[Freesurfer] Demeaning Flag and DODS vs DOSS

Hello Freesurfer experts,

I am doing a whole brain analysis using mri_glmfit to determine if there is a significant difference between two groups (controls-con VS Schizophrenic -Scz). I have set up the following fsgd file: [cid:8afe40fb-8a2d-433e-9a97-5ddebc7bde68]

What I am wondering is if I should have a demeaning flag, there was not much documentation as to when or when not to do this but I was hoping I can get an answer here.

Also below is the contrast vector that I am using:

[cid:10993abb-2888-45d8-94ca-78110f8b2697]

A follow-up question would be whether to use DODS or DOSS I am still confused which model to use? The independent variable is Myelin.

Kind Regards,

Hossein Rejali