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 nitenson@nmr.mgh.harvard.edu Phone: 617-643-3215