Directional Tolerance of Electrode Displacement in STN-DBS: An Analysis Based on Volume of Tissue Activated.

The therapeutic efficacy of deep brain stimulation for Parkinson's disease critically depends on accurate electrode placement. While previous studies have described the side effects associated with directional displacements, their direct impact on stimulation efficacy remains insufficiently characterized. This study systematically evaluated how directional electrode displacements within and around the subthalamic nucleus (STN) affect the spatial distribution of stimulation, thereby establishing a basis for defining the three-dimensional correlation between the electrode and the STN. Electrode placement and stimulation fields were modeled using the Lead-DBS toolbox. Simulations examined the volume of tissue activated (VTA) under varying displacement directions (lateral, anterolateral, anterior, anteromedial, medial, posteromedial, posterior, posterolateral) and radial distances (1.0-2.0 mm) at consistent stimulation intensities. VTAs were quantified within the STN functional subregions (motor, associative, limbic), as well as adjacent structures including the zona incerta and substantia nigra. Directional displacements produced distinct patterns of spatial overlap between the VTA and STN and adjacent regions. Notably, anterolateral displacement led to a marked reduction in VTA within the motor subregion, whereas displacements toward medial or anterior directions substantially increased VTA within the associative or limbic subregions. As the stimulation intensities increased, each electrode contact exhibited different changes in stimulation effect. The direction of electrode displacement is a critical determinant of stimulation selectivity within the STN and adjacent regions. Beyond distance, displacement direction should be considered when evaluating electrode placement accuracy. These findings provide valuable anatomical and functional insights for neurosurgeons to determine whether the placement was deemed suboptimal.