The Scientific Basis of Cryonics
technologyreview.com
technologyreview.com
The bugger that haunts human cryonics is that thawing is never perfect because the cryoprotectants used to prevent ice-crystals within the cells are usually toxic. If you freeze cells that are measured to be 100% viable/alive at the time (very common) then thaw them using best practices, you're going to have some cell death-- maybe 1-5% if you're fast (less time spent in toxic cryoprotectant) and lucky. If you're unlucky or slow, you can look at 25-45% of your originally healthy cells being dead upon completion of the thawing process. The remaining cells are usually extremely discombobulated, and can take days to return to their baseline. This is completely fine if you're tooling around in a research lab or industrial lab, but even a 1% loss is probably too much for a human brain to bear and remain the same as before.
I suppose that if you work under the assumption that the future technology cryonics relies on for thawing will exist, cell loss during thaw will not be a problem; I find this possibility to be fairly likely over a long time span. Alternatively, you could assume that there will be advanced ways of restoring brain function or generating fresh neurons after systemic damage-- quite a stretch if you ask me, but it's conceivable. I think that ultimately the goals of cryonics will be scientifically realizable for those who were most recently preserved.
You probably lose at least that many neurons over a lifetime; consider the shrinking volume of the brain with age. And losses definitely easily exceed 1% in early Alzheimer's or dementia, but while not fun, people with early Alzheimer's clearly have not died or ceased to exist!
(And anyway, the real question about the dead cells is whether they still have the information about their synaptic weights and other functional information. Being able to revive the cell is overkill; the focus on revival is as an _a fortiori_ argument, since any revival proves that, even in the absence of future scanning advances, it must be possible.)
It would seem like there should be a difference between an operational brain losing neurons and a suspended brain losing neurons?
I'd assume that if inter-neuron communication speed is anywhere on the same order as the time-between-individual-neuron-loss, then that would alleviate the effect somewhat, no? My understanding was there was a lot of redundancy up there, so it would make sense that the brain would resilver itself in certain scenarios.
The brain is remarkably resilient and adaptive; people manage to recover at least partial function even after major strokes. And, quite frankly, I'd take "functioning like a stroke victim" over "dead" any day.
Has anyone tested this on a macroscopic creature? In particular, one complex enough to demonstrate memory, which could be tested afterward?
I've seen one or two reports of such tests, but nothing going into detail about the degree of function afterward.
The above video is a short demonstration of one such amphibian
Won't work so smoothly on most living creatures or organ structures for a few reasons. First, for cells in a liquid media solution or very small/simple animals, you can guarantee that the cryoprotectant is going to permeate into all the proper places, preventing destructive ice crystals from forming inside of the cells. For an entire living creature, there's a bunch of barriers-- rate of seeping of cryoprotectant through tissues, large internal solid and liquid volumes, and difficult-to-permeate epithelial tissue or fur. The cryoprotectants can seep through outer skin without additional help, but there are likely to be some spots where they can't or don't get to. It's important to remember that this process would have to occur in a race against two separate death clocks: race one is against irreversible damage as a result of stalled metabolic output (death of neurons or other irreplaceables from lack of oxygen or nutrients) and race two is against the toxicity of the cryoprotectant/freezing process causing irreversible damage in the first-permeated tissues before metabolic activity is completely stopped by freezing temperatures. I have no idea if these spots are understood or identified.
Second, the far larger problem is removing the toxic cryoprotectant once metabolic activity has resumed during thawing. For cells in a liquid media solution, you can pellet cells to the bottom of a test tube in a centrifuge, then suction off the cryoprotectant. For an entire living creature, I don't even know where you'd begin, or how you'd guarantee all the cryoprotectant was flushed out. For cells in liquid media, you have about a 30 minute time window to remove the cryoprotectant before your cells are kaput.
http://www.evidencebasedcryonics.org/scientists-open-letter-...
You might also look at the Alcor FAQ for scientists:
http://www.alcor.org/sciencefaq.htm
Some of the ongoing information generated by the Brain Preservation Foundation's technology prize competition is also interesting.
http://www.brainpreservation.org/competitors/
The perspective of the BPF folk is perhaps a useful calibration point for those coming into this as a new topic; they are critical of cryonics for some detailed technical reasons, with plenty of room for debate, think that plastination should be developed as an alternative technology, but are firm supporters of the concepts of brain preservation and the evidence to date for fine structure preservation. For example, see this response to an earlier and very shoddy article critiquing cryonics at the Technology Review:
http://www.brainpreservation.org/ken-hayworths-personal-resp...
It is, without exaggeration, the greatest tragedy in the world, and it's happening because superstition and our society's anti-superstition memetic immune system misfired simultaneously.
Agreed. Though I would argue we should be spending even more effort and funding on anti-aging research and AI, the two routes to what people will need at the other end of cryopreservation. (The latter being much more comprehensive than the former.)