I have a fairly simple question, but it is not immediately clear to me how to solve it. 

I have a statistical parameter map representing the results of a group-level analysis. After thresholding the map (p<.05), several significant clusters remain, and I want to assign each cluster a unique index number (e.g. 1,2,3 etc).  This unique index will be useful to me later, but it is not clear how I could do this using freesurfer tools.