I’m pretty sure that if Dante had known about locked-in syndrome he would have rewritten the chapter in the Inferno devoted to the ninth circle of hell. In the most recent Esquire, Joshua Foer has an excellent profile of Erik Ramsey, who suffered a devastating injury to his brain stem, leaving him entirely paralyzed. (The only muscles Erik could consciously control were the ones that moved his eyeballs up and down.)
There are stories of people being locked-in for years before anyone notices the fully conscious person hiding inside the paralyzed body. In 1966, a thirty-two-year-old woman named Julia Tavalaro became locked-in after a brain hemorrhage and was sent to Goldwater Memorial Hospital on Roosevelt Island, New York, where the staff took to calling her “the vegetable”. It wasn’t until six years later that a family member noticed Tavalaro trying to smile after she heard a dirty joke. She was immediately taught to communicate with eye blinks and became a poet and author. She died in 2003 at the age of sixty-eight, having never spoke for thirty seven years.