Hi Gang, thanks for your reply. Yes, I don't have groups, so 3dRegAna seems to be good for me. I have a question though, I have ran the script as Example 1 from the manual, and I seem to get always the same region of activation, no matter what dataset (before -em1z- or after -em2z- treatment) and no matter what behavioral scores I input. Below are examples of two scripts that yield very similar clusters although they are different PET datasets and different scores:

3dRegAna \
-rows 14 \
-cols 1 \
-xydata 19 ../503/em1z.nii.gz \
-xydata 18 ../505/em1z.nii.gz \
-xydata 16 ../506/em1z.nii.gz \
-xydata 12 ../510/em1z.nii.gz \
-xydata 13 ../512/em1z.nii.gz \
-xydata 17 ../513/em1z.nii.gz \
-xydata 22 ../515/em1z.nii.gz \
-xydata 5 ../516/em1z.nii.gz \
-xydata 7 ../519/em1z.nii.gz \
-xydata 20 ../521/em1z.nii.gz \
-xydata 21 ../522/em1z.nii.gz \
-xydata 15 ../524/em1z.nii.gz \
-xydata 12 ../525/em1z.nii.gz \
-xydata 19 ../528/em1z.nii.gz \
-diskspace \
-rmsmin 1.0 \
-fdisp 10 \
-model 1 : 0 \
-flof 0.01 \
-fcoef 0 em1z.constant \
-fcoef 1 em1z.linear

**OR**

3dRegAna \
-rows 14 \
-cols 1 \
-xydata 20 ../503/em2z.nii.gz \
-xydata 14 ../505/em2z.nii.gz \
-xydata 6 ../506/em2z.nii.gz \
-xydata 19 ../510/em2z.nii.gz \
-xydata 3 ../512/em2z.nii.gz \
-xydata 5 ../513/em2z.nii.gz \
-xydata 7 ../515/em2z.nii.gz \
-xydata 1 ../516/em2z.nii.gz \
-xydata 8 ../519/em2z.nii.gz \
-xydata 3 ../521/em2z.nii.gz \
-xydata 0 ../522/em2z.nii.gz \
-xydata 3 ../524/em2z.nii.gz \
-xydata 5 ../525/em2z.nii.gz \
-xydata 13 ../528/em2z.nii.gz \
-diskspace \
-rmsmin 1.0 \
-fdisp 10 \
-model 1 : 0 \
-flof 0.01 \
-fcoef 0 em2z.constant \
-fcoef 1 em2z.linear

I have ran this with other scores also and keep getting the same cluster. Do you have suggestions of what can be wrong? Thanks, Jazmin.