Dear Jonathan, Cyril

thanks for your answers.

Yes actually i meant parametric modulators (not regressors).

My main target is to find correlates for PB. However I also need to make sure
that the correlates are specific to PB and not to PA and potentially also not to PE.
Is it an acceptable way if I start with PB and then put PA and  PE?
Or shall I put PB at the end, with the risk that PA might absorb all variance?
What is the best way to do it?
Thanks

J