X-Message-Number: 9767 Date: Sun, 24 May 1998 10:03:07 -0400 From: Thomas Donaldson <> Subject: CryoNet #9759 - #9765 Hi everyone! While I too am optimistic that "information-theoretic survival" will usually happen in present and past suspensions, I must point out that most of what Dr. Merkle provides to indicate that remains irrelevant. Yes, certainly, we will be able to image the damaged brain far better than we can now, and in very great detail (here he presents various numbers to tell just how much detail). The real issue is that of the survival of memory and identity. If memory and identity survive, I think we'd all agree that there was information theoretic survival. If not, not. However it's much harder to prove this than to throw around a lot of numbers. Although we do have to husband our money, and for that reason I think that the current attempts to produce reversible brain suspensions should take first place, there is a different line of investigation which will produce actual DATA bearing on memory survival and even on identity. What we want is very detailed maps of brains, not just visual maps but maps of the many different chemicals. For instance, pyramidal cells are one of the central important types of neurons in our cortex. They receive innervation from a variety of other neurons. We'd like to be able to tell what kind of neuron formed a synapse on another, even if the synapse has been severely damaged. That looks to be possible, but the chemical maps required have only been done in some special areas. There are several different kinds of neurons, for instance, that connect pyramidal cells with one another. The general term for them is "interneurons"; usually they use GABA, the transmitter involved in Long Term Depression. Neurons from the base of the brain, using transmitters such as acetylcholine, dopamine, noradrenaline, etc, reach widely through our entire brain. Again, synapses tend to be highly durable compared to cell membranes. But even so, what chemistry might tell us just where a synapse was if it has been destroyed? And of course, synapses differ, and those differences may tell us a lot. Finally, with all the discussion of cracks and movement, it would be of great interest to get some experimental numbers on both. This would naturally require not just a few EMs showing EXISTENCE of cracks and movement, but a much more detailed study involving many EMs to quantify and possibly characterize the different kinds of cracks and movement. As of now, we don't even know the statistics of such things, and any serious attempt at repair would need estimates of just how far a particular structure has moved... if indeed movement occurs. Especially since our memories may be encoded in the fine structure of our neural connectivity, it would be very useful to get some idea of just how much disruption that fine structure may suffer. Axons are fine, but it's dendrites that may be critical here. (And dendrites have their own chemistry and might be traced even if they have moved or no longer exist). There are other such studies which might be done. Clearly this would be a very large project, made even larger because suspension methods have varied in the past and individual suspensions have varied too. What would happen with it, of course, is that we will find some cases in which memory has NOT survived, others in which it has mostly survived, and so on. Ditto identity, though identity may not require structures special to each individual. And over time it would tell us just what tools we REALLY need for repair: what our tools must be able to do and even something of how they might do it. Besides, it would allow us to really talk about "information-theoretic survival" rather than throw around some impressive but meaningless numbers. Best and long long life to all, Thomas Donaldson Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=9767