My goal is to compare the difference in power between two groups for all the vertices in the head model (using warped ICBM152 anatomies).
I have made a mixed head model consisting of the default cortex (constrained) and the thalamus (unconstrained). So in anatomy view, each of my subjects have a head model consisting of 16557 vertices (15002 for the cortex and 1555 for the thalamus). Subsequently I have warped each subject's anatomy using the polhemus head points. Then I created a source model (Minimum Norm) and computed the average power in a frequency band. This worked well for each individual, resulting in the figure below (this is one subject with 1 value for every vertex):
However, the number of values (when I click view file contents) is different from what I expected; 14475 in stead of 16557. Also, for every subject the number of values varies (14474, 14450, 14480, etc). Am I doing something wrong or do you know what causes the difference in number of values?
From the tutorial I understood that I should not have to project the results back on the default anatomy for the group analysis, because I'm using warped templates. However, because I had a different number of values for each subject, I did try this. This worked well, however the number of values again didn't make sense to me (15386) and I'm not sure how reliable this group average would be?
I hope my question is clear, if not please let me know!