Could be a number of things. I'll say that it's not
THAT unusual to have activation outside of the brain. SPM tends to mask this by default. They also used to mask the cerebellum, not sure if that's ever changed. When you adjust the threshold slider to a suitable p-value, do you still see activation in areas that you would expect? Have you tried to plot the activity of a particular voxel in activated areas against the ideal or design?
It looks like your afni_proc.py has options that are usually more recommended for resting state processing (e.g. despike, motion derivatives), and less so in processing of task-based designs. You might take a look at example 6 in the
afni_proc.py help as a guideline.
Perhaps post some photos of thresholded maps vs. the SPM? A copy of your X.jpg would also be useful.
-PM
