Display of relative ACD maps

[joerlema]

Dear all,

I am currently working with intracranial EEG data to perform source localization of a certain ERP-component. I have used unconstrained current source density analysis using a volume head model. The CSD maps are displayed like this:

I have also created scouts for a ROI-based approach and I have seen that is possible to display the relative current density waveforms in 3 orientations:

I am, however, very interested to visualise the current sources and sinks with respects to their anatomical location. I have read online that you can uncheck the 'absolute value' option when looking at CDMs, but when I try this nothing really changes (it looks exactly the same as the absolute value option):

Am I doing something wrong? Also, I would expect the relative current density map to be displayed in the 3 orientations, is that the case?

Are there any other ways I can look at the current sources and sinks relative to the anatomy using Brainstorm(or maybe even with another software)?

Many thanks for your help!

Kind regards,

Joyce

[Sylvain]

Because there are three source components at each brain location, the volume brain maps can only show a summary statistic of these three measures at once, likely the norm of the 3 local values at each time point, yielding an all positive map. An alternative would be to flatten this 3D map by right-clicking on the source file and selecting a projection function such as 'mean' or 'PCA'.

[joerlema]

Hello, Sylvain

Thank you for your suggestion. I have added the source file to processes --> sources --> unconstrained to flat map --> PCA and this is the result:

I am not really sure how to interpret this. What does the PCA do exactly?

[Sylvain]

The PCA extracts the time series component that captures the most variance at each voxel. You know can appreciate the maps area showing negative values as expected. You may want to use a different colormap to emphasize the sign changes.