[Eeglablist] Source localization and hippocanpus

Fri Feb 6 21:10:44 PST 2026

Diego and all,

    sorry to have stepped away from this fascinating conversation in 
order to deal with the start of term madness.  I totally agree that 
intracranial EEG has the same issues that scalp EEG has since they are 
simply voltage recordings made in different locations, but I also think 
that you're underselling the special value that intracranial EEG 
research like your own brings to the table, compared to scalp 
recordings, although perhaps it is because you are focusing on 
frequency-domain analyses and I am focusing on time-domain 
analyses.  It's more than just additional data points for source 
modeling.  If you have a string of intracranial electrodes, and you get 
a strong spatial gradient for an evoked potential between two of them, 
then there is a strong case that a source is between the two.  It's the 
same logic used by CSD transforms of scalp EEG, except that since you're 
actually measuring inside the skull, you can have much more precision, 
to the extent that you are able usefully to place electrodes (always the 
main limitation of intracranial recordings).  Likewise, if you have a 
broad sampling of the brain space and one isolated electrode has a much 
larger relative voltage compared to the others, it is much likelier to 
be closer to a source than the others.  Although mathematically it would 
be possible that all the other electrodes are experiencing an equivalent 
potential field from a diffuse source that is close to all of them due 
to the ambiguities of reference, that possibility is much less likely 
than that it is a localized source closer to the isolated electrode 
(again speaking of phasic evoked potentials, as simultaneous massed 
oscillations over long distances seems more plausible than it does for 
information streams cascading through functional regions from the 
sensory organs).  The other thing you get when working with time-domain 
is the latency.  So for example, there is very little uncertainty about 
the brain stem source of scalp-recorded ABRs simply because their 
latency is far too short to be cortical.  Going further out, studies 
like that of Nobre and McCarthy (1995) provide a nice example of what 
you can do with evoked cortical potentials in the time domain and the 
way latencies inform interpretation.  That said, I agree that the term 
"unambiguous" was overstating it.  But I think that "strong support" is 
very warranted.  I'm sure you'll agree we need more studies!  It's kind 
of nuts that it is now 2026 and we still don't have a consensus on what 
we can measure at the scalp from subcortical structures.  For some 
perspective, I recommend looking back at Rafael Lorente De Nó's 1947 
paper, which first proposed the distinction between closed and open 
fields (which is to say, massed potential fields that cannot and can be 
measured at a distance, such as at the scalp surface).  His anatomical 
drawings of the way neuronal assemblies are arranged differently in 
different structures is the reason why he felt it necessary to propose 
the two terms in the first place.  One could take his words as a warning 
to be wary of making broad assumptions about what potential fields can 
or cannot be measured at a distance due to the heterogeneity of neuronal 
geometries.  As a community, we seem to have remembered his terminology, 
but not the message behind it.

Joe

On 1/22/26 06:21, Diego Lozano-Soldevilla via eeglablist wrote:
> Hi Cedric and all,
>
> It's hard to conclude anything when comparing scalp and intracranial
> recording in-vivo. Even when simultaneously recorded (
> https://urldefense.com/v3/__https://www.biorxiv.org/content/10.1101/2020.06.05.136515v1.abstract__;!!Mih3wA!HCzm9RvUl5xekT1JHjl7NVV5ws_JDwhw_1KiYYg3yCT6ifQMWc5FBKWZg_-ygmUoX8I-WGuk784wJpKflKg_liIK_WoccuID$ ,
> https://urldefense.com/v3/__https://pubmed.ncbi.nlm.nih.gov/19349241/__;!!Mih3wA!HCzm9RvUl5xekT1JHjl7NVV5ws_JDwhw_1KiYYg3yCT6ifQMWc5FBKWZg_-ygmUoX8I-WGuk784wJpKflKg_liIK_a3I45F4$ ) finding correlations between
> scalp and intracranial (hippocampal) components does not guarantee you that
> the intracranial is the source and you are picking it up at the scalp.
>
> Intracranial recordings are indeed extremely valuable, but they do not
> provide unambiguous evidence IMHO (see Oscar Herrera's review about it
> https://urldefense.com/v3/__https://pubmed.ncbi.nlm.nih.gov/28018180/__;!!Mih3wA!HCzm9RvUl5xekT1JHjl7NVV5ws_JDwhw_1KiYYg3yCT6ifQMWc5FBKWZg_-ygmUoX8I-WGuk784wJpKflKg_liIK_elIGkjo$ ). Intracranial EEG and ECoG
> recordings are still field potentials, and as such they remain subject to
> volume conduction, signal mixing, relative referencing and the influence of
> brain geometry (sulci/gyri, etc). One can find hippocampal alpha (
> https://urldefense.com/v3/__https://pubmed.ncbi.nlm.nih.gov/11018305/__;!!Mih3wA!HCzm9RvUl5xekT1JHjl7NVV5ws_JDwhw_1KiYYg3yCT6ifQMWc5FBKWZg_-ygmUoX8I-WGuk784wJpKflKg_liIK_XsGMedG$ ) that comes from somewhere else (
> https://urldefense.com/v3/__https://pubmed.ncbi.nlm.nih.gov/30941394/__;!!Mih3wA!HCzm9RvUl5xekT1JHjl7NVV5ws_JDwhw_1KiYYg3yCT6ifQMWc5FBKWZg_-ygmUoX8I-WGuk784wJpKflKg_liIK_bIjOXtU$ ). The same general logic applies
> to other subcortical structures, including the basal ganglia (
> https://urldefense.com/v3/__https://pubmed.ncbi.nlm.nih.gov/28966971/__;!!Mih3wA!HCzm9RvUl5xekT1JHjl7NVV5ws_JDwhw_1KiYYg3yCT6ifQMWc5FBKWZg_-ygmUoX8I-WGuk784wJpKflKg_liIK_YxDNdr-$ ). The meaning of other metrics or
> measurements associated with the LFPs (spikes, CSDs) can be affected too
> due to this ambiguity (https://urldefense.com/v3/__https://pubmed.ncbi.nlm.nih.gov/27471451/__;!!Mih3wA!HCzm9RvUl5xekT1JHjl7NVV5ws_JDwhw_1KiYYg3yCT6ifQMWc5FBKWZg_-ygmUoX8I-WGuk784wJpKflKg_liIK_Uq031IO$ ). So
> intracranial EEG can be a useful estimate to constraint the inverse
> solution but there's no free lunch.
>
> All the best,
>
> Diego
>
>
>
> On Wed, 21 Jan 2026 at 18:20, Евгений Машеров via eeglablist <
> eeglablist at sccn.ucsd.edu> wrote:
>
>>
>>> I see a lot of papers, mainly MEG, that use forward solutions from
>> beamformers and claim to be measuring activity in subcortical structures
>> with no measure of forward model errors or cross-validation with other
>> modalities. It seems to me that if you can't localize a pattern of activity
>> using an inverse method, you can't just generate a forward solution from a
>> region of interest and assume your results are valid.
>>> There are old papers (late 80s - 90s) from when people first started
>> using dipole localization to measure activity in auditory subcortical
>> structures (MGN, IC, etc.). Those data seemed reasonable to me because of
>> the SNR of the input data, the spatial separation between cortical and
>> putative subcortical sources, and the comparison of different dipole models
>> to establish validity.
>>> Kevin
>>>
>> ---------------------------------------------------------------------------------
>>> Kevin M. Spencer, Ph.D.
>>> Research Health Scientist, VA Boston Healthcare System
>>> Associate Professor of Psychiatry, Harvard Medical School
>> A study was recently conducted that involved recording signals from the
>> brainstem while simultaneously recording an EEG from the scalp.
>>
>> EVOKED POTENTIALS OF THE MIDBRAIN ASSOCIATED WITH THE BEGINNING AND END OF
>> A SOUND OF A SIMPLE TONE Kantserova A.O., Oknina L.B., Pitskhelauri D.I.,
>> Podlepich V.V., Masherov E.L., Vologdina Y.O. Human Physiology. 2022. Т.
>> 48. № 3. С. 229-236.
>> EVOKED POTENTIALS APPEARING IN THE HUMAN MIDBRAIN AFTER SOUNDING OF A
>> SIMPLE TONE Kantserova A.O., Oknina L.B., Pitskhelauri D.I., Podlepich
>> V.V., Masherov E.L., Vologdina Ya.O., Sieber I.A. Neuroscience and
>> Behavioral Physiology. 2023. Т. 53. № 3. С. 358-364.
>> THE ROLE OF THE MIDBRAIN IN THE PERCEPTION OF TONE SEQUENCES AND SPEECH:
>> AN ANALYSIS OF INDIVIDUAL STUDIES Oknina L.B., Kantserova A.O.,
>> Pitskhelauri D.I., Podlepich V.V., Portnova G.V., Sieber I.A., Vologdina
>> Y.O., Slezkin A.A., Lange A.M., Masherov E.L., Strelnikova E.V. Human
>> Physiology. 2023. Т. 49. № 4. С. 347-356.
>> INCREASES IN THE PEAK FREQUENCY OF THE EEG ALPHA RHYTHM ON PRESENTATION OF
>> OWN NAMES DURING DEEP ANESTHESIA Portnova G.V., Kantserova A.O., Oknina
>> L.B., Pitskhelauri D.I., Podlepich V.V., Vologdina Ya.O., Masherov E.L.
>> Neuroscience and Behavioral Physiology. 2024. Т. 54. № 1. С. 91-101.
>> FEATURES OF PERCEPTION OF A PERSON’S OWN NAME COMPARED TO THE PERCEPTION
>> OF NAMES WITH SIMILAR AND DIFFERENT SOUNDS: ANALYSIS OF EVENT-RELATED
>> POTENTIALS Oknina L.B., Podlepich V.V., Vologdina Ya.O., Sieber I.A.,
>> Masherov E.L., Slezkin A.A., Strelnikova E.V., Kantserova A.O. Human
>> Physiology. 2025. Т. 51. № 2. С. 79-88.
>>
>>
>> Using the surviving recordings, the correlation between the brainstem
>> signal and a linear combination of scalp signals reached 17%. The reference
>> leads for the brainstem and scalp recordings are different, so this is not
>> a common electrode effect. On the other hand, this recording was made
>> during surgery, so cortical activity is suppressed. Nevertheless, this
>> demonstrates signal transmission even over such a long distance.
>>
>> Your truly
>>
>> Eugen Masherov
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-- 
--------------------------------------------------------------------------------

Joseph Dien, PhD
Senior Research Scientist
Department of Human Development and Quantitative Methodology
University of Maryland, College Park
https://urldefense.com/v3/__http://joedien.com__;!!Mih3wA!FKLTZm2TnuXwWpKt4Rw1CG5927i5_2VgXnFLfvk-SUQb0AvNgNeyaF58mnq89KAQXAByc9EnIvcyPaWAxos$ 