Neural activity of the globus pallidus interna and its anatomical relations to the optic tract in Parkinson's disease

Summary. Summary.   Background: To reveal landmarks for placing the globus pallidus interna (GPi) target on MR images, visual evoked potentials (VEPs) of the optic tract (OT) and neural activities of the GPi were studied retrospectively.   Methods: The dorsal and lateral border of the OT were determined by VEPs of the OT, and neural activity in the pallidal region was recorded with a semimicro-electrode in 20 patients. The Unified Parkinson's Disease Rating Scale (UPDRS) was used to assess the condition of each patient before and 6 months and 12 months after surgery.   Findings: The location of trajectories relative to the lateral border of the OT were 3 mm medial (−3) in 6, 2 mm medial (−2) in 7, 1 mm medial (−1) in 8, at the lateral border (0) in 6, 1 mm lateral (+1) in 5, 2 mm lateral (+2) in 6, and 3 mm lateral (+3) in 5. The mean amplitudes along trajectories −3 and −2 mm were significantly higher than the others (post-hoc, p<0.01). In dorsoventral relations, the amplitudes from 5.1 mm to 6.8 mm of the medial trajectories (−3 to 0 mm) were significantly higher than others (post-hoc, p<0.01). The lesions placed medial to the lateral border of the OT located just above the lateral border of the OT on postoperative MR images (n=12) and brought better surgical benefits of total motor score, rigidity and bradykinesia than those placed lateral to the OT (n=8).   Interpretation: Our data indicate that hyperactive cells of the GPi are located medial to the lateral border of the OT and at least 5.1 mm above its dorsal surface, and this corresponds to the area just above the lateral border of the OT on MR images. Published online August 12, 2002