Hi KC

1. Volumes are typically correlated with TIV and so if you don’t care about TIV itself you probably want to include it as a nuisance variable (both cortical and subcortical)
2. Thickness does not show this correlation and typically does not need to be correlated. Surface area does, and so it should be included (possibly to the 2/3 power, perhaps someone else can comment on this?). Not sure about curvature, but I would assume not as least to first order

Cheers

Bruce

From: freesurfer-bounces@nmr.mgh.harvard.edu <freesurfer-bounces@nmr.mgh.harvard.edu> On Behalf Of Koustav Chatterjee
Sent: Monday, November 22, 2021 12:03 AM
To: Freesurfer support list <freesurfer@nmr.mgh.harvard.edu>
Subject: [Freesurfer] Requesting to clarify doubts on data analysis

        External Email - Use Caution        

Dear FreeSurfer team,

I have a few questions to clarify the confusion regarding data analysis.

1. For each subject, is it recommended to normalize the raw volumetric data by total intracranial volume? If so, is it true only for volumes of  subcortical structures or, both subcortical and cortical structures?
2.  In the same way, do I suppose to normalize

• Different cortical thickness with mean cortical thickness  
• Cortical surface area with total surface area
• Different cortical curvature with mean cortical curvature

Thank you for your time and help.

Regards,

KC