[ExI] destructive uploading.
eugen at leitl.org
Wed Sep 7 20:07:46 UTC 2011
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
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
> 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.
Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
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