Stanford just created a HUMAN-MOUSE CHIMERA whose cerebral cortex is 92% HUMAN BRAIN TISSUE.

Stanford team led by Sergiu Pasca created mice genetically missing 98% of cortex and hippocampus then transplanted human cortical organoids into 2-day-old animals. By three months human tissue occupied nearly 92% of the cortical space, formed connections to mouse brain and spinal cord, and produced rare cells like von Economo neurons. Goal is studying autism, epilepsy, and other neurodevelopmental disorders. Science AAAS piece today notes the Nature results from September 16. Pasca’s group in 2022 transplanted human organoids into newborn rats where they grew to about one-third of a hemisphere and integrated into circuits.

https://www.science.org/content/article/human-neurons-flourish-mouse-brains-offering-new-view-neurodevelopmental-disorders

https://www.nature.com/articles/d41586-026-02912-8

https://arstechnica.com/science/2026/09/researchers-swap-in-human-brain-cells-for-a-mouses-cortex/

https://www.nytimes.com/2022/10/12/science/human-brain-cells-organoids-rats.html

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