I’m trying to create ROIs for resting state analysis from each subject’s task fmri. I wanted to pick ROIs from the peak activation of the largest clusters after cluster correcting to p<0.05. The problem I ran into was how to restrict to regions that are considered “language.”

To solve this issue, I’ve made a mask from meta-analysis of the term “language.” Then I use 3dcalc to find where the meta-analysis mask and my stats file for each subject overlap. Now, my question is whether it is better to threshold to significant clusters before or after the mask. I’ve used 3dClust to make a cluster mask before intersecting with the meta-analysis mask, and the resulting clusters are pretty much the same except the peak voxel is different. Again, why is that? From a significance standpoint, what is the best approach here?

On a different note, if instead I wanted to create a group activation map for one task, how would I do that? I tried using 3dMean and it works up until about 15 subjects. As the number of subjects increases, the size of the clusters decreases until there is nothing (around 15 people). If I have closer to 40-50 subjects, how could I make a group map that would result in one or a few peak clusters?

Thank you!!