Dear SPM Experts,<div><br></div><div>I am trying to run a PPI analysis and want to make sure I am interpreting it the correct way.  Using the GLM, I compared two groups (Group A and Group B) using a simple task. I found that with the contrast Interest - Control Condition, Group A had greater activation in my ROI than Group B.  I then wanted to run a PPI based on this ROI.  However, Group B did not demonstrate any significant activation in the ROI in the contrast Interest - Control Condition.  So I ran a contrast with Interest - Fixation. With this contrast, both groups showed activation in my ROI.  Here are my questions:</div>
<div><br></div><div>Question 1) To me, it does not back sense to run the PPI with the Interest - Control Condition b/c with this contrast in my ROI Group B does not demonstrate significant activation - is that correct?? </div>
<div><br></div><div>Question 2) If Group A has greater activation than Group B in my ROI during the Interest - Fixation condition, how does this affect the PPI when I compare across the groups?  My understanding is that the ROI activation serves as a regressor in the PPI. So even if one group has greater activation in the ROI, this should not matter. In other words, a region with a stronger interaction in Group A vs Group B still means the that there is stronger connectivity between the ROI and the region identified in the PPI in Group A.  Is that correct?</div>
<div><br></div><div>Thanks!!!</div><div>Fred</div>
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