[Freesurfer] A question as to subcortical volumetric measurement

Dear Doug and experts

I've analyzed structural changes of the subcortical GM by using both VBM (DARTEL in SPM8) and subcortical volumemetric measurement using FreeSurfer 5.1. While there is no significant volumetric difference between the groups in VBM (corrected p<0.05), FS results showed that some subcortical GM had significant volume reductions in patients relative to controls (MANCOVA controlling for the effect of ICV, age, gender, followed by Bonferroni correction). One of the referees raised the question regarding this discrepancy between the VBM and FS findings. How can I cope with it?

Thank you in advance for your help.

Kim