Neuropreservation is a type of cryonics procedure where the brain is preserved with the intention of future resuscitation and regrowth of a healthy body around the brain. Usually the brain is left within the head for physical protection, so the whole head is cryopreserved. A cryonics patient who undergoes neuropreservation is said to be a neuropatient.
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The procedure is often done because vitrification of the entire body is not yet available. Vitrification essentially eliminates the mechanical and chemical damage caused by ice formation, at the cost of cryoprotectant toxicity and side effects of dehydration of tissue due to the blood-brain barrier. Although not a direct consequence of vitrification itself, storage of the vitrified brain directly in liquid nitrogen raises the further aspect of fractures, which are fewer in number but larger in scale in vitrified tissue than frozen tissue, a consequence of cooling from Tg (-135 °C) to liquid nitrogen's boiling point (-196 °C).
Advantages
Neuropreservation has several advantages over whole body preservation. It costs less; neuropatients are easier to transport in case of legal, social, or physical problems; it is possible to do a better job of perfusing and therefore cryoprotecting the brain when there is no need to consider other tissues, and its smaller volume allows more rapid and less expensive cooling. Aubrey de Grey has theorized that neuropatients will be revived after procedures have been perfected on whole body patients, and therefore have better chances for revival.
History
Neuropreservation was first proposed in 1965 by cryonics co-creator Evan Cooper, proposed again in a speculative scientific paper by gerontologist George M. Martin in 1971, and independently proposed yet again in 1974 by Mike Darwin, and Fred and Linda Chamberlain. The Chamberlains were the founders of the Alcor Life Extension Foundation. In 1976 Fred’s father became the first of many neuropreservation patients at Alcor.
Prior to the year 2000, neuropreservation was performed by surgical separation of the body from the head (called cephalic isolation or "neuroseparation") at the end of cryoprotectant perfusion performed on the upper body via the ascending aorta. After that year, Alcor began performing cephalic isolation before cryoprotectant perfusion, in deep hypothermia, and then using the carotid and vetebral arteries directly for perfusion with cryoprotectants.
As of 2014, Alcor, Oregon Cryonics, and KrioRus are the only cryonics organizations that offer neuropreservation. Other organizations, such as the other major provider, the Cryonics Institute, avoid it because they are concerned about neuro's negative effect on the public’s perception of cryonics and, especially, because of the negative impact on the families of patients. Journalists & horror novelists invariably have a field day with "frozen severed heads," and focus not on the scientific or humanitarian purposes of cryonics, but on sensationalizing cryonics as grotesque or ridiculous. Their policy to always preserve the entire body prevents anyone leveling those claims at CI. Their goal is to preserve and eventually revive people, so they avoid processes like neurocryopreservation that could damage or otherwise put their patients at risk. Alcor claims there are good technical justifications for neuropreservation, and that they will continue to offer it. Approximately three quarters of the cryonics patients stored at Alcor are neuropatients.