Dear FreeSurfer experts,

thanks a lot for your solution.

It works fine.

I have some further questions to polynomial fitting with qdec, to  prevent misunderstandings from my point of view.

Only to be sure:

1) Linear effects of age: age as continuus factor.

2) Quadratic effects of age: age (quadratic) as continuus factor and age (linear) as nuisance factor.

3) Cubic effects of age: age (cubic) as continuus factor and age (linear) as nuisance factor.

4) Linear+quadratic+cubic effects together: i will have to use mri_glmfit with FSGD file.

Best wishes 

Daniel...