Biomedical research has shown us some of the brain's secrets, but we've hardly scratched the surface. That's why growing brain cells in the lab has become a great way for us to learn more.

Since stem cells can be coaxed to become any cell type, they can grow into mini-organs called organoids. They possess many of the same properties of the real tissue or organ. This has allowed work that leads to new drugs and new therapies. They also help us understand human development and genetic diseases.

Recently, they've been able to grow human brain organoids the size of a cherry tomato seed. They've been implanted into mouse brains that had injuries to their visual cortex. It's where vision is processed.

Researchers wanted to see if the human brain cells would begin to repair the damage. After three months, the implanted organoid became incorporated into the mouse brain where the mouse and human neurons became integrated.

Here is the cool part. When the mice were exposed to flashing light, the human neurons in the mouse brains responded with electric impulses to the visual stimulus. This means the cells of the implanted organoids had restored part of the animal's visual response.

The implications are major. It shows that brain organoids can potentially repair an injured brain. Maybe someday the brain of a stroke victim.

It's way too early to get excited about real applications but if scientists continue to make progress in this area, one day we can make huge inroads for people with all sorts of brain injuries.

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