‘Alien-cortical’ mice: Can human brain cells grow inside animals?

What the report says

Al Jazeera reports that researchers at Stanford University have implanted lab-grown human brain cells into genetically modified mice in California, creating animals with human neurons inside parts of their brains that normally help control movement, learning and memory. The study, published in Nature and described by the researchers as a model for studying the human brain, used human organoids grown from stem cells and inserted them into newborn mice that were missing much of the cerebral cortex and nearby hippocampus.

According to the article, the human tissue expanded rapidly over several months, connected to the mice’s blood supply and occupied much of the brain space left open by the genetic edits. The mice generally behaved normally, but performed better in maze tests than mice without the implants. The researchers also said some of the implanted cells developed into rare von Economo neurons, which are not normally found in mice. Al Jazeera notes the work may help scientists study disorders including schizophrenia, cerebral palsy and dementia.

The report says the experiment is part of a broader effort to create useful models for human brain research, since direct study of living human brain tissue is limited by ethics and complexity. At the same time, it highlights growing concern over “neurohybrid” research and the lack of clear boundaries for experiments that mix human and animal cells. The researchers ended the work before signs of consciousness appeared, but outside experts cited in the article warned that the field could eventually raise more difficult ethical questions as it moves beyond rodents.