X-Message-Number: 91
From arpa!Xerox.COM!merkle.pa Wed May 31 14:55:41 PDT 1989
Received: from Salvador.ms by ArpaGateway.ms ; 31 MAY 89 14:55:54 PDT
Date: Wed, 31 May 89 14:55:41 PDT
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Subject: Re: Whole-Body Frostbite (CRYONICS): Can It Be Cured?
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Status: R
The following was posted to sci.nanotech. I'm cross posting in case anyone
on the cryonics mailing list has not or cannot subscribe to sci.nanotech.
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Date: Wed, 31 May 89 13:10:36 PDT
From: merkle.pa
Subject: Re: Whole-Body Frostbite: Can It Be Cured?
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(Mark Robert Thorson) said:
>I see two problems with cryonics. I've mentioned the first one before,
>the fact that the electrical state of your brain will be destroyed by
>freezing. This should be an experience similar to shock therapy; expect
>memory loss and personality changes.
>The other is radiation. If you're frozen for 50 years, your body will
>absorb 50 years of background radiation. Because your DNA repair enzymes
>will be inoperative during that time, it will be like being hit with a
>big flash of radiation.
To quote from "Freezing of living cells: mechanisms and implications" by
Peter Mazur:
"The only reactions that can occur in frozen aqueous systems at -196
degrees C are photophysical events such as the formation of free radicals
and the production of breaks in macromolecules as a direct result of "hits"
by background ionizing radiation or cosmic rays (96). Over a sufficiently
long period of time, these direct ionizations can produce enough breaks or
other damage in DNA to become deleterious after rewarming to physiological
temperatures, especially since no enzymatic repair can occur at these very
low temperatures. The dose of ionizing radiation that kills 63% of
representative cultured mammalian cells at room temperature (1/e survival)
is 200-400 rads (19). Because terrestrial background radiation is some 0.1
rad/yr, it ought to require some 2,000-4,000 yr at -196 degrees C to kill
that fraction of a population of typical mammalian cells.
Needless to say, direct experimental confirmation of this prediction is
lacking, but there is no confirmed case of cell death ascribable to storage
at -196 degrees C for some 2-15 yr and none even when cells are expose to
levels of ionizing radiation some 100 times background for up to 5 yr (48).
Furthermore, there is no evidence that storage at -196 degrees C results in
the accumulation of chromosomal or genetic changes (6).
Stability for centuries or millennia requires temperatures below -130
degrees C. Many cells stored above ~-80 degrees C are not stable, probably
because traces of unfrozen solution still exist (54). They will die at
rates ranging from several percent per hour to several percent per year
depending on the temperature, the species and type of cell, and the
composition of the medium in which they are frozen (52)."
References:
96. Rice, F. O. History of radical trapping. In: Formation and Trapping
of Free Radicals, edited by A. M. Bass and H. P. Broida. New York:
Academic, 1960, p. 7.
19. Elkind, M. M., and G. F. Whitmore. The Radiobiology of Cultured
Mammalian Cells. New York: Gordon and Breach, 1967.
48. Lyon, M. F., P. Glenister, and D. G. Whittingham. Long term viability
of embryos stored under irradiation. In: Frozen Storage of Laboratory
Animals, edited by G. H. Zeilmaker. Stuttgart, FRG: Fischer Verlag, 1981,
p. 139-147.
6. Ashwood-Smith, M. J., and G. B. Friedmann. Lethal and chromosomal
effects of freezing, thawing, storage time, and X-irradiation on mammalian
cells preserved at -196 degrees in dimethyl sulfoxide. Cryobiology 16:
132-140, 1979.
54. Mazur, P. Cryobiology: the freezing of biological systems. Science
168: 939-949, 1970.
52. Mazur, P. Physical and chemical basis of injury in single-celled
microorganisms subjected to freezing and thawing. In: Cryobiology, edited
by H. T. Meryman. London: Academic, 1966, chapt. 6, p. 213-315.
The theory that long-term storage of memory involves "reverberating
circuits" that are subject to disruption by transient changes in brain
neurochemistry has long since been laid to rest. All current generally
accepted theories of long term memory involve chemical and physical changes
at the synaptic level. Given the very redundant nature of the human brain,
the level of damage required to seriously damage the long term mechanisms
of memory storage would have to be extensive. To quote "Principles of
Neural Science" by Kandel and Schwartz, page 813: "Although the physical
changes representing learning are likely to be localized to specific
neurons, the complex nature of learning ensures that these neurons are
widely distributed in the nervous system. Therefore, even after extensive
lesions, some trace can remain. Furthermore, the brain has the capacity to
take even the limited information remaining, work it over, and reconstruct
a good reproduction of the original." This quote is based on observations
today of spontaneous recovery by patients with varying degrees of cerebral
damage when "treated" by current medical technology. We can reasonably
presume that analysis and repair at the molecular level using future
technologies will be substantially more effective.
In this regard, it is interesting that Bailey saw differences visible under
the electron microscope in the appearance of identified synapses from
trained sea snails (aplysia) versus the appearance of the same synapse in
untrained sea snails. That is, training produced physical changes in the
synaptic structure (larger synapse size, more pre-synaptic vessicles, etc.)
[Craig H. Bailey, Mary Chen, 'Morphological basis of long-term habituation
and sensitization in Aplysia' Science 220, 1983.04.01, 91-93]. Again, we
can reasonably presume that electron microscopy is less effective than
future methods at analyzing the structure of the synapse. It seems
unlikely that all traces of the changes produced in this model system would
be eliminated or even seriously altered by freezing.
It seems very likely that the human brain stores information by the
alteration of synaptic structure. Even if we presume that a mechanism
which is fundamentally different from those already observed, (a
presumption for which there is no positive evidence), it must still be a
mechanism that is robust in the face of the wide range of physiological
conditions encountered over many decades of life, and robust against the
observed experimental manipulations of test animals that have recovered and
display intact memories. This makes it likely that the proposed
hypothetical memory mechanism will also be preserved by freezing.
Finally, in the event that some information is in fact lost, the result of
molecular repair is not "...doddering idiots with major brain damage and
radiation sickness", but instead normal human beings with loss of some
memories. If sufficient memory is lost, we can reasonably argue that
cryonic suspension failed (the "repaired" person remembers little more than
a new-born child) but the prospect of creating half-dead zombies must be
dismissed as unlikely. Such a scenario presumes both that there are
medical conditions which are inherently incurable by any future technology,
and further that someone who has been cryonically suspended will be
deliberately "restored" to such an incurable state (rather than left in
cryonic suspension to await further technical developments).
Ralph C. Merkle
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