Stanford Scientists Create Mice with Half-Human Brains to Study Neurological Disorders

Researchers at Stanford University have transplanted lab-grown human neurons into genetically modified mice, creating "xenocortical" mice whose brains are roughly half human. The study, published in Nature on September 16, was co-authored by neuroscientist Sergiu Pașca. The mice were engineered to lack a cortex and hippocampus, and at two days old received injections of human brain organoids containing about 100,000 cells each. Within three months, human tissue occupied over 90 percent of the cortex and integrated into the animals' neural circuitry. The mice performed similarly to controls on behavioral tests, while mice with simple brain lesions showed memory and gait issues. Some human-derived tissue developed into von Economo neurons, which are among the first to die in frontotemporal dementia. Pașca now plans to use these mice to study that dementia and cerebral palsy. The research raises ethical concerns about organoid consciousness and pain, prompting independent bioethicist review. The work offers a new model for studying schizophrenia, cerebral palsy, and dementia.