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This pencil-eraser-sized mass of cells is something called a brain organoid.
这团橡皮大小的细胞被称为类脑器官。
It's a collection of lab-grown neurons and other brain tissue
它由实验室培养的神经元细胞以及其他一些脑部组织组成，
that scientists can use to learn about full-grown human brains.
科学家可以通过它来了解人类大脑。
And it can be grown from a sample of your skin cells.
你身上的皮肤细胞就可以分化出这样的组织。
Why would we need such a thing? Neuroscientists face a challenge:
那我们为什么需要这个东西呢？神经科学家正面临着一项挑战，
shielded by our thick skulls and swaddled in layers of protective tissue,
人类大脑受到头盖骨和周围覆盖的多层组织保护，
the human brain is extremely difficult to observe in action.
因此，观察人类大脑是一件非常困难的事情。
For centuries, scientists have tried to understand them using autopsies,
几个世纪以来，科学家尝试通过尸体解剖、
animal models, and, in recent years, imaging techniques.
动物模型以及近几年的成像技术来了解大脑。
We've learned a lot through all these methods, but they have limitations.
这些方法让我们收获良多，但它们存在着局限性。
Conditions like Alzheimer's and schizophrenia,
对于阿尔茨海默症、精神分裂症
and the effect on the human brain of diseases like Zika, continue to hide beyond our view, and our understanding.
和寨卡这种影响大脑的疾病，我们依然不了解其作用机制。
Enter brain organoids, which function like human brains but aren't part of an organism.
类脑器官的功能与人脑类似，但并非生物体的一部分。
Each one comes from an undifferentiated stem cell,
它们来自于未分化的干细胞，
which is a cell that can develop into any tissue in the body, from bone to brain.
这种细胞可以分化成身体中从骨骼到大脑的任一组织。
Scientists can make undifferentiated stem cells from skin cells.
科学家可以从皮肤细胞中提取未分化的干细胞。
That means they can take a skin sample from a person with a particular condition and generate brain organoids from that person.
也就是说，从具有特定条件的人身上提取出一些皮肤组织，就可以培养出这个人的类脑器官。
The hardest part of growing a brain organoid, which stumped scientists for years,
科学家曾耗费数年才实现培养类脑器官，该过程中最大的困难在于
was finding the perfect combination of sugars, proteins, vitamins, and minerals
找到糖、蛋白质、维生素和矿物质的最佳配比，
that would induce the stem cell to develop a neural identity.
只有这样才能诱使干细胞分化成神经细胞。
That was only discovered recently, in 2013. The rest of the process is surprisingly easy.
直到2013年，我们才攻克了这个难关。培养过程中的其他环节则出奇的简单。
A neural stem cell essentially grows itself, similar to how a seed grows into a plant,
神经干细胞通常会自我发育，这就像从种子生长成植物，
all it needs are the brain's equivalents of soil, water, and sunlight.
只需要大脑提供类似土壤、水分、阳光等物质。
A special gel to simulate embryonic tissue, a warm incubator set at body temperature,
这种物质包括一种模拟胚胎组织的特殊凝胶、一个设定在人体温度的恒温箱、
and a bit of motion to mimic blood flow.
以及模拟血液流动的运动。
The stem cell grows into a very small version of an early-developing human brain,
干细胞会发育成为初期的大脑组织，这种类脑组织很小，
complete with neurons that can connect to one another and make simplified neural networks.
其中含有神经元细胞，它们彼此相连，构成了简化版的神经网络。
As mini brains grow, they follow all the steps of fetal brain development.
类脑的继续发育遵循胚胎时期大脑发育的一切步骤。
By observing this process, we can learn how our neurons develop,
通过观察这个过程，我们可以了解神经元如何生长，
as well as how we end up with so many more of them in our cortex,
为何我们比起其他物种拥有更多的神经元细胞，
the part responsible for higher cognition like logic and reasoning, than other species.
从而拥有更高层次的认知，例如逻辑和推理。
Being able to grow brains in the lab, even tiny ones, raises ethical questions, like:
在实验室中培养大脑，即便是迷你版的类脑器官，也引发了一些伦理道德问题，例如，
Can they think for themselves, or develop consciousness?
这些大脑是否能够自行思考或者发展出意识？
And the answer is no, for several reasons.
答案是否定的，原因如下。
A brain organoid has the same tissue types as a full-sized brain, but isn't organized the same way.
类脑器官虽然拥有与正常大脑相同的组织类型，但组织的方式却不相同。
The organoid is similar to an airplane that's been taken apart and reassembled at random;
类脑就像是一架飞机，先被拆散，后又重新随机组装；
you could still study the wings, the engine, and other parts, but the plane could never fly.
虽然你可以继续研究机翼、发动机和其他部件，但这架飞机却无法飞行。
Similarly, a brain organoid allows us to study different types of brain tissue, but can't think.
同样，类脑器官能帮助我们研究不同类型的大脑组织，但是它并不能思考。
And even if mini brains were organized like a real brain, they still wouldn't be able to reason or develop consciousness.
即便类脑器官与正常大脑的组织方式一样，它依然无法推理或建立意识。
A big part of what makes our brains so smart is their size,
智力在很大程度上取决于脑的大小，
and mini brains have only about 100,000 neurons compared to the 86 billion in a full-sized brain.
小型类脑器官只有约10万个神经元，而正常大脑则有860亿个神经元。
Scientists aren't likely to grow larger brain organoids anytime soon.
科学家不太可能在近期培育出更大的类脑器官。
Without blood vessels to feed them, their size is limited to one centimeter at most.
如果没有血管供给养分，类脑器官最多只能生长到1厘米左右。
Finally, mini brains aren't able to interact with the outside world.
最后一点，类脑器官无法与外界交流。
We learn by interacting with our environments:
我们通过与环境互动来学习，
receiving inputs through our eyes, ears, and other sensory organs, and reacting in turn.
通过眼、耳及其他感受器官接受信息，再做出反应。
The complex neural networks that underlie conscious thoughts and actions develop from this feedback loop.
有意识的思考和行为的背后是复杂的神经网络，但神经网络需通过反馈循环才能发展。
Without it, the organoids can never form a functional network.
若没有反馈，类脑器官就永远不能形成功能性的网络。
There's nothing quite like the actual human brain,
虽然类脑器官与实际的人脑并不相同，
but mini brains are an unprecedented tool for studying everything from development to disease.
但它作为一个前所未有的工具，能够用来研究从发育到疾病的任何问题。
With luck, these humble organoids can help us discover what makes the human brain unique,
运气好的话，这些类脑器官可以帮我们发现决定人类大脑独特性的因素，
and maybe bring us closer to answering the age-old question: what makes us human?
从而使我们能够回答长久存在的那个问题：人何而为人？
