Hi Gang,
I am interested in a voxel-wise searching for regions with an imaging measure (call it variable M, could be activation, connectivity, or gray matter volume...) mediating the association between behavioral variables of B1 and B2. Specifically, I want to do a "mediation analysis", examining if the following 3 things are true:
(1) in model B1=a+b*B2+error1, b is significant
(2) in model B1=c+d*M+error2, d is significant
(3) in model B1=e+f*B2+g*M+error3, g is significant; and f is significantly smaller than b
Based on descriptions in
[en.wikipedia.org])
and
[en.wikipedia.org]
Do you think that AFNI can easily handle this "mediation" analysis with a "Sobel test"? If so, how would you specifically approach it?

I did search on this message board on similar discussions such as these:
[afni.nimh.nih.gov]
[afni.nimh.nih.gov]
[afni.nimh.nih.gov]
However, "mediation" and "moderation" were used interchangeably in these discussions, and all of your suggested solutions were for "moderation" (to examine the interaction term) but not for "mediation". Here is a clarification of the difference between these concepts:
[www.theanalysisfactor.com]

Thank you so much for your help as it has always been!