[Eeglablist] Source localization and hippocanpus

Fri Jan 23 00:14:02 PST 2026

Comparing intra- and extracerebral recordings is a poor source of information, but we have no other way to assess the actual propagation of signals throughout the brain. This is especially true if the recordings are obtained on people, since they are not only obtained accidentally during surgeries or therapeutic interventions on brain structures, but also relate exclusively to patients. But this is real data. No matter how thorough the modeling, it primarily reveals the assumptions inherent in the model, even if the researcher themselves are unaware of them. I recall the dispute between Newton and Descartes. Descartes constructed an excellent model explaining the motion of the planets by vortices. And Newton declared "Hypotheses non fingo" and began deriving the theory of gravity from astronomical observations. So, it seems to me that directly observed data is more convincing than models.
The links you provided are very interesting, thank you. But they do not imply that an intracerebral signal cannot be recorded on the scalp, even from deep regions. The task is difficult, but not impossible. Certain facts suggest that not all generators are dipole. For example, slow activity decays with distance more slowly than other types, and this can be explained by attributing it to a monopole source. This could be significant for reconstructing the deep signal from scalp data.

Eugen Masherov

> 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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