[ExI] Nice Article on Brain Preservation

[John Clark]

On Tue, Sep 18, 2012  Anders Sandberg <anders at aleph.se> wrote:

> Freezing did cause a mess due to crystal formation and cracking, and is
> still mechanically a bit nasty, but I don't think (cryo-gurus please chime
> in) it causes regions to scramble. They just turn to puzzles.
>

If its scrambled then we're dead, literally, but I think you're probably
right and fixing a frozen brain is more like gluing the parts of a broken
vase together than unscrambling a egg; I certainly hope so!

> The biochemical changes of both processes are hard to judge, but this is
> where I would be most worried: the brain is dependent on a lot of
> biochemical states that might only partly survive either treatment.
>

Well, if molecule X and molecule Y got together and produced molecule Z and
you find Z then you can deduce that X and Y must have existed and been
close together at a previous time, and if X was one of the chemicals used
to preserve the brain then your only concern will be Y and where it was
before the reaction. I'd be much more worried about turbulence, if a
particle got where it was by a turbulent fluid flow then I don't think even
Nanotechnology could figure out where it was originally.

> This is where I really would like to know how much happens in a synapse,
> in particular to whether receptors remain bound to membranes
>

It doesn't matter if a receptor in a synapse is no longer bound to the
membrane provided you can figure out that it must of been bound there in
the past and you can make that deduction with a reasonable number of
computations;  in other words if the fluid flow that pushed that receptor
out of place was laminar, if it was turbulent then you're dead.

> In freezing mobility of stuff goes down a lot quickly, while I get the
> impression the fixation is a bit slower.
>

My intuition tells me the opposite, that the chemical reaction of the
fixation chemical would start to hold things in place  faster than the
increased viscosity caused when water temperature is slowly decreased, and
the decrease would be slow because the brain is a large bulky object so you
can't cool things off super fast; and the phase change when water turns to
ice worries me, I don't think it would induce turbulence but I'm not sure.
And my intuition could be entirely wrong.

> Then there is the problem of chemical change in fixed tissue
>

But those chemical reactions fix things in place, and you know the chemical
used, so you should be able to run the movie backward without needing a
absurd amount of computations as you'd need if you wanted to run turbulence
backward. At least I think it wouldn't be absurd, I hope so anyway.

> I don't know if anything diffuses much, but that is worth watching for.
>

Although in some ways based on randomness tiny changes in initial
conditions don't lead to huge changes in outcome after diffusion, in fact a
living brain relies on diffusion to get neurotransmitters to cross the
synapse, its a dependable process. The real enemy is chaotic fluid flow,
turbulence.

John K Clark
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