Dear FreeSurfers,

I would like to study the interaction between age and cortical thickness in patients and controls.

My hypothesis is that there is an interaction and that cortical thickness is decreasing faster with age in patients than in controls.

I have both Male and Female included in 6 different centers.

I would like to consider also Gender and Site (6 centers) as confounds.

My understanding is that I should perform a surface based group analysis with freesurfer.

I am not able to find an example for my problem in the documentation https://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf2G0V

Would anyone had some tips to build the Fsgd file and the contrast file ?

Thank you very much in advance.

Best,

Charles