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.
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).
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.
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 say it is bad for public relations. 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.
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- Fahy, Gregory M.; Wowk, Brian (2015). "Principles of Cryopreservation by Vitrification". 1257: 30–33. doi:10.1007/978-1-4939-2193-5_2. ISSN 1064-3745.
Interestingly, the concentrations generated by freezing actually exceed the concentrations required for the vitrification of even large living systems
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In 1977, Fahy  and Fahy and Karow  pointed out that damage after freezing and thawing in certain cases is actually correlated not with the amount of ice formed but with the concentration of permeating cryoprotectant during freezing and thawing, and that therefore cryoprotectants can exert damaging effects as they are concentrated in the frozen state. Meryman et al. independently reported in the same year that toxic effects of methanol, ethanol, and ammonium acetate in the frozen state are also detectable in thawed erythrocytes . These non-nucleated cells did not show injury attributable to glycerol or Me2SO in the latter experiments, but evidence continued to emerge in support of putatively toxic effects of cryoprotectants during freezing [2,10,12,14,28], including such effects even in glycerolized erythrocytes [47,50,53], and by 1986 the overall evidence had become quite strong .
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