Hi all,

This might be a strange question, I controlled everything twice but….

We did an experiment with a 2 x 2 factorial design (Factor A (A1 A2) Factor B (B1 B2).

In the “normal analysis” we found a significant interaction resulting in a frontal and posterior activation.

To explore this interaction further, we extracted the signal changes which showed high signal changes for A1 and B2 compared to low signal changes in A2 B1.

In the next step we use DCM to look whether it is a top down / bottom up regulation.

Preliminary results of the DCM analysis show higher modulatory effects for condition A2 or B1 but not for that found in the interaction (A1/B2).

Can this be the case? Or is DCM and its results more or less independent from results shown in a GLM or with signal changes.

Many thanks

boris