Cranial and peripherial nerve behavior after resection Options

[Marko]

Hello everyone.

For a while I've been researching possible improvements of sensory prosthesis, such as hearing or even visual prosthesis in disabled people which is at present day still fairly in the science fiction category. While I've come up with some promising looking ideas on the electrical engineering side, it still all depends on cooperation of the biological parts, and my knowledge about this is very limited and I'd be very thankful to receive some information input on that side.
I'm first going to say a few words about the proposed implant (call it brain-computer interface, or whatever).
Most today's experiments of this type only involve a few electrodes usually implanted perpendicular to nerve axis through many axons on their path, or, in case of cochlear implant, cochlea itself. This gives a fairly poor resolution and till this day only seems to have been usable in form of cochlear implants.
The dream of expanding this technology into restoring sight and other functions is obviously going to have to wait for this axon-connectivity resolution to improve much, much more.
My proposal was the following:

- the whole implant would be created using microelectronics technology, as a single monolithic integrated circuit that attaches cleanly to an end of a nerve.

- the integrated circuit would consist of several components integrated together on it, which all are an existing technology in some form. The first would be a CCD sensor, whose purpose would be to act as a miniature microscope. The pixel size of today's CCD chips is already in range of few um; it should not be hard to reduce this to 1 micrometre or less for a monochromatic chip, which is close to practical wavelengths of visible light anyway. No lens would be required since the sensor is in very contact with the tissue.

- The light source for the 'microscope' would consist of led's a few mm upstream the nerve, shining into it. Hopefully, with the aid of some non-toxic staining agents this tiny contraption would produce an image much like the following, only in much higher resolution to the point where the very individual axons can be identified:

//Url didn't work, I'm asked to make more posts before posting url's! Anyway, it's an image of a cross-section of an optic nerve//

- Now, there comes the final and the most important part of the chip: on every corner of every CCD pixel there would be a metal electrode, connected to programmable gating logic underneath. Every electrode could be programmed as input, output, or driven high impedance by the gating logic.

- The whole implant would likely be no bigger than a match head, attached to an end of nerve and powered and communicated to external main computer wirelessly much like cochlear implant.

The computer would first scan an image of the nerve, identifying the location of almost every axon in it. Then, it would program the electrodes accordingly and establish connection to outside world (like sending image from an external camera).
Digital information from the camera would need to be recoded into form that is understandable for the brain which is another challenge, but I think it's an achievable one considering today's knowledge on neuroscience.



Of course, this whole dream falls into water if the biological part decides not to cooperate. The nerve is a living tissue and may change over time after resection in many different ways. This is where my question starts: how would the exposed surface of a nerve react a week, month, year after resection? And how would introduction of materials like SiO2 and metals like copper or titanium affect it?

Here are some of my ponderings:

- The cranial nerves, and especially the optic nerve are attractive for this becuse of two reasons: firstly, optic prosthesis is relatively simple to construct with today's technology while being very valuable. Secondly, unlike the peripherial nerves, the cranial nerves won't attempt to regenerate after being resected.

- Of course, they may still produce scarring or some other sort of a layer with poor electrical properties between the nerve and the electrodes.

- Unlike copper wires, the axons themselves are more like tiny, squishy tubes. I have no idea what would actually happen to them after they are severed - they may shrink/collapse and become unusable.

- As it can be seen in the upper image, there are blood vessels going through the centre of the optic nerve, which used to power the retina (before the eye was removed). I'm somewhat clueless what would be the proper way to manage them - cauterize them shut, or perhaps interconnect them somehow in order to keep the blood flow somehow? The babysit glial cells that surround the cranial nerve axons would need to be kept alive in any case.

So, this is where I need your help - basically any information on nerve behavior following resection is welcome. Scientific criticism and general evaluation of my sanity is also appreciated!

Cheers,

Marko