Human Brain Organoids Restore Cognition in Mice Missing Half Their Cortex

Researchers at Stanford’s S. Pașca lab transplanted human cerebral‑cortex organoids into mice that had been genetically engineered to lack more than 90 % of their cortex, a region essential for memory, movement and thought. The grafts, grown from human stem cells over 40 days, filled the skull cavities and integrated with the mice’s neural circuitry, forming cortex‑like tissue that covered roughly 90 % of the missing volume. Behavioral tests showed that the mice with organoid transplants—named XCX mice—performed almost as well as normal mice on a maze‑navigation memory task, while control mice without grafts fell behind. The organoids also contained von Economo neurons and corticospinal projections, which likely contributed to the partial recovery of motor function and to a hypoxia response that mirrors human physiology. These findings suggest that human organoid‑transplanted mice could serve as more accurate models for studying conditions such as cerebral palsy and for screening drugs that target cortical dysfunction.