In 2020, Ujwal Chaudhary, a biomedical engineer then at the University of Tübingen and the Wyss Center for Bio and Neuroengineering in Geneva, watched his computer with amazement as an experiment that he had spent years on revealed itself. A 34-year-old paralyzed man lay on his back in the laboratory, his head connected by a cable to a computer. A synthetic voice pronounced letters in German: "E, A, D . "