LCMV Beamformer output interpretation

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Hello!
First, thank you for the absolutely amazing software you keep maintaining and improving, it’s a mindblowing library :slight_smile:

Now, onto the topic.

I have the most naive question: what is exactly the output of a LCMV beamformer?
To be more specific, assume a grid of source locations spanning the whole brain. We conduct source estimation with a beamformer at each such source, in a volumetric way. We thus obtain in MNE-python a volumetric source estimate, with one scalar value at each source location.
There is my fundamental question: what is this scalar expressing? In which units? It could not be the dipole moment of the source, as a moment is a vector. Is it expressing a notion of charge?
Cheers!

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@britta-wstnr Could you have a look at this one?

Thanks,
Mathieu

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Hi @Shrecki

Thanks for the compliments :slight_smile:
Your question is not easily answered: this depends on the intricacies of the options you choose (e.g., weight normalization etc). Generally speaking, many beamformers give not back units that are easily biophysically interpretable, except for the unit-gain beamformer.
For more information I would like to refer you to this paper, especially the last part of paragraph 2.1:
10.1016/j.neuroimage.2021.118789

Hope this helps,
Britta

PS: Thanks a lot @mscheltienne for pinging me!

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