Hi Gang (or anyone available to help me).

First, I hope this finds you well during these crazy times. Second, I am writing to you hoping that you can help me determine whether 3dMVM or 3dLME (or something else) is suited for my data. I have the following mixed factorial repeated measures event-related fMRI design:

- 5 functional runs
- 180 trials per subject
- within person variable with 2 levels: emotion
- within person variable with 2 levels: situation
- between person variable with 2 levels: nationality
- quantitative variable: time spent in the United States (a variable of interest)
- quantitative variable: age (a variable of NO interest that we’d like to control for since it is correlated with the above variable, time spent in the US)

I am interested in running whole-brain analyses that test for significant main and interaction effects for the variables of interest. Specifically, I’d like to test the following and their ensuing post-hoc comparisons:

whole-brain BOLD ~ emotion*situation*nationality

whole-brain BOLD ~ emotion*situation*[time spent in the US] + age

Importantly, if the interaction effects prove non-significant, is it safe to still interpret the main effects using 3dMVM or 3dLME? Or would I need to rerun the analyses and omit the interaction terms?

Please let me know if there’s anything I can clarify.

Thank you so much.

Joseph