I really appreciate it, I've learned a lot!
My mistake with the first question was that I thought that all fMRI data comes from the same scan, but now I understand that there are different scans that produce anatomical and functional data.
Is there any rationale for choosing a 6mm kernel?

Regarding my second question; In Table 2. in the paper by Tzourio-Mazoyer et al. they list only 45 anatomical ROIs, which I believe are identical for both hemispheres?, that would make the total number of ROIs 90. I hope you understand my point.

 - Niels