Carl Schoonover: How to look inside the brain

カール・シューノーヴァー: 脳の中身を見る方法

翻訳: Mizuki Anzai 校正: Akiko Hicks

This is a thousand-year-old drawing of the brain.

これは千年前の脳のスケッチです

It's a diagram of the visual system.

視覚系を表す図で

And some things look very familiar today.

現代では見慣れたものも いくつかあります

Two eyes at the bottom, optic nerve flowing out from the back.

眼球があって 後部から視神経が伸びています

There's a very large nose

大きな鼻がありますが

that doesn't seem to be connected to anything in particular.

特に何ともつながっていません

And if we compare this

この図を最近の

to more recent representations of the visual system,

視覚系の解説図と比べると

you'll see that things have gotten substantially more complicated

千年を経て物事が非常に

over the intervening thousand years.

複雑になったと分かります

And that's because today we can see what's inside of the brain,

脳の内側を見る事が

rather than just looking at its overall shape.

可能になったためです

Imagine you wanted to understand how a computer works

PCの仕組みを知りたいのに

and all you could see was a keyboard, a mouse, a screen.

見えるのはキーボード・マウス・画面だけ

You really would be kind of out of luck.

これではどうにもなりません

You want to be able to open it up, crack it open,

ふたを開けて

look at the wiring inside.

配線を見られたらいいのに

And up until a little more than a century ago,

百年ほど前までは

nobody was able to do that with the brain.

ふたを開けて 脳の

Nobody had had a glimpse of the brain's wiring.

配線を見るなんて不可能でした

And that's because if you take a brain out of the skull

脳を頭蓋骨から取り出し

and you cut a thin slice of it,

薄く切って

put it under even a very powerful microscope,

強力な顕微鏡で見ても

there's nothing there.

何も見えないのです

It's gray, formless.

灰色の混沌

There's no structure. It won't tell you anything.

構造が無く 何も分かりません

And this all changed in the late 19th century.

しかし19世紀末に変化が起こります

Suddenly, new chemical stains for brain tissue were developed

脳組織用の化学染色が開発され

and they gave us our first glimpses at brain wiring.

脳の配線が見られるようになりました

The computer was cracked open.

PCのふたが開いたのです

So what really launched modern neuroscience

現代神経科学の夜明けは

was a stain called the Golgi stain.

ゴルジ染料がもたらしました

And it works in a very particular way.

その原理はと言うと

Instead of staining all of the cells inside of a tissue,

組織内の全細胞でなく

it somehow only stains about one percent of them.

1％だけを染色します

It clears the forest, reveals the trees inside.

すると 森が消え 中から木が姿を現します

If everything had been labeled, nothing would have been visible.

全部が染色されたら 何も見えません

So somehow it shows what's there.

特定の染色で 何かが見えてくるのです

Spanish neuroanatomist Santiago Ramon y Cajal,

現代神経科学の祖として名高い

who's widely considered the father of modern neuroscience,

神経解剖学者 ラモン・イ・カハールは

applied this Golgi stain, which yields data which looks like this,

ゴルジ染色を使い このようなデータを得て

and really gave us the modern notion of the nerve cell, the neuron.

神経細胞（ニューロン）の解明に寄与しました

And if you're thinking of the brain as a computer,

脳をコンピュータに例えると

this is the transistor.

これはトランジスタです

And very quickly Cajal realized

カハールはすぐに気がつきました

that neurons don't operate alone,

ニューロンは単体では機能せず

but rather make connections with others

他のニューロンとつながって

that form circuits just like in a computer.

コンピュータ内の回路の様なものを 形成するのだと

Today, a century later, when researchers want to visualize neurons,

百年後の今 ニューロンの可視化には

they light them up from the inside rather than darkening them.

染色よりも発光が使われます

And there's several ways of doing this.

複数の手法がありますが

But one of the most popular ones

最もよく使われるのは

involves green fluorescent protein.

緑色蛍光タンパク質（GFP）です

Now green fluorescent protein,

このGFPという物質は

which oddly enough comes from a bioluminescent jellyfish,

なんと発光クラゲから採取でき

is very useful.

至極便利です

Because if you can get the gene for green fluorescent protein

GFPの遺伝子を準備し

and deliver it to a cell,

細胞に注入すると

that cell will glow green --

その細胞は緑色に発光します

or any of the many variants now of green fluorescent protein,

GFPには様々な種類があり

you get a cell to glow many different colors.

細胞を色分けし発光させることが出来ます

And so coming back to the brain,

脳の話に戻りましょう

this is from a genetically engineered mouse called "Brainbow."

これは「ブレインボー」という 遺伝子操作したマウスのものです

And it's so called, of course,

そう呼ばれるのは

because all of these neurons are glowing different colors.

ニューロンが虹のように見えるからです

Now sometimes neuroscientists need to identify

神経科学者は時に

individual molecular components of neurons, molecules,

細胞全体ではなく ニューロンの分子成分を

rather than the entire cell.

特定せねばなりません

And there's several ways of doing this,

複数の手法がありますが

but one of the most popular ones

最もよく使われるのは

involves using antibodies.

抗体を使うものです

And you're familiar, of course,

ご存知の通り抗体は

with antibodies as the henchmen of the immune system.

免疫システムの忠実な下僕ですが

But it turns out that they're so useful to the immune system

他にも便利な事が分かりました

because they can recognize specific molecules,

特定の分子を認識できるのです

like, for example, the coat protein

体内に侵入するウイルスの

of a virus that's invading the body.

コート蛋白質などです

And researchers have used this fact

研究者はこれを

in order to recognize specific molecules inside of the brain,

脳内の特定分子の認識に使います

recognize specific substructures of the cell

細胞内の特異的微細構造を認識し

and identify them individually.

個別に特定するのです

And a lot of the images I've been showing you here are very beautiful,

ここでお見せしている写真はどれも美しく

but they're also very powerful.

同時に非常に力強く

They have great explanatory power.

説明力があります

This, for example, is an antibody staining

例えばこれはマウスの脳の

against serotonin transporters in a slice of mouse brain.

セロトニン輸送体を抗体染色したものです

And you've heard of serotonin, of course,

セロトニンは

in the context of diseases like depression and anxiety.

鬱や不安神経症の解説に使われます

You've heard of SSRIs,

SSRI は

which are drugs that are used to treat these diseases.

これらの病気のための薬で

And in order to understand how serotonin works,

セロトニンがどう作用するのかは

it's critical to understand where the serontonin machinery is.

その作用場所を突き止めねばならず

And antibody stainings like this one

こういった抗体染色は

can be used to understand that sort of question.

この質問を理解するのに役立ちます

I'd like to leave you with the following thought:

最後にお話ししたいのが

Green fluorescent protein and antibodies

GFPと抗体は どちらも

are both totally natural products at the get-go.

全くの天然物質です

They were evolved by nature

自然がこれらを進化させた目的は

in order to get a jellyfish to glow green for whatever reason,

クラゲを緑に発光させたり

or in order to detect the coat protein of an invading virus, for example.

侵入ウィルスのコート蛋白質を 検出するためでした

And only much later did scientists come onto the scene

ずっと後になって やっと科学者が現れ

and say, "Hey, these are tools,

「おい これは使えるぞ」

these are functions that we could use

「この機能は俺たちの研究にぴったりだ」

in our own research tool palette."

と言うのです

And instead of applying feeble human minds

貧弱な人類の頭で

to designing these tools from scratch,

ゼロから ツールを作り出す代わりに

there were these ready-made solutions right out there in nature

何百万年もの年月をかけ着々と

developed and refined steadily for millions of years

解決策を用意してくれていたのは

by the greatest engineer of all.

自然という偉大な技術者なのです

Thank you.

ありがとうございました

(Applause)

（拍手）