I know of no evidence. Closest I know is the promising result that a percentage of pinewood nematodes (a favourite of cryobiology researchers, having about the simplest known nervous system that is definitely a nervous system) survive cryoprotectants and vitrification and, if they survive, go on to parasitise pinewoods much like they did before. (E. Riga and J. M. Webster. “Cryopreservation of the Pinewood Nematode, Bursaphelenchus spp.”J. Nematol. 1991 October; 23 (4): 438–440.) Preserving a neural network is of course the holy grail. But this is getting way off topic for a blog about the art of human rationality.
Of course it is what happens to whole brains that are vitrified that really matters to cryonics. The only paper published so far on the technology presently used in cryonics applied to whole brains is this one
Unlike slices, there is no expectation that cell viability is preserved in whole brains because the cryoprotectant exposure time is longer. However connectivity and extensive biochemical information is believed to be preserved, as these micrographs suggest. It is presumed, but not proven, that the effect of thermal stress fractures at cryogenic temperatures is displacement of fracture planes. This would theoretically still preserve connectivity information, although requiring hyper-advanced technology to do anything with that information.
First off, for it to preserve no information at all would be extremely surprising. If there are physical structures, that’s some kind of information. But that’s not the question we’re interested in—we are interested in relevant information. As you say, preserving a neural network is the “holy grail” (at least if you aren’t counting loftier yet less crucial goals like reversible whole-body suspension). Notwithstanding, we do have evidence that there is at least some brain structure being preserved—there are pictures and everything.
Er. You do know what “information” is, right? Any structure whatsoever contains information. If you can make out discernible shapes under an electron microscope, that’s information.
But anyway… Given our present lack of precision cellular repair tech, this seems like it would be more relevant than revival experiments. Not that the nematode example isn’t insanely cool.
I know of no evidence. Closest I know is the promising result that a percentage of pinewood nematodes (a favourite of cryobiology researchers, having about the simplest known nervous system that is definitely a nervous system) survive cryoprotectants and vitrification and, if they survive, go on to parasitise pinewoods much like they did before. (E. Riga and J. M. Webster. “Cryopreservation of the Pinewood Nematode, Bursaphelenchus spp.” J. Nematol. 1991 October; 23 (4): 438–440.) Preserving a neural network is of course the holy grail. But this is getting way off topic for a blog about the art of human rationality.
Animals with more sophisticated nervous systems than nematodes can survive vitrification.
http://www.ncbi.nlm.nih.gov/pubmed/20086136
Even more sophisticated neural networks, mammalian brain slices, can now be vitrified with present technology.
http://www.21cm.com/pdfs/hippo_published.pdf
Of course it is what happens to whole brains that are vitrified that really matters to cryonics. The only paper published so far on the technology presently used in cryonics applied to whole brains is this one
http://www.alcor.org/Library/pdfs/Lemler-Annals.pdf
with more micrographs from that study here
http://www.alcor.org/Library/html/cambridge.html
and many more here
http://www.alcor.org/Library/html/micrographs.html
Unlike slices, there is no expectation that cell viability is preserved in whole brains because the cryoprotectant exposure time is longer. However connectivity and extensive biochemical information is believed to be preserved, as these micrographs suggest. It is presumed, but not proven, that the effect of thermal stress fractures at cryogenic temperatures is displacement of fracture planes. This would theoretically still preserve connectivity information, although requiring hyper-advanced technology to do anything with that information.
First off, for it to preserve no information at all would be extremely surprising. If there are physical structures, that’s some kind of information. But that’s not the question we’re interested in—we are interested in relevant information. As you say, preserving a neural network is the “holy grail” (at least if you aren’t counting loftier yet less crucial goals like reversible whole-body suspension). Notwithstanding, we do have evidence that there is at least some brain structure being preserved—there are pictures and everything.
Er. You do know what “information” is, right? Any structure whatsoever contains information. If you can make out discernible shapes under an electron microscope, that’s information.
But anyway… Given our present lack of precision cellular repair tech, this seems like it would be more relevant than revival experiments. Not that the nematode example isn’t insanely cool.