MIT Technology Review—Michael Hendricks opinion on Cryonics
http://www.technologyreview.com/view/541311/the-false-science-of-cryonics/
Michael Hendricks is a neuroscientist and assistant professor of biology at McGill University.
http://www.technologyreview.com/view/541311/the-false-science-of-cryonics/
Michael Hendricks is a neuroscientist and assistant professor of biology at McGill University.
Straw man. Connectonomics is relevant to trying to explain the concept of uploading to the lay-man. Few cryonics proponents actually believe it’s all you need to know to reconstruct the brain.
The fact that someone can be dead for several hours and then be resuscitated, or have their brain substantially heated or cooled without dying, puts a theoretical limit on how sensitive your long-term brain state can possibly be to these sorts of transient details of brain structure. It seem very likely that long-term identity-related brain state is stored almost entirely in relatively stable neurological structures. I don’t think this is particularly controversial, neurobiologically.
This is not, to the best of my knowledge, true, and he offers no evidence for this claim. Cryonics does a very good job of preserving a lot of features of brain tissue. There is some damage done by the cryoprotectants and thermal shearing, but it’s specific and well-characterized damage, not total structural disruption. Although I will say that ice crystal formation in the deep brain caused by the no-reflow problem is a serious concern. Whether that’s a showstopper depends on how important you think the fine-grained structure of white matter is.
Bad philosophy on top of bad neuroscience!
I don’t think so, Cryonics is predicated upon the hypothesis that the fine structural details which probably can’t be preserved with current methods are not important to reconstruct personal identity.
I don’t think that substantial heating is survivable. Where did you get that information?
Anyway, the type of disruptions that occur to brain tissue during cryopreservation (hours-long warm ischemia, cryoprotectant damage and ice crystal formation and thermal shearing) are very different than those which occur in all known survivable events. Warm ischemia can be reduced with prompt cryopreservation (but even in the highly publicized case of Kim Suozzi, where death was expected and a lot of preparation took place, they still couldn’t avoid it), it’s unclear how much ice crystal formation can be reduced (it’s believed to also depend on cryopreservation promptness, but that’s more speculative) and cryoprotectant damage and thermal shearing are currently unavoidable.
You are reversing the burden of evidence. It’s the cryonics supporters that have to provide evidence that cryonics preserves relevant brain tissue features. To my knowledge, this evidence seems to be scarce or absent. AFAIK, no cryopreserved human brain, or a brain of comparable size, was ever analyzed. There were some studies done by ALCOR on dog brains, but these were never replicated by independent researchers. Dog brains, anyway, are smaller and hence easier to vitrify than human brains.
I feel like the dog brain studies are at least fairly strong evidence that quite a bit of information is preserved. The absence of an independent validation is largely down to the poor mainstream perception of cryonics. It’s not that Alcor is campaigning to cover up contrary studies—it’s that nobody cares enough to do them. Vis-a-vis the use of dogs, there actually aren’t that many animals with comparable brain volume to humans. I mean, if you want to find an IRB that’ll let you decorticate a giraffe, be my guest. Dogs are a decent analog, under the circumstances. They’re not so much smaller you’d expect drastically different results.
In any case, if this guy wants to claim that cryonics doesn’t preserve fine-grained brain detail, he can do the experiment and prove it. You can’t just point at a study you don’t like and shout ‘the authors might be biased’ and thus refute its claim. You need to be able to provide either serious methodological flaws, or an actual failure to replicate.
Dog brains are 20 times smaller than human brains: 70 g vs 1,300 − 1,400 g. Given the square-cube law, this means that dog brains have a much higher surface to mass ratio, therefore they can be cooled faster without cracking and using a lower concentration of cryoprotectant. (Cow brains, on the other hand, are just 3 times smaller than human brains and about the same size of chimp brains, hence you don’t need to experiment on an exotic animal to get more comparable results).
And we don’t know how much information was preserved anyway.
And the only studies being made by an organization that has ideological and financial stakes in the outcome is a big problem. As far as we know, they could have selected the best micrographs, hiding under the rug those that showed substantial damage.
Cryonics organization should encourage independent replication instead or playing the victim.
The default position is that cryonics doesn’t work. It’s the proponents that have the burden of providing evidence that it works. ALCOR dog brain studies are weak for the aforementioned reasons.
Independent would mean research for which they aren’t paying. How should Alcor go about encouraging such research in your opinion?
Doing PR, essentially. I think that if ALCOR acted more as a research organization and less as McImmortality it would have an easier time getting external researchers interested, instead of the current hostile relationship it has with professional cryobiologists.
Considering that damaging large amounts of white matter gives you things like lobotomy and alien hand syndrome, or sensorimotor impairment, and that subcortical structures are vitally important...
Sorry, I probably should have more more specific. What I should really say is ‘how important the unique fine-grained structure of white matter is.’
If the structure is relatively generic between brains, and doesn’t encode identity-crucial info in its microstructure, we may be able to fill it in using data from other brains in the future.
Since I don’t have much academic knowledge on this subject, I appreciate Your feedback a lot. Can I just ask what is Your level of competence in this field?
BR
Just an enthusiastic amateur who’s done a lot of reading. If you’re interested in hearing a more informed version of the pro-cryonics argument (and seeing some of the data) I recommend the following links:
On ischemic damage and the no-reflow phenomenon: http://www.benbest.com/cryonics/ischemia.html
Alcor’s research on how much data is preserved by their methods: http://www.alcor.org/Library/html/braincryopreservation1.html http://www.alcor.org/Library/html/newtechnology.html http://www.alcor.org/Library/html/CryopreservationAndFracturing.html
Yudkowsky’s counter-argument to the philosophical issue of copies vs. “really you”: http://lesswrong.com/lw/r9/quantum_mechanics_and_personal_identity/
You might be interested in Aaronson’s proposed theory for why it might be physically impossible to copy a human brain. He outlined it in “The Ghost in the Quantum Turing Machine”: http://arxiv.org/abs/1306.0159
In that essay he discusses a falsifiable theory of the brain that, if true, would mean brain states are un-copyable. So Yudkowsky’s counter-argument may be a little too strong: it is indeed consistent with modern physics for brain simulation to be impossible.
Yudkowsky’s counter-argument is a counter-argument to a straw man, since I don’t think anybody ever argued in modern times that personal identity is linked to a specific set of individual atoms. Everybody knows that atoms in the brain are constantly replaced.
I don’t know if this is true.
http://askanaturalist.com/do-we-replace-our-cells-every-7-or-10-years/ http://rebrn.com/re/theseus-body-is-there-any-part-of-a-human-that-is-cellularly-or-873979/ http://www.theguardian.com/science/neurophilosophy/2012/feb/23/brain-new-cells-adult-neurogenesis All 3 links suggest the opposite.
Can You provide a source for this claim?
BR
If I understand correctly, long lived and highly metabolically active cells like neurons still replace most, if not all, of their atoms during their lifetime, since metabolism and environmental radiation cause chemical damage which needs to be repaired in order to keep the cell functional.
There’s actually been some cool studies on DNA extracted from brain tissue from people born before the first nuclear tests...
DNA is turned over for the most part during DNA replication. Neurons are terminally differentiated and do not divide, and thus their DNA is more or less frozen in place even as other molecules turn over (barring small repair events). People born before the first nuclear tests have neurons bearing a different carbon isotope ratio in their DNA than people born afterwards, and this was used in a study to determine the rate over a human lifetime of new neurogenesis versus nerve cells that stick with you for your whole life. Turns out most neurons stick around but in particular regions like your hippocampus there is a good deal of turnover of cells, with only about two thirds of the DNA there with you from birth:
http://www.physicscentral.com/explore/action/images/Neuron-by-age.jpg
The turnover of DNA molecules doesn’t really make any difference, just something fun that lets you track cells incidentally.
Nice information!
The claim isn’t that the cells are constantly replaced, but that the atoms are; see e.g. this blog post as an example of the claim being made. [EDITED to add:] More specifically, an example where the claim is made and “new cells” and “new atoms” are explicitly distinguished.
I have found this reddit discussion:
https://www.reddit.com/r/askscience/comments/1q16hw/im_32_is_there_a_single_cell_or_even_molecule/
and there are some pro and contra comments in there about atoms and molecules of the nerve cells. Probably I need a lot more reading on this subject , txs for the guidance.
BR
KEN HAYWORTH’S PERSONAL RESPONSE TO MIT TECHNOLOGY REVIEW ARTICLE
http://www.brainpreservation.org/ken-hayworths-personal-response-to-mit-technology-review-article
Why all those capital letters?