EFFECTS OF SUBTHALAMIC NUCLEUS LESIONS ON PALLIDAL DISCHARGE IN THE PRIMATE

In order to gain a better understanding of the pathophysiology of hemi ballismus in primates and to test directly the hypothesis that the sub thalamic nucleus (STN) provides an excitatory drive on globus pallidus (GP) neurons, we recorded neuronal activity in GP in two awake monkey s before and after ibotenic acid lesions of the STN. Neurons were syst ematically recorded from both pallidal segments before and after lesio ning while the monkeys performed a simple holding 'torque' task. We fo und that, consistent with the proposed scheme, the tonic discharge rat es of neurons in both segments of GP were significantly reduced follow ing STN lesions. The percentage of cells responding to torque applicat ion decreased in both segments of GP after lesioning. These findings s upport the view that the STN provides excitatory input to both segment s of GP and provides further evidence for the hypothesis that hyperkin etic disorders result from a decrease in pallidal output.