Absence of consciousness

In human beings the medical condition called coma is the only one known in which all consciousness is believed to be absent. In this state all voluntary mental activity is considered impossible. Even reflex functioning disappears and the individual cannot be wakened. The patient's life functions are maintained however, and recovery from coma and comatose conditions is common. On recovery there is complete amnesia about the period of coma.

Life without consciousness, the state of coma, raises interesting problems in that life functions must be regulated by something internally. To deny the internal controls or regulators a status of being a species of consciousness is to evade the issue in the philosophical mind-body problem. The state of coma and other conditions illustrate that the taxonomics for the properties and kinds of consciousness are far from being complete or coherent.