From: randy (cryofan@mylinuxisp.com)
Date: Mon Jul 07 2003 - 03:40:12 MDT
>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.
>>
>> 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.
>
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. 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?
>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
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