Hello SPM experts,
I would like to apply DCM on surface-based mean time series. Given the image data were pre-processed and modeled with FreeSurfer, I cannot use SPM to extract times series or to get the X0 matrix directly from the SPM.mat. I know I could use "spm_filter.m" to get xY.X0, but how could I acquire Y.X0 or how to calculate it? I also found that in "spm_regions.m" the Y.X0 was directly taken from SPM.xX.xKXs.X(:,[SPM.xX.iB SPM.xX.iG]). It seems Y.X0 was generated in "model estimation", is it correct? I found that if I feed the 1st-level GLM in SPM with different images (e.g. smoothed vs non-smoothed images), the Y.X0 would be different.
If the Y.X0 is not accessible without SPM, may I know that if Y.X0 influence the DCM modelling a lot or if it could be ignored? Any suggestions would be appreciated.
Thanks and best withes,