Implanting hardware in the brain is dangerous, but the reward for patients could outweigh the risks. For companies like Paradromics, the goal is to significantly refine and expand the current methods, providing a faster and more complete way for patients to operate machines with their thoughts.

Mr. Musk’s Neuralink is moving in a similar direction, but the company’s ambitions appear to stretch much further, to eventually implanting chips in healthy people’s brains.

The dangers of brain surgery make this unlikely. But Mr. Boyden said there were some possibilities.