Basal ganglia outputs and motor control.

Several lines of evidence suggest that the role of the basal ganglia in motor control is of a higher order than control of movements per se. First the striatum receives inputs from cortical areas that subserve mnemonic and other cognitive processes. Furthermore, the supplementary motor area (a zone that receives outputs from the globus pallidus via thalamus) exhibits changes in neuronal discharge and metabolic activity during movement planning as well as during movement. It is possible that this activity reflects its pallidal inputs. In addition, cells in another part of the basal ganglia, the pars reticulata of the substantia nigra, exhibit activity that reflects mnemonic as well as oculomotor and visual processes. Finally, there are striatal neurons that respond to stimuli when these stimuli trigger movement but not when responses to the stimuli are extinguished. Taken collectively, these observations are consistent with the view that the basal ganglia may provide an interface between motor centres and cortical areas for higher brain function.