So, one of the technologies I've been researching while working on my BCI, is the interception of action potentials in a manner that's reversible and doesn't require you to perform a nerve block with anesthetic every time you want to do it. In order to achieve effective immersion, without interference from ambient stimuli, and get the most of a virtual reality experience, this is kind of a must. So, I turned to electrical nerve blocks. In my research thus far, electrodes have always been placed on the nerve itself. However, logic dictates that if I use skin-contact electrodes, and place them far enough apart, and run enough current through them, the same results can be achieved.

I've almost got everything I need to do a test of my theory together, I just need to finish assembling my electrodes, acquire a decent AC signal generator, and figure out how to hold everything in place. I'll be attempting to block the radial, median, and ulnar nerves in my left arm starting from just below my elbow, since the nerves are closer to the surface of the skin there. I'll probably attempt to do a cathodic block with DC while I wait on the AC signal generator, but based on the numbers I've seen, which label the skin as a 1000 ohm resistor when wet, I'm looking at 3000 ohms of resistance. According to one study, a human sacral nerve was blocked with a current of 7 mA applied directly to the nerve, and since the current saturation of the tissue of the body behaves in a uniform way the further you move from the electrode,  I estimated that 20 mA's would be sufficient to block the nerves without direct contact. Using Ohm's law, that puts me at 60 volts.


  • This sounds really cool. :3

    Don't forget to put in all of the redundant failsafe and thresholds. ^^

  • How long would this be able to be used for safely?
  • AC seems to be safe indefinitely, but their haven't been any trials testing chronic usage on humans. DC, when applied via a needle-type electrode, is inherently unsafe. I suspect that it's probably fine for 20 minute usage now and again, like tourniquets. 
  • I don't see how logic dictates that indirect stimulation will provide any blocking.
    It's like estimating that by running 200 volts on the walls I'll end up charging my phone.
  • Well, You can stimulate nerves with electricity indirectly. Why not block 'em? You're right that the logic I presented was flawed, though.
  • edited February 2016
    So this really is not a substitute for lidocaine?
  • Might be. I'll know for sure after I actually do the test. 
  • Please be careful, 20mA across the heart will kill you.
    The human skin model for normal skin is in the megaohms, but still.
  • And don't forget the redundant failsafes!

    Better redundant than something stupid happening. c_c
  • Yea I think I goes with out saying (to you who was wondering the Internet and found this read on) don't try this on your head or across the chest. Fails safes are not a substitute for smart electode placement, or not protection for bad electrode placement.
  • edited February 2016
    I've spent the last few days looking for a conductive backing suitable for my experiment. I've settled on using strips cut from a large steel can, which I'll cover with a few layers of heavy duty aluminium foil to prevent the saline from attacking the steel. Before I go waste 2 hours trying to do this, does anyone know whether or not aluminum and steel will bond with solder nicely?

    As far as mechanics go, if 60 V and 20 mA's works, I'll be able to power the DC portion of the experiment with nothing more than 8-9 AA batteries, assuming I don't lose too much in the way of current when I transform the voltage.
  • I know that aluminum Is a mess to work with for welding. It melts rather easily. I'm not sure how well that would work.

    I can't give you a definite answer of yes or no, I would expect it to go badly though, working with the two's heat tolerance differences. >~<
  • Aluminum does not solder.
  • You may want to use stainless steel instead of aluminum. At least stainless steel can be soldered with the right solder/flux.
  • Thought so but wasn't absolutely certain. Thank you.
  • edited March 2016
    That helps. Now I need to go find some stainless steel plate or foil lying around, and go buy the right kind of solder. Is stainless steel foil even a thing? In the interim, if I wrap 20 layers of aluminium foil around a piece of steel, and press it all down nicely, will the aluminium act as a suitable conductor (The steel's just acting as structural support)?

    I seem to have made a mistake. Human skin doesn't like following Ohm's law, for a number of reasons. I'll be doing more research into finding a model that effectively describes its behavior, but for now, I'll go ahead with my experiment using the numbers I got with Ohm's law. After each block, I'll flip the polarity of all the electrodes and pass current and voltage for the same amount of time in the opposite direction to "recharge" the region, and minimize any effects that build up over time. I'm not just pulling this concept out of the air. One of the studies I used as a reference did this, though they weren't really clear about why they did it, other than mentioning something about the electrolyte at each site. And on second thought, I think that I'll test whether or not that's an effective way of ensuring a less variable resistance at the electrode sites.

    I'm bumping up against the variability of the human body, and it's a bit of a pain. So, I'll rely on the good old principle of "P for Plenty" to start with (Safety first, though), and refine my design when I've got better data on how everything's going to behave. @ElectricFeel Is there some special sheet or document that you were referring to when you said the "human skin model"? I've been looking for a compilation of all the stats, like impedance, resistance, resistivity, breakdown voltages, magnetic permeability, permittivity, and,,, Anything else that could be useful.

  • Can anyone explain why TENS(Transcutaneous Electrical Nerve Stimulation) works? Sure, you're running electricity through a region, like I intend to do, but the device seems to be working on an entirely different mechanism to prevent pain.

    Also, to be abundantly clear, I am not building a TENS machine. As far as I can tell, TENS prevents pain, while I'm attempting to intercept pain signals.

  • Tens units basically activate the voltage gated channels of nerves, either causing depolarization.. such as is evidenced by muscle contraction.. or making depolarization more likely. Now, the reason they work to treat pain is a little weird.

    Basically you have different fiber types carrying the impulses communicating pain. There are fibers related to chronic pain.. the stuff we describe as aching and dull and hard to locate exactly.. and fibers related to sharp, stabbing, acute pain. Your body has a preexisting relationship between these fibers... acute pain basically down regulates chronic. This is (partially) why massage works.. if you are sore and you get a deep painful massage, it relieves some of the aching dull pain for a period. So, a TENS unit activates the fibers in a way that results in muffling of the chronic pain fibers.
  • edited March 2016
    Oh good. I'm not reinventing the wheel, then... As a side note, has anyone ever tried substituting a TENS unit for anesthetic during an implant? I doubt it would work, but it'd be interesting to see.

    Built the my current supply circuit yesterday, and did a bit of testing. It's a bit annoying, because I only had a small transistor on hand, and it heats up really fast if I set it to output more than about 20 mA's. Other than that, it worked. I'm in the process of build the electrode rig that'll hold everything in place right now. 

    I'm not expecting anything dramatic out of this first test, like a proper nerve block, but it's going to provide a lot of great data for my next tests. I'll be shocked and amazed if it works perfectly, though. The current set up, if I were to go out and buy everything, would cost... Maybe $30. That alone excites me, considering the PMK costs $40, and my system is totally reusable, aside from replacing sponges occasionally.
  • Sorry for not providing any updates for awhile. Finally finished my electrode array, and I'm starting to source the parts for my power supply. I haven't abandoned this project, I've just been poking along on it. 1-2 months till it's ready to run. Does anyone have any suggestions for a source of pain that'll be a good measure of whether or not the block is effective, that I can repeat for several tests?
  • Stinging nettle plant
  • I use a small cheap commercial TENS unit to help with shoulder pain and it works wonders, I've also read about it being used as an effective anaesthetic during dentistry so I have to assume that the more powerful units would be suitable for implant procedure... however... it might depend on the implant and how sensitive it was to electrostatic shock.

    For a pain source you might try capsaicinoids... a small scratch (or sensitise the skin with a little and paper) and a drop of hot sauce (or rub with a small red chilli/pepper) will give you a reasonable level of pain with no real damage to you and no interference with your device. Wash with soap and alcohol when your done.

    Also you can buy a pack of TENS pads online (ebay?) for a few dollars, and they conduct pretty well, they can be re-used too if you clean the skin well before you apply them, plus they adhere, so no need for any special rigging to keep them in place.
  • Electrostatic shock and the voltage I'm using for my system are pretty far apart. A shock is in the thousand volt range, while this is gonna be 400 Volts at most(for the DC portion). Also, the electrodes'll be on the arm. An implant's typically going to be taking place in the hand. A good 4-5 inches away at least. 

    Eventually want to work up to a spinal block, but... I want full life support with paramedics standing by for that. 

    I'll be buying the parts tomorrow. Assembly will commence in like... 2 weeks. Gotta find a good chunk of iron for my transformer...
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