Steffi,

The effects of Task A and Task B separately tell you how each task behaves
relative to the implicit baseline. If one is positive then the slope of the
relationship is greater than baseline. If one is negative then the slope of
the relationship is less than baseline.

I haven't run the simulations to test if you can add the seed region beta
to the individual tasks to get an overall measure of if the connectivity is
positive or negative, but it is on my to do list. From a theoretical
perspective, it should work, but there may be some issues with the
collinearity between the task and seed regressors that could lead to poor
estimates.

I'll work on coming up with some test cases that could be used to validate
the idea of adding the task connectivity to the baseline connectivity to
get more of an absolute positive/negative connection.

Keep in mind, at rest, most areas are positively coupled unless you regress
out the GSR. It's only then do you really see the negative connectivity. I
would not be surprised that the connectivity is always positive.

When I talk about PPI I talk in terms relative to the other conditions and
relative to baseline in the same way I talk about activation in terms
relative to the other conditions and relative to baseline. We know that
there is never negative neural activity (just neural activity less than
baseline).