Stanford researchers reported in Nature that they engineered mice whose brains contain extensive human neuronal cells, creating what they call “xenocortical mice.” By genetically modifying mice to leave space in cortex and hippocampus development, the team increased the take-up of injected human cells. Behavioral testing showed differences on maze tasks, with the human-cell–containing mice demonstrating improved performance relative to controls, while animals with reduced native brain tissue showed memory deficits. The platform is proposed as a tool for studying brain injury and potentially drug testing. Independent commentary from within Stanford’s research ecosystem frames the work as a demonstration of how genetic engineering and stem-cell methods can reshape experimental biology across species boundaries.