Subcortical connections of the basal ganglia

Cortico-basal ganglia-thalamo-cortical loops are believed to function for the selection of appropriate movements, actions and goals. However, de-corticated rats are able to make appropriate selections of simple movements, actions and goals. We argue here that subcortical connections with the basal ganglia make important contributions to these selections which must be incorporated into our framework of hypothesized basal ganglia function. Using the pedunculopontine tegmental nucleus (PPN) and superior colliculus (SC) as subcortical examples, we review their anatomical connections with basal ganglia, consider their hypothesized functions and discuss various ways in which these structures might functionally interact with the basal ganglia. We conclude that subcortical connections with basal ganglia might facilitate important switches to occur between slow, complex selections processed via cortico-basal ganglia loops and faster, simpler selections processed via subcortical-brainstem circuits.