which input pins when using multiple EEG channels?

MikeMike
edited April 2015 in Electrodes
Hi, 

I'm planning to run some tests where 2 electrodes are connected to the front of the head and two other are connected to the back. So, total of 4 electrodes. 

I would like to get some advice on what is the best way to connect these electrodes to OpenBCI input pins. Would it make sense to connect the frontal electrodes to pin 1(positive and negative) and to pin 2(negative and positive) connect the two back electrodes?

What about biasing and reference? I have noticed in the example in "getting started with OpenBCI" that you were using both SRB2 and biasing - what is the advantage of using both?

Thanks, 
Mike  

 

Comments

  • wjcroftwjcroft Mount Shasta, CA
    edited April 2015
    Mike,

    The most common setup is using the ear lobe or mastoid as reference, on SRB2. Then your 4 electrodes on IN1N through IN4N on the head. You can place Bias anywhere: the other ear lobe / mastoid. Or on the head.

    You need to include Bias (also called Ground) in all electrode montages. It is part of the noise cancellation circuitry.

    Most EEGs are done with ear references like this. However (technically), there are other possibilities for montages, such as listed below. (Such as Referential / Bipolar / Sequential / Laplacian.)  I would stick to the simple ear reference, which is Referential.


    A common setup with ear reference is to "link" or electrically tie together, both left and right earlobes, and run that to SRB2. But then you would need to move your Bias say to the head (or mastoid). The Electro-caps put Bias on the centerline at AFz. The linked ear technique is used frequently in neurofeedback, BCI, and qEEG, for better accuracy, but is not strictly necessary. So consider that optional.

    Those that use linked ears typically use a Y-adapter to join the two ear lobe electrodes into a single lead that plugs into the SRB2.

    William

  • MikeMike
    edited April 2015
    Very informative. Thank you.

     

       
  • bcieegbcieeg
    edited April 2015
    what electrodes wiring is like for 8 channels EEG?
    Is this supposed to be standard?  Did not find it in docs.
  • wjcroftwjcroft Mount Shasta, CA
    @bcieeg , hi.

    I merged your question into this existing thread. Your 8 electrodes would be on IN1N through IN8N. Reference on SRB2. Ground on Bias.

  • ayushmhayushmh
    Which 8 Bio-potential input channels  are used to set it up for EEG
    Please it will be helpful if u explain step by step...
  • wjcroftwjcroft Mount Shasta, CA
    @ayushmh , I merged your question into this existing thread.

    Setting up 8 channels is just the obvious extension of the process in the tutorial docs. Your 8 actives go on the 'N' pins. Reference on SRB2.

  • AgustinSAgustinS
    When you say that "Ground go on Bias", it would be GND to the BIASREF pin? In the board this pin is directly connected to ground.

    Why the actives channels go on 'N' pins? I would connect actives to 'P' pins and reference to 'N' pins.
  • AgustinSAgustinS
    Looking at the board I realised that BIAS is the input of the bias circuit. So there I sould connect the GND electrode, don't I?
  • wjcroftwjcroft Mount Shasta, CA
    The Bias is connected just as in the tutorial docs, regardless of how many channels you are using.


    IN*N pins are the default with reference on SRB2. You can change this using the Chan Set tab if you want. But easiest just to use the defaults.

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