Robert J. Bradbury writes:
> Generally speaking as you cool down, you are going to get the lipid membrane
> becoming less fluid, so receptor proteins are going to get locked in place.
Unless we're talking about ultrarapid freezing you'll get phase transition in the lipid bilayer, possible poration and aggregation of membran-integral proteins with subsequent possible loss of function.
> Now the problem will occur if ice crystals form that punch through the
> membrane or become large enough to physically move the synapses around.
"large enough to physically move the synapses around" is a remarkable understatement. One of these days I should really scan some of these freeze-substitution etch EM slides vs. controls. Bad, bad, bad.
> (Thats why we have all this emphasis on cryoprotectants, ice-blockers, etc.)
> > Synaptic connections are one thing - are we still talking about perfect
> > reconstruction?
> Ralph Merkle goes into some discussion about this in his reanimation
> paper. He essentially assumes that nanobots will be able to go in
> do localized reliquification after establishing anchors. Then they
> map the surfaces and gradually pull things back into the proper locations.
Of course this assumes that they know what the proper locations are. It is _impossible_ to predict the original shape of color clouds in a glass of water after stirring it a little.
Some of what happens during freezing (=NOT vitrification) is comparable to above case.
> If you have ever seen a freeze fracture electron micrograph you can
> easily imagine how mating the two ~mirror-image surfaces back together
> should be straight forward. If the chemical cocktails work really
It is sure straightforward, but the problem only occurs with macroscopic cracking. Fixing cracking with nano is trivial; it's just a DSP problem.
> well, then you should be able to do the reanimation without nanotech.
If you could redo Suda's stunt using vitrification and modern signal processing techniques on the EEG that would really be impressive news.
> If it turned out that the physical location of the receptors within
> a synapse (rather than just their overall "density") was significant
> things would be more difficult. But I doubt very much that the cells
> have mechanisms for locking receptors at specified locations. Most
Freely diffusable ion channels are a pathological case. Pathological both in restricted to certain types/locations and ischaemic trauma.
> The brain has a lot of redundancy and can probably tolerate a fair
> amount of "mismatching" before you would experience significant
> memory or self-awareness loss. You might start out fuzzy, but
> over time neuronal maintenance & repair should normalize things.
> Much more serious would be large regions of damage in some specific
> critical brain region. I'm under the impression however that the
> brain is one of the tissues more tolerant of freezing. The kidney
> is the difficult one due to the microstructure it requires for
> filtering & pumping small molecules.
Recently (as in yesterday) I learned there is a rare type of brain trauma (20-30 cases/year) which wipes out the entire memory irreversibly, leaving only algorithmic memories. This leads to frequent divorces, because the original personality is wiped out. Fun, huh?