[Eeglablist] Why most of good 'brain' ICs are 'dipolar' with show 'red'-centerd scalp topos, although 2/3 of the cortex is in sulci?

[Евгений Машеров]

Hi Makoto

Thank you very much for the interesting and valuable article Pitfalls in the dipolar model for the neocortical EEG sources: Riera JJ, Ogawa T, Goto T, Sumiyoshi A, Nonaka H, Evans A, Miyakawa H, Kawashima R, 
Doubts about the dipole model arose in me after my experience using the dipole localization program (BrainLoc by Yuri Koptelov). It used a single-dipole (it was also possible to require a search for two dipoles for each sample) model without forcing their coordinates with a selection of dipoles found throughout the EEG segment, leaving those points for which the single-dipole approximation of the signal is quite accurate, so it can be assumed that at the moment there is one dipole of high amplitude, and all the others have low amplitude and can be considered as noise. The found sources could be verified by an intracranial encephalogram during surgery, and the accuracy was quite high. However, in the case of deep sources, the signal attenuation from the dipole would be too high, and impossibly large amplitudes at the source would have to be assumed to obtain the signal observed on the scalp.
A possible resolution of the contradiction would be to take into account the potential of not only dipole sources, but also monopoles.
The specified dipole localization program, when trying to search for two dipoles simultaneously, usually did not give a good result, with the exception of searching for the source of a sharp wave of a peak-wave complex. In this case, two oppositely directed dipoles were observed emanating from the same point. It is possible that in reality there is a quadrupole source approximated by two dipoles.
As for the connection between the activity of the thalamus and the occipital cortex, I can only assume that this may be a synchronization effect (like the synchronization of two pendulums connected by a weak spring). The synchronization mechanism can be through nerve impulses, purely electrically (ephaptically), or by diffusion of ions. But these are just assumptions that require criticism.

Perhaps you can find a clearer explanation here
https://urldefense.com/v3/__https://istina.msu.ru/download/621221220/1rFvVB:v1u5Qu1hRQWAPGg01ncDoTXd1eU/__;!!Mih3wA!GEHLL9rrAsXq-m5dlGhhgMaoZvR3WCbZBR718UDMgG_VPWLwkW2Khw5G13s5Kz9oaTukJHePt1du0cgQUMRvqr3Q-Bk$ 
PowerPoint presentation
https://urldefense.com/v3/__https://istina.msu.ru/download/621282647/1rFw9L:1mcijNri7_vw2sz2onVQOFByo9A/__;!!Mih3wA!GEHLL9rrAsXq-m5dlGhhgMaoZvR3WCbZBR718UDMgG_VPWLwkW2Khw5G13s5Kz9oaTukJHePt1du0cgQUMRv_cf98NU$ 
And this is a small demo script in MATLAB.
https://urldefense.com/v3/__https://istina.msu.ru/download/621281264/1rFvWt:v2A1PXPZdikElRoSyGK9sMlyBjs/__;!!Mih3wA!GEHLL9rrAsXq-m5dlGhhgMaoZvR3WCbZBR718UDMgG_VPWLwkW2Khw5G13s5Kz9oaTukJHePt1du0cgQUMRv9IiLBz0$ 

Understanding that the material presented is very crude and not fully developed, I still hope that something useful will be found in it, and I will also be grateful for harsh criticism.

Eugen Masherov

> Hi Eugen,
> 
> Thank you for your comment!
> 
>> Therefore, the amplitude of the (summarized) recorded activity depends on
> 
> the distance between the place of generation and the point of activity
> registration. This may be due to the difference in the frequency
> composition of EEG and ECoG.
> 
> Yes, that fits my following understanding.
> When we consider the recording EEG at scalp, the distance from the
> electrode to the pole center of a cortical dipole is about 10-15 mm
> according to the Electric Fields of the brain. Since the pole distance is
> about 3-4 mm, the cortical source can be approximated as a dipole. If a
> distance from the measurement point is 3-4 times larger than the pole
> distance, the dipole approximation works well. This is explained in the
> Electric Fields of the Brain (Nunez and Srinivasan, 2006) p.109.
> 
>> Therefore, the amplitude of the (summarized) recorded activity depends on
> 
> the distance between the place of generation and the point of activity
> registration.
> 
> For the sub-cortical recording, see Jorge's following paper. It's a
> good one. You can find empirical evidence for your (theoretical) claim. I
> visited their lab in early 2010's.
> 
> Pitfalls in the dipolar model for the neocortical EEG sources.
> Riera JJ, Ogawa T, Goto T, Sumiyoshi A, Nonaka H, Evans A, Miyakawa H,
> Kawashima R
> J Neurophysiol. 2012 Aug; 108(4) 956-975
> DOI: 10.1152/jn.00098.2011, PMID: 22539822
> 
>> I would like to offer an explanation by the mutual synchronization of the
> 
> sources of oscillations in the presence of a connection between them.
> 
> Thank you for sharing your paper.
> In your 2019 paper I noticed the thalamus is not modeled, but I also
> thought that thalamus may be still there as an input and modulating factor.
> Do you have any comments on that?
> 
> Makoto
>