I found a cluster X1, which showed significant difference in cortical thickness between two groups C1 and P1, determined using mris_preproc, mri_surf2surf and mri_glmfit commands.

I am interested in determining if the same cluster X1 has significantly different cortical thickness group between two other groups P2 and P3.

I would really appreciate if you could please give me the step-by-step guidance how this can be done.

Thanks.