Hello,

Thanks so much for the excellent posts explaining gPPI versus weighted GLM for use with block task designs! They have been very helpful! I had some further follow-up questions that have arisen from a reviewer for a manuscript for publication.

1. I chose to do a weighted GLM but they were insisting that I do a gPPI analysis. However, I noticed in one of your posts, weighted GLM and gPPI are both perfectly valid approaches for task block designs and are about equally as prevalent in the literature. I was wondering if you know of any relevant literature that may help back up these statements?

2. I wanted to ensure that I have correctly set up my weighted GLM.

My task consists of a "trauma" block that included in each trial a a) 60 fixation period  b.) a 30 second presentation of a trauma narrative, c. a 30 second recall period, and d.) a 60 second relax period where they were asked to let go of the traumatic event

*The same structure was present in the neutral block, except the trauma narrative was replaced with a neutral narrative

In my analysis I modeled the 30 second narrative presentation, the 30 second recall period, and the 60 second recovery period for both trauma and neutral blocks. I did not model the initial 60 second fixation period. Does this seem correct?

3. I examined both "absolute" and "relative connectivity" measures. We were specifically interested in the "recall" period so I examined amygdala-whole brain resting state connectivity in relation to PTSD symptoms during both trauma and neutral recall period separately (absolute connectivity) and also looked at PTSD symptoms in relation to trauma recall relative to neutral recall resting state connectivity (1, -1 contrast; relative connectivity). Is their merits to looking at both relative and absolute measures of connectivity, or perhaps just relative?

I really appreciate any guidance! And my apologies for the long winded post!

Emily