One more reason to get a good night’s sleep | Jeff Iliff

譯者: Yesbydefault 倪文娟 審譯者: Adrienne Lin

Sleep.

睡眠

It's something we spend about a third of our lives doing,

用掉我們生命整整 1/3 的時間。

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

但是有誰真正了解睡眠呢？

Two thousand years ago, Galen,

兩千年前，蓋倫，

one of the most prominent medical researchers

古代數一數二的醫學專家，

of the ancient world,

proposed that while we're awake,

認為我們醒著的時候

our brain's motive force, its juice,

大腦的動力—腦汁，

would flow out to all the other parts of the body,

會流出腦外，流到全身各部位

animating them but leaving the brain all dried up,

活絡全身，

但是讓大腦枯竭。

蓋倫認為當我們睡著，

and he thought that when we sleep,

all this moisture that filled the rest of the body

身體的汁液

would come rushing back,

會流灌回大腦，

rehydrating the brain

重新濕潤大腦，

and refreshing the mind.

使大腦甦活。

Now, that sounds completely ridiculous to us now,

現在我們覺得這個看法很荒唐，

but Galen was simply trying to explain

但蓋倫只是想解釋睡眠現象，

something about sleep

that we all deal with every day.

是我們每天都在面對的。

See, we all know based on our own experience

我們憑經驗都知道

that when you sleep, it clears your mind,

睡眠會清理我們的頭腦。

and when you don't sleep,

不睡覺，

it leaves your mind murky.

頭腦會變得昏昏沉沉。

But while we know a great deal more about sleep now

我們現在雖然更認識睡眠，

than when Galen was around,

比蓋倫的時代更了解，

we still haven't understood why it is that sleep,

但是我們還是搞不懂

為什麼所有人體活動中，

of all of our activities, has this incredible

睡眠獨具這種奇妙的修復大腦功能。

restorative function for the mind.

So today I want to tell you about

所以今天我要分享最新研究

some recent research

that may shed new light on this question.

提供的可能答案。

We've found that sleep may actually be

我們發現，睡眠可能是

a kind of elegant design solution

一種精密的設計，

to some of the brain's most basic needs,

用來滿足大腦某些最基本的需求。

a unique way that the brain

大腦用這種獨特的方式

meets the high demands and the narrow margins

來應付本身的高度需求和不容差錯，

that set it apart from all the other organs of the body.

這些特性使大腦和其他器官截然不同。

So almost all the biology that we observe

我們觀察到的幾乎所有生物現象

can be thought of as a series of problems

都可以看成是一連串的問題

and their corresponding solutions,

和相對的解決方法。

and the first problem that every organ must solve

而所有器官都必須解決的頭號問題是

is a continuous supply of nutrients to fuel

如何源源不絕的供應營養素

all those cells of the body.

以提供身體細胞所需。

In the brain, that is especially critical;

對大腦而言，這更是至關重要。

its intense electrical activity uses up

大腦密集強烈的電子活動

a quarter of the body's entire energy supply,

耗用全身能量的 1/4，

even though the brain accounts

雖然大腦只占

for only about two percent of the body's mass.

全身質量的 2%。

So the circulatory system

循環系統

solves the nutrient delivery problem

負責解決輸送營養的問題，

by sending blood vessels to supply nutrients

利用血管傳送營養素和氧氣

and oxygen to every corner of our body.

到全身每一個部位。

You can actually see it in this video here.

你可以從這個影片看到

Here, we're imaging blood vessels

這是一隻活體老鼠的大腦血管影像。

in the brain of a living mouse.

The blood vessels form a complex network

這些血管形成複雜的網絡

that fills the entire brain volume.

充滿整個大腦，

They start at the surface of the brain,

從大腦的表層

and then they dive down into the tissue itself,

一直深入到組織本身。

and as they spread out, they supply nutrients

隨著血管延伸，供應營養素和氧氣

and oxygen to each and every cell in the brain.

給大腦裡面每一個細胞。

Now, just as every cell requires

接著，

就像每個細胞都需要養分才能生存，

nutrients to fuel it,

every cell also produces waste as a byproduct,

所有細胞也都會產生副產品—廢物。

and the clearance of that waste

要怎麼清理這些廢物

is the second basic problem

是每個器官都要解決的第二個問題。

that each organ has to solve.

This diagram shows the body's lymphatic system,

這是人體的淋巴系統。

which has evolved to meet this need.

經過演化，現在負責清除身體的廢物。

It's a second parallel network of vessels

淋巴系統是第二套循環系統，

that extends throughout the body.

網絡遍佈全身。

It takes up proteins and other waste

它會帶走細胞之間的蛋白質和其他廢物，

from the spaces between the cells,

it collects them, and then dumps them into the blood

收集起來，排到血液裡，

so they can be disposed of.

藉此把廢物清除。

But if you look really closely at this diagram,

可是如果你仔細看這張圖，

you'll see something

會發現很奇怪的地方。

that doesn't make a lot of sense.

So if we were to zoom into this guy's head,

我們如果把頭部放大來看，

one of the things that you would see there

你會發現

is that there are no lymphatic vessels in the brain.

大腦裡面沒有淋巴管。

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

但是這樣不合理，對吧？

I mean, the brain is this intensely active organ

大腦明明是非常活躍的器官，

that produces a correspondingly large amount of waste

每天製造非常大量的廢物，

that must be efficiently cleared.

必須有效地清除。

And yet, it lacks lymphatic vessels, which means that

可是大腦卻沒有淋巴管，

the approach that the rest of the body takes

這表示身體其他器官清理廢物的方法

to clearing away its waste

won't work in the brain.

並不適用於大腦。

So how, then, does the brain solve

那麼，大腦究竟要怎麼解決

its waste clearance problem?

廢物清理的問題？

Well, that seemingly mundane question

這個看似很普通的問題

is where our group first jumped into this story,

引發我們團隊開始深入研究。

and what we found

我們發現，

as we dove down into the brain,

當我們探進大腦的深層，

down among the neurons and the blood vessels,

來到神經元和血管之間，

was that the brain's solution

我們發現大腦清理廢物的方法

to the problem of waste clearance,

it was really unexpected.

超乎我們的想像。

It was ingenious,

實在太天才了，

but it was also beautiful.

也非常美。

Let me tell you about what we found.

我來說明一下。

So the brain has this large pool

大腦有一個很大的「水池」，

of clean, clear fluid called cerebrospinal fluid.

裡面充滿乾淨、透明的液體， 叫做「腦脊髓液」，

We call it the CSF.

簡稱 CSF。

The CSF fills the space that surrounds the brain,

腦脊髓液充滿大腦周圍的空間，

and wastes from inside the brain

廢物會從大腦裡面

make their way out to the CSF,

排出到腦脊髓液，

which gets dumped, along with the waste, into the blood.

然後跟著腦脊髓液一起流到血液裡。

So in that way, it sounds a lot like

原理聽起來有點像淋巴系統，對吧？

the lymphatic system, doesn't it?

But what's interesting is that the fluid and the waste

但是特別的是，

大腦裡面的液體和廢物

from inside the brain,

they don't just percolate their way randomly

並不是隨便滲透到腦脊髓液裡，

out to these pools of CSF.

Instead, there is a specialized network of plumbing

而是有一個專門的「打水系統」

that organizes and facilitates this process.

來指揮、促進這個過程。

You can see that in these videos.

你可以從這些影片裡看到

Here, we're again imaging into the brain

這些也是活體老鼠大腦的影像。

of living mice.

The frame on your left shows

左邊是大腦表層的活動，

what's happening at the brain's surface,

and the frame on your right shows

右邊是大腦表層下面

what's happening down below the surface of the brain

組織裡面的活動。

within the tissue itself.

We've labeled the blood vessels in red,

我們把血管標成紅色，

and the CSF that's surrounding the brain

大腦周圍的腦脊髓液會標綠色。

will be in green.

Now, what was surprising to us

我們很驚訝地發現，

was that the fluid on the outside of the brain,

大腦周圍的腦脊髓液

it didn't stay on the outside.

沒有留在外面，

Instead, the CSF was pumped back into

而是被打回大腦裡面，穿透進去，

and through the brain

along the outsides of the blood vessels,

發生在沿著血管外緣的地方。

and as it flushed down into the brain

當血管旁邊的腦脊髓液，沖進大腦裡，

along the outsides of these vessels,

it was actually helping to clear away,

其實是在幫忙清除

to clean the waste from the spaces

腦細胞間的空隙裡的廢物。

between the brain's cells.

If you think about it,

你仔細想，就會知道

using the outsides of these blood vessels like this

像這樣利用血管外緣

is a really clever design solution,

是很聰明的設計。

because the brain is enclosed

因為大腦是包在堅硬的腦殼裡，

in a rigid skull

and it's packed full of cells,

裡面裝滿了腦細胞，

so there is no extra space inside it

沒辦法再塞進一整組

for a whole second set of vessels like the lymphatic system.

像淋巴系統那樣的管路。

Yet the blood vessels,

而腦中的血管

they extend from the surface of the brain

從大腦的表面

down to reach every single cell in the brain,

一直擴散深入，到最裡面的每一個細胞。

which means that fluid

這表示

這些沿著血管外緣跑的液體，

that's traveling along the outsides of these vessels

can gain easy access to the entire brain's volume,

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

so it's actually this really clever way

to repurpose one set of vessels, the blood vessels,

叫大腦血管多做一件事，

to take over and replace the function

負責淋巴管該做的工作，取而代之，

of a second set of vessels, the lymphatic vessels,

to make it so you don't need them.

這樣就不需要淋巴管了。

And what's amazing is that no other organ

最奇妙的是，

takes quite this approach

身體其他器官，都沒有用這種方式

to clearing away the waste from between its cells.

清除細胞之間的廢物。

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

這是大腦特有的方法。

But our most surprising finding

我們最驚人的發現是，

was that all of this,

大腦這整個設計，

everything I just told you about,

我剛才講的所有過程，

with all this fluid rushing through the brain,

這些腦脊髓液滲透大腦

it's only happening in the sleeping brain.

只發生在我們睡著的時候。

Here, the video on the left

左邊的影片

shows how much of the CSF is moving

可以看出有多少腦脊髓液流進大腦，

through the brain of a living mouse while it's awake.

這是活體老鼠醒著時候的大腦。

It's almost nothing.

幾乎沒有滲透。

Yet in the same animal,

但是同樣這隻老鼠，

if we wait just a little while until it's gone to sleep,

如果我們等一下，等牠睡著，

what we see is that the CSF

就會看到腦脊髓液

is rushing through the brain,

大量湧進腦裡。

and we discovered that at the same time

我們也發現

when the brain goes to sleep,

大腦睡著的同時，

the brain cells themselves seem to shrink,

腦細胞似乎會縮小，

opening up spaces in between them,

使細胞之間的空隙變大，

allowing fluid to rush through

開路讓液體流過

and allowing waste to be cleared out.

把廢物帶走。

So it seems that Galen may actually have been

這麼說，

蓋倫很可能看出一些端倪，

sort of on the right track when he wrote about

fluid rushing through the brain

他說腦汁會在人睡著時

when sleep came on.

沖進大腦。

Our own research, now it's 2,000 years later,

我們的研究在蓋倫兩千年以後

suggests that what's happening is that

發現，

大腦醒著

when the brain is awake

and is at its most busy,

而且最忙的時候，

it puts off clearing away the waste

會把清理工作暫時擱著，

from the spaces between its cells until later,

暫時先不管細胞間囤積的廢物。

and then, when it goes to sleep

等我們睡著了，

and doesn't have to be as busy,

大腦比較沒那麼忙，

it shifts into a kind of cleaning mode

就會啟動清除模式

to clear away the waste

開始倒垃圾，

from the spaces between its cells,

打掃細胞之間的空間，

the waste that's accumulated throughout the day.

清除堆積了一整天的廢物。

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

所以其實有點像你跟我

we put off our household chores during the work week

週間不打掃家裡，

when we don't have time to get to it,

因為太忙沒時間打掃。

and then we play catch up on all the cleaning that we have to do

堆積如山後，再來個大掃除，

when the weekend rolls around.

利用週末打掃乾淨。

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

我剛講了很多廢物清除，

but I haven't been very specific

但是還沒有說明

about the kinds of waste

大腦要利用睡眠時，清除哪些廢物，

that the brain needs to be clearing

during sleep in order to stay healthy.

才能維繫健康。

The waste product that these recent studies

近期研究關注的大腦廢物

focused most on is amyloid-beta,

是乙型澱粉樣蛋白。

which is a protein that's made in the brain all the time.

這是大腦中不斷產生的一種蛋白質。

My brain's making amyloid-beta right now,

我的大腦正在產生乙型澱粉樣蛋白，

and so is yours.

你的大腦也是。

But in patients with Alzheimer's disease,

但是阿茲海默症的病患，

amyloid-beta builds up and aggregates

乙型澱粉樣蛋白會不斷增加、聚集，

in the spaces between the brain's cells,

囤積在大腦細胞之間的空隙，

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

無法正常清除。

and it's this buildup of amyloid-beta

這種乙型澱粉樣蛋白的累積

that's thought to be one of the key steps

被認為是發展阿茲海默症的 關鍵步驟之一。

in the development of that terrible disease.

So we measured how fast amyloid-beta is cleared

於是我們測量大腦清除它的速度，

from the brain when it's awake

比較大腦清醒和睡著兩種狀況。

versus when it's asleep,

and we found that indeed,

我們發現，果然，

the clearance of amyloid-beta

乙型澱粉樣蛋白的清除，

is much more rapid from the sleeping brain.

在大腦睡覺時，比清醒時快很多。

So if sleep, then,

所以，睡眠就是

is part of the brain's solution

大腦用來清除廢物的方法。

to the problem of waste clearance,

then this may dramatically change how we think

那麼，這可能大大改變我們如何看待

about the relationship between sleep,

amyloid-beta, and Alzheimer's disease.

睡眠、乙型澱粉樣蛋白， 和阿茲海默症的關係。

A series of recent clinical studies

一連串的近期臨床研究指出，

suggest that among patients

未罹患阿茲海默症的病人當中，

who haven't yet developed Alzheimer's disease,

睡眠品質變差，或者睡眠時間變少

worsening sleep quality and sleep duration

are associated with a greater amount

都跟腦中囤積大量 乙型澱粉樣蛋白相關。

of amyloid-beta building up in the brain,

雖然我必須提醒大家，

and while it's important to point out

that these studies don't prove

這些研究並沒有證明

that lack of sleep or poor sleep

睡眠不足或不良會導致阿茲海默症，

cause Alzheimer's disease,

they do suggest that the failure of the brain

但確實有發現，

大腦如果不能保持清潔、

to keep its house clean

by clearing away waste like amyloid-beta

清除乙型澱粉樣蛋白等各種廢物，

may contribute to the development

可能導致像阿茲海默症這樣的疾病。

of conditions like Alzheimer's.

So what this new research tells us, then,

所以，這項新研究告訴我們的，

is that the one thing that all of you

也就是各位都已經知道的

already knew about sleep,

睡眠的作用。

that even Galen understood about sleep,

連蓋倫都有發現的，

that it refreshes and clears the mind,

就是睡眠會更新、清理大腦這件事，

may actually be a big part

可能就是我們為什麼要睡覺的主因。

of what sleep is all about.

See, you and I, we go to sleep

你跟我，我們每天晚上睡覺。

every single night,

but our brains, they never rest.

可是我們的大腦

從來不休息。

While our body is still

我們的身體躺著不動，

and our mind is off walking in dreams somewhere,

思緒飄去神遊夢境時，

the elegant machinery of the brain

大腦的精密儀器悄悄地努力工作

is quietly hard at work

cleaning and maintaining

清潔、維修

this unimaginably complex machine.

這部複雜到難以想像的機器。

Like our housework,

這就像清掃家裡一樣，

it's a dirty and a thankless job,

是份骯髒又沒人感激你的工作，

but it's also important.

但是卻非常重要。

In your house, if you stop cleaning your kitchen

在你家，如果一個月不清掃廚房，

for a month,

your home will become completely unlivable

很快就會髒亂得住不下去。

very quickly.

But in the brain, the consequences

但是在大腦裡，

積垢不除的後果

of falling behind may be much greater

可能遠超過流理台骯髒的尷尬。

than the embarrassment of dirty countertops,

because when it comes to cleaning the brain,

因為大腦的清潔

it is the very health and function

攸關全身、心的健康和功能。

of the mind and the body that's at stake,

which is why understanding these

這是為什麼現在了解

very basic housekeeping functions of the brain today

大腦的這些基本清潔排毒功能，

may be critical for preventing and treating

可能攸關未來精神疾病的預防與治療。

diseases of the mind tomorrow.

Thank you.

謝謝！

（觀眾掌聲）

(Applause)