| Traditional models of basal ganglia function have de-emphasized the role of the subthalamic nucleus (STN) in information processing strategies. However, mounting evidence suggests that the STN may play an active role in the processing of motor, associative, and limbic information. While STN manipulation has arisen as an important therapeutic strategy for Parkinson's disease, it may cause unexpected non-motor side effects, due to our lack of knowledge about the STN's overall role in basal ganglia function, and in particular its role in non-motor processes like learning and reward. To assess this role, we have recorded STN neuronal activity in awake, unrestrained rats undergoing operant training, as well as following systemic administration of the psychomotor stimulant d-amphetamine. We found that STN neurons respond to a variety of task-related events, including tone stimuli, discriminative nose pokes, and reward related activity; furthermore, the nature and number of these responses are similar to those observed in concurrently recorded striatum, suggesting parallel roles for the two structures in basal ganglia function. STN responses to systemic amphetamine were mixed, with approximately 50% of neurons being excited, 45% being unchanged, while the remaining neurons were inhibited. The majority of STN excitations were reversed by systemic haloperidol, a drug known to block the behavioral effects of amphetamine. Taken together, these results suggest that, rather than acting as a passive relay for information from the striatum, the STN actually makes a more important contribution to basal ganglia function by forming one of two parallel information processing channels, each of which can respond to cortical information in an independent manner. |
