I want to run a GLM on the subjects Area and Thickness from the differences (Left minus Right). When stacking subjects asymmetry maps, I wanted to use a "--cache-only". 

The post at https://www.mail-archive.com/freesurfer@nmr.mgh.harvard.edu/msg27657.html seems to imply this requires running 

> recon-all -qcache -measure area -target  fsaverage_sym -fwhm 10 -no-isrunning -s subjid -hemi lh

for area at FWHM = 10.

This would create files with the left hemisphere area registered to fsaverage_sym at smoothing FWHM = 10: 

$subjid/surf/lh.area.fwhm10.fsaverage_sym.mgh

However, how do I do this also for the xhemi registration? I.e. create a file like $subjid/xhemi/surf/lh.area.fwhm10.fsaverage_sym.mgh

Then, if I do this, can I stack the subjects using something like:

Thank you.

Best,

Chintan

mris_preproc --target fsaverage_sym --hemi lh 
  --xhemi --paired-diff \

  --srcsurfreg fsaverage_sym.sphere.reg \
  --meas thickness \
  --out lh.lh-rh.thickness.sm00.mgh \
  --s subj1 --s subj2 ...