Legal definition of death often encounters controversies between moral and ethical values. A person is said to be legally dead if there is no detectable brain activity in that person. Brain death is considered as an irreversible coma. Vegetative state is often confused with the brain death; in case of vegetative state, a person loses consciousness due to severe brain damage but is awake. Person in a vegetative state often opens his eyes or respond to feeding but his brain is almost dead i.e. he has no awareness.
After a legal death of a person, the brain structure encoding personality and the long term memory persists in the brain. The exact timing of this retention of long term memory is unknown. The point at which this retained memory is lost is called information-theoretic death.
Cryonic preservation is the method in which humans and animals are preserved by use of contemporary medicine before information–theoretic death, so that can they can be recovered in future by more advanced technology. Cooling a body to a very low temperature decreases further degradation of cells and helps the body to remain in good condition for longer time.
It is possible to preserve the long term memory and the identity of a person in present technology by cryonics. This might seem a bit sci-fi but some animals can survive prolonged exposure to freezing temperatures.Successful experiments have been done which clearly show that cryogenically preserved worms retain specific acquired memories after reanimation.
If worms can handle these freezing conditions with successful reanimation, it could be a big step towards cryogenic preservation of larger organisms.
Dozens of people are frozen in cryogenic facilities waiting to be revived soon, the first person to get cryogenically preserved was Dr. James Bedford who was suspended in 1967 and his body is still in good condition at the Alcor Life Extension Foundation.