Bad segments, source localization, and ICA decomposition

Hello Brainstorm Community!

I've recently started using Brainstorm to do source localization, and later, ICA decomposition, on resting-state EEG data. I have read some of the discussions relevant to the topic of bad segments and how these are handled in various procedures. Can you please confirm my understanding of the following points?

(1) Segments which have been marked as "bad", such as in my case, highlighted pieces in the continuous dataset marked "rejected" and boundary events marked "bad", all of which are colored red, are still used during source localization and ICA decomposition, unless explicitly removed.
(2) However, calculating the noise covariance matrix automatically excludes these red-marked segments or points from the calculation.
(3) It is valid and recommended to still include the bad segments in the source localization and ICA decomposition procedures to prevent discontinuities in the dataset which can be a huge problem for these procedures.
(4) Since the noise covariance matrix calculation excluded contributions from the bad segments, we can still generate a valid source localization of the data. It only remains for us to extract those time segments that are deemed "good" for subsequent analyses.
(5) So, we can run source localization and then ICA decomposition without first extracting those bad segments (or importing only the concatenated good segments) and we should be able to get valid results. After all of these have been done, we can simply extract the time intervals that are deemed good segments for subsequent analyses.
(6) Question: At which point can I do a mapping of the EEG data to a functional atlas?

-Gin

Hello Gin,

Welcome to the Brainstorm community. If you are a new Brainstorm user, we strongly recommend you start by following the introduction tutorials first (section "Get started" on the tutorial page), using the example dataset that is provided. By doing so, you will get familiar with Brainstorm features, processes and jargon. In fact, most of your questions are addressed in there, more specifically in these tutorials 11 to 14 and 21 to 23

https://neuroimage.usc.edu/brainstorm/Tutorials

Here the clarification to your questions:

  1. Segments marked as BAD are not used from ICA decomposition

  2. This is right, noise covariance matrix is computed only with good data (bad segments are ignored for the computation)

  3. As per Point 1, bad segments are not considered for ICA decomposition. Source estimation is computed from the head model and noise covariance matrix (which is computed ignoring the bad segments).

  4. There is no need to extract the "good" segments since they will be ignored in further analysis

  5. Usually ICA is used as a tool to remove artifacts from the sensor (EEG) data, and then this cleaned data is used to estimated the sources, not the other way around. No need to extract good segments, see Point 4.

  6. EEG data is not directly used with atlases. You would need first to estimate the sources, and then you can use atlases in the source space.

Thanks so much! I will go over the tutorials as recommended.

I just have one other question regarding source localization. How do I activate the function Output Mode>Full Results (Kernel*Recording) when computing the sources? I could not use this option with any type of source computation selection.

This options is enabled if Compute sources [2018] is called from a Data file (iconEeg or iconRawData), not from a HeadModel file (iconHeadModel).