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

Tue Dec 12 12:12:28 PST 2023

Hi,

Congrats on the paper Makoto and colleagues, interesting piece (and comments)!

> "2/3 of the cortex is in sulci? [...] the result
confirms that ICA is mostly blind to 2/3 of the cortex"

Is this really accurate? 

> (1) Why do good 'brain' ICs show dipolar scalp topos although 2/3 of the cortex is in sulci? It is because scalp-recorded EEG is insensitive to sulcal sources compared with gyral sources. [...] This finding justifies the use of lissencephalic (i.e. no sulci) brain model proposed in Electric Fields of the Brain (Nunez and Srinivasan, 2006) together with Spline Laplacian.

Isn't this simply because EEG mainly captures radial gryal sources, producing strong scalp dipoles on the topos? What does this have to do with sulcal tangential sources? 
There are dipolar topos with MEG data too, even though it captures mainly sulcal tangential sources, no? 

To answer your question, I would ask instead: do you still see this phenomenon after applying surface Laplacian, when you remove most of the large-scale radial synchrony, and focus mainly on local (small-scale) tangential activity. It looks like you only looked at this phenomenon after average reference. 

My understanding is that the Surface Laplacian is sensitive to local sources with small spatial scale, filtering out source activity that is synchronous over large regions. This is not the same as saying that it excludes sulcal activity, is it? You can have gryal tangential sources to some extent, and some sulcal radial sources (even though it is to a smaller extent). 

> The synchrony is achieved via thalamo-cortical loops.

Sorry I can't see the wiki page for some reason, but this feels like an oversimplification. There are many other significant factors underlying large-scale synchrony in my view, like the inhibitory or PING circuit motifs (e.g., https://urldefense.com/v3/__https://www.nature.com/articles/nn.3764__;!!Mih3wA!BSHp1vfvJv4CxEW_xNFHQjKaivTpL-frZvigEmM4H60RqAJsB4C1bM6IAtIfoe06s_04DFrq3xP8YQVfyY87sWUcDQ$ 
), astrocyte CA2+ modulation (https://urldefense.com/v3/__https://www.nature.com/articles/35058528__;!!Mih3wA!BSHp1vfvJv4CxEW_xNFHQjKaivTpL-frZvigEmM4H60RqAJsB4C1bM6IAtIfoe06s_04DFrq3xP8YQVfyY8NDnNKDQ$ ), or traveling wave properties (e.g. https://urldefense.com/v3/__https://journals.plos.org/ploscompbiol/article?id=10.1371*journal.pcbi.1009827__;Lw!!Mih3wA!BSHp1vfvJv4CxEW_xNFHQjKaivTpL-frZvigEmM4H60RqAJsB4C1bM6IAtIfoe06s_04DFrq3xP8YQVfyY8YDJpzNw$ ), etc. But maybe the thalamocortical loops control them all? ;)

Cedric

On Tuesday, December 12th, 2023 at 8:10 AM, Ramesh Srinivasan via eeglablist <eeglablist at sccn.ucsd.edu> wrote:

> I've been enjoying this discussion because it taps into one of those EEG
> truths/inconsistencies we never talk about.
> 
> 1. We artifact edit EEG data mostly based on the idea it should be smooth
> low spatial frequency information. We don't trust very (channel,
> frequency, time) localized EEG signals.
> 
> 2. Then after we clean the EEG data we want a story for our paper that is
> time, frequency, source localized as compact as possible because it makes a
> nice narrative.
> 
> Regarding synchrony in adjacent gyri, u-fibers are helpful and yes, I think
> most of it is corticocortical rather than thalamocortical but I think the
> 2% is just a guess. It's clearly not as thalamocortical as animal models
> 
> Ramesh Srinivasan
> Professor
> Cognitive Sciences
> Biomedical Engineering
> 
> On Tue, Dec 12, 2023, 6:40 AM Pål Gunnar Larsson via eeglablist <
> eeglablist at sccn.ucsd.edu> wrote:
> 
> > Just want to add. In rats about 50% of all fiber going in and out of the
> > cortex are connected to the thalamus. In humans connections are about 2%,
> > according to Nunez. Hence, we should be very careful when you try to
> > extrapolate from animal research to humans.
> > 
> > Pål G. Larsson
> > 
> > Ikke sensitiv
> > 
> > -----Opprinnelig melding-----
> > Fra: eeglablist eeglablist-bounces at sccn.ucsd.edu På vegne av Makoto
> > Miyakoshi via eeglablist
> > Sendt: 11. desember 2023 19:06
> > Til: EEGLAB List eeglablist at sccn.ucsd.edu
> > Emne: Re: [Eeglablist] Why most of good 'brain' ICs are 'dipolar' with
> > show 'red'-centerd scalp topos, although 2/3 of the cortex is in sulci?
> > 
> > Hi Scott,
> > 
> > > "How are LFP signals across each of these gyrii synchronized across
> > > the
> > > dataset?"
> > 
> > The answer is not so special. The synchrony is achieved via
> > thalamo-cortical loops.
> > In the following Wiki article, I linked to my presentation at an NIH
> > summer seminar in which I showed multiple evidence that cortical synchrony
> > and coupling is controlled by thalamus.
> > 
> > https://urldefense.com/v3/__https://sccn.ucsd.edu/wiki/Makoto*27s_preprocessing_pipeline*Two_presentations_at_a_seminar:_EEG_preprocessing_and_generative_mechanism_.28For_240.2C000_page_views.2C_09.2F21.2F2023_added.2C_10.2F18.2F2023_updated.29__;JSM!!CzAuKJ42GuquVTTmVmPViYEvSg!IxfdnbB611_BrP_68EFD1xVZHKoKQu6E2vLO7VJL104Il5HhWcGfwu-K0btGTDMoDcUuo0-5NDYMK30iA7NCfDue$
> > 
> > So, when thalamus makes different cortical regions to fire together, then
> > you see the synchronous activity. That's it. The distant cortical regions
> > do not have to be directly connected via each neuron's lateral branches
> > (which does exist, but the conduction speed is very slow compared with that
> > of white matter) Note this is not a one-way 'imposing' the rhythm from the
> > thalamus to the cortex, like the historical 'pace-maker' hypothesis by
> > Andersen and Andersen (1967) but it is a bi-directional interaction.
> > 
> > One fact that might help you see the situation is that only 1% of neurons
> > need to be synchronized to form 95% of the amplitude of the observed signal
> > according to Hari (1997).
> > 
> > Also, it might also help to remember that there is no general guarantee
> > that an EEG source is stationary and localizable. See Izhikevich's
> > classical simulation.
> > 
> > https://urldefense.com/v3/__https://www.izhikevich.org/publications/large-scale_model_of_human_brain.htm__;!!Mih3wA!FLAtrGcNSxCRup1LcnfgWIJkdfC5HMOr_rPujEIjdmGug69GeOA7PxjXg5NqsRrbtx3VtKZRJhKrQ9HIAFxdjg0n5Fg$
> > There is an established principle of functional brain mapping but it is a
> > product of statistical processing such as (heavy) averaging. ICA model is
> > the same, hence it is stationary across time. The small and localizable EEG
> > source is heavily a statistical concept. The actual ongoing EEG is
> > stochastic, dynamic, and diffuse. When we see ICA results, therefore, we
> > should distinguish properties of the filter from properties of data.
> > 
> > Makoto
> > 
> > On Mon, Dec 11, 2023 at 11:42 AM Scott Makeig smakeig at gmail.com wrote:
> > 
> > > Makoto -
> > > 
> > > When you repeat the claim that EEG sources 'found' by ICA
> > > decomposition must be at least several adjacent gyrii in size, you
> > > fail to ask, "How are LFP signals across each of these gyrii
> > > synchronized across the dataset?"
> > > Doesn't this require some physiological basis, and if so, what is it??
> > > 
> > > Scott Makeig
> > > 
> > > On Mon, Dec 11, 2023 at 11:17 AM Makoto Miyakoshi via eeglablist <
> > > eeglablist at sccn.ucsd.edu> wrote:
> > > 
> > > > Hello EEGLAB list,
> > > > 
> > > > For those who have wondered so, here are my answers.
> > > > I asked two questions:
> > > > 
> > > > (1) Why do good 'brain' ICs show dipolar scalp topos although 2/3 of
> > > > the cortex is in sulci?
> > > > (2) Why do these dipolar IC scalp topos show red (positive) centers?
> > > > 
> > > > The answer was published a few days ago.
> > > > 
> > > > https://urldefense.com/v3/__https://onlinelibrary.wiley.com/doi/10.10
> > > > 02/hbm.26540__;!!Mih3wA!FPOThEiX2hsD7TJBq7WyhlV8v6HSkTe_swsBEoB2RM-Bh
> > > > -BGerduzZBnmEtDBamyosThbqv9Xrc1gGPSmdm52LpO7jM$
> > > > 
> > > > The answer to (1): It is because scalp-recorded EEG is insensitive to
> > > > sulcal sources compared with gyral sources. This finding justifies
> > > > the use of lissencephalic (i.e. no sulci) brain model proposed in
> > > > Electric Fields of the Brain (Nunez and Srinivasan, 2006) together with
> > > > Spline Laplacian.
> > > > This also supports the view that the major source of scalp-recordable
> > > > EEG is pretty broad (minimum 6.45 cm^2) which requires a continuum of
> > > > multiple gyral crowns.
> > > > 
> > > > I did not write it in the paper, but the result basically refutes the
> > > > claim that ICA is a high-resolution EEG spatial filter because the
> > > > result confirms that ICA is mostly blind to 2/3 of the cortex. In
> > > > fact, it seems ICA results are always dominated by high-power,
> > > > low-frequency, and very broad sources. I will publish this view in
> > > > the near future.
> > > > 
> > > > The answer to (2): It is because EEGLAB's ICA sets the initial topos
> > > > of all ICs red centered (i.e. positive dominant). Thus, unless
> > > > necessary, the algorithm does not flip the polarities.
> > > > 
> > > > Now you wonder--when does the ICA algorithm flip the polarity to
> > > > produce 'blue' centered (i.e. negative dominant) ICs? I found that
> > > > those blue-centered ICs tend to show poor physiological validity with
> > > > large index numbers. A known clear exception for this rule is ICs
> > > > localized for the motor cortex.
> > > > 
> > > > People use ICA to clean EEG. I use EEG to glean ICA, which is more fun.
> > > > 
> > > > Makoto
> > > > _______________________________________________
> > > > Eeglablist page:
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> > > 
> > > --
> > > Scott Makeig, Research Scientist and Director, Swartz Center for
> > > Computational Neuroscience, Institute for Neural Computation,
> > > University of California San Diego, La Jolla CA 92093-0559,
> > 
> > https://urldefense.com/v3/__http://sccn.ucsd.edu/*scott__;fg!!CzAuKJ42GuquVTTmVmPViYEvSg!IxfdnbB611_BrP_68EFD1xVZHKoKQu6E2vLO7VJL104Il5HhWcGfwu-K0btGTDMoDcUuo0-5NDYMK30iA0yMHq0i$
> > 
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