A few decades ago, the idea of being able to interact directly with a computer using only your thoughts would have sounded like science fiction. But today researchers and companies are testing brain-computer interfaces that allow patients to move a computer cursor or control a prosthetic limb directly with their thoughts. Nicholas Hatsopoulos, PhD, discusses the future of brain-computer interfaces, how they work, the practical challenges researchers face, and what scientists have learned about the brain as they develop this technology.