The locked-in syndrome results from de-efferentation, such that a patient is awake, self-ventilating and alert, but unable to speak or move; vertical eye movements and blinking are usually preserved, affording a channel for simple (yes/no) communication.
The most common cause of the locked-in syndrome is basilar artery thrombosis causing ventral pontine infarction (both pathological laughter and pathological crying have on occasion been reported to herald this event). Other pathologies include pontine hemorrhage and central pontine myelinolysis. Bilateral ventral midbrain and internal capsule infarcts can produce a similar picture.
The locked-in syndrome may be mistaken for abulia, akinetic mutism, coma, and catatonia.
Bauby J-D. The diving-bell and the butterfly. London: Fourth Estate, 1997 Feldman MH. Physiological observations in a chronic case of locked in syndrome. Neurology 1971; 21: 459-478