Mechanisms for selection of basic motor programs--roles for the striatum and pallidum.

The nervous system contains a toolbox of motor programs in the brainstem and spinal cord--that is, neuronal networks designed to handle the basic motor repertoire required for survival, including locomotion, posture, eye movements, breathing, chewing, swallowing and expression of emotions. The neural mechanisms responsible for selecting which motor program should be recruited at a given instant are the focus of this review. Motor programs are kept under tonic inhibition by GABAergic pallidal neurons (the output nuclei of the basal ganglia). The motor programs can be relieved from pallidal inhibition through activation of striatal neurons at the input stage of the basal ganglia. It is argued that the striatum has a prominent role in selecting which motor program should be called into action.