[Eeglablist] Question regarding source localization using DIPFIT

[Makoto Miyakoshi]

Hi Sravani,

I thought Fieldtrip uses automated anatomical labeling (AAL:
Tzourio-Mazoyer et al., 2002). I know it supports various others recently,
which I've never used myself.

Scalp-recorded EEG data do not have sensitivity to basal ganglia including
thalamus because

   1. These relatively small nuclei cannot form a stable and broad electric
   source. According to 'Electric Fields of the Brain' (Nunez and Srinivasan,
   2006), in order to observe 20-30 microV unaveraged scalp EEG signal, 6-7
   cm^2 of active synchronous cortical patch is required.
   2. Distance-dependent attenuation is too large for the deep sources.

Assuming that ICA finds physiologically valid cortical EEG sources. Now,
the question is why ICA always finds much more ICs with radial dipolar
projections than the tangential ICs although 2/3 of cortex are in sulci.
The answer is, scalp-recorded EEG is much more sensitive to the gyral
sources than the sulcal sources. My observation about this fact will be
soon published from Human Brain Mapping. My point her is, even a few
centimeter difference in depth from the scalp can greatly suppress the
scalp-measurerability in this way. Even if our brain has relatively large
area of synchronous electric source in the deep part of the brain, the
electric field generated by it would be nearly entirely suppressed near the
scalp region in terms of EEG amplifier's sensitivity limit (=thermal noise
floor with a few microV).

If you are curious about these topics, see also
https://sccn.ucsd.edu/wiki/Makoto%27s_preprocessing_pipeline#Physiologically_invalid_deep_dipoles.3F_.28For_130.2C000_page_views.2C_07.2F26.2F2021_Update.29

Makoto

On Sun, Nov 19, 2023 at 9:06 PM Sravani Varanasi via eeglablist <
eeglablist at sccn.ucsd.edu> wrote:

> Hello,
>
> I trust this message finds you well.
>
> I have recently started to work with EEG data and am eager to incorporate
> source localization results into our ongoing lab analysis. Currently, I am
> utilizing the DIPFIT plugin within EEGLAB for this purpose. I have
> successfully generated the leadfield matrix, but I am seeking clarity on
> the specific atlas used for source localization—whether it is the DK atlas
> or the LORETA-Talairach-BAs. Additionally, I am looking for guidance on
> interpreting the leadfield matrix and acquiring individual Region of
> Interest (ROI) data.
>
> While examining the LORETA-Talairach-BAs.mat file, we noticed the inclusion
> of the thalamus in the atlas. I am particularly interested in understanding
> whether the source localization extends to the basal ganglia as well.
>
> Your insights into these inquiries would be greatly appreciated.
>
> Thanks in advance!
> Best regards,
> Sravani Varanasi
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