[Freesurfer] Multiple regression FreeSurfer

Hi,

I am interested in correlating cortical volume measures with behavioral data X1, after regressing out the effect of age and sex. For that I ran following commands:

mri_glmfit --y lh.X1.CV.15.mgh --fsgd X1.fsgd dods --C Corr-X1-cor.mtx --surf fsaverage lh --cortex --glmdir lh.X1_CV.glmdir

mri_glmfit-sim --glmdir lh.X1_CV.glmdir --cache 2 abs --cwp 0.05 --2spaces

where X1.fsgd is following:

GroupDescriptorFile 1 Class Male Class Female Variables X1 Age Input S001 Male 127 36 .... so on

and Corr-X1-cor.mtx is 0 0 0 0 1

I was wondering how can I use multiple regression approach e.g. how can I correlate CV and X1 after accounting for thickness and area or how can I correlate gyrification and X1 after accounting for CV and thickness etc.

I am not sure what will be my commands for that and what will be fsgd and mtx files?

Thanks for your help.