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

[Makoto Miyakoshi]

Hi Pål,

Thank you again for your comment.
To save your time, here is the quote from Electric Fields of the Brain
(Nunez and Srinivasan, 2006) p.6.

%%%%%%%%%%%%%%%%
Each square centimeter of human neocortex may contain 10^7 input and output
fibers, mostly corticocortical axons interconnecting different regions of
the cortex, as shown in fig 1-2. A much smaller fraction of axons that
enter or leave the underside of human cortical surface radiates from (and
to) the thalamus (thalamocortical fibers). This fraction is only a few
percent in humans, but substantially larger in lower mammals. This
difference partly accounts for the strong emphasis on thalamocortical
interactions (versus corticocortical interactions), especially in
physiology literature emphasizing animal studies.
%%%%%%%%%%%%%%%%

With reference info on p. 179.

%%%%%%%%%%%%%%%%%%
In humans, about 98% of the input fibers are corticocortical; only a few
percent are thalamocortical (Braitenberg 1977, 1978; Katznelson 1981; Nunez
1995), suggesting a dominance of corticocortical interactions in dynamic
behavior.
%%%%%%%%%%%%%%%%%%

I think an explanation for the reduced thalamo-cortical connection in
humans is that (1) the human brain have the largest neocortex ratio, (2)
which would require propertionally larger thalamocortical connections
beyond the size limit, (3) hence the density of the thalamo-cortical fibers
were sacrificed.

The 'Brain facts and figures' you shared is a fantastic source of
information. Let me share it here for other readers.
https://urldefense.com/v3/__https://faculty.washington.edu/chudler/facts.html__;!!Mih3wA!EcfPK4HkHL82GsNGUaxTpHyLYzJM3gdP2AS9uTyxxO2Hhbvx2pjiC2trs6lj6ZigDkpshgB_aQTDlkL6mheBLTf884M$ 

> Thalamus is an important gateway, but do not have the same position in
the human brain as we learned from animal models.

Yes, anatomically that is correct. But functionally, I still believe that
it plays a substantial role in determining the spatial mode of the cortical
activation, though I can't show you any quantitative data here other than
the anatomical statistics.
In my past presentation below, you can see the highlights of studies on
spatial mapping of the thalamo-cortical network. The functional aspects of
the thalamo-coritcal network can be, at least qualitatively, seen here. I
think these studies are all excellent and inspiring.
https://sccn.ucsd.edu/mediawiki/images/1/13/On_EEG%27s_generative_mechanism.pdf
Slide 14: Larson et al. (1998)
Slide 29: Shine et al. (2023)
Slide 38, 39: Mueller et al. (2020)
Slide 42: Garrett et al. (2018)
Slide 43: Greene et al. (2020)

You can also see topographic mapping between (specific and associate)
thalamic nuclei and cortex in the human brain in Figure 26-5 below.
https://urldefense.com/v3/__https://what-when-how.com/neuroscience/the-thalamus-and-cerebral-cortex-integrative-systems-part-2/__;!!Mih3wA!EcfPK4HkHL82GsNGUaxTpHyLYzJM3gdP2AS9uTyxxO2Hhbvx2pjiC2trs6lj6ZigDkpshgB_aQTDlkL6mheBwnAONXQ$ 
By the way, I found this contents is probably a ripped one from Siegel and
Sapru (2014) 'Essential Neuroscience' 4th ed. It's a bad thing, to be clear!

The importance of understanding scale dependency in studying a complex
system is repeatedly emphasized in the 'Electric Fields of the Brain'. I
totally agree with you on this point.
Coincidentally, there is a discussion on a potential contribution of
monopole to EEG on this thread. I'll jump to it now.

Makoto