Cryonics – Wikipedia, the free encyclopedia

For the study of the production of very low temperatures, see Cryogenics. For the low-temperature preservation of living tissue and organisms in general, see Cryopreservation. For the Hot Cross album, see Cryonics (album).

Cryonics (from Greek 'kryos-' meaning 'icy cold') is the low-temperature preservation of animals and humans who cannot be sustained by contemporary medicine, with the hope that healing and resuscitation may be possible in the future.[1][2]

Cryopreservation of people or large animals is not reversible with current technology. The stated rationale for cryonics is that people who are considered dead by current legal or medical definitions may not necessarily be dead according to the more stringent information-theoretic definition of death.[3] It is proposed that cryopreserved people might someday be recovered by using highly advanced technology.[4]

Some scientific literature supports the feasibility of cryonics.[4][5] An open letter supporting the idea of cryonics has been signed by 63 scientists, including Aubrey de Grey and Marvin Minsky.[6] However, many other scientists regard cryonics with skepticism.[7] As of 2013, approximately 270 people have undergone cryopreservation procedures since cryonics was first proposed in 1962.[8][9] In the United States, cryonics can only be legally performed on humans after they have been pronounced legally dead, as otherwise it would be considered murder or assisted suicide.[10]

Cryonics procedures ideally begin within minutes of cardiac arrest, and use cryoprotectants to prevent ice formation during cryopreservation.[11] However, the idea of cryonics also includes preservation of people long after legal death because of the possibility that brain structures that encode memory and personality may still persist and be inferable in the future. Whether sufficient brain information still exists for cryonics to successfully preserve may be intrinsically unprovable by present knowledge.[12] Therefore, most proponents of cryonics see it as an intervention with prospects for success that vary widely depending on circumstances.

A central premise of cryonics is that long-term memory, personality, and identity are stored in durable cell structures and patterns within the brain that do not require continuous brain activity to survive.[13] This premise is generally accepted in medicine; it is known that under certain conditions the brain can stop functioning and still later recover with retention of long-term memory.[14][15] Additional scientific premises of cryonics[16] are that (1) brain structures encoding personality and long-term memory persist for some time after legal death, (2) these structures are preserved by cryopreservation, and (3) future technologies that could restore encoded memories to functional expression in a healed person are theoretically possible. At present only cells, tissues, and some small organs can be reversibly cryopreserved.[17][18]

Cryonics advocates say it is possible to preserve the fine cell structures of the brain in which memory and identity reside with present technology.[19] They say that demonstrably reversible cryopreservation is not necessary to achieve the present-day goal of cryonics, which is preservation of brain information that encodes memory and personal identity. They say current cryonics procedures can preserve the anatomical basis of mind,[11] and that this should be sufficient to prevent information-theoretic death until future repairs might be possible.[20]

A moral premise of cryonics is that all terminally ill patients should have the right, if they so choose, to be cryopreserved.[21] Some cryonicists believe as a matter of principle that anyone who would ordinarily be regarded as dead should instead be made a "permanent patient" subject to whatever future advances might bring.[22]

Long-term cryopreservation can be achieved by cooling to near 77.15 Kelvin (approximately -196.01C), the boiling point of liquid nitrogen. It is a common mistaken belief that cells will lyse (burst) due to the formation of ice crystals within the cell, since this only occurs if the freezing rate exceeds the osmotic loss of water to the extracellular space.[23] However, damage from freezing can still be serious; ice may still form between cells, causing mechanical and chemical damage. Cryonics organizations use cryoprotectants to reduce this damage. Cryoprotectant solutions are circulated through blood vessels to remove and replace water inside cells with chemicals that prevent freezing. This can reduce damage greatly,[24] but freezing of the entire body still causes injuries that are not reversible with present technology. The difficulties of recovering complex organisms from a frozen state have been long known. Attempts to recover large frozen mammals by simply rewarming were abandoned by 1957.[25]

When used at high concentrations, cryoprotectants stop ice formation completely. Cooling and solidification without crystal formation is called vitrification.[26] The first cryoprotectant solutions able to vitrify at very slow cooling rates while still being compatible with tissue survival were developed in the late 1990s by cryobiologists Gregory Fahy and Brian Wowk for the purpose of banking transplantable organs.[27][28] These solutions were adopted for use in cryonics by the Alcor Life Extension Foundation, for which they are believed to permit vitrification of some parts of the human body, especially the brain.[29] This has allowed animal brains to be vitrified, warmed back up, and examined for ice damage using light and electron microscopy. No ice crystal damage was found.[20][30] The Cryonics Institute also uses a vitrification solution developed by their staff cryobiologist, Yuri Pichugin, applying it principally to the brain.[31]

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Cryonics - Wikipedia, the free encyclopedia