[Freesurfer] mcprextreg file structure and X

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Dear all,

I am trying to figure out the structure of X.dat and where the mcprextreg parameters are in the table. It is my understanding that the mcprextreg is the resulting PCA on the motion to generate a nuisance variable for motion.

I see the following regressors clearly: my ROI, global regressor, PCA-wm, and PCA-csf. There are however, additional columns none of which line up with the mcprextreg file for that participant. Can someone explain how the mcprextreg file gets processed and entered into the X.dat file with it is used as a nuisance regressor? I have also checked the fmcpr.mcdat but I also cannot find this in the X.dat data set

~Erik Jahner