[ExI] Nice Article on Brain Preservation

[John Clark]

On Thu, Sep 20, 2012  Anders Sandberg <anders at aleph.se> wrote:

>>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?
>

If W and U are molecules not normally found in the brain, or if they were
found in the brain but judging by the surrounding structure it didn't  make
sense for them to be at that particular spot then you can rule them out;
and even if it is reasonable for them to be there you still might be able
to make a good educated guess because the XY and WU reactions probably
don't proceed at the same rate, so one is more likely than the other.
However if they do both proceed at the same rate and its equally reasonable
for all 4 to be found at that point and if X,Y,W and U are important
molecules then you could have a serious problem.

> That is where the entropy comes in.
>

Yes, entropy seems to sneak its way into just about everything. Even if the
universe was as deterministic as Newton thought it was if  XY and WU both
made Z at the same rate then you could predict the future but you couldn't
figure out what the past was.

> Now you don't know whether there was XY or WU.
>

If you used the plastic infusion method one of those 4 chemicals was
probably introduced by you.

> 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.
>

Yes simple regularities is the name of the game, or if not simple at least
not astronomically complex as with turbulence.

> 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.
>

Yes there are lots of unknowns, but the question is which method has the
fewer unknowns, plastic or freezing?

>> The real enemy is chaotic fluid flow, turbulence.
>>
> > You *really* mean fluid flow, and not just as a metaphor?!
>

Yes, if the brain always acted as a solid there really wouldn't be any
problem and preserving it would be easy, or at least easier, but we know
that isn't the case and after death the parts of it refuse to stay put
because they are battered around by fluid; we don't want that fluid flow to
be chaotic.

> But the Reynolds numbers in tissues are *far* into the laminar! There *is
> no turbulence*, except maybe in some bigger blood vessels.
>

if true then that is very good news for both methods.

  John K Clark
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