Nerve-wire Interface?

[joekgamer]

Is it possible (and if so, how, and if not, why) to simply 'connect' organic nerves and metal wires together (like you would two metal wires)?

[Saulomo]

I've thought about the same thing myself. Between two humans this would be rather realistic, but a human and a dog probably has a lesser chance of success as the bodies and chromosomes are so different.

[CraigD]

Is it [a nerve-wire interface] possible (and if so, how, and if not, why) to simply 'connect' organic nerves and metal wires together (like you would two metal wires)?

Simply connecting nerves to wires is quite possible, and has been done for a long time (Brodmann and others were laying down the foundations of modern neuroscience by, among other things, sticking electrodes in to brains, around the turn of 1900). Getting a really useful interface – say, something that would let you see computer-generated images other than with your eyes, and control remote manipulators just by thinking, is more difficult, and if not quite in its infancy, IMHO still in its toddlerhood.

 

Most of these technologies involve making semiconductor chips with special biological scaffolds and doped with various hormones and neurochemicals in such a way that nerve fibers grow connections into them when they are implanted. It’s a pretty big field, with lots of public and private players (including such biggies as the US military), so I’ll leave summarizing it to the many good articles on it online, such as this wikipedia article.

 

Its major current application is, as best I can surmise, neuroprosthetics – replacing damaged or lost sense organs or limbs with mechanical ones by “wiring” them to the nerves used by the lost limbs and organs. Some of these devices have been around so long and are implanted in so many people, it’s easy to forget they’re actually direct neural interfaces, rather than a sort of high-tech speaker-using hearing aid. Cochlear implants, for example, have been around in a sizable numbers of people since the 1990s, and to date have been implanted in nearly 200,000 people.

[joekgamer]

Then why don't people who have lost limbs get new ones 'wired' in all the time? It can't be all that difficult, can it?

[CraigD]

Then why don't people who have lost limbs get new ones 'wired' in all the time? It can't be all that difficult, can it?

It can be all that difficult, for at least a couple of kinds of reasons.

 

1st, robotic technology hasn't produced something the size of a human limb that has nearly its same performance - strength, speed, fine control, etc. The human body is a marvel, most artificial replacement parts for it, less marvelous.

 

2nd, direct nerve-machine connections require an invasive surgical procedure, then some sort of means of connecting the parts inside the patient's body to those outside it, a significant engineering challenge.

 

This second challenge has lead to some interesting work-around approaches. One involves not attaching the motor nerves for the amputated limb to a nerve-machine interface, but to an existing muscle elsewhere in the body, then using external sensors to convert the motion of those muscles into control signals for the mechanical arm (see this Technology Review article, and this earlier one it links to).

 

In short, nerve-controlled replacement limbs are still an emerging, experimental technology, not yet able to compete in their market with older technology.

[joekgamer]

Why would it be difficult? Couldn't you just 'clamp' the nerve with the wire (or something similar)? What is the problem?

[CraigD]

Why would it be difficult? Couldn't you just 'clamp' the nerve with the wire (or something similar)? What is the problem?

Yes, you can clamp a conductor to a bundle of nerve fibres. In principle, you could clamp individual wires to individual nerves, but practically, it's a difficult surgical task, as individual nerves (neurons) are very small, on the order of 10^-5 m, and very easy to sever with anything metal small enough to clamp them.

 

The major bioengineering problems here isn't making contact with the neuron - we've been able to do this with a simple thin needle electrode for over a century (though saline water filled glass electrodes are preferred nowadays) - but making such a contact permanent enough to be useful. Nerves are in a squishy, dynamic medium - inside the body - where things that stay together do so because they have many binding points, and are constantly self-repairing under the guidance of complicated biochemical processes. These processes tend to react to simple metal objects shifting around in squishy conditions by killing the cells with which they're in contact, surrounding them with special cells (puss), and ultimately ejecting them through the skin. In short, they treat them like splinters.

 

Another challenge is getting an electrical signal from a conductor attached to a nerve to something outside of the body. For short experiments, a simple thin sterile needle through the skin is OK, but over time, holes in the skin can result in dangerous infections. This is why mature neural interface technology, like cochlear implants, implant a electromagnetic coil under the skin, then send to it via a coil held in place magnetically outside the skin.

 

"Don't break the skin" is a pretty good biomedical engineering rule.

 

The conventional wisdom about "neuro-chips", as they've been called in their community-of-interest, is that it's best to make them so that they fool the body into "thinking" they're nerve or muscle cells, so that the nerves attach themselves using their normal self-repair functionality.

 

To my surprise, I've not been able to find a lot of online articles about neuro-chips (eg: This 2006 LiveScience article), though I recall coming across them in various literature every month or two a few years ago.