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Dear Yuko, Let's say you have a negative estimate for a modulatory input A from Region X to Region Y. This would suggest that Region X causes a reduction in the rate of change of Region Y. This isn't exactly a negative correlation, but it matches the interpretation you are looking for. Best, Peter. From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On Behalf Of Yuko Sent: 09 March 2014 03:05 To: [log in to unmask] Subject: [SPM] About DCM design Dear SPM experts, I would like to know if I can detect negative correlations between ROIs using DCM. My hypothesis is that a neural projection from ROI(1) to ROI(2) suppresses neural activity in ROI(2) during condition A. I would like to test this hypothesis. Can I test this hypothesis using DCM (or PPI)? Any suggestion would be highly appreciated. Many thanks. Yuko