Cryonics refers to preserving humans and other animals with low temperatures. This is often done on patients who are too ill to be helped by present-day medicine. Although cryopreservation is not reversible in humans, it is hoped that in the future, advances in medicine will make this possible. Currently, human cryonics can only be performed on people who have been declared legally dead.

Proponents of cryonics claim that a person’s personality, memories, and entire identity are stored in the brain. However, the brain rarely handles death well. Under certain circumstances, the brain may completely stop all activity, only to resume it later, but this is rare. Supporters insist that the cryo protectant is circulated through the brain, preventing damage from freezing and hopefully preserving the cells which contain our memories and identity.

Those who are against cryonics point to our technological and biological limitations. Some creatures, like frogs, can survive in a partially frozen state for months before being revived, though this is not truly cryonic preservation. Current technology allows us to cryopreserve small bits of tissue – blood vessels, tissues, cells, and even small animal organs. However, technology does not allow us to reverse cryonics in humans.

Cryopreservation is done by cooling the body to -196°C (-321°F). When a body is frozen to below the freezing point, ice forms in between the cells. This can cause damage, both mechanically and chemically. In cryonics, cryoprotectant solutions are circulated through the blood vessels, replacing water with chemicals to prevent much of the damage.

Because patients undergoing cryonics must be declared legally dead, they run the risk of Ischemic injury – injury caused by a lack of blood circulation. If the brain has no oxygen for several minutes or hours, the damage to the brain could be impossible to surmount. Supporters of human cryonics insist that advances in medical technology will allow for future revival, even in these cases.

Perhaps the biggest challenge to cryonics is currently the issue of revival. Currently, there is no technology on the horizon that will permit a reversal of human cryopreservation. Revival will require repairing extensive damage caused by freezing, lack of oxygen, and other problems.

For many, preserving the entire body is a waste of time. They aim for neuropreservation, preserving the brain while disposing of the body. Since the brain holds our memories and personality, and since reversing cryonic preservation in large bodies is problematic, many hope to preserve their brains. They gamble that future technology will allow tissue regeneration, so they can grow a new body.

Others prefer to have “whole body” preservation, preferring not to gamble on future technology. In either case, it’s an expensive proposition. Preserving the whole body can cost up to $150,000, not including annual maintenance fees. Cryopreserving just the head costs about half as much. Cryonics is an expensive proposition, with costs comparable to major transplant surgery. A large sum of money must be put aside to pay for annual maintenance, approximately $500 each year.

Cryonics has caused a divide between many people. This is based on questions of whether cryonics is medicine or internment. For those with strong religious beliefs, only God has the power of resurrection. If cryonics is medicine, on the other hand, then patients are in a coma, and the prognosis is uncertain. Only the future will tell whether cryonics is indeed reversible, or whether it is death.

Technicians prepare a patient for cryopreservation. Courtesy Wikipedia.