Dear SPMexperts
I need some help with the interpretation of my PPI results.
In my task, I perform a PPI analysis from seed region X (source) under condition A compared with condition B.
When I perform a one sample T test with the interaction term I donīt find any significant result (testing for both positive and negative possible effects). Nevertheless, in a whole-brain voxelwise multiple regression analysis I found that a personality score display a negative correlation with the PPI term for region Y. Previous studies have interpreted similar results as the higher the personality factor, the lower the X-Y connectivity for the condition A relative to condition B (i.e. Cremers et al. 2010)
Due to previous literature I assume that is more plausible that the direction of connectivity goes from Y to X. Following previous discussion in the SPM list the PPI can be interpreted as the contribution from Y to X but with the reverse sign.
Then, if I interpret that the direction goes from Y to X the sing of my ppi term will be reversed so the correlation with the personality factor becomes positive. I interpret this positive correlation as the higher the psychological score, the higher the contribution from Y to X activity in condition B relative to condition A. Or conversely, the higher the personality factor, the lower the contribution from Y to X activity in condition A relative to condition B.
My question is: Is there any error in the rationale of the previous paragraphs? May I get to both conclusions?
I appreciate any advice.
Thank you in advance.
Victor.