Hi Markus,
the algorithm stops at -15.5 mm but that is just a line of the electrode trajectory, it doesnt say anything about the electrode position itself. You can use the coordinate of the lowermost contact (e.g. for right hemisphere stored as reco.mni.coords_mm{1}(4,:) in ea_reconstruction.mat – {2} is left hemisphere). Based on the next contact (coords_mm(3,:)) you could then easily compute the position of the tip (if you have the electrode dimensions).
For zona incerta I only know the Chakravarty atlas but it features the whole thing (not caudal ZI – handled as target for PD by e.g. Blomstedt/Plaha (but see Schmitz-Hübsch 2015 MDS and Welter 2014 Neurology) or the “zona incerta” some people refer to as the subthalamic area – handled as target for ET).
Hope that helps!
Best, Andy
