Neuropreservation is the speculative procedure of cryopreservation of the human brain 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. Neuropreservation is a type of cryonics procedure. 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).
Simple organisms, including Caenorhabditis elegans and related species, have been cryopreserved by freezing and revived; a recent study further claims to have revived C. elegans with memories of trained behavior intact, with a new as-yet-unpublished vitrification protocol. Cryopreservation of humans, whether just the brain or the whole body, remains dependent on future technology for advanced repairs if it is to work.
Future recovery prospects
The hypothetical technologies required to revive today's cryonics patients, such as nanomedicine and molecular nanotechnology, should be capable of tissue and organ regeneration and thus should be able to revive neuropatients as well. Neuropreservation is typically less expensive than whole body cryopreservation, and can potentially result in better brain preservation because the process can be optimized for the brain.
One scenario posited by cryonics organisation Alcor involves programming cells on the brain to regenerate a new body around the repaired brain inside a fluid life support environment, after cell-by-cell repair technology has first restored the brain. Other potential cryonics revival technologies for both neuropatients and whole body patients have been considered. News media sometimes report that new bodies are expected from cloning, but some cryonics experts dismiss cloning, claiming that nothing as crude as nuclear transfer or transplants will ever have to be used in cryonics. They believe the methods used for recovery of neuropatients will be an extension of mainstream medical technologies that will someday be developed to regrow lost limbs and treat severe trauma.
Mind uploading is another possibility that is frequently discussed. Transferring the information content of a cryopreserved brain into an artificial brain may be no more or less feasible than re-growing a biological body, especially to a society with technology capable of reviving cryopreserved brain tissue.
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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Interestingly, the concentrations generated by freezing actually exceed the concentrations required for the vitrification of even large living systems
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