[Eeglablist] Source localization and hippocanpus

[Makoto Miyakoshi]

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