Per PZ Myers, the state of the art in neural preservation doesn’t recoverably preserve usable amounts of state in zebrafish brains, which are a few hundred microns on a side. How thin slices were you thinking of? And how fast were you going to be slicing?
I’ve worked with tiny little zebrafish brains, things a few hundred microns long on one axis, and I’ve done lots of EM work on them. You can’t fix them into a state resembling life very accurately: even with chemical perfusion with strong aldehyedes of small tissue specimens that takes hundreds of milliseconds, you get degenerative changes. There’s a technique where you slam the specimen into a block cooled to liquid helium temperatures — even there you get variation in preservation, it still takes 0.1ms to cryofix the tissue, and what they’re interested in preserving is cell states in a single cell layer, not whole multi-layered tissues. With the most elaborate and careful procedures, they report excellent fixation within 5 microns of the surface, and disruption of the tissue by ice crystal formation within 20 microns. So even with the best techniques available now, we could possibly preserve the thinnest, outermost, single cell layer of your brain…but all the fine axons and dendrites that penetrate deeper? Forget those.
Human embryos are routinely cryogenically preserved, can be thawed and reimplanted to birth healthy human beings. Yet a blastocyst is roughly spherical, not homogenous, about 150-200 micrometers large, totals about 60 cells.
Also, even rabbit kidneys, which are a few centimeters large, can be preserved. Not very often, not very reliably so, but some could still function and sustain life for days after being thawed.
I believe such freezing is normally done at eight cells, no bigger. And you can in fact remove one of the eight cells and the child develops (apparently) normally—it’s the one sure-fire way to sex-test an embryo (recalling from memory).
What we’re talking about here is not making sure you can grow a brain at all (the embryo) nor making sure a filter can filter again (the kidney), but preserving the information that makes you you. It’s a different kind of problem from getting a filter to work again. The people who actually work with this stuff day to day and would love to be able to recover state from preserved neurons, even in principle, say it’s literally impossible with the present state of the art.
Which is obvious nonsense. PZ Meyers thinks we need atom-scale accuracy in our preservation. Were that the case, a sharp blow to the head or a hot cup of coffee would render you information theoretically-dead. If you want to study living cell biology, frozen to nanosecond accuracy, then, no, we can’t do that for large systems. If you want extremely accurate synaptic and glial structural preservation, with maintenance of gene expressions and approximate internal chemical state (minus some cryoprotectant-induced denaturing), then we absolutely can do that, and there’s a very strong case to be made that that’s adequate for a full functional reconstruction of a human mind.
As you’ll see if you read his text, he’s responding to proposals to emulate a brain without understanding how it all works, and is noting just how fine you’d need to actually go to do that.
If you want extremely accurate synaptic and glial structural preservation, with maintenance of gene expressions and approximate internal chemical state (minus some cryoprotectant-induced denaturing), then we absolutely can do that, and there’s a very strong case to be made that that’s adequate for a full functional reconstruction of a human mind.
I’ve heard the case made at length, but not of, e.g., a C. elegans that’s learnt something, been frozen and shows it stil remembers it after it’s unfrozen (to name one obvious experiment that, last time this precise Myers article was discussed, apparently no-one had ever done) or something of similar evidentiary value. Experiment beats arguing why you don’t need an experiment. Edit: Not the last time this Myers article was discussed, but the discussion of kalla724′s “what on earth” neuroscientist’s opinion on cryonics practice.
Right, but (virtually) nobody is actually proposing doing that. It’s obviously stupid to try from chemical first principles. Cells might be another story. That’s why we’re studying neurons and glial cells to improve our computational models of them. We’re pretty close to having adequate neuron models, though glia are probably still five to ten years off.
I believe there’s at least one project working on exactly the experiment you describe. Unfortunately, C. elegans is a tough case study for a few reasons. If it turns out that they can’t do it, I’ll update then.
Clarification: the current state of the art in neural preservation doesn’t preserve amounts of state in zebrafish brains that are recoverable in usable form by the current state of the art.
If we had the ability to recover the information in usable form today, there would be no need for cryonics to exist.
Per PZ Myers, the state of the art in neural preservation doesn’t recoverably preserve usable amounts of state in zebrafish brains, which are a few hundred microns on a side. How thin slices were you thinking of? And how fast were you going to be slicing?
I didn’t have anything definite in mind; was just throwing the idea out there. Thanks for the info.
Odd.
Human embryos are routinely cryogenically preserved, can be thawed and reimplanted to birth healthy human beings. Yet a blastocyst is roughly spherical, not homogenous, about 150-200 micrometers large, totals about 60 cells.
Also, even rabbit kidneys, which are a few centimeters large, can be preserved. Not very often, not very reliably so, but some could still function and sustain life for days after being thawed.
I believe such freezing is normally done at eight cells, no bigger. And you can in fact remove one of the eight cells and the child develops (apparently) normally—it’s the one sure-fire way to sex-test an embryo (recalling from memory).
What we’re talking about here is not making sure you can grow a brain at all (the embryo) nor making sure a filter can filter again (the kidney), but preserving the information that makes you you. It’s a different kind of problem from getting a filter to work again. The people who actually work with this stuff day to day and would love to be able to recover state from preserved neurons, even in principle, say it’s literally impossible with the present state of the art.
Embryos in this context are a handful of cells and they end up reorganizing if they have a problem. And they don’t have delicate connections.
Kidneys are an interesting example but they are one of the simplest organs in the body.
Which is obvious nonsense. PZ Meyers thinks we need atom-scale accuracy in our preservation. Were that the case, a sharp blow to the head or a hot cup of coffee would render you information theoretically-dead. If you want to study living cell biology, frozen to nanosecond accuracy, then, no, we can’t do that for large systems. If you want extremely accurate synaptic and glial structural preservation, with maintenance of gene expressions and approximate internal chemical state (minus some cryoprotectant-induced denaturing), then we absolutely can do that, and there’s a very strong case to be made that that’s adequate for a full functional reconstruction of a human mind.
As you’ll see if you read his text, he’s responding to proposals to emulate a brain without understanding how it all works, and is noting just how fine you’d need to actually go to do that.
I’ve heard the case made at length, but not of, e.g., a C. elegans that’s learnt something, been frozen and shows it stil remembers it after it’s unfrozen (to name one obvious experiment that, last time this precise Myers article was discussed, apparently no-one had ever done) or something of similar evidentiary value. Experiment beats arguing why you don’t need an experiment. Edit: Not the last time this Myers article was discussed, but the discussion of kalla724′s “what on earth” neuroscientist’s opinion on cryonics practice.
Right, but (virtually) nobody is actually proposing doing that. It’s obviously stupid to try from chemical first principles. Cells might be another story. That’s why we’re studying neurons and glial cells to improve our computational models of them. We’re pretty close to having adequate neuron models, though glia are probably still five to ten years off.
I believe there’s at least one project working on exactly the experiment you describe. Unfortunately, C. elegans is a tough case study for a few reasons. If it turns out that they can’t do it, I’ll update then.
You might find this earlier discussion useful on how far we’ve gotten with emulating C elegans: http://lesswrong.com/lw/88g/whole_brain_emulation_looking_at_progress_on_c/
Clarification: the current state of the art in neural preservation doesn’t preserve amounts of state in zebrafish brains that are recoverable in usable form by the current state of the art.
If we had the ability to recover the information in usable form today, there would be no need for cryonics to exist.
You’re assuming the information is even preserved. Neuroscientists look at what cryonics does and say “what on earth, the information is lost.” (Again, that post wasn’t that long ago.)