From: Smigrodzki, Rafal (SmigrodzkiR@msx.upmc.edu)
Date: Mon Jun 17 2002 - 10:34:15 MDT
Anders Sandberg [mailto:asa@nada.kth.se] wrote:
On Sun, Jun 16, 2002 at 08:41:34PM -0400, Smigrodzki, Rafal wrote:
>
> Some time ago I had an idea which should help: make electrodes in the
shape
> of pigtails, or helical springs. This shape would anchor the electrode
much
> better and it would allow it to accomodate the stretching and shrinking
that
> our brains undergo as we age.
Sounds like a good idea. But what about the dimensions? If you want
to stimulate cortex, you will likely want to do it in layer IV, so
you have around 1.5-3 mm of cortex to screw through. If the helix
has a small radius it will essentially be like current electrodes.
If the radius is larger it will fix better but also affect more
tissue, which might be bad, and you cannot put the electrodes much
closer. There is likely some optimal size here, but you have to
test it experimentally on tissue to find it.
### I would electrically insulate the electrode (a thin layer of teflon?),
with a few small contacts at the tip and along the length - just like in the
multichannel cochlear implants (but smaller - I wonder what manufacturing
technique would be up to making a bundle of wires less than 50 micrometers
in diameter), so I could get a more localized excitation and reception. Yes,
somebody will do the testing someday (I work on mitochondria, cells are too
big for me).
-------
> Another element would be small areas on the
> electrodes covered with a dried, tissue-compatible plastic gel - after
> implantation the gel would take up water and swell into small beads,
firmly
> anchoring the electrode. The helical part of the electrode would extend
> through the subarachnoid space (again allowing for movements of the brain
> within the cranium, as in running and under acceleration) to chips
attached
> to the dura, with the circuitry for sending information in and out through
> the skin (the current Dobelle implant contains a pedestal open to the
> outside, traversing the skin, which in practice could pose the risk of
> infection).
You can also cover the electrode with tissue attractive protein
chains or glucoproteins.
### But they would have to be resistant to enzymatic lysis, to allow
extended stay in the tissue.
Rafal
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