[Eeglablist] Source localization and hippocanpus

Joseph Dien jdien07 at mac.com
Thu Jan 15 11:44:50 PST 2026 

Eric, it is indeed an uncommon opinion to argue that only pyramidal 
neurons can summate to produce far-field potentials as they are aligned 
in the same direction while simultaneously positing that the hippocampal 
pyramidal neurons could be producing far-field potentials even though 
its tubular configuration means that they are not in fact aligned in the 
same direction at the macroscopic level (and in fact will be arranged to 
cancel each other out).

We are in agreement, however,  that empirical data is critical. Because 
source analysis is an ill-defined problem (meaning that the data from 
the scalp electrodes is insufficient to provide an unambiguous 
solution), it is possible to fit any number of solutions to a given 
scalp topography.  Thus, for the same reason that simply fitting an 
equivalent dipole at the hippocampus is not strong support, simply 
fitting one at an alternative favored location is not strong 
disconfirmation.  All a source solution provides is evidence that a 
given location is a plausible source, and a one source solution is more 
parsimonious than a two-source solution.

That said, our paper did not rely alone on dipole solutions. What was 
critical for our striatal source argument was the intracranial EEG work 
by Rektor and colleagues.  Intracranial EEG data are especially valuable 
because, unlike scalp EEG, they do provide unambiguous information about 
the sources of signals. They found empirically, contrary to your rather 
unsupported claim, that the basal ganglia were indeed producing EEG 
signals (the Bereitschaftspotential).  They are far from the only such 
research group to make such a finding.  In order to discount this 
argument, you will need to first explain away the empirical data.

We were also careful, however, to state that our data only showed that 
the basal ganglia are plausible generators for the Feedback Negativity, 
and therefore a strong candidate given also the extensive literature on 
the role of these structures in reward processes.  Conclusive evidence 
would require, for example, intracranial EEG data in a Feedback 
Negativity paradigm.  Cohen and colleagues (2011) attempted to argue 
based on their 2009 data that such intracranial signals were not seen, 
but our rebuttal pointed out that their participants did not produce a 
typical scalp Feedback Negativity.

Now, this all said, there has been continuing movement on this topic.  
For example, Oerlemans and colleagues (2025) just published some 
combined ERP and intracranial EEG analyses that point towards the caudal 
ACC for the Reward Positivity (but did not address the Feedback 
Negativity and also did not address the statistical power available for 
each region).  Rektor and colleagues (2002) were also careful to state 
that they observed both cortical and subcortical sources and suggested 
that neither alone could account for their observed 
Bereitschaftspotential scalp recordings.  It is quite possible that the 
same goes for the Feedback Negativity (and I have no opinion on the 
question of how it relates to the Reward Positivity).

What all of this demonstrates clearly is that we need more convergent 
empirical data (e.g., intracranial EEG, fMRI, lesions, etc.)  in order 
to form well-founded conclusions.  So, for example, while I cannot 
accept the statement that only laminar cortex can produce measurable 
potentials (as Kevin points out, brain stem potentials are a 
well-established tool in audiology, albeit weak and therefore requiring 
many many trials for the averaging, so the question is not whether 
subcortical structures can produce far-field potentials, but merely how 
strong a field is produced by a given subcortical structure, and the 
caudate is not small), I am also open to the possibility that the 
hippocampus might produce scalp potentials, insofar as we cannot rule 
out the possibility that sometimes only one side of the tube is active.

I look forward to the continued progress on this topic!

Joe


On 1/15/26 12:04, Rawls, Eric via eeglablist wrote:
> I perhaps have a different opinion on this than some of those who have responded, but in my own reading of the literature, hippocampus has always seemed a more plausible solution for source generator of scalp recorded event related potentials than other subcortical structures.
>
> For example, the basal ganglia do not have the required cellular architecture, that is a laminar organization with arrayed pyramidal neurons and dendrites which are aligned spatially to produce synchronous postsynaptic potentials.
>
> Prior results implicating the basal ganglia in the generation of, for example, the reward positivity are more easily explained by a superposition of two sources in the brain, which my current research suggests being medial frontal cortex and posterior cingulate cortex. The same argument was made in a rebuttal to that paper, in which a simulation showed that the same pattern could be easily explained by a two-generator motif.
>
> On the other hand, the hippocampus has the necessary physiology of spatially aligned pyramidal cells which can form synchronous potentials projecting to the scalp surface. This is according to simulation and empirical recordings, for example, depth recordings from hippocampus simultaneous with ecog grid recordings. In this regard, hippocampus is physiologically somewhat unique, and in fact, might be better classified as cortical tissue rather than subcortical based on some of these features.
>
> Best,
> Eric Rawls
>
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> ________________________________
> From: eeglablist <eeglablist-bounces at sccn.ucsd.edu> on behalf of Philip Zeman via eeglablist <eeglablist at sccn.ucsd.edu>
> Sent: Thursday, January 15, 2026 10:45:51 AM
> To: Евгений Машеров <emasherov at yandex.ru>
> Cc: eeglablist at sccn.ucsd.edu <eeglablist at sccn.ucsd.edu>
> Subject: Re: [Eeglablist] Source localization and hippocanpus
>
> [This email originated from outside of UNCW]
>
> Hi Eugen,
>
> in my own past work I found sources (expected) in hippocampal/temporal
> regions. The ICA and volume localization I used implicated parts parts of
> the temporal lobe together with the hippocampus.
>
> I'm glad you're looking into this.
>
> Philip
>
> On Thu, Jan 15, 2026 at 5:24 AM Евгений Машеров via eeglablist <
> eeglablist at sccn.ucsd.edu> wrote:
>
>> Using source localization methods, we were able to find foci located in
>> the hippocampus. These were confirmed during surgery. This is difficult to
>> explain from the standpoint of pure dipole theory, and is one of the
>> motivations for me to develop a method that takes into account non-dipole
>> sources. The field they generate may weaken with increasing distance less
>> dramatically than that of a dipole, and the task of reconstructing the
>> signal from deep sources may not be so hopeless.
>>
>> Eugen Masherov
>>
>>> We made a good case that the Feedback Negativity (FN) originates from
>>> the striatum (Foti, Weinber, Dien, & Hajcak, 2011, 2011). It's not a
>>> claim to be made lightly. The cortex is a strong candidate as far-field
>>> generators because it is rich on pyramidal neurons, which have
>>> asymmetrical dendrites and tend to be oriented in the same direction,
>>> but that does not mean it is the only possible source. To make a case
>>> for a subcortical generator, you have to be able to demonstrate
>>> convergent validity with data from methods like intracranial EEG
>>> recordings. See our papers for arguments and references.
>>>
>>> The hippocampus, on the other hand, is the classic example of a
>>> structure that is likely to be a closed field generator because it is in
>>> the form of a tube, wherein the field from a given neuron is likely to
>>> be canceled out by the field from a neuron pointing the opposite
>>> direction on the other side of the tube, resulting in a net zero voltage
>>> field when measured from outside the tube. No amount of electrodes or
>>> computational sophistication is going to help with that. Of course,
>>> it's all complicated because the entire tube isn't necessarily equally
>>> active. Also, the adjoining parahippocampal cortex isn't a tube. There
>>> seems to be a lot of discussion going on right now about what can be
>>> measured. But yeah, making a plausible claim for a hippocampal
>>> generator would require very strong evidence. As John says, it's easy
>>> to put a equivalent dipole in the hippocampal region and get non-zero
>>> results, so not strong evidence by itself. But I'd also be wary of
>>> making sweeping generalizations.
>>>
>>> Joe
>>>
>>> Foti, D., Weinberg, A., Dien, J., & Hajcak, G. (2011). Event-related
>>> potential activity in the basal ganglia differentiates rewards from
>>> nonrewards: Temporospatial principal components analysis and source
>>> localization of the feedback negativity. /Hum Brain Mapp/, /32/(12),
>>> 2207–2216.
>> https://urldefense.com/v3/__https://nam12.safelinks.protection.outlook.com/?url=https*3A*2F*2Furldefense.com*2Fv3*2F__https*3A*2F*2Fdoi.org*2F10.1002*2Fhbm.21182__*3B!!Mih3wA!F6lfB756tGdH_QFKwL5mIWetNG672s_aafnqgyt9T8wO7nrcuWuqfT_GvDz4sGND_j85H6f_kjzDtWSplqI*24&data=05*7C02*7Crawlse*40uncw.edu*7C238d864b84a4401caa6b08de54571c18*7C2213678197534c75af2868a078871ebf*7C0*7C0*7C639040930287599901*7CUnknown*7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ*3D*3D*7C0*7C*7C*7C&sdata=XQzDyx7Fz72*2BN3NhWktVpA4qfO10WaaQSLuxofAMOiU*3D&reserved=0__;JSUlJSUlJSUlJSUlJSUlJSUlJSUlJSUlJSUlJSUl!!Mih3wA!C2eTgr5iCaCFZ_g6V1tvubkxCI-7YPqfxTxDcTu15VWELjkJhrNv4IFKudn0-gHqVeh52miAnJhoPix8fi4_rg$ <https://urldefense.com/v3/__https://doi.org/10.1002/hbm.21182__;!!Mih3wA!F6lfB756tGdH_QFKwL5mIWetNG672s_aafnqgyt9T8wO7nrcuWuqfT_GvDz4sGND_j85H6f_kjzDtWSplqI$>
>>> Foti, D., Weinberg, A., Dien, J., & Hajcak, G. (2011). Event-related
>>> potential activity in the basal ganglia differentiates rewards from
>>> nonrewards: Response to commentary. /Hum Brain Mapp/, /32/(12),
>>> 2267–2269.
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>>> On 1/14/26 18:52, Richards, John via eeglablist wrote:
>>>
>>>> The hippocampus, caudate, putamen, amygdala, sometimes are classified
>> with "cortex" as gray matter and people might try to do source analysis.
>> However, only the cortex has the perpendicular pyramidal structure that
>> conducts current to the scalp, and the "subcortical" brain areas do not
>> have the correct structure to generate current on the scalp. If you put
>> source locations in these areas and do source analysis you will get
>> "something", likely due to activity in other brain areas, noise, or other
>> non-neuron activity.
>>>> I think that a couple of the "internal" cortex ROIs, like the insula,
>> have the cortex structure to generate current. But its possible that it
>> cannot be measured because the area is relatively far from the scalp and
>> any current would be small.
>>>> John
>>>>
>>>> ***********************************************
>>>> John E. Richards
>>>> Carolina Distinguished Professor
>>>> Department of Psychology
>>>> University of South Carolina
>>>> Columbia, SC 29208
>>>> Dept Phone: 803 777 2079
>>>> Fax: 803 777 9558
>>>> Email:richards-john at sc.edu
>>>>
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>>>> ***********************************************
>>>>
>>>> -----Original Message-----
>>>> From: eeglablist<eeglablist-bounces at sccn.ucsd.edu> On Behalf Of Cedric
>> Cannard via eeglablist
>>>> Sent: Wednesday, January 14, 2026 3:43 PM
>>>> To: EEGLAB List<eeglablist at sccn.ucsd.edu>
>>>> Subject: [Eeglablist] Source localization and hippocanpus
>>>>
>>>> Hi everyone,
>>>>
>>>> My understanding is that it is impossible to reliably pick up activity
>> from the hippocampus when doing any form of source
>> localization/reconstruction from 64 channels EEG data (or more?). Is that
>> still correct or are there solutions I am not aware of?
>>>> Thanks,
>>>>
>>>> Cedric
>>>>
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>>> --
>>>
>> --------------------------------------------------------------------------------
>>> Joseph Dien, PhD
>>> Senior Research Scientist
>>> Department of Human Development and Quantitative Methodology
>>> University of Maryland, College Park
>>> E-mail:jdien at umd.edu
>>>
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-- 
--------------------------------------------------------------------------------

Joseph Dien, PhD
Senior Research Scientist
Department of Human Development and Quantitative Methodology
University of Maryland, College Park
E-mail: jdien at umd.edu
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