Hi Freesurfers,
Is there a minimum number of subjects that should be used in
isxconcat groups and subsequent glmfit analysis? I recently generated
activation maps from a group with only 2 subjects, but the resulting
image (too large to attach) is very strage. The activation patterns are
"whispy", almost looking like someone just doodled red and blue over
parts of the brain, sometimes forming hollow circles. Is this just a
consequence of only using 2 subjects or is there another problem I'm
missing. I find it strange that both of the subjects' individual maps
have rather robust (negative) activation)...much more than the group
map would suggest.
Another group of three subjects is also a bit strange (not nearly as
bad as 2) and it doesn't seem until I reach a group of 4 or 5 that
the patterns appear "normal".
For the record here are the commands I used:
isxconcat-sess -sf
/cluster/roffman/users/Stable5_PerRun/Subject_Files/Apr2011/2_FB_DEP_TT_1T3T5T7T
-d /cluster/roffman/users/Stable5_PerRun -analysis SIRP_Stable5 -c Cond1v3
-c Cond1vFix -c Cond3vFix -c Cond1v5 -c Cond1v7 -c Cond5vFix -c Cond7vFix
-hemis -o
/cluster/roffman/users/Stable5_PerRun/April_2011/2_FB_DEP_TT_1T3T5T7T
mri_glmfit --y
/cluster/roffman/users/Stable5_PerRun/April_2011/2_FB_DEP_TT_1T3T5T7T/SIRP_Stable5/Cond1v7/lh.ces.nii
--fsgd /cluster/roffman/users/fsgd/April_2011/2_FB_DEP_TT_1T3T5T7T.fsgd
--osgm --glmdir
/cluster/roffman/users/Stable5_PerRun/April_2011/2_FB_DEP_TT_1T3T5T7T/SIRP_Stable5/osgm/LH1v7
--surf fsaverage lh --fwhm 4.6
Thanks!
Adam Nitenson, B.S.
Brain Genomics Lab
Massachusetts General Hospital
niten...@nmr.mgh.harvard.edu
Phone: 617-643-3215
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