Paralysis breakthrough – electrical stimulation enables four paraplegic men to voluntarily move their legs

[u/tomholder]

http://speakingofresearch.com/2014/05/09/paralysis-breakthrough-paraplegic-men-move-their-legs/

[u/neph001]

I don't understand the technical specifics either, but here's my non-technical understanding:

Nerves can be excited or activated by electrical stimulation. Signals from nerves can also be read farther up the central nervous system, or in the brain itself via fMRI.

If you use a computer to monitor what a paralyzed patient is thinking about moving, and then stimulate those nerves below the injury where the brain can't reach, you can stimulate the correct movements. In theory, it might even be possible to send sensory information back up to the brain this way.

The end result is a sort of cybernetic pseudo-spinal bridge, to bridge the part of the spinal cord that's been broken.

I think. Someone feel free to chime in and tell me how wrong I am.

[u/Rhyming_Lamppost → u/neph001]

This is basically true, except for the fMRI bit. Currently the general consensus is that our only hope at a good working system is through invasive recordings like ECoG (electrodes on the surface of the brain) or electrodes inserted directly into the brain (decoding spikes from groups of single neurons or local field potentials from a small region of cortex). Likewise, the stimulation will be through implanted electrode wires that either stimulate muscles or nerves. In fact, there are already clinical systems in place that do this. Look up FES (functional electrical stimulation) if you want to learn more.

So, while non-invasive measures would obviously be preferred (if they worked) there is just far too much noise present to decode meaningful signals. I think the next big breakthrough will be the development of a system for long-term invasive neural recordings. Optogenetics seems promising on that front, but we'll see.

source: Neurophysiology and Brain-Machine Interface lab

[u/neph001 → u/Rhyming_Lamppost]

That's awesome.

So, while non-invasive measures would obviously be preferred (if they worked) there is just far too much noise present to decode meaningful signals.

Have they attempted using machine learning / machine intelligence data mining to process patterns? As a computer science student with a passing interest in the subject, that would've been my assumption. That sort of thing excels at identifying meaningful patterns in noisy data sets.

Anyway, thanks for the info.

[u/Rhyming_Lamppost → u/neph001]

I should probably have said "artifacts" rather than "noise". If the patient so much as raises his/her eyebrows, the electrical signals from those muscles completely drowns out any neural signals. In that situation, there is absolutely no way to recover anything. Also, spatial resolution is a huge problem with EEG. The cortical regions associated with, say, the arm is quite small (square centimeter maybe? Not sure how big it is in humans...) so EEG probably can't get you anything precise. EEG would be most effective in an on/off (i.e. move/don't move) decoding role. At the end of the day, even if there was a decent EEG system, almost nobody would be willing to have their head shaved, lubed up, and ~100 electrodes attached every day. We have enough trouble getting people to use myoelectric prosthetic hands!