Hi Elisabetta, The cortex measure (surface-based) reported in the aseg.stats file would be best. See this site for details on various morphometry measures:

https://surfer.nmr.mgh.harvard.edu/fswiki/MorphometryStats

-Louis

On Thu, 5 Jun 2014, Elisabetta del Re wrote:

Dear Freesurfer team,what is the best measure for neocortical gray matter from the FS output? Thank you so much, best, Elisabetta