Recordings of the parkinsonian BG. A, Sagittal view of an example trajectory (red) towards the STN, passing through the thalamus, zona incerta (ZI), and substantia nigra (SN). Microelectrode recordings (MERs; right) demonstrate typical cell recordings from these structures. The dorsolateral (0%) and ventromedial (100%) borders of the STN, as defined by MERs, were used to normalize recording locations across trajectories and STNs. a, Anterior; p, posterior. B, A triplet of targeting electrodes were simultaneously advanced, separated from each other in the anterior, posterior, medial, or lateral directions by 2 mm. Each targeting electrode comprises a macroelectrode (solid arrow) located 3 mm superior to the microelectrode (dotted arrow). Lat, Lateral; Cen, central; Post, posterior. C, Cumulative number of analyzed macroelectrode/microelectrode recordings at each recording depth across all trajectories demonstrating STN MERs.