Dear FreeSurfer Developers,

I am trying to merge two atlases on the fsaverage brain for my project: aparc+aseg.mgz and brainstemSsLabels.v13.mgz. My goal is for brainstemSsLabels.v13.mgz to serve as a subdivision of the single brainstem label in aparc+aseg.mgz, so that I can obtain a more fine-grained brainstem parcellation.

Could anyone suggest a recommended way to merge these two label volumes and save the resulting atlas either through Freeview or via the command line? Thank you very much for your help.

Best,
Zoe