Hi,
In my first-level GLM, I'm interested in a task period, which had 2 conditions (ON and OFF), with a parametric modulator (PM; a trial-by-trial subjective rating during ON and OFF conditions) for each condition. That is, the design matrix for this period had 4 regressors: ON, ON_PM, OFF, OFF_PM. In a PPI analysis, I want to know the extent of coupling with a seed region between different psychological contexts.
The first aim is to identify brain regions whose connectivity with the seed region was significantly different between ON and OFF. In gPPI, I set it as below (I think it should be correct).
P.Contrasts(1).left={'ON'}
P.Contrasts(1).right={'OFF'}
P.Contrasts(1).STAT='T'
My question is for the second aim. I want to isolate brain regions whose connectivity with the seed region (1) covaried with the parametric modulator during the ON condition, (2) covaried with the parametric modulator during the OFF condition, and (1) differently covaried with the parametric modulator between ON and OFF conditions. Any expert knows how to do? What should I enter for P.Contrasts.left and P.Contrasts.right?
Thank you very much.
Manuel
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