的後果 可能遠超過流理台骯髒的尷尬。 因為大腦的清潔 攸關全身、心的健康和功能。 這是為什麼現在了解 大腦的這些基本清潔排毒功能， 可能攸關未來精神疾病的預防與治療。
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. 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.
11:28
謝謝！ （觀眾掌聲）
Thank you.(Applause)
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