X-Message-Number: 6597
From: 
Date: Wed, 24 Jul 1996 10:59:56 UTC
Subject: Memory Assay

Keith Lynch writes,

>This is the main reason I haven't made any pledge yet.

>* How do you cool a brain embedded in a warm body?  Sure you can use
>  perfusion, but only until the perfusate becomes too cold and viscous
>  to flow.

>* How do you keep the vitrified brain cold when it's embedded in a
>  warm body?

>* How do you keep the parts of the body adjacent to the vitrified
>  brain from freezing?

>* How do you rapidly rewarm the brain without roasting the rest of
>  the animal?

>I will make a pledge when I get a believable answer to each of these
>questions.  Or when I hear of some plausible method of testing viability
>which doesn't involve a vitrified brain in a warm body.


Hi Keith,
        I understand your concerns--I'm not sure how you would practically
keep the head cool and body warm with the head still attached to the body.
Perhaps someone else has some ideas on how it might done.

        However, one alternate memory assay which might satisfy you is the
following:  

1.  Rats and other mammals can be conditioned to blink in response to a
tone.  Eye-blink conditioning is a widely used measure of memory deficits in
animal models of brain disease, since it can be performed on animals from
infancy to old age.  It also doesn't depend very heavily on the physical
health of the animal.  For our purposes, eye-blink conditioning is ideal
since it requires only an intact head to assay for memory retention.

2.  Dr. Robert White demonstrated that the intact head of a small monkey
could be surgically attached to the side of the neck of a larger monkey.  He
also demonstrated that the donor head could be attached in place of the head
of the recipient.  In one paper, he said that the transplanted head regained
consciousness, that the eyes would track moving objects, and that the head
would even try to bite.

This suggests a skeletal protocol to assay for memory retention in a
vitrified brain.

-  Condition animal to blink in response to tone.
-  Remove head from donor animal.
-  Perfuse head with cryoprotectant while simultaneously cooling.
-  Once vitrified, store for x days.
-  Rewarm head with RF heating
-  Wash out cryoprotectant
-  Attach head to donor animal.
-  Assay for retention of eye blink conditioning in response to tone.

        Note that this assay depends on the survival of the ear and eyelid,
in addition to the brain.  Achieving such simultaneous survival will not be
easy  This assay also requires a high degree of surgical skill.  However, is
this assay plausible enough to you for making a pledge?  If not, what
additional criteria must be met?  I welcome any suggestions for a
better/improved assay.      

"Michael Swift"

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