This describes a condition in which a patient is awake and retains the power of sense perception, but is unable to communicate except by limited eye movements because the motor nervous system is paralysed. Several diseases can cause this syndrome, which results from interruption of some of the nerve tracts between the mid brain and the pons (see BRAIN). Sometimes the syndrome is caused by severe damage to muscles or the nerves enervating them. Locked-in syndrome may sometimes be confused with a PERSISTENT VEGETATIVE STATE (PVS).