Scientists create mice whose brains are filled with millions of human neurons. Experiments raise ethical questions.

Scientists have made mice with a remarkable amount of room for human brain tissue to grow.

By genetically engineering animals lacking part of their brain, researchers created a living model in which pea-sized clumps of human neurons could expand, mature and wire into a developing nervous system, ultimately coming to dominate the mouse cortex, the brain’s outer layer.

The model offers a new way to study human neural circuits and brain disease, researchers report September 16 in Nature.

“Our goal has been to make aspects of human brain development and function accessible for investigation, so we can develop therapeutics,” says Sergiu Pașca, a neuroscientist at Stanford University.

The idea of growing miniature brain structures in a lab dish emerged in the early 2010s, when researchers in Austria showed that stem cells could self-organize into 3-D tissue resembling aspects of the developing human brain. But these tiny clusters of human nerve cells, called organoids, lacked the connections and sensory inputs of a living brain.

https://www.sciencenews.org/article/mice-brain-human-organoid-cells

The studies may help reveal the causes of brain disease in people and point the way to treatments. But researchers already are calling for new ethical guidelines.

https://archive.is/A0An7#selection-8113.0-8113.162