Contraversive eye deviation during deep brain stimulation of the globus pallidus internus

Clinical signs help determine correct electrode positioning during stereota ctic implantation for chronic high-frequency pallidal stimulation in Parkin son's diease (PD). The authors describe a patient who had marked, sustained , contraversive eye deviation caused by stimulation during pallidal surgery . The underlying mechanism is probably an excitation of fibers in the inter nal capsule by volume-conducted current spread. Such conjugate eye deviatio n is thus not necessarily an indication of incorrect electrode placement.