Dear Freesurfer experts, 

I want to apply FDR correction to a sig.mgh map I have loaded onto tksurfer, but noticed that the FDR-correction is inconsistent. 

When I load multiple sig.mgh overlays on tksurfer and then apply FDR correction on all layers I get the following sig.mgh map for the measure I am interested in. 

Whereas when I load just the overlay that I am interested in and apply FDR correction to that one layer, I get this FDR-corrected map: 

Is there any reason why the two FDR corrected maps are expected to differ? 

Any insight would be much appreciated.

Best, 

Amaryllis