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Thanks so much for the reply.

I am performing linked-ICA on cortical thickness, grey-/white matter contrast (GWC), and cortical surface area, and I must admit I sampled the surfaces onto fsaverage in an identical way across modalities using surf2surf. I have attached the code for fsaverage re-sampling of area. 

While I found a global signal for GWC and thickness in my analyses, I found no global signal for surface area (and also no main effect of sex which was unexpected).

So if I understand correctly:
-my results are probably off as I have not performed the Jacobian correction that retains the information of global surface area when mapping onto fsaverage using surf2surf?  
-Is there a "Jacobian flag" that can be added to the surf2surf code? If else it appeared that the correction is default if running mri_preproc on area,​ is that correct? 

Thanks so much for helping me out with this, I really appreciate it!
Linn 


From: freesurfer-bounces@nmr.mgh.harvard.edu <freesurfer-bounces@nmr.mgh.harvard.edu> on behalf of Greve, Douglas N.,Ph.D. <DGREVE@mgh.harvard.edu>
Sent: 07 October 2019 16:50
To: freesurfer@nmr.mgh.harvard.edu
Subject: Re: [Freesurfer] Main effect of sex for total surface area, but not for summed vertex-wise surface area
 
How did you map the area to fsaverage? If you don't do it properly, you can get some funny results because area has to be jacobian corrected.

On 10/3/2019 8:03 AM, Linn Christin Bonaventure Norbom wrote:

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Hello all Freesurfer experts!

 

 Through my analysis I found that, if I plot the "white surface total area" found in subjid/stats/?h.aparc.stats by sex, I as expected find that males have overall larger surface area as compared to females.

 

When plotting the summed verticies of ?h.area for each person on the other hand (albeit after mapping the ?h.area to fsaverage), this main association with sex is not at all present. I am a bit puzzled by this and I am wondering if some sort of global scaling is performed when computing vertex-wise surface area? So that corresponding differences in vertex-wise area are relative sex differences?  

 

I understand that area at a single vertex does not hold biological relevance in the same way that for instance thickness does, but unfortunately I still don't quite understand the differing sex associations between aparcs total surface area and the summed vertex-wise surface area.

 

Thanks so much in advance!
Kind regards Linn


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