Well, neither thickness nor surface area are gaussian to begin with, so
volume is definitely non-gaussian. I'm not sure how much difference that
will make in terms of parametric statistics. You can do permutation
using mri_glmfit-sim if you have an orthogonal design. If not, you can
use PALM b
Dear Freesurfer Experts,
A review questioned the validity of examining volume in addition to cortical
thickness and surface area within the same study. In particular, he commented
that "The volume is the product of the thickness and area ...As the product of
two Gaussian-distributed variables
