Scientists Create Mice With Brains Largely Composed of Human Tissue

Scientists at Stanford University have created a new type of laboratory mouse with a brain that is largely composed of human neural tissue, a breakthrough designed to provide an unprecedented platform for studying neurological disorders. The research, published in the journal Nature on September 16, 2026, involves genetically engineering mice to lack most of their own cerebral cortex and hippocampus, creating a vacant space into which human brain organoids are transplanted. The technique, which the researchers have termed "xenocortication," allows the human tissue to grow and integrate more extensively than in previous models. Within three months of transplantation, the human organoids expanded to occupy over 90 percent of the cortical volume in the mice. The human neurons formed connections with the mouse's existing nervous system, including extending projections into the spinal cord. A key finding was the unexpected development of von Economo neurons (VENs) within the human tissue. These rare, specialized cells, previously observed only in autopsied human brains and linked to social cognition, had never been successfully generated in laboratory cultures.