Help with mri analysis

I have two related but different tasks - task A and task B. I find that when you do task A regions x, y, z light up and when you do task B regions x, y, z, and w light up. As we all know all regions of the brain light up to varying degrees regardless what's going on but what I want to be able to demonstrate is that w really is a region unique to task B. I should add the data for tasks A and B were collected under different conditions so no simple 'contrast' is possible. Any help gratefully received. Philip. ******************************************************************** Philip Quinlan E-Mail: ptq1(a)york.ac.uk Department of Psychology FAX: (01904) 323181 The University of York Tel: (01904) 320000 Ext. 3135 Heslington Direct : (01904) 323135 York YO10 5DD U.K. ********************************************************************