[Eeglablist] Source localization and hippocanpus

[Qian, Yongxian]

Dear Eugen and Makoto,

I am very interested in this discussion about the EEG source localization, especially at deep brain regions like the hippocanspus.

Accidentally, we just completed a research work about quantum sensing MRI (qsMRI) for detection of neuronal electrical activity (https://urldefense.com/v3/__https://arxiv.org/pdf/2601.16423__;!!Mih3wA!A5WTWbxQ1Fe5li2NSeeVa9LvVA5-JOIOgdygiOdvNUggK74DYpMfj4VuVR1y50JThTDHm-jp_iZrnUZdrXmd8Yz2ZPcYNUvvSQ$ ), in which neuronal firing source localization is definitive through MRI imaging.

The qsMRI may help you all to clarify some issues regarding the EEG signal source localization.

By the way, our group uses an MRI-compitable EEG system (32Ch, Brain Vison) to study sleep impact on CSF flow in normal aging population (25 - 100 years old).

Best,

Yongxian
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Yongxian Qian, PhD

Assistant Professor, Center for Biomedical Imaging, Department of Radiology

Investigator, Neuroscience Institute, Department of Neuroscience and Physiology

Training Faculty, Vilcek Institute of Graduate Biomedical Sciences

NYU Grossman School of Medicine


Editorial Board Member, Scientific Reports, a Nature portfolio journal

Guest Editor, "Quantum Technologies for Healthcare", Scientific Reports, a Nature portfolio journal
https://urldefense.com/v3/__https://www.nature.com/collections/bebgeadadf/guest-editors__;!!Mih3wA!A5WTWbxQ1Fe5li2NSeeVa9LvVA5-JOIOgdygiOdvNUggK74DYpMfj4VuVR1y50JThTDHm-jp_iZrnUZdrXmd8Yz2ZPfsJw6mfQ$ 


NYU Langone Health

Center for Biomedical Imaging (CBI)

660 First Avenue, 4th Floor

New York, NY 10016

T: 212-263-1159

Yongxian.Qian at nyulangone.org

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________________________________
From: eeglablist <eeglablist-bounces at sccn.ucsd.edu> on behalf of Евгений Машеров via eeglablist <eeglablist at sccn.ucsd.edu>
Sent: Saturday, January 31, 2026 7:10 AM
To: Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
Cc: EEGLAB List <eeglablist at sccn.ucsd.edu>
Subject: Re: [Eeglablist] Source localization and hippocanpus

[EXTERNAL]

The question of what source amplitude is required for a signal from deep brain regions to be registered on the scalp arose when Professor Olga Grindel, then head of the Clinical Neurophysiology Laboratory, suggested I study and use the dipole localization method (Yu. M. Koptelov's BraibLoc program) for clinical applications. Preliminary calculations showed completely non-physiological amplitude values, and I approached the task with extreme skepticism. However, not only were deep brain sources detected by this method, but they were also confirmed during surgeries. Since I didn't want to portray Admiral Nelson putting a telescope to his missing eye and declaring "I see nothing," I also didn't like the explanation that the signal from deep brain sources travels along neural pathways to the cortex and we see the signal from the cortex, as this contradicted the entire mathematical apparatus of localization. I tried to find other explanations. One of them is monopole sources, the potential from which decreases more slowly than from dipole sources. But then it's unclear why they are detected by algorithms that implicitly assume dipoles. It's possible that we're dealing with a pair of monopoles with opposite signs, so a dipole at the point between them provides a good approximation. Another explanation is a system of synchronized dipoles along the surface, creating a potential that decreases significantly more slowly at distances comparable to the size of the surface. Secondary dipoles arising at the boundaries of regions of different conductivity may also contribute. It seems to me that all of these mechanisms are at work, along with something else that's still unclear. Sources of these two types—monopole and dipole—as well as quadrupole, operate in all brain structures, but the ability to register a signal from them on the scalp depends on the distance and orientation of the source, to varying degrees for these three types, but also on the synchronization between them. It seems to me (but this doesn't even deserve the title of a full-fledged hypothesis, only a suggestion) that monopoles are associated with low-frequency activity (but not just delta, possibly up to alpha or even slightly higher) and the formation of sinusoidal oscillations, and their physiological role is the regulation of biochemical processes, in particular metabolism and ion concentration levels. Dipoles are a product of neural activity itself, EPSPs and IPSPs, while quadrupoles (not recorded from the scalp, except in cases of synchronization of groups of sources) are associated with action potentials. Perhaps such a complication of the generation model will not only clarify the physiology of the brain but also provide a mathematical framework more adequate to the problem.

Eugen Masherov

> Hi all,
>
> I've read this discussion with great interest!
> Here are my thoughts.
>
> 1. If I adopt a conventional dogma of generative mechanism of EEG i.e.,
> all/most of scalp-measured EEG signals entirely generated by post-synaptic
> membrane potential in cortical surface (Electric Fields of the Brain, EFB,
> by Nunez and Srinivasan 2006 adopts this assumption, for example),
> measuring EEG signals generated in the hippocampus using a conventional EEG
> recorder (i.e., sensitivity limit > 1 microV) would be impossible primarily
> because of the geometry (too small, too deep, rolled shape, etc..)
> 2. However, a modern electrodiffusive neural-extracellular-glia (edNEG)
> model indicates the possibility that non-synaptic source activity affects
> scalp EEG as well, which is much less studied. See Saetra et al. (2021) for
> full details (but this one is super technical).
> https://urldefense.com/v3/__https://journals.plos.org/ploscompbiol/article?id=10.1371*journal.pcbi.1008143*libraryItemId=11397962__;LyM!!Mih3wA!HKOkIU0i7obnN2bi48-tFzXvjoC4GDRCU_PNDuM4JjgXO5eU64BD7_JedfcOwGzJ1sa-MaQUQsJcYI8SaWZ6uQfdIgo$
> 3. I read the dispute between Joseph's group and Mike's group with great
> interest. If I stand on the conventional viewpoint, I agree with Mike, and
> I usually stand on it. But that does not mean non-conventional source
> cannot exist, particularly if it is observed in a low-frequency range
> (below delta). After all, we do not know EEG phenomenon completely, so we
> are not there yet to make an a priori prediction that can properly bound
> the observation (i.e., "If we observe X under certain conditions, it MUST
> BE noise because it cannot be there from biophysics!")
> 4. That said, I still want to emphasize that learning the conventional
> synaptic dogma and EEG's unique scaling law (i.e., volume conductor theory,
> including what I call 'transducer array effect' of a dipole layer) is very
> important. For those who are curious, below I provide two sources of
> information:
>
> The first material to read is an excerpt from EFB 2nd ed page 81-83. Here,
> the authors demonstrate a typical misconception/misuse of both equivalent
> current dipole model and assumption of EEG source distributions (i.e.,
> small vs. large cortical patches). As a result, such an incorrect
> application leads to an implicit conclusion that there was a 5V (=5,000,000
> microV) source inside the brain. The authors' following concluding remark
> suggests there exists this known pitfall/misconception in literature
> reporting dipole source models in general (ouch...)
>
> *Of course, such extracellular potentials are too large by a factor of 1000
> or more to be physiologically realistic. However, such considerations have
> not prevented reports of such magical dipoles. One wonders if this explains
> why source magnitudes are often not reported.*
>
> https://urldefense.com/v3/__https://drive.google.com/open?id=1LGyydB9ZucbBG9EQoZDKAg4CEUJlAWon__;!!Mih3wA!HKOkIU0i7obnN2bi48-tFzXvjoC4GDRCU_PNDuM4JjgXO5eU64BD7_JedfcOwGzJ1sa-MaQUQsJcYI8SaWZ6jRpcvKE$
>
> The second material to read is my manuscript under review, in which I
> described what I believe is the correct 'scaling law' of scalp-recorded EEG
> signals. Please find the section "Where did the small patch model come
> from, and what does it miss?" in Discussion.
>
> https://urldefense.com/v3/__https://www.medrxiv.org/content/10.64898/2026.01.23.26344529v1*libraryItemId=18612094__;Iw!!Mih3wA!HKOkIU0i7obnN2bi48-tFzXvjoC4GDRCU_PNDuM4JjgXO5eU64BD7_JedfcOwGzJ1sa-MaQUQsJcYI8SaWZ6Qhjxqso$
>
> I will submit a separate post about this manuscript, as this 'scaling law'
> is a tool for a larger aim.
>
> I have one more thing I wanted to report here, which would make a practical
> (and I believe substantial) contribution to this debate. But because Komal
> wants to keep it a low profile until he comes up with some proof of
> concept, I cannot tell you what it is ha ha. I believe that this solution
> provides a clear answer to the question "Can EEG measure the hippocampus'
> at least within the limitation of the conventional synaptic dogma + volume
> conductor theory.
>
> Makoto
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