[Eeglablist] Source localization and hippocanpus

[m za]

Hi ,

 Reading this, I noticed an interesting structural parallel with the
ROI-assignment step in the pipeline I shared last month, although the
direction and the scientific question are different. My approach is
bottom-up: starting from empirical scalp EEG, each ICA component is given a
regional score based on its scalp-weight distribution and is assigned to an
anatomical ROI if it meets the assignment criterion. Your approach is
top-down: starting from an assumed ROI-level source, the forward-projected
scalp amplitude is evaluated against a detectability threshold. So, in both
cases, a quantitatively defined regional measure is compared with a
criterion to support a decision, but the decision target differs—ROI
attribution in my pipeline versus scalp detectability in yours. I thought
that was a neat and potentially complementary parallel, but I would be
interested to hear whether you see it differently.

Marjan Zamani

On Sat, Aug 22, 2026 at 12:18 AM Cedric Cannard via eeglablist <
eeglablist at sccn.ucsd.edu> wrote:

> Hi Makoto,
>
> Exciting development. Thanks for working on this, I've always thought it
> is a big gap in the EEG field to have such questions unanswered.
>
> Quick curiosity questions:
> 1) why not including subiculum?
> 2) is this only using dipole fitting tools? what about other methods like
> eLoreta or LCMV beamforming?
> 3) "Destrieux Atlas is based on Colin27, which is a single-subject head
> model and has annotated gyri and sulci. But it does not come with
> hippocampi. So I used HippUnfold (DeKraker et al., 2022, 2023) to
> auto-demarcate hippocampi on the Destrieux Atlas."
>
> -> I'm surprised, I remember clearly the Colin atlas having the hippocampi
> included when using the ROIconnect plugin for LCMV beamforming, which I had
> to exclude in the code as I suspected it was not reliable, but it was there.
>
> -> is a single subject head model the way to go for validating this kind
> of thing? aren't the findings vulnerable to be specific to this person only?
>
>
> Cedric
>
>
> Sent with Proton Mail secure email.
>
> On Friday, August 21st, 2026 at 1:00 PM, Cedric Cannard <
> ccannard at protonmail.com> wrote:
>
> > Hi Makoto,
> >
> > Exciting development. Thanks for working on this, I've always thought it
> is a big gap in the EEG field to have such questions unanswered.
> >
> > Quick curiosity questions:
> > 1) why not including subiculum?
> > 2) is this only using dipole fitting tools? what about other methods
> like eLoreta or LCMV beamforming?
> > 3) "Destrieux Atlas is based on Colin27, which is a single-subject head
> model and has annotated gyri and sulci. But it does not come with
> hippocampi. So I used HippUnfold (DeKraker et al., 2022, 2023) to
> auto-demarcate hippocampi on the Destrieux Atlas."
> >
> > -> I'm surprised, I remember clearly the Colin atlas having the
> hippocampi included when using the ROIconnect plugin for LCMV beamforming,
> which I had to exclude in the code as I suspected it was not reliable, but
> it was there.
> >
> > -> Are you sure using an automated method like HippUnfold is fully
> reliable?
> >
> > -> is a single subject head model the way to go for validating this kind
> of thing? aren't the findings vulnerable to be specific to this person only?
> >
> >
> > Cedric
> >
> >
> > Sent with Proton Mail secure email.
> >
> > On Friday, August 21st, 2026 at 10:48 AM, Евгений Машеров via eeglablist
> <eeglablist at sccn.ucsd.edu> wrote:
> >
> > > First of all, thank you very much for this fascinating and important
> work.
> > > The threshold for EEG amplitude that allows signal registration, 1.65
> μV, seems reasonable. By comparison, when diagnosing brain death, an
> amplitude of oscillations of 2-3 μV does not prove brain function and is
> considered an artifact.
> > > However, the conclusion regarding whether signals from the hippocampus
> can be recorded on the scalp relies on several assumptions, and these can
> be challenged. The first is that the source is necessarily a dipole. The
> second is that it is a single dipole, not a set of synchronized dipoles
> distributed over a certain area and similarly oriented.
> > > The question of the validity of these assumptions arose in my mind
> quite a while ago, when I was tasked with using the BrainLoc dipole
> localization program (developed by Yuri Koptelov) to analyze clinical EEGs.
> I was immediately skeptical about the possibility of recording a signal
> from a non-cortical dipole on the scalp, since the dipole potential
> decreases inversely with the square of the distance. However, practical
> experience has shown that sources deep in the brain are localized quite
> accurately, and their location is confirmed by recordings during surgery or
> from implanted electrodes.
> > > In an attempt to explain this paradox, I proposed two explanations.
> > > 1. In addition to the dipole component, a monopole component also
> contributes to the EEG. Its potential decreases less rapidly with distance
> and can therefore be recorded at a greater distance. A possible source of
> this component could be fluctuations in the ionic composition inside and
> outside the neuron (the contribution of glia may also be significant).
> > >
> https://urldefense.com/v3/__https://link.springer.com/article/10.1134/S0006350919030138__;!!Mih3wA!GQ6tkO0-y-UdiBpSSa5dvJ5WwALJ32XNjpXJS-5N7m99k4m-659LlesRaG8YmhUmYS88D71nxC6knyaGTmLBp4yz1xU$
> > >
> > > 2. The potential from a system of dipoles changes differently than
> from a single dipole and propagates over a greater distance. Likewise, the
> potential from a system of quadrupoles can propagate over a greater
> distance than from a single dipole.
> > >
> https://urldefense.com/v3/__https://link.springer.com/article/10.1134/S0006350921040114__;!!Mih3wA!GQ6tkO0-y-UdiBpSSa5dvJ5WwALJ32XNjpXJS-5N7m99k4m-659LlesRaG8YmhUmYS88D71nxC6knyaGTmLBvqm70Fw$
> > >
> > > It is quite possible that both of these mechanisms need to be taken
> into account, and even then the complexity of the EEG generation process
> may not be exhausted.
> > >
> > > Your truly
> > >
> > > Eugen Masherov
> > >
> > > > Hi list,
> > > >
> > > > Earlier this year, we discussed whether scalp EEG can measure
> > > > hippocampus. Komal
> > > > and I developed a forward model simulator, L-EEGiability Atlas, to
> answer
> > > > this question. The Github repository is still private. It'll be
> published
> > > > after Komal registers it to Zenodo. This is a follow up. Technical
> detail
> > > > of this forward model is provided after my signature.
> > > >
> > > > In this forward model simulation, the parameters uses are:
> > > >
> > > > Dipole moment: 0.17 nAm/mm^2 (which is the strength of sleep spindle)
> > > > Uniform recruitment rate: 66.6% (arbitrary choice, but for a specific
> > > > reason--you will find the reason below)
> > > > Selected regions: CA1, CA2, CA3, CA4 in the left hemisphere (no
> subiculum)
> > > > Total ROI area: 9.59 cm^2
> > > >
> > > > A critical fact is that EEG signals smaller than 1.65 microV are not
> > > > guaranteed to be measured (Nuwer et al., 1998). I guess this reflects
> > > > realistic requirements of an EEG recorder's noise floor. Thus, < 1.65
> > > > microV means 'not eligible for scalp EEG'.
> > > >
> > > > In this condition, the maximum scalp potential observed is 1.649
> microV!
> > > >
> > > > Thus, to measure hippocampal EEG, average dipole moment needs to be
> > 0.17
> > > > nAm/mm^2 and/or average recruitment rate needs to be > 66.6%. Our
> next
> > > > question is therefore: can we obtain empirical evidence supporting
> these
> > > > numbers?
> > > >
> > > > By the way, if the left hippocampus becomes epileptic (uniform
> recruitment
> > > > 100%, 0.77 nAm/mm^2), you would measure 11.126 microV at the scalp.
> If I
> > > > apply the Murakami-Okada limit of 2 nAm/mm^2, the measured signal
> would be
> > > > 19.402 microV.
> > > >
> > > > Here is the comparison table to get a feeling of how much depth and
> folding
> > > > penalty the hippocampus EEG undergoes
> > > > (all left hemisphere ROIs, 0.17 nAm/mm^2, uniform 66.6% recruitment,
> > > > amplitude shown is positive peak only at the scalp maximal,
> three-layer
> > > > BSCR=40 model)
> > > >
> > > > Hippocampus, 9.59 cm^2, 1.649 microV
> > > >
> > > > Sup Occipital Gyrus, 15.71 cm^2, 36.283 microV
> > > > Sup Parietal Gyrus, 34.94 cm^2, 42.330 microV
> > > > Postcentral Gyrus, 28.94 cm^2, 26.263 microV
> > > > Sup Temporal Gyrus, 24,17 cm^2, 24.420 microV
> > > > Inf Front Opercular, 19.75 cm^2, 18.194 microV
> > > >
> > > > Insula, 30.77 cm^2, 16.238 microV
> > > >
> > > > All pure Gyri, 784.19 cm^2, 49.404 microV
> > > > All pure Sulci, 338.03 cm^2, 48.325 microV
> > > >
> > > > Whole brain, 2348.56 cm^2, 29.956 microV
> > > >
> > > > Angular + Supramarginal + Sup Parietal + IntraParietal Sulcus,
> 113.42 cm^2,
> > > > 80.957 microV
> > > >
> > > > Note that the area of the selected ROI and the scalp-measured EEG
> amplitude
> > > > do not correlate. This is because (1) cancellations due to foldings,
> (2)
> > > > the effect of volume conduction is actually limited locally so that
> source
> > > > effects do not add up at one measurement point.
> > > >
> > > > If you have a request to test some hypothesis/question, let me know.
> > > > L-EEGiability will be publically available in a week or two.
> > > >
> > > > Makoto
> > > >
> > > > %%%%%%%%%%%%%%%%%%%%%%
> > > > Technical note
> > > >
> > > > Leadfield-based EEG eligibility (L-EEGiability, pronounced as
> > > > 'eligibility') Atlas is an extended version of the Destrieux Atlas
> > > > (Destrieux et al., 2011). Destrieux Atlas is based on Colin27, which
> is a
> > > > single-subject head model and has annotated gyri and sulci. But it
> does not
> > > > come with hippocampi. So I used HippUnfold (DeKraker et al., 2022,
> 2023) to
> > > > auto-demarcate hippocampi on the Destrieux Atlas.
> > > >
> > > > Then I determined a physiological plausible range of current dipole
> moments
> > > > in nAm/mm^2 for the human brain (Murakami & Okada, 2015; Inverso et
> al.,
> > > > 2016; Rosen et al., 2019). The reported values are like 0.17 for
> sleep
> > > > spindle, 0.2-0.35 for visual evoked potential at V1, and 0.16-0.77
> for
> > > > interictal spikes. Murakami & Okada also proposed a physiological
> limit of
> > > > 1-2 nAm/mm^2.
> > > >
> > > > I also set a few other open parameters, such as synchronization
> rate. This
> > > > is completely arbitrary. We need empirical data to fill this in.
> > > >
> > > > The brain-to-skull-conductivity (BSCR) ratio precalculated are 26,
> 40, 80.
> > > > Although BSCR=26 is the modern estimate, because the model is three
> tissue
> > > > layers without CSF, using BSCR=40 compensates for the lack of CSF
> layer
> > > > (EFB Chapter 6).
> > > >
> > > > On Fri, Jan 30, 2026 at 5:29 PM Makoto Miyakoshi <
> mmiyakoshi at ucsd.edu>
> > > > wrote:
> > > >
> > > >> 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!BJz_jI7amVJIO4yLx16kUNcvtKfKz2Vq2a8fn-buH6yEmuldbNRSNq8JZ679B42teXAZ4sz3nMIKlNimhKtMlKPZmVs$
> > > >> 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!BJz_jI7amVJIO4yLx16kUNcvtKfKz2Vq2a8fn-buH6yEmuldbNRSNq8JZ679B42teXAZ4sz3nMIKlNimhKtMHlzFVrk$
> > > >>
> > > >> 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!BJz_jI7amVJIO4yLx16kUNcvtKfKz2Vq2a8fn-buH6yEmuldbNRSNq8JZ679B42teXAZ4sz3nMIKlNimhKtMsEnkBo8$
> > > >>
> > > >> 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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