Should I remove the first component with small amplitude when using ICA?

Discussions
1

Hello,

I have a MEG data set which is about 5 minutes long for each subject. I want to detect and correct existing artifacts using the ICA approach using the Brainstorm toolbox. When I performed ICA, the first component (the dominant one) has a very small amplitude, (about 1000 times smaller in comparison to other components) and looks like a DC signal. Should I remove this component? It is the first component and I want to be sure about this decision as it may be a signal, not an artifact. In the following, you can see the components.Thanks!
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the first component (the dominant one)

The ICA components are not ordered, unless you selected a channel to sort them. In that case, they are sorted based on the correlation score with this data channel:
https://neuroimage.usc.edu/brainstorm/Tutorials/Epilepsy#Artifact_cleaning_with_ICA

has a very small amplitude, (about 1000 times smaller in comparison to other components) and looks like a DC signal.

All the IC components capture equivalent amounts of signal.
If you see a signal that looks noise compared to the others, this is because the component is already removed, i.e. selected in the window "Select active projectors".

3

Dear Francois,
Thank you so much for your response.
I did not remove this component but it looks like noise with a very small amplitude. you can see the "Select active projectors" window in the following picture:
index
Thanks

4

Then it might have some very large values at a different time in the recordings?
It seems unlikely that Infomax would create a separate IC with such low values compared with the others.

5

Dear Francois,
Yes, in some subjects there are some large values at a different time but this has not happened in all subjects. In other words, in some subjects, there are no large values but when I use ICA I can see the first component with a very small amplitude.
I have tested Jade ICA as well. Again, like Infomax the first component with a very small amplitude is extracted.
Thanks!

6

Unfortunately I can't you much with this, we do not have any ICA experts in our team.
Maybe you could try if you get the same results with EEGLAB and ask the EEGLAB community about these results.

7

Thank you so much