Human Brain Cells Grafted Into Mice Raise Ethical Questions

Stanford scientists created mice with brains containing millions of functioning human neurons, nearly half their brain volume, to study neurocognitive disorders. The feat raises ethical questions about consciousness. Published in Nature, researchers genetically engineered mice lacking cortex neurons and implanted human cells, which multiplied and connected with the mouse brain. The mice behaved normally but showed human-like brain damage from oxygen deprivation, unlike typical mice. The human neurons resembled fetal cells and included von Economo neurons linked to dementia. Researchers stopped experiments at six months to avoid potential consciousness, prompting bioethicists to question the animals' rights and welfare.