At Stanford, scientists have crossed a threshold long approached but never quite reached: the creation of mice whose brains carry living human neural tissue, grown from organoids and integrated into a functioning animal nervous system. The technique, called developmental xenocortication, offers researchers something neither a petri dish nor a mouse alone could provide — a living window into how the human brain forms, misfires, and might be healed. It is the kind of advance that arrives quietly in a laboratory and reverberates loudly in the larger questions humanity asks about mind, identity, a