1. A method of locating the position of the subthalamic nucleus in the central nervous system of an animal comprising the steps of: a) stimulating neurons at a first central nervous system position by applying a stimulus to the brain; b) measuring the field potential evoked at a second central nervous system position; c) comparing the evoked field potential against a known characteristic evoked field potential from the subthalamic nucleus resulting from stimulation of the brain; and d) locating the subthalamic nucleus with the comparison in step c.