Short-latency visual input to the subthalamic nucleus is provided by the midbrain superior colliculus.

The subthalamic nucleus (STN) is one of the principal input nuclei of the basal ganglia. Using electrophysiological techniques in anesthetized rats, we show that the STN becomes responsive to visual stimuli at short latencies when local disinhibitory injections are made into the midbrain superior colliculus (SC), an important subcortical visual structure. Significantly, only injections into the lateral, but not medial, deep layers of the SC were effective. Corresponding disinhibition of primary visual cortex also was ineffective. Complementary anatomical analyses revealed a strong, regionally specific projection from the deep layers of the lateral SC to neurons in rostral and dorsal sectors of the STN. Given the retinocentric organization of the SC, these results suggest that lower-field stimuli represented in the lateral colliculus have a direct means of communicating with the basal ganglia via the STN that is not afforded to visual events occurring in the upper visual field.