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

它是由實驗室培育的神經細胞和腦組織組成

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

科學家可藉由它了解完整發展的人類大腦。

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

而且使用你的皮膚細胞取樣即可培育出來。

Why would we need such a thing?

我們為何會需要這樣的東西呢？

Neuroscientists face a challenge:

神經科學家面對著一項挑戰：

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

因包覆於厚頭骨與層層防護組織中，

the human brain is extremely difficult to observe in action.

人腦的活動是格外難以被觀察到的。

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

幾世紀以來，科學家試著以屍體解剖、

animal models,

動物樣本、

and, in recent years, imaging techniques.

以及近年的腦造影技術來了解人腦。

We've learned a lot through all these methods,

我們已從這些方法中了解了很多，

but they have limitations.

但它們仍有其限制。

Conditions like Alzheimer's and schizophrenia,

像是阿茲海默氏症以及思覺失調症（俗稱精神分裂）的症狀，

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

以及疾病對人腦造成的影響，如茲卡病毒，

continue to hide beyond our view, and our understanding.

仍然是超出我們所知的範圍。

Enter brain organoids, which function like human brains

讓我們進入功能如同人腦的類大腦器官

but aren't part of an organism.

雖然他不屬於生物體的一部分

Each one comes from an undifferentiated stem cell,

其中每一個細胞來自未分化的幹細胞，

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

幹細胞能發展成為體內任何一種組織，

from bone to brain.

包含骨骼至大腦

Scientists can make undifferentiated stem cells from skin cells.

科學家可以從皮膚細胞中培育出未分化的幹細胞。

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

這表示他們可以從個人獨特的皮膚樣本

and generate brain organoids from that person.

製造出特定的類大腦器官。

The hardest part of growing a brain organoid,

培育類腦器官中最困難的部分，

which stumped scientists for years,

一個困住科學家多年的難題，

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

是找到完美的糖、蛋白質、維生素、礦物質組合

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

以培育出相同的神經

That was only discovered recently, in 2013.

直到 2013 年科學家才發現，

The rest of the process is surprisingly easy.

後續的步驟是出奇的容易。

A neural stem cell essentially grows itself,

神經系統中的幹細胞基本上會自己成長，

similar to how a seed grows into a plant,

類似於種子長成植物，

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

它所需要的就是大腦的泥土、水、陽光。

A special gel to simulate embryonic tissue,

也就是特殊的膠體模擬胚胎組織、

a warm incubator set at body temperature,

設置於體溫的恆溫箱、

and a bit of motion to mimic blood flow.

以及微量的運動以模擬血液流動狀態。

The stem cell grows into a very small version

幹細胞便成長為縮小版的

of an early-developing human brain,

發育初期人腦，

complete with neurons that can connect to one another

具備神經細胞相互連結的功能

and make simplified neural networks.

成為簡化的神經網路。

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

當迷你腦長大，其發展階段會依照胎兒的腦發育歷程進行。

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

藉由觀察這歷程，我們可以學習到神經細胞如何發育，

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

以及最終如何形成富含神經細胞的大腦皮質，

the part responsible for higher cognition like logic and reasoning,

也就是負責與其他物種相比

than other species.

更高階的認知（如邏輯、推理）的地方

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

能夠在實驗室裡培育出腦，即使是很小的，

raises ethical questions, like:

引發了許多倫理上的問題，像是：

Can they think for themselves, or develop consciousness?

他們是否會獨立思考？或是發展出意識？

And the answer is no, for several reasons.

答案是「不會」，基於以下原因

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

類大腦器官與完整發展的腦有相同種類的組織，

but isn't organized the same way.

但並非以同的方式建構起來。

The organoid is similar to an airplane

類大腦如同一架飛機

that's been taken apart and reassembled at random;

一架被拆解又隨意組裝的飛機；

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

你仍然能研究機翼、引擎與其他部分，

but the plane could never fly.

但這架飛機並不會飛。

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

相同地，類大腦器官能讓我們了解腦的不同組織，

but can't think.

但他並不能思考。

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

而且即使是發展得像真實腦的迷你腦，

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

他們仍不能推理或發展出意識。

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，決大部分是由於其大小

and mini brains have only about 100,000 neurons

而迷你腦只擁有大約100,000個神經細胞

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

相較於完整發展的腦有860億個。

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

科學家目前不太可能培育出更大的腦。

Without blood vessels to feed them,

在沒有血管供應給腦的情況下，

their size is limited to one centimeter at most.

他們的大小最多也只能一公分

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

最後，迷你腦無法與外在世界互動。

We learn by interacting with our environments: receiving inputs

我們藉由與環境互動來學習：接收訊息

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

（從我們的眼、耳與其他感官而來）並給予相對應反映。

The complex neural networks that underlie conscious thoughts and actions

掌控著意識的思維與動作的複雜神經網路

develop from this feedback loop.

正是藉由此迴路發展而來的。

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

沒有此迴路，類大腦永遠無法形成一個功能性網路

There's nothing quite like the actual human brain,

類大腦與真實人類大腦仍有相當大的差距，

but mini brains are an unprecedented tool

但迷你腦仍是一個空前絕後的工具

for studying everything from development to disease.

幫助我們研究從發展到疾病的各個環節。

With luck, these humble organoids can help us discover

如果夠幸運，這些低階的類器官可以幫助我們發現

what makes the human brain unique,

人類大腦的特殊之處，

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

並且或許能引領我們去回答那古老的問題：

what makes us human?

什麼讓我們成為人類？