Mice with human brain cells offer a tool to study disease. Ethicists ask: What's next?

Researchers have developed a new way to install millions of human brain cells into mice, as a way of creating better scientific models for studying neurodegenerative disease.

Treatments Brain organoids are helping researchers, but their use also creates unease Using genetic tools, the scientists bred mice that were missing most of their cerebral cortexes – the outermost layer of the brain involved with reasoning, memory and consciousness. Then, they replaced a large part of those missing mouse cells with lab-grown human brain cells, creating mice with human neurons that can be altered to approximate human brain conditions researchers are eager to study.