X-Message-Number: 4117
Date: 31 Mar 95 14:44:43 EST
From: Mike Darwin <>
Subject: SCI.CRYONICS Memory after rewarming

The question was asked about conservation of memory after freezing: To deal
DIRECTLY and bluntly with this issue is to say the following:

There is no direct proof or evidence that memory can survive freezing in a
mammal.  More specifically, Audrey Smith did not train her hamsters and then
evaluate them later.

Furthermore, there are several different "kinds" of memory in higher animals.
There is no guarantee that the survival of "procedural memory" (such learning
how to ride a bike) will guarantee the survival of "declarative memory" such as
knowledge of who you are or your first grade teacher's  name.  In fact there is

considerable evidence that relatively benign (compared to cryoinjury) trauma can

wipe declartative memory in humans.  People who suffer severe head injuries (and
who subsequently recover almost completely) occassionally lose all or some of
their declarative memories.  Very often this is permanent.  This is what is
portrayed as "amnesia" in the movies.  Clinically, it happens most often to
people who experience prolonged coma following traumatic head injury, almost
invariably with cerebral edema as a consequence.

Procedural memory takes a long time to encode: for instance it is quite easy to

tell someone how to do a particular procedure involving skill, and quite another
to have them master it (I call this the hands teaching the brain).

There are, of course, two ways to solve this problem of the question of the
persistence of memory:

1) Directly by recovering a mammal (preferably one you can evaluate declarative
memory in) after cryopreservation.

2) Indirectly by understanding *how* memories of various types are stored
physically in the brain and then look and see if the structures encoding such
memories survive cryopreservation in a state which allows inference of the
(healthy, intact) state prior to cryopreservation.

An intermediate step is to recreate Smith's work with hamsters and teach them a
task such as how to retrieve food or run a maze and see if they remember.  If
anyone (competent to do so) wants to do this project here they are welcome to:
Jerry Leaf had completed almost all the preparations and the hardware is just
sitting here: all it needs is hamsters (which I'll happily supply) and someone
else's time.

An important caveat here has to do with why *I* am not doing this experiment.
While I think it would be useful, I can pretty well assure you that freezing a

hamster brain to -0.5xC and converting about 50% of its brain water to ice is in
almost no way comparable to what happens when a human brain (or other mammalian
brain for that matter) is loaded with multimolar concentrations of

cryoprotectant and then frozen to deep subzero temperatures.  The lesions we see
after such treatment are incompatible with the resumption of any integrated

brain function such as EEG, and the biochemical milieu created by freeze-induced

concentration of normal cell solutes and cryoprotectant are in no way comparable
to the situation seen in Smith's hamsters.


Since we are apparently grinding brains into chopped steak (I won't go so far to
say hamburger, and get everybody upset) with existing techniques I see little
point in spending my time on evaluating memory in a model which does not have

much to do with what we are REALLY doing to human cryopreservation patients.  It
is my opinion that the *first* step is to get good (i.e., acceptable) EMs of
brains prepared under those conditions which are clinically relevant.  Brain
hash isn't going yeild EEGs, or, for that matter, any functional indices which
could be used to evaluate the preservation of memories.  Improving preservation
will.


Finally, I might add that the intact brain seems to be hardest hit by cryoinjury
of the organs we have examined.  This is in sharp contrast to what we had
previously thought based on Suda's work and on work with embryonic brains: both

of which have proved to be decidely (and unfortunately) poorly predictive models
of what is really going on.


Mike Darwin


Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=4117