Hello, 

I've overlayed two independent meta-analytic activations. Adjusting the colours and additive overlay function, I can view which regions overlap between the two studies in a different, third colour. Is there a way to view these overlapping activations alone, i.e. without the regions that do not overlap? I can achieve this two an extent by reducing the opacity of one of the overlays so that only the overlap is viewed, but when I additionally do this to the other set of activations, the overlapping regions too loose opacity and cannot be seen. 

Best, 
Molly

First of all, you may want to try toggling "Additive Overlay Blending" on (press the "Options" button in the "Layers" panel. With this mode, regions where green and red overlap will appear a salient yellow. This allows people to visualize the regions where there is only one of the two activations, as well as regions where they are both seen.

If you want to do something more complex, you will want to create your intersection image using a simple script. With Matlab you could use my scripts: use the nii_thresh to threshold each image, and then use nii_mask to find the intersection:
  https://github.com/rordenlab/spmScripts
You could also do this with a Python script. If you are not familiar with these, you could ask on the NeuroStars web site.
  https://neurostars.org