Hi Alfonso,
One more thing- output of the  spm_icalc uses the logic of 0 or 1. So the voxels of the pFDR corrected map goes through a threshold and those above it will have value 1 and others 0. The problem is the output image doesn't contain any information about how strongly the voxels are correlated ( no colour weighting if I visualize it in MRIcron). It shows a uniform colour all through out. Is there a way out to keep FDR corrected p values less than 0.05 as it is so that there is gradation of colour when I visualize it?
-Shounak