Hi,
I have recently conducted several analyses using FSL-FIRST. I am questioning myself however about the between-group results I tend to have with subcortical structures. Indeed, in many structures, results appear as opposite-sign clusters. For instance, I can get one cluster whose scalar values may be negative as well as an opposite cluster, not always symmetrical but almost, showing positive scalar values. Is this a spurious effect that has been observed in FSL-FIRST analyses before such as consequence of some abnormalities in preprocessing? Does it necessarily suggest problems with the data? Am I wrong to interpret it as a combination of shape displacement and expansion? I did check every step of preprocessing and haven't found any 'abnormalities'.
I always used vertex analysis with --useReconMNI option.
Thank you very much,
Shady
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