Dear SPM experts,
I used traditional PPI to analyze the task dependent interaction between different brain areas. I’ve got multiple seed regions and 2 conditions, both contrasted against a baseline.
One region is activated in both conditions, but the other region only activated in one of the two conditions of interest. I can thus identify seed regions using the contrast Condition1>Baseline in which both regions are activated in each single subject. But I am interested in the change of functional connectivity between two regions as a function of the 2 psychological factors: The change between Condition1>Baseline and Condition 2>Baseline.
I thus ran 2 separate PPIs with the same timecourse, but different psychological variable (see above). How dependent are PPIs on the activity of a given brain region? Shouldn't PPIs reflected in the change of the regression slope be independent of the amount of activity? Can I test PPIs for psychological variables that do not show a change in activity in a region of interest if I safely identified individual seed regions using another contrast? What would even happen if I see deactivation of region 2 in Condition 2>Baseline?
I would greatly appreciate your thoughts within this regard,
Best wishes
Christian
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