Stanford University researchers led by Prof Sergiu Pașca have successfully implanted human brain organoids into mice genetically engineered to lack their own cerebral cortex. The human cells, derived from reprogrammed skin cells, integrated with the mouse brain circuitry and began functioning like the animal's own outer brain layer after six months. Behavioral tests showed the modified mice performed largely like normal mice, with no cognitive enhancement.

This breakthrough aims to address psychiatry's low clinical trial success rate by creating models for human-specific conditions like epilepsy, autism, and cerebral palsy that cannot be studied in standard rodents. Pașca stated the model captures aspects of human brain function previously impossible to observe.

Dr Sarah Chan, bioethics reader at the University of Edinburgh, confirmed there is no indication these mice think like humans, but noted the research prompts important questions about altering animal cognition. The study, published in Nature, represents a significant advance in neurodevelopmental disease research while raising ethical considerations about human-animal chimeras.