Dear CONN toolbox experts,

Hi, I'm learning how to use CONN (version 19) for ROI-to-ROI gPPI analyses. Although I have studied the manual carefully and watched the data analysis videos shared by others, I am still not sure about some details. My questions are as follows.

1. If I have only one experimental condition, should I select ROI-to-ROI gPPI analysis or functional connectivity (weighted GLM) in the analysis type section? I have found that most of the previous studies only perform gPPI analysis when there are multiple experimental conditions.

2. If ROI-to-ROI gPPI analysis is possible, should I select "regression (bivariate)" in the analysis options section when there is only one experimental condition? Is it possible to select "correlation (bivariate)"?

Thank you very much in advance.

Best regards,

Ling

Dear Ling,

gPPI analyses allow you to estimate task-dependent connectivity, so you can still apply these analyses if you have only one task-condition -assuming there is a "baseline" reference to compare that condition to. For example, you may have an event-related design with a single finger-tapping task, and you may use gPPI to estimate connectivity related to the tapping task (the estimated gPPI interaction terms will tell you whether connectivity increases or decreases during the tapping task compared to the baseline). Of course, you cannot use gPPI to analyze a pure resting state analysis or an analysis of a task that encompasses the entire scanning session, since in those cases you do not have a "baseline" reference to compare that connectivity to.

In general weighted-GLM is often used to look at either resting-state data or task-dependent connectivity when the tasks are "long" (e.g. block designs with >10s blocks, or when comparing entire sessions/runs), and gPPI is often used to look at task-dependent connectivity when the task conditions are "short" (e.g. block-design with <10s blocks, or event-related designs)

Hope this helps clarify
Alfonso
Originally posted by Huiling Li: