Cyton bipolar montage

nicoaranicoara
in Cyton

Hello, I am an owner of a Cyton Board.


TLDR;  Is there a way to have a bipolar montage with the Cyton board (as in image below)?


We use two types of montages in medical clinical practice:
1. Referential montage (also called "monopolar"), example: the referential electrode on the ear (ex. A1, A2), which shows the difference of potentials between each electrode on the scalp and the referential electrode 
2. Sequential or bipolar montage. The bipolar (sequential) montage has no common reference, it shows the difference of potentials between two electrodes on the scalp, sequentially - or site to site measurements. 
   
Types of EEG montages in the atlas below (sequential or bipolar - longitudinal - double banana, transversal, etc and referential or monopolar - ....):


Indeed, with Cyton board, if we have two electrodes P and N  in the same pin, we have one signal on the screen  which is all right  - We checked that, for example we placed the 2 electrodes similar to Fp1 (left fronto-polar aria)-F3 (left frontal aria), etc.
  
But is there possible to make any connection between the electrodes from different pins, in order to make a sequential (bipolar) montage?

We found these explanations in your tutorials:

The bottom pins are (N) inputs, and the top pins are (P) inputs. The default board settings look at all N channels in reference to SRB2 (the bottom SRB pin). SRB1 (the top SRB pin) can also be used as a reference, but when it is activated, it is activated for ALL channels. If using SRB1 as the reference electrode, P inputs (the top pin inputs) must be used as the other input of the potential difference measurement. On the contrary, individual channels can be removed from SRB2. If a channel is removed from SRB2, it can be examined as a unique voltage potential, between the N and P pins of that channel. We will be doing this for the heart measurement in this tutorial, while examining 2 EEG channels in reference to SRB2, using the channel 2 and 7 N pins. For more information on this, refer to page 16 of the ADS1299 datasheet. The ADS1299 chip is the analog front-end at the core of the Cyton board.


Shall we understand that the only referential pins are SRB1 and SRB2 (the white wire)?

Thank you

image

Comments

  • wjcroftwjcroft Mount Shasta, CA
    Nico, hi.

    Here is a search result (using button in right column) and thread discussing sequential montage,



    Regards,

    William

  • nicoaranicoara
    edited November 2018

    Thanks William. We knew about the forum link you mentioned before asking the question. 

    Yes, probably bipolar and sequential montage are the same thing.

    If your solution is to use Y-cables, then:

    Who can assist is through this process (could be from openBCI)? Can we pay an hour of your time and understand better via Skype what the setup should be? Do you know of anyone who has done this who we can talk to? 

    Can you confirm the following understanding of sequential montage is correct: 

    Sequential montage is based on unique site measurement. 

    So mathematically, to measure Fp1-F3, we would measure the signal from electrode at Fp1, the signal from electrode at F3, and subtract the signals F3 from Fp1 to get the difference Fp1-F3. And F3-Fp1 is minus that. 

    Thank you,

    Nicoara

  • wjcroftwjcroft Mount Shasta, CA
    Nico, hi.

    Yes your math is correct. The Y-cable suggestion given in the linked thread should be easy to implement. Did you look at the Adafruit links to see the cables? Have you ever cut and spliced cables before? You use a tool called a wire-stripper. Then splice the cables, twisting the bare wires, then put a small piece of tape on the splice to ensure it does not touch other bare metal. Pretty easy, and only takes a few minutes per cable.

    The other thread also made the point that software that does what is called "re-referencing", may be able to accomplish what you want without hardware. Given say a standard referential montage using a centrally located reference lead, for example at AFz, the one used by Electro-cap. Ear lobe references would probably not give the best re-reference mathematical operations, because ear lobes have a certain amount of temporal / parietal 'noise' included.

    Could also do a Skype if you wish.

    Regards,

    William

  • wjcroftwjcroft Mount Shasta, CA
    "So mathematically, to measure Fp1-F3, we would measure the signal from electrode at Fp1, the signal from electrode at F3, and subtract the signals F3 from Fp1 to get the difference Fp1-F3. And F3-Fp1 is minus that. "

    And of course, if you have wired up the sequential montage cabling as in the thread linked above, the 'math' is performed all electronically by the EEG amplifier. Because Fp1 will be on (for example) pin IN1P, and F3 on pin IN1N.

    Again, I'm not convinced you need to go to all this trouble of the actual hardware sequential montage. I do know that certain medical contexts use or require it. But mathematical re-referencing has become so common these days. It might not have fully reached all medical applications. As it is more commonly used in research environments.

    Regards,

    William

  • wjcroftwjcroft Mount Shasta, CA
    edited November 2018
    Just found this recent paper,

    Understanding the Influences of EEG Reference: A Large-Scale Brain Network Perspective

    Irene wrote this tutorial in 2016,


    Based on this EEGLAB page,


  • wjcroftwjcroft Mount Shasta, CA
    Nico, hi.

    One more comment on the 'hardware' way to do sequential montage using the Y-cables. As you can see by the wiring, this will require on the order of 16 of these little Y-cables to be installed at the pins of the Cyton and Daisy (16 channel limit). (Clinical sequential montage uses all 19 channels.) I guess you would omit the Fz, Cz, Pz??

    One of the characteristics of EEG cabling, is that it is subject to artifacts when the cables are moved around, and there can also be some 'coupling' between cables. This is not generally an issue, but should be checked out in any given recording situation.

    With all the Y-cables required to do this in hardware, the addition of all those wires may result in some coupling effects. If you implement this, I would suggest some test recordings to confirm that your signals are clean. For example, you could tap (lightly) on one 10-20 site at a time, and confirm that you are not picking up artifacts in the other channels.

    Can you also mention your motivation for the sequential montage? What specific types of EEG recording / processing are you doing? There are many other montage types, and some of these may be more amenable to mathematical re-referencing. 

    ---

    Finally, I was doing another search just now, and came across the Brainstorm open source EEG / MEG analysis system. This is free. It comes with the ability to change montages, and includes as that set the one called 'longitudinal' or double-banana; same as what we've been calling sequential. See this tutorial.


    Regards,

    William

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