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

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

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

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

  • Why would we need such a thing?

  • Neuroscientists face a challenge:

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

  • the human brain is extremely difficult to observe in action.

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

  • animal models,

  • and, in recent years, imaging techniques.

  • We've learned a lot through all these methods,

  • but they have limitations.

  • Conditions like Alzheimer's and schizophrenia,

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

  • continue to hide beyond our view, and our understanding.

  • Enter brain organoids, which function like human brains

  • but aren't part of an organism.

  • Each one comes from an undifferentiated stem cell,

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

  • from bone to brain.

  • Scientists can make undifferentiated stem cells from skin cells.

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

  • and generate brain organoids from that person.

  • The hardest part of growing a brain organoid,

  • which stumped scientists for years,

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

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

  • That was only discovered recently, in 2013.

  • The rest of the process is surprisingly easy.

  • A neural stem cell essentially grows itself,

  • similar to how a seed grows into a plant,

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

  • A special gel to simulate embryonic tissue,

  • a warm incubator set at body temperature,

  • and a bit of motion to mimic blood flow.

  • The stem cell grows into a very small version

  • of an early-developing human brain,

  • complete with neurons that can connect to one another

  • and make simplified neural networks.

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

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

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

  • the part responsible for higher cognition like logic and reasoning,

  • than other species.

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

  • raises ethical questions, like:

  • Can they think for themselves, or develop consciousness?

  • And the answer is no, for several reasons.

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

  • but isn't organized the same way.

  • The organoid is similar to an airplane

  • that's been taken apart and reassembled at random;

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

  • but the plane could never fly.

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

  • but can't think.

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

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

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

  • and mini brains have only about 100,000 neurons

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

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

  • Without blood vessels to feed them,

  • their size is limited to one centimeter at most.

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

  • We learn by interacting with our environments: receiving inputs

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

  • The complex neural networks that underlie conscious thoughts and actions

  • develop from this feedback loop.

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

  • There's nothing quite like the actual human brain,

  • but mini brains are an unprecedented tool

  • for studying everything from development to disease.

  • With luck, these humble organoids can help us discover

  • what makes the human brain unique,

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

  • what makes us human?

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

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B1 US TED-Ed brain tissue stem cell human brain develop

【TED-Ed】What are mini brains? - Madeline Lancaster

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    Samuel posted on 2018/02/26
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