[ExI] destructive uploading.
eugen at leitl.org
Wed Sep 7 20:19:48 UTC 2011
On Wed, Sep 07, 2011 at 10:07:46PM +0200, Eugen Leitl wrote:
> On Wed, Sep 07, 2011 at 10:43:38AM -0700, john clark wrote:
> > Eugen Leitl <eugen at leitl.org> wrote:
> > "You don't need full-blown nanotechnology for destructive scanning."
> > I assume you mean brain slicing and electron microscope photography
> There are several ways to skin the cat. I personally like the
> serial block face scanning electron microscopy (SBFSEM)
> which might or might not have enough resolution (though
> can't resolve fundamental properties which can be inferred
That should mean can't be inferred, sorry. I really shouldn't
post when tired and drunk.
> from shape and pattern alone, but latter might be inferrable
> from immunostaining, which can be apparently done
> post-fixation, but requires soaking of thin sections)
> but can do very fine interslice resolution, is low-artefact
> (you're imaging the block, not the flimsy slice) and automatable
> but that requires extensive heavy metal staining (including
> osmium tetroxide for membrane fixation which is expensive),
> so it's incompatible with the current cryonics approach of
> using tissue viability as proxy for structure preservation,
> and as I mentioned, you can't devitrify and then stain as
> it would cook the goose that lays the golden eggs.
> Maybe Ken Hayworth can validate his approach (I'm quite
> leery of combination of fixation via vascular perfusion
> *and* water substitution by monomers by the same route
> and subsequent polymerization, but the proof of the pudding
> is in the eating, and the pudding isn't even cooked
> yet, and it might taste awful, or very yummy indeed).
> > with the slices 30 nanometers thick, Jeff Lichtman
> I think SBFSEM can do even less, but I don't recall.
> I just pulled up http://hebb.mit.edu/courses/connectomics/Smith%20circuit%20reconstruction%20tools%2007.pdf
> which is slightly dated (things move quite quickly now),
> but looks relevant enough to skim as a review.
> > is already doing that in his lab for mouse brains,
> Mice are nice in that you can fix and stain them
> by perfusion alone, but even so it takes many weeks
That means diffusion, sorry.
> to months.
> > if he can do that for an entire human brain and keep
> > the cost down it might be an alternative to Cryonics.
> I'm personally am not optimistic it's going to work,
> but I'm quite ready to uncork the champagne in case
> Hayworth et al. can show it actually works in practice.
> > Or were you thinking of something else, and do you
> > have any thoughts on MRI?
> I think the only MRI relevant is fMRI for characterisation
> prior to suspension (composite contributor to create a functional
> fingerprint for validation other than primary or secondary
> behaviour observers, which is obviously not enough)
> and proximal-probe MRI in the solid state, aka flying
> along the exposed/vacuum-etched brain glass surface.
> It's the only thing that can image the freshly exposed surface
> nondestructively, and has about enough resolution.
I hope I haven't made even more mistakes I didn't catch.
Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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