Leadfield Matrix calculated at which surface?

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Dear Brainstorm experts,

I am new to Brainstorm. I am posting to ask a simple question: when I calculate the Leadfield Matrix with the forward model, each element of the matrix correspond to a specific vertex and a specific EEG sensor, however it is unclear to me to which vertex does the LF Matrix refers...I assume it is the "i" vertex of the surface and the "j" sensor, however how can I find the list of vertices and sensors in the exact order they refer to? And the "i" vertex of which surface (merged pial? merged white? merged mid?).

Thanks, appreciated,

Mic

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Hi @michefabb,

This information is located in the head model file:

  1. The field HeadModelType indicates the type of source space: surface, volume or mixed.

  2. The field GridLoc that has the locations of the vertices size [nVertices, 3].

  3. For surface models, the surface that was used is indicated in the field SurfaceFile.

More info about the contents of the head model file in here:
https://neuroimage.usc.edu/brainstorm/Tutorials/HeadModel#On_the_hard_drive

:bulb: For surface head models, the current default cortex is used. This cortex can be identified by the green color in the Anatomy view.

image

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Thanks @Raymundo.Cassani ! Just a last question: where can I find the coordinates of the EEG sensors that refer to the Leadfield Matrix?

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Those are in the channel file in the Channel(iChannel).Loc.
https://neuroimage.usc.edu/brainstorm/Tutorials/ChannelFile#On_the_hard_drive

In Brainstorm, all coordinates are in SCS:
https://neuroimage.usc.edu/brainstorm/CoordinateSystems

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Thanks @Raymundo.Cassani ! Last question, is it possible to see also the coordinates in "World" reference system instead of SCS?

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https://neuroimage.usc.edu/brainstorm/CoordinateSystems#Converting_between_coordinate_systems

1 Like
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Dear @Raymundo.Cassani , thanks for your prompt reply!
I would ask another point if possible: in which coordinate system are the eeg sensors? scs?

Appreciated!

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Yes, all coordinates in Brainstorm are SCS