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Dear SPM- and DCM-experts, I performed a study on healthy subjects, who received experimental pain stimuli in presence or absence of a drug. So far, I have identified three pain-relevant regions from GLM and PPI analysis and I would like to know by means of a DCM analysis on which connections the drug exerts an influence. However, there are a lot of issues I don’t know how to handle… 1. Besides of modelling a connection between to regions, is it possible to test an influence on a region itself? For instance, by testing a drug influence on the self-connection versus no influence? 2. Is it possible to modulate the direct input (pain stimuli)? 3. I am not really sure where the direct input enters the model. However, if I am only interested in the modulation of connections, does it matter where the direct input enters? Theoretically, is it possible to place the direct input anywhere just to “activate” the system? 4. Is it valid to include a region in my model isolated from all other regions of my model, i.e. without any intrinsic connections to any other region? Thank you very much for your help!! carmen