Locked-in patients have lost the ability to control the body voluntarily, but they retain some ability to control the face. Often they can move only their eyes. Although they are conscious, they are unable to communicate.
—David E. Levy, Discover, May 1998
A locked-in diagnosis (the term was first used in 1966 by the American neurologists Jerome Posner and Fred Plum) means that although a person has been abandoned by his or her body, the brain still functions. The most clear evidence for this is usually some residual voluntary eye movement, a deliberate response to “Blink if you hear me.”