I'm working on a DCM project. So far the best fitting model looks like this:
DI--->R1 ==> R2 ==> R3
* there are three regions, with intrinsic connections from R1 to R2 and R2 to R3
* there is one driving input DI acting on R1
* there are two modulatory connections MI1 and MI2 acting on the two between-regions intrinsic connections
(The experimental variables for MI1 and MI2 are identical.)
At the group level, the second connection (R2 ==> R3) is significant, but the first (R1 ==> R2) isn't. Conceptually, this doesn't make sense, insofar as the only way the system perturbations introduced by the DI can get to (R2 ==> R3) is through (R1 ==> R2).
Does this reduce the credibility of the model? Or is it alone not enough to do that because of the possible vagaries of what is significant?