but do any of us really understand what it's all about?

但有人知道睡眠到底對我們有什麼幫助嗎？

Two thousand years ago, Galen, one of the most prominent medical researchers of the ancient world,

兩千年前，世界醫學研究權威，Galen

proposed that while we're awake, our brain's motive force, its juice, would flow out to all the other parts of the body,

曾提出人類清醒時，頭腦的動力來源，腦汁，會擴散到全身各部位

animating them but leaving the brain all dried up,

讓全身活起來，只剩腦部沒有腦汁

and he thought that when we sleep, all this moisture that filled the rest of the body would come rushing back,

他還提出，人類睡覺時，分布全身的腦汁都會流回腦部

rehydrating the brain and refreshing the mind. Now, that sounds completely ridiculous to us now,

使腦部再次濕潤，提起精神。我們現在聽了會覺得非常荒謬

but Galen was simply trying to explain something about sleep that we all deal with every day.

但Galen只是在解釋我們每天都需要的睡眠

See, we all know based on our own experience that when you sleep, it clears your mind,

我們都知道睡覺可以消除疲累

and when you don't sleep, it leaves your mind murky.

但如果不睡覺，你的思緒就會不清楚

But while we know a great deal more about sleep now than when Galen was around,

但我們比Galen更了解睡眠時

we still haven't understood why it is that sleep, of all of our activities, has this incredible restorative function for the mind.

我們其實還搞不清楚人類為什麼需要睡眠，才能恢復體力，完成所有工作

So today I want to tell you about some recent research that may shed new light on this question.

今天，我想要告訴你有關這個問題的近期研究

We've found that sleep may actually be a kind of elegant design solution to some of the brain's most basic needs,

我們已經發現睡眠是提供腦部最基本需求的一種方法

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.

大腦用這種獨特的方式滿足需求，所以能在所有器官中鶴立雞群

So almost all the biology that we observe can be thought of as a series of problems and their corresponding solutions,

所以幾乎所有我們注意到的生物都有一系列的問題及解決方式

and the first problem that every organ must solve is a continuous supply of nutrients to fuel all those cells of the body.

而每個器官首要解決的問題就是持續供應所有細胞營養

In the brain, that is especially critical;

腦部是最重要的器官

its intense electrical activity uses up a quarter of the body's entire energy supply,

雖然腦部只佔全身百分之二的重量

even though the brain accounts for only about two percent of the body's mass.

但強烈的腦電活動卻耗用了全身四分之一的能量

So the circulatory system solves the nutrient delivery problem by sending blood vessels

所以循環系統利用血管解決了營養傳送的問題

to supply nutrients and oxygen to every corner of our body.

輸送養分和氧氣到全身各部位

You can actually see it in this video here. Here, we're imaging blood vessels in the brain of a living mouse.

你們可以從影片這裡看到，我們正在放一部老鼠頭腦裡面的血管影像

The blood vessels form a complex network that fills the entire brain volume.

血管築起一道複雜的網絡，以填滿整個腦部

They start at the surface of the brain, and then they dive down into the tissue itself,

他們從腦部表面著手，再迅速進入腦組織裡

and as they spread out, they supply nutrients and oxygen to each and every cell in the brain.

擴散的時候，他們會供應養分和氧氣給每一個腦細胞

Now, just as every cell requires nutrients to fuel it,

每個細胞需要足夠養分才能刺激成長

every cell also produces waste as a byproduct,

它們同時也會製造出副產品這種廢物

and the clearance of that waste is the second basic problem that each organ has to solve.

而如何清理廢物是每個器官都要解決的次要基本問題

This diagram shows the body's lymphatic system, which has evolved to meet this need.

這個圖表顯示了身體中的淋巴系統可以解決這個問題

It's a second parallel network of vessels that extends throughout the body.

淋巴系統是第二條貫穿全身的血管

It takes up proteins and other waste from the spaces between the cells,

它會吸收細胞間的蛋白質和其他廢物

it collects them, and then dumps them into the blood so they can be disposed of.

它先收集它們，再一起倒入血液中，把它們清除乾淨

But if you look really closely at this diagram, you'll see something that doesn't make a lot of sense.

但如果你再看清楚一點，你會發現那不合常理

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.

我們近看這個人的腦部，你會發現腦部根本沒有淋巴系統

But that doesn't make a lot of sense, does it?

那實在不合常理，對不對？

I mean, the brain is this intensely active organ that produces a correspondingly large amount of waste that must be efficiently cleared.

腦部是非常活躍的器官，它也會製造出大量需要被清除的廢物

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.

然而，腦部缺少了淋巴系統，就代表其他器官清除身體廢物的方式，不適用於腦部

So how, then, does the brain solve its waste clearance problem?

到底腦部如何解決廢物清理的問題呢？

Well, that seemingly mundane question is where our group first jumped into this story,

這看似稀鬆平常的問題是我們團隊著手的第一步

and what we found as we dove down into the brain, down among the neurons and the blood vessels,

我們研究腦部時，發現神經元和血管下面

was that the brain's solution to the problem of waste clearance, it was really unexpected.

就是腦部解決廢物清除問題的所在之處，我們完全沒想到會在這裡

It was ingenious, but it was also beautiful. Let me tell you about what we found.

它非常精緻，也非常漂亮，我告訴你們我們發現了什麼

So the brain has this large pool of clean, clear fluid called cerebrospinal fluid.

腦部有個大型廢物處理槽，它叫作腦脊液蛋白

We call it the CSF. The CSF fills the space that surrounds the brain,

我們簡稱為CSF，CSF包圍著大腦

and wastes from inside the brain make their way out to the CSF, which gets dumped, along with the waste, into the blood

腦中的廢物被送到CSF，然後廢物隨著CSF排入血液中

So in that way, it sounds a lot like the lymphatic system, doesn't it?

如此一來，它的功能就像淋巴系統一樣了，對吧？

But what's interesting is that the fluid and the waste from inside the brain,

但有趣的是，腦部的廢物和液體

they don't just percolate their way randomly out to these pools of CSF.

不會隨便被過濾到CSF中

Instead, there is a specialized network of plumbing that organizes and facilitates this process.

反而有特殊的配管網絡，有系統地處理這項程序

You can see that in these videos. Here, we're again imaging into the brain of living mice.

你可以從這些影像上看到，現在，我們再次觀看老鼠頭腦內的血管影像

The frame on your left shows what's happening at the brain's surface,

左畫面顯示的是腦部表面

and the frame on your right shows what's happening down below the surface of the brain within the tissue itself.

而右手邊的畫面，顯示了腦表面下的組織

We've labeled the blood vessels in red, and the CSF that's surrounding the brain will be in green.

我們把紅色當作血管，綠色當作腦部周圍的CSF

Now, what was surprising to us was that the fluid on the outside of the brain, it didn't stay on the outside.

現在，我們很驚訝腦部外面的液體竟然不在腦部外面

Instead, the CSF was pumped back into and through the brain along the outsides of the blood vessels,

CSF反而順著腦部外面的血管一起注入腦部

and as it flushed down into the brain along the outsides of these vessels,

而且它和腦部外面的血管一起被沖入腦部時

it was actually helping to clear away, to clean the waste from the spaces between the brain's cells.

確實能清理腦細胞間的廢物

If you think about it, using the outsides of these blood vessels like this is a really clever design solution,

你仔細想想，會覺得利用腦部外的血管確實是個清除廢物的好辦法

because the brain is enclosed in a rigid skull and it's packed full of cells,

因為腦部被堅硬的頭蓋骨蓋住，而且裡面有大量細胞

so there is no extra space inside it for a whole second set of vessels like the lymphatic system.

所以沒有空間放像淋巴系統這樣的血管

Yet the blood vessels, they extend from the surface of the brain down to reach every single cell in the brain,

然而，血管從腦部表面延伸到腦部裡面的每個細胞

which means that fluid that's traveling along the outsides of these vessels can gain easy access to the entire brain's volume,

那表示流動在血管外的液體可以更容易進入整個腦部

so it's actually this really clever way to repurpose one set of vessels,

所以它其實用一個非常聰明的方法，重複利用一副血管來清除腦部廢物

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.

來占據和取代淋巴系統的功能，所以你不需要淋巴系統

And what's amazing is that no other organ takes quite this approach to clearing away the waste from between its cells.

令人吃驚的是，沒有其他器官用這種方式來清除細胞間的廢物

This is a solution that is entirely unique to the brain.

這是腦部獨特的清理方式

But our most surprising finding was that all of this, everything I just told you about,

但我們發現最出乎意料的是我告訴你們的每件事

with all this fluid rushing through the brain, it's only happening in the sleeping brain.

有關液體流經腦部的事，都只發生在睡眠中的腦部

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.

這裡，左邊的影片顯示了當我們清醒時，有多少CSF像活老鼠一般流經腦部

It's almost nothing. Yet in the same animal, if we wait just a little while until it's gone to sleep,

答案是幾乎沒有，然而，同一種動物，如果等牠睡著

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,

我們會看到CSF流經腦部，同時我們會發現腦部休眠時

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.

腦細胞會不停地收縮，讓液體流經並清除廢物

So it seems that Galen may actually have been sort of on the right track

所以當Galen寫到睡覺時，液體會流經腦部

when he wrote about fluid rushing through the brain when sleep came on.

的想法可能是正確的

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,

我們的研究，現在已經是兩千年後了，提出了人類清醒時，腦部最忙碌的理論

it puts off clearing away the waste from the spaces between its cells until later,

它延後清除細胞間的廢物

and then, when it goes to sleep and doesn't have to be as busy,

之後，睡覺時，腦部就不會那麼忙碌了

it shifts into a kind of cleaning mode to clear away the waste from the spaces between its brain,

它轉變成在清除腦細胞間廢物

the waste that's accumulated throughout the day.

清除那些累積一整天的廢物

So it's actually a little bit like how you or I,

其實它有點像你我

we put off our household chores during the work week when we don't have time to get to it,

我們把家事拖到周末才做，因為平日我們沒有時間處理

and then we play catch up on all the cleaning that we have to do when the weekend rolls around.

周末時，我們才把所有打掃的進度都補上

Now, I've just talked a lot about waste clearance,

我已經說了那麼多有關清除廢物的事，

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.

但我還沒有詳細說明到底腦部的哪種廢物需要在睡覺時被清除，才能保持健康

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.

近期比較多學者研究澱粉樣蛋白，這種廢物一直都在腦中

My brain's making amyloid-beta right now, and so is yours.

現在，我的頭腦正在製造澱粉樣蛋白，你們的也是

But in patients with Alzheimer's disease, amyloid-beta builds up and aggregates in the spaces between the brain's cells,

但在阿茲海默病患的腦中，澱粉樣蛋白聚集在腦細胞間

instead of being cleared away like it's supposed to be,

而不是正常地被清除乾淨

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.

這種澱粉樣蛋白的累積被視為成為嚴重疾病的關鍵

So we measured how fast amyloid-beta is cleared from the brain when it's awake versus when it's asleep,

所以我們測試清醒時和睡眠時澱粉樣蛋白能多快被清除乾淨

and we found that indeed, the clearance of amyloid-beta is much more rapid from the sleeping brain.

我們發現，在睡覺時清除澱粉樣蛋白的速度比較快

So if sleep, then, is part of the brain's solution to the problem of waste clearance,

所以如果睡眠是腦部清除廢物的辦法之一

then this may dramatically change how we think about the relationship between sleep, amyloid-beta, and Alzheimer's disease.

那這會戲劇性地改變我們對睡眠、澱粉類蛋白和阿茲海默症的關係

A series of recent clinical studies suggest that among patients who haven't yet developed Alzheimer's disease,

最近一系列臨床調查顯示還沒有得到阿茲海默症的病人

worsening sleep quality and sleep duration are associated with a greater amount of amyloid-beta building up in the brain,

睡眠品質都會下降，睡眠時間和腦部累積的澱粉類蛋白有極大的關係

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,

這些研究無法證實缺乏睡眠或睡眠品質不好會造成阿茲海默症

they do suggest that the failure of the brain to keep its house clean

但他們卻提出腦部無法將

by clearing away waste like amyloid-beta may contribute to the development of conditions like Alzheimer's.

澱粉類蛋白這種廢物清除乾淨可能會引發阿茲海默症

So what this new research tells us, then, is that the one thing that all of you already knew about sleep,

所以這項新研究到底告訴我們什麼事情呢？其實大家都很熟悉

that even Galen understood about sleep, that it refreshes and clears the mind,

Galen也了解睡眠可以讓頭腦清醒

may actually be a big part of what sleep is all about.

確實是睡眠的重要因素

See, you and I, we go to sleep every single night, but our brains, they never rest.

你們和我，我們每天晚上都需要睡覺，但我們的頭腦，他們從來不休息

While our body is still and our mind is off walking in dreams somewhere,

我們的身體靜止不動、我們的心也被夢偷走時

the elegant machinery of the brain is quietly hard at work cleaning and maintaining this unimaginably complex machine.

腦中最優雅的裝置正靜靜地清除廢物，並維持這個令人難以想像的複雜裝置

Like our housework, it's a dirty and a thankless job, but it's also important.

就像我們的家事，它是個又髒又得不到獎勵的工作，但它非常重要

In your house, if you stop cleaning your kitchen for a month, your home will become completely unlivable very quickly.

在家裡，如果你一個月不打掃廚房，你們家一定馬上就髒到不能住人

But in the brain, the consequences of falling behind may be much greater than the embarrassment of dirty countertops,

但在腦中，落後的清掃工作可能還比骯髒的工作平台還要嚴重

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,

因為清掃腦部時，它代表了頭腦的健康和功能，也代表身體正在冒風險

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.

所以為什麼了解腦部這些基本打掃功能會那麼重要，能保護我們遠離腦部疾病

Thank you.

謝謝大家