ciphergoth: (Default)
Paul Crowley ([personal profile] ciphergoth) wrote2010-01-21 09:29 am
Entry tags:

Cryonics

I'm considering signing up with the Cryonics Institute. Are you signed up? I'd be interested to hear your reasons why or why not. It does of course sound crazy, but when you press past that initial reaction to find out why it's crazy, I haven't heard a really satisfactory argument yet, and I'm interested to hear what people think. There are many reasons it might not work, but are there reasons to think it's really unlikely to work? How likely does recovery need to be for it to be worth it?
djm4: (Default)

[personal profile] djm4 2010-01-21 03:33 pm (UTC)(link)
Ah, thanks. That bit is written by someone who understands the technology (and IMO the introductory paragraph is a terrible summary of it), but I still wouldn't get your hopes up. As far as I can see, it offers no way to discern the state of the neurons, and admits that while it might be possible to get the structure for a small slice of the brain, getting it in 5nm detail for the whole volume is currently impossible, with no known way to overcome the current technological limitations. Many of those limitations are imposed by the wavelength of the medium you're scanning with, and there's just no easy way round that. The speed of scanning (which is also currently a showstopper for the ~5nm technologies that might otherwise be attractive) might be able to be improved, but bear in mind that you're working at levels where the energy of the electrons/photons that you're using to scan risk damaging the sample, and using more of them in parallel may damage it more. The data transfer/storage problem probably is solvable, by contrast.

I find it a bit worrying that the most promising technologies in the table on page 43 - SOM and SEM, especially combined with array tomography - have relatively little discussion in the text that I can see. This makes me suspect that they're only even superficially attractive because not enough is known about them to know they don't work.

Also, given that the conclusion says 'this sets a resolution requirement on the order of 5 nm at least in two directions,' there's far too much discussion of technologies that can only scan down to resolutions two orders of magnitude higher than this. So the text gives the optimistic prediction that '[KESM] enables the imaging of an entire macroscopic tissue volume such as a mouse brain in reasonable time', but what good is that given that KSEM only scans down to 300nm x 500nm? It's an obvious question, and I'd expect an honestly-written paper to answer it. Because this paper doesn't, I smell a rat (or, more likely, someone clutching at straws).

The discussion starts 'As this review shows, WBE on the neuronal/synaptic level requires relatively modest increases in microscopy resolution...' which may be technically true but vastly understates the difficulty of increasing the resolution of the techniques discussed.

Again, though, I'll defer to someone who's done this stuff more recently than I have (and in a medical area - I was mostly looking at metal-matrix composites rather than anything organic).

[identity profile] ciphergoth.livejournal.com 2010-01-23 07:43 am (UTC)(link)
Do you mind if I ask Sandberg to comment on your remarks?
djm4: (Default)

[personal profile] djm4 2010-01-23 08:36 am (UTC)(link)
Not at all. I was aware this post was public, and I did explicitly suggest you seek more expert opinion. Don't expect me to have any good rebuttals; I've reached about the limit of my knowledge on the subject, which is OK for engaging with what's written in that PDF, but probably inadequate for detailed discussion of the techniques.
djm4: (Default)

[personal profile] djm4 2010-02-11 08:00 pm (UTC)(link)
Did he/she ever reply?

You seem to be still treating the PDF as a serious roadmap. I'd characterise it as a 'map of the swamp, with several of the circling alligators marked with an "X"', which I suppose is a roadmap of sorts, but not one that's going to show you the way home.

I'm not sure if you simply don't find my objections credible (fair enough, given the source; my blog reply is hardly a peer-reviewed paper) or whether you have a rebuttal of them.

[identity profile] ciphergoth.livejournal.com 2010-02-12 09:23 am (UTC)(link)
I haven't asked yet; I'm trying to work towards getting the whole discussion into a more tractable form broken into component parts on my blog, rather than pointing him to a 200-comment LiveJournal thread! When I do, may I copy in what you write here?
djm4: (Default)

[personal profile] djm4 2010-02-13 08:20 am (UTC)(link)
Yes, certainly.

[identity profile] ciphergoth.livejournal.com 2010-02-20 02:42 pm (UTC)(link)
Done: http://blog.ciphergoth.org/blog/2010/02/20/david-matthewman-whole-brain-emulation-roadmap/

though I haven't pointed Sandberg to it yet.

Thanks again!