Dear SPMers,
I would really appreciate to get some hints, in layman's words, about a
VBM issue. Are the modulated and unmodulated analyses supposed to give the
same results? If they actually do, we can say that both volume and
concentration of that component (GM or WM) are increased/decreased in that
area. If not, how should we interpret the finding of, let's say, an
increased concentration, but not volume, of GM in the vicinity of the
caudate nucleus of group A compared to group B? If this increase of GM
concentration in group A is coupled with an increase in WM concentration
in the other group close to the same area, would I be right if I
interpreted these findings by suggesting that, despite comparable absolute
amounts of GM in the caudate nucleus of the two groups (because I did not
find any significant differences in modulated analysis), the two groups
differ for a different proportion of the two components (GM and WM) in
that area (i.e., there is a redistribution of the two components)? Does
the VBM technique allow me to speculate like that? Or should I simply
report my data without giving such an interpretation? Finally, if "volume"
means absolute amount and "concentration" means relative amount (relative
to the other components, I presume), what is the difference between the
two concepts when it comes to voxels located in area made by one component
only (e.g., the caudate nucleus, which is GM by definition)? I thank you
in advance for any comments you are going to provide me with.
Best regards,
Nicola Pannacciulli
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