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

Wed Dec 13 12:32:01 PST 2023

Hi Cedric,

Thank you for your comment! I welcome your input.

> Isn't this simply because EEG mainly captures radial gryal sources,
producing strong scalp dipoles on the topos?

That's right. Scalp-recorded EEG is primarily sensitive to gyral sources.
My paper confirmed that ICA does not do any magic to that fact. Otherwise,
we would see 2/3 of the ICs show tangential topos!

> 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.

I'm not sure if we can identify sulcal sources in the spline
Laplacian-transformed data. Maybe Ramesh can comment on this part.

> But maybe the thalamocortical loops control them all? ;)

Ha ha, you think you get me? On the contrary.
I don't know about the astrocytes honestly, but I'm sure PING and traveling
waves are both mediated by thalamo-cortico-thalamic loop. Why not? I paste
other quotes from the same Jones (2002) below for your info.
If it were not the thalamus, then what's the role of the known network
around the reticular thalamic nucleus, for example? It receives collateral
from both thalamo-cortical and cortico-thalamic fibers only to modulate
other thalamic activities with inhibitory inputs. Same applies to the
redundant feedback loop connections by specific (i.e. focal) and
non-specific (i.e. diffuse) thalamic nuclei?

%%%%%%%%%%%
...In this scheme, involving the systematic recruitment of cortical and
thalamic cells by thalamic matrix cells and layer V corticothalamic cells,
large-scale, coherent activity would be set up throughout large  regions
 of  cortex  in  response  to  an  externally  or internally  generated
 stimulus. (p.1669)

...The capacity of the layer V cortico-thalamic projection to bring
activity in one cortical region to thalamic nuclei that project to adjacent
regions, and even to distant regions located in other lobes of the cerebral
 hemisphere,  could  extend  the  binding  process  by providing a basis
for unifying activity in the somatosensory  and  motor  cortex  during
 movement  performance (Ribaryet  al.  1991;  Murthy  &  Fetz  1992,
 1996a,b; Sanes & Donoghue 1993), and in parietal areas engaged in
perception with that in frontal areas engaged in planning strategies for
action (Tononiet al.1992; Lumeret al.1997). Corticocortical connections
undoubtedly playa prominent part here as well but they would run parallel
to a system of corticothalamocortical loops in spreading activity across
the forebrain. (p.1670)
%%%%%%%%%%%

Have you thought of what makes ERP components such as P100, N170, and P300
(I did visual ERPs for my PhD hence the choices)? The first P100 is driven
by the 'proximal' input mainly to infragranular layer V that makes the
upward intracellular current, while the next N170 is driven by the 'distal'
input to supragranular layers II and III that makes downward intracellular
current. The input to layer II and III is from non-specific thalamus. In
this way, polarities of ERPs are already connected to the layer-specific
thalamo-cortico-thalamic loop. Do you think this is another
(over)simplification? Maybe, but there is evidence for that. For more info,
check out human neocortical neurosolver (HNN) https://urldefense.com/v3/__https://hnn.brown.edu/__;!!Mih3wA!GYeKl_piY81R70lbPPVjcklQWmPTR1ErF-QSnByiSVeTcqcx_xKP-UcRS0tKQ57pLT6t46kG_G31Bsg4FDA9o_sB94s$ .

I met a couple of EEGLAB novices in the last HNN workshop in Washington DC.
I'm convinced that learning how to apply HNN to our EEG/ERP data is
beneficial for both educational and scientific purposes. It makes us think
where EEG is from and how they relate to the deeper level of physiology,
and it adds more value and insight to our humble EEG observations. I'll
show you some demo soon.

Makoto

On Tue, Dec 12, 2023 at 6:19 PM Cedric Cannard via eeglablist <
eeglablist at sccn.ucsd.edu> wrote:

> 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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> to
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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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