'default' map of channel numbers to 10-20 sites

edited August 2016 in OpenBCI_GUI
Hi,

I couldn't for the life of me get any of the OpenBCI software to work, but luckily Neuromore seems to work out of the box. 

Now I am trying to measure gamma in particular at Fp1 & Fp2 and possibly at F3 & F4 but I have no clue what to connect where on the OpenBCI board. 

Can anyone help?

Thanks in advance!

Comments

  • wjcroftwjcroft Mount Shasta, CA
    http://www.autodidacts.io/getting-started-with-openbci-a-tutorial-on-testing-troubleshooting-and-recording-ekg/#connectelectrodestotheopenbci

    Jay, hi. Any channel number can map to any 10-20 site you wish. But if you want the head diagram shown on the OpenBCI_GUI app to match the numbers and colors in the GUI -- use the color and channel mapping in the tutorial document above. (Created by Isa @brain.) The head diagram in the right panel of the GUI shows the channel numbers. 

    1 - Fp1
    2 - Fp2
    3 - C3
    4 - C4
    5 - T5
    6 - T6
    7 - O1
    8 - O2

    William
  • wjcroftwjcroft Mount Shasta, CA
    Isa's tutorial is a bit more oriented to ECG than EEG. The normal OpenBCI tutorial below covers connection of the SRB (reference, white, right earlobe) and Bias (ground, black, left earlobe). You need these two leads in addition the the channels you are measuring. EEG is measured differentially between the channel and reference. The Bias cancels 60 Hz noise.

    http://docs.openbci.com/tutorials/01-GettingStarted#getting-started-w-openbci-v-connect-yourself-to-openbci-2-connect-your-electrodes-to-openbci

  • Thanks William, you are just super helpful on all forums :)

    I hate to admit this but I am just not technical enough or not versed in this enough to figure it out. The autodidacts tutorial is much more useful but the OBCI one is nearly incomprehensible to me. It is either making assumptions about the level of understanding of the user or I am simply missing something.

    So just to see if I get your instructions. I need one electrode connected to SRB (1? the lower, closer to the board one?) which will be attached to the right earlobe, and a second one to the Bias one, lower, closer to the board second couple of pins from the left (if I am looking at the pins straight on?) which will be attached to the left earlobe. and then the other channels connect where on the board? anywhere?

    Thanks
  • Also, if I specifically want to measure gamma, anything I should consider? (location, settings, etc')?
  • wjcroftwjcroft Mount Shasta, CA
    edited November 2015
    Jay, hi. All your electrode plugs attach to the "closer to the board" row of pins. That SRB pin that is closer to the board is technically called SRB2, the farther SRB is SRB1. The default firmware settings are using these closer to the board pins. The farther row of pins are used for special cases, an example of this is shown in the OpenBCI tutorial. But for your purposes just stick with the closer row.

    So assuming this standard setup, connect

    SRB2 - white - right ear
    Bias - black - left ear
    ch 1 (N1) - grey - Fp1
    ch 2 (N2) - purple - Fp2

    ---

    Gamma amplitude is not so easy to measure at a single site, because 40 Hz is sometimes contaminated with muscle tension, called EMG (electromyography). And also, gamma does not pass through the skull very easily. So amplitudes are usually only a couple microvolts.

    In other words, if you do a reward based training at single sites to try to increase your 'gamma', you may just encourage a subtle muscle contraction at those sites, in this case your forehead area. (Eventually which could possibly lead to a headache.) :-)

    Gamma synchrony / coherence on the other hand, measured between two distant sites, has less chance for this kind of interference. This is what the TAG Sync protocol is doing between Fz and Pz.

    ---

    > and then the other channels connect where on the board? anywhere?

    Remember, the correspondence between 10-20 sites and your channels is up to you. If you use the 'default' GUI settings, then it's channels 1 and 2. But it is up to you how you assign your channels to sites. When you run training protocols, obviously you need to know the site and it's matching channel.

    William
  • Thanks. This is extremely helpful!

    I am not using the OBCI GUI, I could not get it to work, I get a bunch of error messages, I fix one, 3 more show up. But Neuromore seems to pick it up instantly with zero set up. I am hoping that will suffice, unless there is extra setup I need to do there as well that I am not aware of. 

    I am not currently trying to train for gamma using NFB (in this case), I am trying to do something similar to this study, with the a minimal setup. I just want to see if I can illicit/entrain gamma with tacs stim, and detect gamma even after the stimulation is done. 
  • wjcroftwjcroft Mount Shasta, CA
    Interesting. What kind of tACS setup do you have there? I've only done tDCS myself. The paper you cited of course is using MEG and even looking at high band gamma (up to 150 Hz!) Be cautious with applying your tACS simultaneously with the EEG leads hooked up. I don't think a few tens of volts would harm the EEG input sensors, but if the tACS voltage goes too high and the EEG sensors are in the voltage path -- effects on the sensitive input circuits would be unknown. Remember your EEG is responding to microvolt level signals.

    Some tDCS (tACS?) setups use constant current power supplies. Such that as the skin resistance goes up, they apply more voltage to try to achieve a given current level. So while the voltage may have a ballpark range, it may go "out of the park" if an electrode lifts off and the constant current circuit tries to keep raising the voltage.

  • My setup provides 30 seconds of 40hz at around 500 micro amps, not even perceptual. I'm running I think at around 5v peak to peak. It will go higher if resistance changes but I don't think it can go so high as to do damage.

    Now I know that I won't be able to measure clean EEG during stimulation but the idea is to do so right after. But I am wondering if the current that will be picked up by the EEG electrodes could A. interfere with the stimulation itself, or B. do any damage to the OBCI board. 

    Yeah the paper is a whole different setup but the concept is similar. I'm not trying to really replicate the study but to simply see if I can detect any noticeable effect via EEG reading.
  • wjcroftwjcroft Mount Shasta, CA
    The input impedance of the ADS1299 is very high, 1 gigaohm. So will not interfere with the stimulation. Where are your stim electrodes placed? If it's only 5 volts you should be fine.

  • F3 & F4, TP9 & TP10
  • edited March 2016
    [original post title: Could anyone help me with electrodes idk the sequence to arrange or put them?]

    please help me as i dont know how to set this device for an EEG...I've read this document http://docs.openbci.com/tutorials/01-GettingStarted but I'm quite not sure yet if this was about EEG or EMG so please tell me exactly which cable goes where if I've set the device for EEG

    Thank u very much from my brother
  • wjcroftwjcroft Mount Shasta, CA
    edited March 2016
    @ayushmh, hi. I merged your question into this existing thread on electrode mapping to channels.

    Please see the 1st reply above with the default channel mapping. The Getting Started doc you refer to shows a combined hookup of both EEG, ECG, and EMG all simultaneously. If you just want to map the EEG leads to show up on the head map of the GUI, use the channels above.

    Also see,


    William

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