Ah! It hadn't dawned on me how I can use AFNI 3d* commands with *.niml.dset objects. Noice.
After performing 3dVol2Surf with each patient's electrodes to the standard MNI surface, I combined them with:
3dcalc -a s00_lh_ecog.niml.dset -b s01_lh_ecog.niml.dset -expr 'a+b' -prefix all_lh_ecog
I then plotted that on the standard MNI surface, and it's exactly what I wanted.
Go AFNI.
Pete
