What are mini brains? - Madeline Lancaster

譯者: Ting-Yen Tsai 審譯者: Helen Chang

「此刻，神經科學正經歷一場革命」 ──《大腦的未來》（2014）

This pencil-eraser-sized mass of cells is something called a brain organoid.

這一團橡皮擦大小的細胞 被稱為「類腦器官」

It’s a collection of lab-grown neurons and other brain tissue

它是實驗室培養出來的神經元 和其他大腦組織的集合體

that scientists can use to learn about full-grown human brains.

科學家可以透過它 來研究發展完全的人類大腦

And it can be grown from a sample of your skin cells.

而且它可以由你身上的 皮膚細胞培養而來

Why would we need such a thing?

為什麼我們需要這麼一個東西呢？

Neuroscientists face a challenge:

因為神經科學家面臨一個問題：

shielded by our thick skulls and swaddled in layers of protective tissue,

由於在厚厚的頭骨保護下 又被多層保護組織包覆

the human brain is extremely difficult to observe in action.

在活體情況下觀察人類的大腦十分困難

For centuries, scientists have tried to understand them using autopsies,

好幾世紀以來，科學家 已經嘗試透過解剖屍體、

animal models,

動物模型、

and, in recent years, imaging techniques.

還有近年來開始使用的 成像技術來瞭解大腦

We’ve learned a lot through all these methods,

我們透過這些方法已經有很多發現

but they have limitations.

但它們仍有侷限

Conditions like Alzheimer’s and schizophrenia,

像是阿茲海默症和精神分裂症等疾病

and the effect on the human brain of diseases like Zika,

還有對於人腦產生影響的惡疾 例如茲卡病毒

continue to hide beyond our view, and our understanding.

我們依然看不見、不理解

Enter brain organoids, which function like human brains

如同人腦一般運作的類腦器官

but aren’t part of an organism.

不是生物體的一部分

Each one comes from an undifferentiated stem cell,

它們來自尚未分化的幹細胞

which is a cell that can develop into any tissue in the body,

也就是可以發展成從骨頭到大腦

from bone to brain.

任何身體組織的細胞

Scientists can make undifferentiated stem cells from skin cells.

科學家可以從皮膚細胞中 製造出尚未分化的幹細胞

That means they can take a skin sample from a person with a particular condition

這代表他們可以從有某特定症狀的人 身上提取一個皮膚細胞樣本

and generate brain organoids from that person.

來培養那個人的類腦器官

The hardest part of growing a brain organoid,

培養類腦器官最困難、

which stumped scientists for years,

令科學家困擾多年的部分是

was finding the perfect combination of sugars, proteins, vitamins, and minerals

找到由糖、蛋白質、維他命 和礦物質組成的完美比例

that would induce the stem cell to develop a neural identity.

去誘導幹細胞發展為神經細胞

That was only discovered recently, in 2013.

這一直到最近的 2013 年才被發現

The rest of the process is surprisingly easy.

至於剩下的步驟則出奇簡單

A neural stem cell essentially grows itself,

因為神經幹細胞可以自行成長

similar to how a seed grows into a plant,

就像一粒種子長成一棵植物

all it needs are the brain’s equivalents of soil, water, and sunlight.

它只需要大腦的「泥土、水和陽光」：

A special gel to simulate embryonic tissue,

一種可以模擬胚胎組織的特殊膠

a warm incubator set at body temperature,

一個溫度設定在體溫的培養器

and a bit of motion to mimic blood flow.

還有一些模仿血液流動的輕微晃動

The stem cell grows into a very small version

這些幹細胞會長成

of an early-developing human brain,

一個處於發展前期人腦的迷你版

complete with neurons that can connect to one another

擁有可以互相連結溝通的神經元

and make simplified neural networks.

並且組成簡單的神經網絡

As mini brains grow, they follow all the steps of fetal brain development.

這個迷你大腦將會 循著胚胎大腦發展的所有步驟

By observing this process, we can learn how our neurons develop,

經由觀察這個過程 我們就能瞭解神經元是如何發展的

as well as how we end up with so many more of them in our cortex,

以及我們的大腦皮層中 最後怎麼會有這麼多的神經元

the part responsible for higher cognition like logic and reasoning,

讓我們所擁有的 邏輯思考能力之類的感知能力

than other species.

比其他物種更好

Being able to grow brains in the lab, even tiny ones,

但是能夠在實驗室裡培養「大腦」 即使是迷你版的

raises ethical questions, like:

也產生了一些道德問題，例如：

Can they think for themselves, or develop consciousness?

它們能否獨立思考或是發展意識呢？

And the answer is no, for several reasons.

答案是否定的，而原因有好幾個

A brain organoid has the same tissue types as a full-sized brain,

類腦器官和真正完整大腦的 組織種類相同

but isn’t organized the same way.

但是兩者的組織方式不同

The organoid is similar to an airplane

類腦器官就像一架已經被拆解

that’s been taken apart and reassembled at random;

並隨機重組的飛機

you could still study the wings, the engine, and other parts,

你依然可以研究它的機翼、引擎 還有其他部分

but the plane could never fly.

但這架飛機不可能飛起來

Similarly, a brain organoid allows us to study different types of brain tissue,

同樣的，類腦器官讓我們可以 研究不同部分的大腦組織

but can’t think.

但它自己卻不能思考

And even if mini brains were organized like a real brain,

就算「迷你大腦」和真正的大腦 有一樣的組織方式

they still wouldn’t be able to reason or develop consciousness.

它們還是沒辦法思考 或是發展出獨立意識

A big part of what makes our brains so smart is their size,

我們的大腦之所以如此聰明 有很大一部份是因為它的尺寸

and mini brains have only about 100,000 neurons

而「迷你大腦」僅含有十萬個神經元

compared to the 86 billion in a full-sized brain.

無法和擁有 860 億神經元 完整大小的大腦相比

Scientists aren’t likely to grow larger brain organoids anytime soon.

科學家不太可能在短期內 培養更大的類腦器官

Without blood vessels to feed them,

沒有血管來提供細胞團養分

their size is limited to one centimeter at most.

它們的尺寸被限制在一公分以下

Finally, mini brains aren’t able to interact with the outside world.

所以最後可以總結 「迷你大腦」沒有能力和外界互動

We learn by interacting with our environments: receiving inputs

我們透過和環境互動來學習：

接收眼睛、耳朵和其他感官的訊息 並對它們產生回應

through our eyes, ears, and other sensory organs, and reacting in turn.

The complex neural networks that underlie conscious thoughts and actions

這個回饋迴圈可以發展成 主導有意識思考和行為的

develop from this feedback loop.

複雜神經系統

Without it, the organoids can never form a functional network.

沒有它，類腦器官無法產生 可以運作的網絡

There’s nothing quite like the actual human brain,

它們完全不像實際運作中的人類大腦

but mini brains are an unprecedented tool

但「迷你大腦」是個前所未有的工具

for studying everything from development to disease.

可以幫助我們瞭解 從發展到疾病的很多事

With luck, these humble organoids can help us discover

幸運的話，這些低微的類器官 可以幫助我們發現

what makes the human brain unique,

是什麼使人類的大腦與眾不同

and maybe bring us closer to answering the age-old question:

也或許能讓我們距離 能夠回答這個古老問題更近一些：

what makes us human?

是什麼讓我們成為人類？

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