Brain death is the complete loss of brain function, including involuntary activity necessary to sustain life. It differs from persistent vegetative state, in which the person is alive and some autonomic functions remain. It is also distinct from an ordinary coma, whether induced medically or caused by injury and/or illness, even if it is very deep, as long as some brain and bodily activity and function remain; and it is also not the same as the condition locked-in syndrome. A differential diagnosis can medically distinguish these differing conditions.