Because one very important application for brain/computer interfaces is prosthetics. If muscles in the hand are interpreting the signals from motor neurons, and

Because one very important application for brain/computer interfaces is prosthetics. If muscles in the hand are interpreting the signals from motor neurons, and the computer reacts to muscle movements, then it's not useful for that. The amputees have motor neurons, but they don't have hands so you need to get the nerve signals more directly. I don't know anything more than GP with regard to this project, but that's the question they're asking.