Matthew,

> I'd like to specifically test for an interaction that captures a difference in posttreatment resting-state functional
> connectivity (rsfc) between groups when there is no difference in pretreatment rsfc between groups.

I would perform the following 5 tests, and use test 1 combined with tests 2 and 3 (or test 1 combined with tests 4 and 5) to tease apart all the scenarios (test 1 is essentially the same as the interaction F-test from 3dMVM except that it carries the directionality information):

-gltLabel 1 interaction -gltCode 1 'Group : 1*treatment_1 -1*treatment_2 Time : 1*pretreatment -1*posttreatment' \
-gltLabel 2 interaction_t1 -gltCode 2 'Group : 1*treatment_1 Time : 1*pretreatment -1*posttreatment' \
-gltLabel 3 interaction_t2 -gltCode 3 'Group : 1*treatment_2 Time : 1*pretreatment -1*posttreatment' \
-gltLabel 4 interaction_pre -gltCode 4 'Group : 1*treatment_1 -1*treatment_2 Time : 1*pretreatment' \
-gltLabel 5 interaction_post -gltCode 5 'Group : 1*treatment_1 -1*treatment_2 Time : 1*posttreatment' \

Without seeing any justification for the weight of 3 in the spreading interaction specification, I fail to understand the logic of the approach.

Gang