Implantable EEG Electrodes
  • LuaMaterLuaMater February 2016
    So, i've been in the process of designing my own little home EEG setup, and one of the things that i've looked into a lot is the whole business of electrode attachment. Typically, electrodes are either active dry and held by some sort of headband, headset or something similar (reasonably expensive) or the electrodes are passive and are attached via saline gel or paste, possibly in addition to some other adhesive (messy, inconvenient). I was wondering if it would be feasible to have electrode attachment points implanted directly into the scalp, either via a sub-dermal implant or a scalp piercing.

    I have no experience with piercings in general, so how exactly would i go about with something like this? What would be the biggest problems and challenges, and what complications could I potentially run into?

  • JohnDoeJohnDoe February 2016
    I don't know of any that are implanted in the brain through the skull. To my knowledge needle electrodes are implanted along the scalp under the skin, I don't believe them to be permanent either.

    Sincerely,
    John Doe

    Edit:
    I think there are infection protocols like shaving the head and such.
  • SlachSlach February 2016
    EEG signals are very noisy because they have to pass through the skull to get to the electrodes. Going sub-dermal will circumvent the skin, but won't solve the biggest issue, namely the skull. The only thing you might achieve is an easier set-up of the system, of you have some kind of plug implanted in your skin. But this sounds like it would be prone to injury, tearing, etc. Piercing the skull or even shaving off parts of it is generally a bad idea. The skull is very thick and strong but for a good reason: Its job is to protect your most important organ.

    ECoG electrodes offer a very good spatial resolution and a good SNR. Is this what you're talking about? These are implanted or placed under the skull. Needle electrodes are often implanted in the outer layers of the cortex, usually in primate research. Not many people get needle electrodes implanted, and as far as I know not a single person has (had) them implanted permanently. Because they pierce the actual brain tissue, scar tissue due to immune response tends to increase the noise floor after an x amount of time, decreasing signal quality. Moreover, tissue formation in the brain is ethically undesirable, so in humans needle electrodes are explanted as soon as they have served their purpose (which is usually research).

    Grid/strip electrodes are less invasive. They are also applied under the skull, but do not penetrate the skull. These are often used in epilepsy patients to accurately localize seizure location. They are comparable to EEG electrodes since they lie on the brain surface. They do not cause as serious an immune response/scar tissue response as needle eclectrodes. Research with primates shows signal quality stays good for many years and expectedly will provide a good signal for as long as they stay implanted.

    World wide, there is maybe a handful of people with ECoG electrodes implanted. Of those, really only a few are permanent. (Maybe the military has some additional human subjects with implanted ECoG electrodes that we don't know about.)

    Like I said, drilling in the skull isn't really advisable. Transdermal electrode ports are probably also way too risky. If you want to make the EEG system easier to set up, you can just improvise some head band to which you can attach your EEG electrodes! Doesn't have to cost much.
  • kuroro86kuroro86 February 2016
    You need to look to the material that make the electrodes, if they can stay in contact with  the skin or bone. 
    A good reason there are no permanent electrodes i that after a while the body rejects them. The head and skull and even more the brain tissue is very sensitive. 
    And there is also the problem of infection. 
  • LuaMaterLuaMater February 2016
    Hey slach

    I have done (what i think is) a reasonable amount of research on ECoG implants. Unfortunately, I haven't yet found a safe, reliable and cost effective way to get such an implant.

    As of yet, I have no intention of drilling into/penetrating my skull in any way. I understand that having sub/trans dermal attachment points will do little to improve signal fidelity. I wanted to use piercings/implants in order to make the EEG set up more convenient.

    Concerning the headset idea, I'm still considering that as well. A headset, however, may be quite cumbersome (especially if it's cheap) and it'll be difficult to make it in a way that it will reliably rest on the 10-20 points I want to target. The headset also does not circumvent the issue of having to either use saline paste or active electrodes.

    I believe that the issue of mechanical stresses on the attachment point that may cause trauma to the area is something that can be designed around. I was wondering, however, what specifically should I be paying close attention to when designing such an attachment point, and exactly how should it be attached.
  • beta0x64beta0x64 February 2016
    You don't necessarily need to place electrodes under the scalp. You could place them on, for example, your arm or leg to detect the muscle contractions, which could be even more intuitive than straight-up EEG.
  • LuaMaterLuaMater February 2016
    While that is certainly an option for any kind of direct interface, I do specifically want to explor/play around with EEG. 
  • baffo32baffo32 November 2016
    Hi, I am also interested in the idea of using skin piercings as longer-term electrodes for EEG, EMG, etc.

    I found a forum thread at openbci ( http://openbci.com/forum/index.php?p=/discussion/419/electrode-earrings ) which mentions the importance of not introducing new metallic interfaces in custom electrodes.

    It looks like basically nobody has done this before.  After googling a little, I'm thinking that, although the impedance may not be as amazing as desired unless the piercing is lubricated a little, that this would totally work.

    @LuaMater, did you ever try this out?  Are you still interested in it?

    It seems the next step is for somebody to try this and report results.  I guess first you'd mark the 10-20 locations on your scalp and then get somebody to pierce your skin in those places.  Tests could also be done with conventional piercing locations.
  • IvoTheSquireIvoTheSquire November 2016
    @kuroro86: If it is below the dura I wouldn't worry too much about rejection since there is barely any immune cells within the central nervous system (hence electrodes in brain). Infection is a huge problem though esp. if going transdermal as well. Certainly something only done by the experts at least.
  • decaldecal December 2016
    Noobish question, but maybe one of you anatomical neurosurgeon types can satisfy my curiosity: if this thing is subdermal, then why isn't it designed to stimulate that vagus nerve since it's already going to be right there?