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On 20/09/2012 15:37, John Clark wrote:
<blockquote
cite="mid:CAJPayv27mjVQjNTEaBqFVhHxxJKROciTheT7+EY3gfAw=bm1hw@mail.gmail.com"
type="cite">On Tue, Sep 18, 2012 Anders Sandberg <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:anders@aleph.se"
target="_blank">anders@aleph.se</a>></span> wrote:<br>
<div class="gmail_quote"><br>
<blockquote style="margin:0px 0px 0px 0.8ex;border-left:1px
solid rgb(204,204,204);padding-left:1ex" class="gmail_quote">>
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.<br>
</blockquote>
<br>
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</div>
</blockquote>
<br>
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.<br>
<br>
<blockquote
cite="mid:CAJPayv27mjVQjNTEaBqFVhHxxJKROciTheT7+EY3gfAw=bm1hw@mail.gmail.com"
type="cite">
<div class="gmail_quote">
<blockquote style="margin:0px 0px 0px 0.8ex;border-left:1px
solid rgb(204,204,204);padding-left:1ex" class="gmail_quote">>
This is where I really would like to know how much happens in
a synapse, in particular to whether receptors remain bound to
membranes<br>
</blockquote>
<div><br>
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</div>
</div>
</blockquote>
<br>
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. <br>
<br>
<br>
<blockquote
cite="mid:CAJPayv27mjVQjNTEaBqFVhHxxJKROciTheT7+EY3gfAw=bm1hw@mail.gmail.com"
type="cite">
<div class="gmail_quote">
<br>
<blockquote style="margin:0px 0px 0px 0.8ex;border-left:1px
solid rgb(204,204,204);padding-left:1ex" class="gmail_quote">>
Then there is the problem of chemical change in fixed tissue<br>
</blockquote>
<br>
But those chemical reactions fix things in place, and you know
the chemical used, so you should be able to run the movie
backward</div>
</blockquote>
<br>
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. <br>
<br>
<br>
<blockquote
cite="mid:CAJPayv27mjVQjNTEaBqFVhHxxJKROciTheT7+EY3gfAw=bm1hw@mail.gmail.com"
type="cite">
<div class="gmail_quote"> The real enemy is chaotic fluid flow,
turbulence.<br>
</div>
</blockquote>
<br>
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. <br>
<br>
<pre class="moz-signature" cols="72">--
Anders Sandberg,
Future of Humanity Institute
Philosophy Faculty of Oxford University </pre>
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