Did you read the book "The Diving Bell and The Butterfly"? Or see the movie? It's quite an amazing story of a man with so-called "Locked-In Syndrome". It's an absolutely riveting story. Here's a new account of a similar story that occurred in Brussels. From the article:
'A breakthrough came when he was able to indicate yes or no by slightly moving his foot to push a computer device placed there by Laureys' team. Then came the spelling of words using his finger and a touch-screen attached to his wheelchair.
"You have to imagine yourself lying in bed wanting to speak and move but unable to do so — while in your head you are OK," Vanhaudenhuyse said. "It was extremely difficult for him and he showed a lot of anger, which is normal since he was very frustrated," she said.' (from "Son In Coma Heard Everything for 23 Years")