Subthalamic nucleus influences spatial orientation in extra-personal space.

While the role of frontal and parietal cortex in spatial orientation has been studied extensively, the contribution of the basal ganglia and especially the subthalamic nucleus to spatial orientation remains less clear. Here we use subthalamic nucleus (STN) deep brain stimulation (DBS) in Parkinson's disease (PD) as a reversible model of functional lesioning to evaluate the influence of the STN in extra-personal space orientation. To this end, 12 PD patients were examined 1 year after implantation of DBS electrodes in the STN after overnight withdrawal of L-dopa. Patients were tested in a pseudo-randomized order while both stimulators, the right only, the left only, or no stimulator, were switched on. Patients performed line bisection and a reaction time task responding to stimuli of the middle, the left, and the right extra-personal space. A separate assessment of the right and left hand responding to visual stimuli in each hemispace made it possible to distinguish hemi-spatial and hemi-motor impairments. No asymmetries in space orientation were found when both stimulators were switched OFF, when both stimulators were switched ON, and when only the right stimulator was switched ON. When only the left subthalamic stimulation was switched ON, the reaction times of both hands to visual stimuli in the left extra-personal hemispace increased significantly and the line bisection test showed a significant orientation to the right. These results lead to the conclusion that the STN and its cortical projections influence the network involved in visuospatial orientation. These patterns of symptoms of neglect demonstrate the influence of the STN on the attentional system of the nondominant hemisphere.