X-Message-Number: 22148
From: randy <>
Subject: Re: Cryonics and information theory
Date: Mon, 07 Jul 2003 04:55:36 -0500

References: <> 
<>

>Harvey Newstrom wrote:
>> 
>> We have a lot better imaging technology now, and pictures of patients'
>> brains who have been frozen.  The damage is a lot worse than we thought.
>> The cells shrank and pulled apart from each other with gaps between them.
>> Where the cells stayed put, they are disconnected from other cells.  Where
>> the cells stayed connected, they are all pulled together leaving huge gaps.
>> The structure and positional relationship between the cells may or may not
>> be recoverable.  Some people have likened this result to "hamburger", under
>> the analogy that resurrecting a brain in that condition would be like
>> resurrecting a cow from hamburger.

Yes, this is an old theory.



>> 
>> I am still signed up for cryonics, but it seems to be to be a very low
>> probability chance of success, barely better than nothing.  Many people
>> don't even bother to sign up for this reason.  I certainly hope that better
>> methods can reduce this situation before my time comes.
>


But how do they calculate the odds?




Eliezer Yudkowsky wrote:



>I've spoken with Peter Passaro about this, and apparently the main things 
>are (a) get frozen as soon as possible after death (b) use the new 
>oxygenated cryoprotectants (c) keep the brain from being starved of 
>oxygen.  So people are working on it, and if you get frozen with the 
>latest techniques your chance of survival may still be pretty good.
>
>One problem I have, though, is that it still looks to me like it would be 
>better to just chop off the head and drop it into a bucket of liquid 
>nitrogen as fast as possible.  *Large*-scale freezing damage is 
>irrelevant; you can still connect the dots easily enough.  



I think Eugene Leitl has spoken to this--something about a nil potent
vector...



>What you want 
>to ensure is that the information, the Shannon information, is still 
>there.  I would not be surprised to find even the earliest cryonics 
>patients are resurrectable in toto; it is not necessary that the cells be 
>reparable but that their physical state, when scanned down to the atomic 
>level, contain enough information to extrapolate back the original brain 
>and its relevant high-level information.  The critical parameters here are 
>a matter of information theory, not just medicine, and not at all obvious 
>(i.e., how many initial states map to the same post-freezing state, 
>whether critical information is in global patterns or local patterns, 
>whether information makes a distinction in the final molecular state even 
>if the apparent functional characteristics of the neuron have been destroyed).
>
>I worry that cryonics has been approached from the viewpoint of medicine 
>rather than information theory.  Here is a point where lack of optimism 
>about post-Singularity capabilities may have killed people - cryonicists 
>thinking "let's keep the neurons as undamaged as possible from the 
>viewpoint of biological function" rather than "let's try and create a 
>physical freezing process such that the configuration space of pre-frozen 
>brains is mapped to the configuration space of molecularly analyzed frozen 
>brains in a way that does not introduce information-loss on the level of 
>relevant functional information".  These are not at all the same thing; 
>one is concerned not with how much "damage" the freezing process does, 
>from the viewpoint of ice crystal formation and so on, but rather with the 
>question of whether ice crystal formation of just dumping a head into 
>liquid nitrogen is a physical process that maps many initial states into 
>one final molecular-level state to a greater degree than the retraction of 
>axons and dendrites that occurs if you leave the brain without oxygen.
>
>To give an example of how different the viewpoints are, slicing an area of 
>neural tissue in half and translating one of the pieces by several 
>millimeters is extremely destructive from a biological point of view, yet 
>if the slice is a good one and the translation is consistent, almost no 
>information has been lost - each point in the original configuration space 
>maps to a unique point in the new configuration space.  The question about 
>ice crystal formation is not how much "damage" it does to the neurons, but 
>whether as a physical process it tends to map distinct initial conditions 
>onto distinct outcomes.



>If dendrites and axons retract into the cell body within half an hour 
>after the neuron has been starved of oxygen (!!!), 



How do you know this?  I thought autolysis was the main problem.
Autolysis which was supposed to render the brain as a soup within 24
hours at room temps.




>even so the essential 
>information *may* have been preserved; the question is whether scanning 
>the neuron on the *molecular level* would enable you to determine where 
>the original dendrites and axons were, to a degree necessary to reproduce 
>the functional information.  In turn, you can only determine this by 
>running several possible dendritic configurations forward in time under 
>the retraction process, and seeing if several functionally different 
>initial configurations map to exactly the same (molecularly the same) 
>final retracted neuron.  If the mapping is nonunique, however, you're 
>probably toast, unless the gross position of neurons is a constraint 
>sufficient to reconstruct the functionally relevant information of the 
>original circuitry - if there is only one person you could have been such 
>that your neurons would have occupied that gross position.
>
>What determines this?  The degree to which precise details of the final 
>post-freezing configuration constrain the original circuitry, and the 
>degree to which the constraint is global in nature rather than local, 
>relative to the functional space of brains.  For example, suppose that in 
>some area A1 we have a lossy mapping from a set of neural circuits N1 to 
>the post-freezing brainstate F1.  And suppose that the set of possible 
>initial neural circuits N1 that map to F1 contain possibilities that are 
>functionally different from each other.  Are you dead meat?  Perhaps and 
>perhaps not.  Suppose that there is Shannon information between the 
>pre-freezing states of A1 and A2, such that if we know the pre-freezing 
>state of area A1, it would constrain the permissible states or probability 
>distribution of area A2.  And suppose that, on a local level, there are 
>many different circuits N2 that could have frozen to the final state F2, 
>and some elements of N2 are functionally distinct from one another. 
>However, there's only one possible element of N1 that is compatible with a 
>possible element of N2, and only one possible element of N2 that is 
>compatible with that particular element in N1.  This is an idealized 
>example; you can have probability distributions that constrain and narrow 
>each other without this kind of definite certainty emerging from 
>inspection of a mere two areas.
>
>The upshot is that if local areas of pre-frozen brains constrain one 
>another (relative to the space of functionally different brains) in a way 
>that survives mapping to frozen brains, such that local areas of frozen 
>brains constrain information globally rather than locally, then even large 
>local blurs may not destroy global preservation of information.  If, 
>however, local areas do not strongly constrain one another, then even a 
>small local blur may permanently destroy your mind-state.  All the locally 
>uncertain probability distributions will modularly add up to an extremely 
>uncertain global probability distribution, rather than many local 
>uncertainties constraining each other to add up to global certainty.  The 
>greater the *locality* of the brain, in other words, the more easily it is 
>destroyed by blurring.
>
>Blurring may be defined as mapping of functionally distinct local initial 
>conditions to physically identical local final states; or more formally, 
>mapping such that the densest volumes of the probability distribution for 
>the final states tend to overlap one another even for functionally 
>distinct initial conditions.  Whether a given degree of local blurring 
>kills you will depend on the degree to which those functionally distinct 
>local initial conditions permitted by the final local physical state 
>provide Shannon information about each other on a global scale, and 
>whether that Shannon information can constrain the whole brain to a single 
>functional state or whether it only narrows the blur without managing to 
>eliminate it.
>
>It all boils down to the probability distributions for p(brain|mind) and 
>p(frozen|brain), which together will determine p(mind|frozen).  As usual, 
>your life or death depends on - wait for it - Bayes' Theorem.
>
>So whether cryonics will work is a question that intersects biology, 
>physics, and information theory, and the properties that determine whether 
>you live or die are not at all obvious if you are thinking 
>anthropomorphically about "preventing (biological) harm to neurons".  What 
>I worry about is not that cryonics has been misunderstood by the public, 
>but that it has been misunderstood by cryonicists.
>
>Feel free to forward this message to Cryonet.


Interesting set of ideas that I have not yet run across. I will
forward this to cryonet.

































































--Randy


-------------
-Randy

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