[The role of the basal ganglia in movement control]

It is now widely accepted that the basal ganglia (BG) are functionally organized with several segregated loops which start at a certain area in the cortex and project back to the same area in the cortex through the thalamus. The detailed functional organization of the BG motor loop has been described and used successfully to explain the mechanism of hypo- and hyper-kinetic disorders caused by BG disorders. Recent physiological and anatomical studies have provided new information concerning the function of these nuclei. The indirect pathway from the striatum to the external globus pallidus and then to the internal globus pallidus may be much more important than previous thought. The subthalamic nucleus may transmit excitatory input from the cortex as well as acting as a driving force on the globus pallidus. The role of BG output on the thalamus may not be to transfer information to the cortex via thalamocortical neurons, but rather to modulate the activity of cortico-thalamocortical loops. By varying it's discharge rate, the BG can change the membrane potentials of thalamocortical neurons which may result in focusing the activity of a specific cortico-thalamo-cortical loop and/or switching it to another.