[Freesurfer] Directed search for group analysis

Hello Freesurfer experts,

I've been trying to figure out a way to run a directed search in a group analysis. I read the tutorial on ROI analysis and some of the posts here, but we can only do it with individual subject. Simply pout, I want to restrict my search areas to 4 ROIs (determined from the fsaverage or common template) when I run the group analysis (thus lowering the corrected stats threshold based on search criteria). What's the best way of doing it? Also, some posts suggests using the --mask option when running the glmfit command, but it seems some people also used the --label option. What is the difference?

Thank you for your help.

Jeni