[Eeglablist] Comments on EEG and ERP reference

[Richards, John]

I have wondered about the head model used in the REST reference.  In addition to any other issue, if the head model is "incorrect" then are the calculations of the reference also incorrect?  Using an average template for a head model has some issues in source reconstruction, and might have some here also.  Using a participant-defined, individual-based, realistic head model, is better than an average MRI template head model in several ways in source modeling.  Might be so here also?

John

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John E. Richards
Carolina Distinguished Professor
Department of Psychology
University of South Carolina
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Fax: 803 777 9558
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-----Original Message-----
From: eeglablist <eeglablist-bounces at sccn.ucsd.edu> On Behalf Of Ramesh Srinivasan via eeglablist
Sent: Sunday, December 28, 2025 1:25 AM
To: dyao at uestc.edu.cn
Cc: eeglablist <eeglablist at sccn.ucsd.edu>
Subject: Re: [Eeglablist] Comments on EEG and ERP reference

Hi Dezhong,

Id like to comment first on your quote from Luck's book and then about your method REST.

First, Luck is apparently unaware of the argument for the average reference, or of the physical principles underlying them and is intellectually lazy by focusing on whether the models used to test these ideas are spherical or realistic.  That has nothing to do with it.

The critical issue is whether the head is a closed object, not whether it
is a sphere.   In other words, is there evidence that current flows out of
head into neck and vice versa.  The preponderance of  evidence suggests that very little current generated by sources in the brain travels down the neck into the body.  How do we know this?  Well, the simplest evidence is that we can record EEG at all.  If there was a significant current path through the neck, EEG recordings would be overwhelmed by EKG which is orders of magnitude larger signal.  Hence it is reasonable to assume that the neck is like a giant resistor limiting current flow in both directions.
>From the point of view of current flow from brain sources the head is mostly a closed object.  Indeed your REST method hinges on this being true because you dont use a volume conduction model of the whole body, just the
head.   So, this quotation from Luck is just wrong, and is inconsistent
with your views and methods.

If current is contained with the head, then the potentials on the head should sum to zero.  But we can never measure the underside of the head, so the average of the potentials we measure indeed must have some error.
Thus, your papers make a good argument for REST.  I would only caution that the head model is approximate and not exact and is thus a potential source of error as well.

Ramesh Srinivasan
Professor
Department of Cognitive Sciences
Department of Biomedical Engineering



On Sat, Dec 27, 2025 at 7:55 PM dyao--- via eeglablist < eeglablist at sccn.ucsd.edu> wrote:

> Hello everyone,
>     Since the discover of EEG in 1924, EEG reference is continuously a
> debate issue,  which one is the best?
>     1. Prof Arnaud Delorme, the first author of the EEGLAb, has a
> video on "What is the best EEG reference?"
>
> https://urldefense.com/v3/__https://urld/__;!!Mih3wA!D6KIgUTtuE0aTND4KdvKB_fs7ePBbXXOpBIQgb1fJlbxarrafZ4zEUvDQ3wxKSlwpCcSnVqUccH0VFcIJP0CIdm1-OHA0g$ 
> efense.com%2Fv3%2F__https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DioIETU
> X4G4k__%3B!!Mih3wA!H4eUzNmw2tOSr4Yu5olqnIPXoeADBK0vmXkMOIBvk_d6LqSb0l_
> YqNxv43Ug-3I3FuirE3dNqJiL7VkJeJYlMQ%24&data=05%7C02%7CRICHARDS%40mailb
> ox.sc.edu%7Cd8b0ceab7e034c20d0c108de464f8a78%7C4b2a4b19d135420e8bb2b1c
> d238998cc%7C0%7C0%7C639025504614617191%7CUnknown%7CTWFpbGZsb3d8eyJFbXB
> 0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsI
> ldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=uhG13aGkyG7yndRcQFYbgzvTMyeqjWqd9%2
> FlGO2UPFJg%3D&reserved=0
> , the answer is REST
>     2. Prof Steven Luck, in his new textbook(Applied Event-Related
> Potential Data Analysis,2022), in section 6.1 "I’d like to point out
> using the average across sites as the reference in order to
> approximate the absolute voltage assumes that the surface of the head
> sums to zero, but this is only true for spheres. I have yet to meet
> someone with a spherical head. And no neck. Fortunately, there is a
> way to estimate the true zero, called the Reference Electrode
> Standardization Technique (REST), and there is an EEGLAB plugin that
> implements it (Dong et al., 2017). I haven’t tried it myself or looked
> at the math, so I don’t have an opinion about whether it’s useful and
> robust. But if you really want to get an estimate of the absolute voltage, REST seems like the best current approach"
>     3. in 2014, Lepage etal annouanced that they designed an updated
> average reference (robust common average reference(rCAR))being better
> than REST, and since then rCAR were adopted by a few following work.
> however, a recent comment on rCAR,attached here, confirmed that rCAR
> is not an EEG reference method but an "noise removement method on
> various artificial data" as the all illustrative examples adopted in
> rCAR paper were not EEG data (assumed, not generated by sources inside
> a brain). In this comment paper, on Data generated by sources inside a
> head model, REST is much better than rCAR. (Lepage, K.Q., Kramer,
> M.A., Chu, C.J., 2014. A statistically robust EEG re-referencing
> procedure to mitigate reference effect. J. Neurosci. Methods 235, 101–116).
>     In general, REST and average reference(AR) are the best two as
> both of them are based on EEG physics. REST is based on the equivalent
> distributed-sources principle of the scalp potential, it depends on
> the 'equivalence between the unknown neural sources in the brain and
> the reconstructed equivalent sources in the brain', various
> simulations confirmed the equivalence depends on the cover range and
> density of the scalp electrode array. AR is based that the whole
> surface potential integral is zero if the head a sphere, apparently, the weakness is that "
> our head is not a sphere, and the measurment is usually limited to the
> uper surface, not and impossible being the whole surface as we have
> the neck", various simulations confirmed AR depends on the cover range
> and density of the scalp electrode array,too. The conducted
> comparative studies showed that REST is usually better than AR especially when electrode number>20.
> For both methods, the most important factor is the cover range, then
> is the density of the electrode density ,or say, the number and
> distribution of electrodes.
>    wish the above message is meaningful for your work in EEG and ERP.
>    Best wishes
> -----------------------------
> Dezhong Yao, PhD, CheungKong Professor AIMBE Fellow，Cuba Academico
> Correspondiente，CSBME Fellow Director, Brain-Apparatus Communication
> Institute
> Editor-in-Chief，Brain-Apparatus Communication, Taylor & Francis Group
> University of Electronic Science and technology of China, 611731,
> Chengdu, China _______________________________________________
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