Electrodeless Neuro-Interfaces

As of now, there are a lot of projects that use electrodes and indirect interfaces via magnets, or vibrators to supply data to the user. But there are a host of potential issues with these methods that I'd like to avoid. It's easy enough to read the current state of the brain via EEG. We can even use tDCS, TMS to change how our brains work without ever sticking an electrode below the skin. The question is, why can't we use a similar method to create a direct interface with a nerve, even if it isn't the brain?

Any thoughts on how this could be done with precision (not just slapping an electrode on the skin are running current between point A and B to stimulate a nerve)?


  • I found a rather dusty paper from '65 (LINK) that said some interesting things. I'd be interested in repeating their experiments with modern techniques and kit to minimize error (and verify their claims).
  • You might've seen this video already but its very interesting what she's getting at: https://www.solveforx.com/moonshot/5631639635886080#solution

  • edited November 2015
    The answer to this question is one of practicality. In order to generate TMS impulses that are capable of affecting a nerve's membrane potential you need a fairly massive transient current. It's just simply not possible to generate with portable or wearable devices, much less implantable ones. The reason for this has to do with the fact that magnetic fields (which are the only way to feasibly nonlocally influence membrane potential) are weaker with distance. Not only are they weaker, they are also larger and become more difficult to control.

    If you want to affect things from a greater distance, you give up specificity and increase energy required, both of which are extremely important in any neural interface.
  • As for the paper, the very first sentence states why this isn't feasible for a neural interface. "Using wavelengths of the centimeter wavelength". Any waves that have a wavelength of 1 centimeter cannot be controlled on a scale that is meaningful to the nervous system (mm to nm scale), and isn't a candidate for a remotely useful neural interface.
  • edited November 2015
    Could you use weaker fields and pump the targeted nerve with some sort of EM Radiation to increase the transient current?(Just asking for the sake of asking, because what I know about physics dictates it probably wouldn't.)
  • No, you'd just make whatever particles you injected move. Any meaningful increase in conductance would require concentrations that are cytotoxic.
  • Why bother when electrodes work fine?
  • Because cutting a hole in the skull is kinda invasive. For the same reason that haptics exist. 
  • For anything practical, electrodes work fine.

    For high-resolution interfaces, you're not going to get anything both portable and non-invasive.
  • edited November 2015
    I don't think I am completely following, are you trying to connect with something telepathically, or are you trying to just avoid using electrodes? If the latter could nerve cells be engineered to make a wired connection from the brain to a port for example. Almost like a networking cable, ware only these impulses could travel along these special nerves. I am going to start reading that paper.

    John Doe

    "Because cutting a hole in the skull is kinda invasive." May I ask why you are using invasive electrodes? The only place I know for certain they are used is epilepsy research, that just caught my eye.
  • edited November 2015
    For lack of better examples, the supposed "microwave hearing" effect, or Nerve Gear from Sword Art Online are the best examples I can really think of for what I'm thinking of. You can think of it like telepathy, if that works for you.

      @garethnelsonuk What about non-portable systems? If a rig the size of an MRI machine is needed for the first iteration, we can always work on making it smaller later.


    Does anyone know whether the voltage you introduce has a bigger impact on the strength of the signal you introduce into a nerve, or whether it's current?
  • Magnetic fields are responsible for the nerve stimulation, and magnetic fields are induced by a moving charge (current).
  • edited November 2015
    Still has a ways to go, but something Vanderbilt was working on looked really cool: Link

    Apparently they were able to cause nerves to fire using infrared, instead of electrical stimulation. Funny enough, Infrared also happens to include wavelengths as small as, and smaller than the smallest neurons found in humans. Near infrared also penetrates soft tissue, bone, and brain matter according to this. Another interesting article on the subject: Link.

    That said, I happen to have 2 IR laser diodes(no idea what frequency or power rating). I'm going to do some investigating and do my best to get an experiment with this set up.
  • Unfortunately the authors seem to be silent on device design, so I'm not sure what they mean by "low cost" and "compact". Also, they stimulate the exposed nervous tissue directly. it isn't realistic to think you would be able to achieve anywhere near this resolution after dealing with the absorption and scattering of IR by the tissue in between.

    Another issue is that this is only a unidirectional technology: communicating from a device to the brain. The hemodynamic response is too slow for any real neural interfacing (10s+ delay and not consistent). Cool paper and certainly not without application, but still invasive.
  • edited November 2015
    Which kind of resolution are you talking about? Spatial resolution, meaning the smallest quantity of neurons the device is capable of interfacing with at a single time, Or something else?

    If spatial resolution is what you're talking about, couldn't you simply design a device that has an extremely high starting resolution, so that when your IR signals get scattered and absorbed by the tissue, the resolution is decreased to the minimum level needed for an effective neuro-interface? Or does the skin introduce a constant cap for the resolution you'll get?

    Smallest neuron size: ~4 microns(micrometers)
    Device Resolution: 2 microns(micrometers)
    Resolution Loss: 2 microns per tissue-size unit.
    Tissue thickness: 1 tissue-size unit
    End Resolution: 4 microns

    ---- EDIT ----
    I didn't think to use square micrometers when I first came up with the example, but now that I've thought about it, it would just make things more complicated if I had.
  • edited November 2015
    One option for the other half of the problem is EROS(Event-related optical signal). It uses infrared light to measure the optical characteristics of the neuron's themselves, rather than the flow of blood. It's non-invasive too. Here's a link to an article about it, which is unfortunately behind a paywall: LINK
    Could someone grab it, and add it to the community article library( @cassox or @glims)?
    This is another related article, also behind a paywall: LINK
    And here's one that doesn't cost anything: LINK
    Sadly, it sounds like it falls short of the spatial resolution needed for a BCI. Is "within millimeters" accurate enough, because I don't think it is?

    I also found an interesting article on Dynamic Brain Imaging, which seems to give a good rundown on the subject:  LINK
  • edited November 2015
    @ElectricFeel Bless you.

    @TheGreyKnight A spatial resolution of a few millimeters is definitely enough for a working BCI. You can even get a BCI working with EEG, so the mm-range is definitely 'deep' enough. ECoG falls within the same range. Of course, it depends on what you want to do. You're probably not going to control a prosthetic arm with 7 degrees of freedom with minimal training, but doing something like moving a cursor is definitely doable with that type of resolution. I wonder why this EROS method isn't more widely used in research. Can't be that expensive, right? Is it susceptible to signal noise or does the signal easily get messed up with small head movements?
  • edited November 2015
    @Slach The Problem with EROS is the fact that it doesn't go nearly as deep as MRI. Only a few centimeters. It's actually super cheap and easy to use, I believe.

    And @ElectricFeel Thank you so much!
  • edited November 2015
    "Better than a centimeter" does not mean "a few millimeters". The authors also say the relatively low SNR "in reality requires that data is averaged across subjects". I.e. cannot be used reliably in real-time (required by a BCI), but can be useful when studying brain activity across multiple people. While it has better spatial resolution than EEG, it has much worse temporal resolution (millisecond for EROS vs microsecond for EEG). 

    In terms of penetration, most of the interesting cognitive stuff is happening in the neocortex (the outermost layers of brain tissue), so the 3-5cm penetration limitation isn't a huge issue.
  • As long as the millisecond delay is under 50 ms, it's not a big deal, because there's already a 50 ms delay between visual stimuli and auditory stimuli. By that benchmark, it's definitely an acceptable delay.

    In regard to the SNR, do you or @thomasegi know about how to improve that ratio?
  • edited November 2015
    No, that's not exactly how it works. The way EEG activity is typically made meaningful (and really all non-spike neural data) is by sorting the data into frequency bins and plotting the intensity at those bins over time. This is called a spectrogram. If you are only recording at 20Hz, you can only capture 10Hz signals in a perfect world, more realistically less than that. To capture useful data you need to record at higher frequencies (100Hz+). If you are recording individual neurons the story is very different, but that's not an option with this technology.

    No, I don't know how to improve the SNR here.
  • And here's the study on EROS you've all been waiting for. No more "better than a centimeter", or other imprecise nonsense. LINK Here's another one with meaningful data on about and EROS experiment and the configuration used: LINK
    This article(LINK) mentions a more recent study published in the Journal of Cognitive Neuroscience about using EEG and EROS signals together. I'd like to get a copy and see if they mention exactly how they configure their experimental apparatus, and how they used the 2 data sources in conjunction.
  • This may also be worth taking a look at. I was looking at options other than EEG for my project, just in case for what ever reason it proves to be impractical or what ever. No way in hell with current technology could I use that for my project, but it may help you. I would also like to point out that you did say non-portable systems were a option.

    John Doe
  • edited December 2015
    I had a look at this when I was first diving into the subject, but the whole "shielded room" thing was a bit of a problem. Seems like it could work, but pretty expensive, and it suffers from range issues. 
    One paper mentioned something that might make it cheaper, though( Link)

    I might see about making a channel on slack about this soon.

    On another note, if someone has access to this paper (LINK), It'd be a big help if they could download it for me. 
  • Slack channel started. Message me if you want to be added (already added everyone from this thread, if they were on slack).
  • edited December 2015
    I wonder if a magnetic field could not be created around the user to drown out interference and then digitally cancelled out, my foresight tells me the immediate problem would be you would need extremely sensitive sensor’s that can detect across a extremely variable power range of fields. Correct me if I am wrong but are those fields coming off of the brain in the picoteslas? Let me make a comparison to a humbucking guitar pick up. Just in case that was unclear or vague.

    John Doe
  • edited February 2016
    I've made some progress in this project, but I haven't quite gotten all of my information and data into nice, readable format yet. Might be a month or so before that happens.

    Question for @bciuser , or anyone else who might know they answer:  If I've got an interface device designed to pass data into the visual cortex, how many data I/O (In the form of electrodes or laser targets) sites per square millimeter will I need? Do I need to interact with individual neurons, or will dealing with clumps of 10 - 20 be sufficient to allow a good connection? 

    Changed units from mm to mm^2.

  • Are you building a MEG?
  • Not as of now. I'm still sticking to the infrared route, for a number of reasons. Size is a big one. MEG might go somewhere in the future, but right now, the juggernaut of advantages backing optical systems can't really be beat. And they have the added bonus of being multi-purpose. I can stimulate and observe with the same laser/light source. 

    On a similar note, I have something pretty cool I'm about to test that'll be useful for this project, and eliminate the need for chemical-based anesthesia. Reusable, and all that jazz. I just need to order some parts and I'll be able to give it a test. I'll probably be making a thread on it soon. 
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