[Freesurfer] Linear regression

Hi All,

I have a dataset with two subject groups. I'm looking to see if there are different age effects on cortical thickness by diagnosis. Initially we did this by testing the interaction of two categorical variables, diagnosis and age (with a median split on age). We are now trying to look at this with age as a continuous variable, but QDEC seemingly does not allow you to look at interactions with continuous variables. Is there a way of doing this using the command line? I've looked at the Group Analysis tutorial, but haven't been able to satisfactorily answer this question. Any help would be appreciated. Thanks,

Nathan