[Freesurfer] LME contrasts

Dear FreeSurfer experts,

I am following the mass-univariate (spatiotemporal) model in the LME tutorial. My design matrix X has the following columns: intercept, time, time², group1, group1*time, group1*time², group2, group2*time, group2*time², sex, age, mean_thickness

I actually have 3 groups but group1 and group2 in X are dummy coded.

I would like to check whether there are group differences in the quadratic term but I don't understand what this command expresses and how the contrast was formed:

CM.C = [zeros(3,5) [1 0 0 0 0 0 0;-1 0 0 1 0 0 0;0 0 0 -1 0 0 1] zeros(3,5)];

Could you please explain it on the example design matrix so I can adapt it to mine?

Thank you! Clara