Aldehyde-Stabilized Cryonics vs. Vitrification: The Revivalist Case
If you have spent any time around cryonics lately, you have run into aldehyde-stabilized cryopreservation (ASC). It won the Brain Preservation Foundation's prizes, it is the science behind Nectome's "preserve your connectome" pitch, and it keeps showing up in talks as if it were the obvious next step. I have looked hard at it, and I am sticking with ordinary vitrification. Here is the practical reasoning.
What ASC actually is
ASC was demonstrated in 2016 by Robert McIntyre and Gregory Fahy at the cryobiology lab 21st Century Medicine. The brain is perfused with glutaraldehyde, a fixative, and then with cryoprotectant before going into cold storage. The aldehyde instantly locks the fine structure of the brain in place. And it works: the team preserved a whole rabbit brain to win the Small Mammal prize in 2016, then an entire pig brain to win the Large Mammal prize, with synaptic connectivity verified by 3D electron microscopy. This is real, impressive science. I am not knocking the work.
It is not "better." It is aimed at a different goal.
The thing almost nobody says plainly: ASC and vitrification are not two answers to the same question. Glutaraldehyde fixation is essentially permanent. It plasticizes the tissue, and you are not un-fixing that. ASC is built to preserve structure so it can be scanned later and the connectome read out. That is the upload path. Vitrification, the cryoprotectant approach Alcor and the Cryonics Institute use, deliberately avoids fixation so that biological revival stays on the table.
Two details make this concrete. First, the same company that developed ASC, 21st Century Medicine, also developed the vitrification solutions Alcor uses. Second, Alcor has publicly declined to adopt ASC, and not because the preservation is poor, but because restoration from a fixed brain would be far harder. The people closest to the technology chose to keep the biological door open.
Copy people and revival people are arguing about different things
Underneath every one of these debates is a philosophical split. "Patternists" hold that a sufficiently accurate copy of you, your connectome and memories running on some future substrate, simply is you. "Revivalists" hold that identity is tied to the actual, continuing thing: you are whoever wakes up and experiences and controls the body, in the first person.
I am firmly in the revival camp. I do not particularly care whether a future system can reconstruct my memories or personality with perfect fidelity. I care that the thing that comes back is me, that I am the one feeling the world and steering the body, whatever body that turns out to be. If I came back as close to a blank slate and had to relearn everything, I would take that over a flawless simulation of me running on a server while I, the original, am gone. If you are a patternist, ASC and uploading are coherent. If you are not, fixing your brain into a permanent slide is buying the wrong product.
The burden of proof runs the other way
Here is my actual objection. ASC advocates tend to say that standard cryonics might not preserve the connectome, not that it does not. That is a large difference. Before I let anyone perfuse me with a more toxic, irreversible fixative, I want evidence that the ordinary method is actually failing.
And the test is not hard. If you wanted to know whether modern vitrification preserves the connectome, you would do almost exactly what the ASC team did: vitrify a brain with standard cryoprotectants, rewarm it properly, and then use aldehyde fixation if you need it only to prepare the microscopy slides, and look at the connectome. Same readout, fair comparison.
The fact that the aldehyde camp does not seem to have published that head-to-head test, the one that would actually settle it, starts to feel less like they will not and more like they cannot.
Current cryonics is more evidence-driven than its critics admit
A common claim is that cryonics organizations just freeze tissue and hope. That is not fair. Decades of work have gone into cryoprotectant chemistry to raise preservation fidelity and reduce damage. Alcor vitrifies animal specimens and checks them under electron microscopes to confirm structure. The cryoprotectants descend from the same line used to cryopreserve and successfully transplant organs such as kidneys. It is not perfect, and nobody can yet rewarm a person, but "evidence-seeking" is a far fairer description than "meat freezer." The Cryonics Institute in particular charges close to cost, which is not what you do if the plan is to take people's money and freeze idiots.
A reason for optimism (my reasoning, not settled science)
One more thing shapes my view, and I will flag it as my own reasoning rather than established fact. Consciousness seems to live in part of the brain, not in the whole thing all at once. I know that personally: I had a stroke, lost part of my occipital lobe, and lost some vision, but I am still here, still me. Evolution does not tend to build expensive, survival-critical systems with a single point of failure and no backup. If sentience is that important, and the tissue that hosts it can be damaged, there is probably some redundancy baked in. If that is right, then simply bringing someone back may turn out to be more robust than perfectly reconstructing every last detail, which is exactly the outcome a revivalist is betting on.
Practical bottom line
If your goal is to be uploaded, to have a future system read your connectome and run a faithful copy, then ASC is a coherent, prize-winning way to get there, and you should choose it with open eyes. But know what you are buying: a beautiful, permanent slide, not a path back to a living you.
My goal is to actually wake up. So I am choosing vitrification, the method that keeps biological revival possible, and betting on a hundred years of AI, nanotechnology, and medicine to finish the job. If the price of that bet is coming back having forgotten what parmesan tastes like, I will have a lot of time to relearn over a lot of spaghetti.