In almost all electroencephalography (EEG) recording setups, there are two auxiliary electrodes in addition to the ones used to record: the ground electrode and the reference electrode.

I've so far read two explanations for this. First, the explanation provided here is that the ground electrode is used for active grounding in a driven-right-leg (DRL) setup, so as to eliminate the common mode and thus increase the common mode rejection ratio (CMRR). Second, the explanation provided here is that to measure voltage, we need a signal ground, and that an electrophysiological signal only makes sense as the difference between two sites with non-zero value.

The first explanation does make sense to me, but the second one doesn't: can't you just measure everything as the difference between the site and the ground? The two seem quite contradictory...

  • $\begingroup$ May be related: Reference signal when measuring EEG $\endgroup$
    – Arnon Weinberg
    Dec 9, 2021 at 2:55
  • 2
    $\begingroup$ @ArnonWeinberg The accepted answer of that question would be satisfactory, but if the second explanation is just plain wrong, I would appreciate someone confirming it... It would come as a bit of a shock to me to know that technical documentation for products actually sold on the market can be just plain wrong. $\endgroup$
    – David Cian
    Dec 9, 2021 at 3:37
  • 1
    $\begingroup$ I believe the second explanation is referring to things like volume conduction and non-neuronal sources of signal. $\endgroup$
    – Bryan Krause
    Dec 9, 2021 at 15:33
  • $\begingroup$ @BryanKrause could you elaborate a little bit? $\endgroup$
    – David Cian
    Dec 9, 2021 at 16:58


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