On June 12, 2014, a young man named Juliano Pinto stood on a field and, as 1.2 billion people looked on, performed the ceremonial first kick of the World Cup in São Paulo. The pass was unremarkable except that Juliano had been paralyzed from the waist down for almost a decade. Thanks to a robotic exoskeleton he controlled with his brain, he was able to kick the ball a few feet down the field.

That moment was the culmination of two decades of work in brain-machine interface technology, a research field I pioneered with my...