[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]

Dear sir!

I am trying to develop a hypothesis of the origin of EEG, which assumes that elementary sources are not only dipoles, but that monopoles and quadrupoles must also be taken into account. At the same time, different components have different physiological meanings, low-frequency ones, up to and including the alpha rhythm, are associated with the regulation of the level of resting potential, and their frequency and other characteristics reflect the level of metabolism, and are predominantly monopoles in nature. Dipole components are associated with the neural activity at the level of the neuron body, and the action potential is quadrupole. 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.
I have no right to talk about the originality of this approach; already in the work of 1944 a similar explanation of the EEG was proposed, but it was forgotten. The accumulated facts allow us to return to this approach again. Perhaps it will improve EEG analysis methods and clarify some of the observed effects.
As for the question of synchronization of the activity of the thalamus and occipital cortex, I would like to offer an explanation by the mutual synchronization of the sources of oscillations in the presence of a connection between them.
Let me bring to your attention two articles in which I try to present my hypothesis.

https://urldefense.com/v3/__https://link.springer.com/article/10.1134/S0006350919030138__;!!Mih3wA!AcFA1OQEzrKlpefP_MkNc_UaS8zDW5t4lEuCnPho6cYvzAW2OnLA6nciH03UFilU1TQTOwjwQz9FPHUaKz4qCDJMJh0$ 
https://urldefense.com/v3/__https://link.springer.com/article/10.1134/S0006350921040114__;!!Mih3wA!AcFA1OQEzrKlpefP_MkNc_UaS8zDW5t4lEuCnPho6cYvzAW2OnLA6nciH03UFilU1TQTOwjwQz9FPHUaKz4qS_efcN0$ 

Your truly

Eugen Masherov
Clinical neurophysiology laboratory, Burdenko neurosurgery institute, Moscow, Russian Federation

> Hi Makoto
> 
> I hope I did not open Pandoras box. First a small history.
> Andersen and Andersson publish in 1968 that alpha activity came from pacemaker cells in Thalamus. This was a cat study. In 1971 Sturm van Leuwen and Lopez da Silva showed in dog that there were no good coherence between the thalamus activity and the alpha. Even the frequencies didn’t match. Then Nunez suggested alpha was generated by standing waves in cortex with some human data. However, also his hypothesis was more or less shot down. Now, it seems like a leading hypothesis is that alpha is generated by cortical spreading activity that to some extend is influenced by standing waves. My point here is that model and methods to a large extend influences your results.
> 
> Let me make some points
> 1. Propagating takes time, hence you get a phase shifted as a function of distance in cortex. This will give cancellations in the EEG due to the spatial averaging. Therefore our electrodes "sees" patchy activity.
> 2. The cortico-cortical fibers propagate AP with up to 9 m/s and intracortical propagation is 0.2m/s- 0.5 m/s.
> 2. The nature is not redundant in the way that many neurons are used for the same function. You will not expect close by neurons to be in synchrony. Why should they? But there will be coherent elements.
> 3. The amplitudes of EEG will be linear to the number of synchronous firing neurons. If they are firing stochasticly the amplitude will be closer to the square root. E.g. 1000000 neurons will in synchrony give an unite amplitude of 1000000 as if they have a stochastic firing 1000. Coherences gives amplitudes somewhere in between.
> 4. The EEG we record are to a large extend from not highly correlated neurons with coherences waxing and waning depending on the activity. E.g. Evoked potentials gives higher coherences and hence, higher amplitudes.
> 5. Thalamus is an important relay station in the brain, but I am not convinced that it has an important pacemaker function, at least not in humans.
> 6. I think I have to go back to the PL Nunez book to find his references on the human vs rodent brain wiring.
> 
> To me the EEG is mostly modulated by changing activities in the brain and not by some pacemakers.
> 
> Best
> Pål
>