Ground and Reference nodes position (on forehead)

nickplaynickplay Univ.
edited January 2017 in Electrodes
Hi.
I am new on OpenBCI. I'm working on a project about wearable brain signal acquisition device with minimum number of electro-nodes. As I known, Ground and Reference nodes are very important to get good quality of brain signals. And Ground node is located at earlobes or mastoid and Reference node is located at a center of other EEG channel node position. (Is it right?). 

However, I want to apply theses electrodes to forehead with other EEG nodes. Is there any solution for applying ground and reference nodes to forehead using OpenBCI board channels: such as SRB(Ref) and BIAS(Gnd)?

Comments

  • wjcroftwjcroft Mount Shasta, CA
    edited January 2017
    EEG channels are measured by the differential voltage between the channel and reference. If you place both reference and channel electrodes on the forehead, then your microvolts will be very low and less meaningful. Ground (Bias) can be placed basically anywhere.
  • wjcroftwjcroft Mount Shasta, CA
    On the other hand, here is the Muse tech spec,

    https://storage.googleapis.com/ix_choosemuse/uploads/2015/07/tech_specs.pdf

    They use Fpz as reference and AF7 AF8 as forehead channels. TP9 and TP10 (ears) as the rear channels. My hunch is that they may do a "re-referencing" operation in software to derive the differential microvolts between left forehead and left ear, and right forehead and right ear. They could also measure the difference between the two TP sites and use that as a measure of temporal / parietal activity.

  • wjcroftwjcroft Mount Shasta, CA
    If you look at the electrode arrangement on the back of the Muse band (resting on forehead), there are FIVE electrodes, with Fpz in the center. So it might be: AF7 Gnd Fpz Gnd AF8. The tech sheet labels Gnd as DRL (driven right leg) which is the same thing.


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