[ExI] Nice Article on Brain Preservation

[Anders Sandberg]

On 20/09/2012 15:37, John Clark wrote:
> On Tue, Sep 18, 2012  Anders Sandberg <anders at aleph.se 
> <mailto:anders at aleph.se>> wrote:
>
>     > 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

But if W and U can also react and make Z? That is where the entropy 
comes in. Now you don't know whether there was XY or WU.

>     > 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

Receptors can be bound or unbound: this changes due to synaptic 
potentiation. It likely matters a lot to get the right number, since 
this partially sets the synaptic strength. But if freezing makes some 
unbound you cannot deduce the original number, unless the unbinding has 
some very simple regularities.


>
>     > 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

There are thousands of different chemicals around, not all react by 
fixing. And some things might not fix properly, like g-proteins or high 
energy compounds.


> The real enemy is chaotic fluid flow, turbulence.

You *really* mean fluid flow, and not just as a metaphor?! But the 
Reynolds numbers in tissues are *far* into the laminar! There *is no 
turbulence*, except maybe in some bigger blood vessels.

-- 
Anders Sandberg,
Future of Humanity Institute
Philosophy Faculty of Oxford University

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