page_title: Basal ganglia disease
section_title: Basal ganglia circuits
hierarchical_section_title: Basal ganglia disease / Basal ganglia circuits
context_page_description: Basal ganglia disease is a group of physical problems that occur when the group of nuclei in the brain known as the basal ganglia fail to properly suppress unwanted movements or to properly prime upper motor neuron circuits to initiate motor function. Research indicates that increased output of the basal ganglia inhibits thalamocortical projection neurons. Proper activation or deactivation of these neurons is an integral component for proper movement. If something causes too much basal ganglia output, then the ventral anterior and ventral lateral thalamocortical projection neurons become too inhibited, and one cannot initiate voluntary movement. These disorders are known as hypokinetic disorders. However, a disorder leading to abnormally low output of the basal ganglia leads to reduced inhibition, and thus excitation, of the thalamocortical projection neurons which synapse onto the cortex. This situation leads to an inability to suppress unwanted movements. These disorders are known as hyperkinetic disorders.
  Reasons for abnormal increases or decreases of basal ganglia output are not yet well understood.
context_section_description: The basal ganglia is a collective group of structures in the brain. These include the striatum, (composed of the putamen and caudate nucleus), globus pallidus, substantia nigra, and the subthalamic nucleus. Along with other structures, the basal ganglia are part of a circuit that is integral to voluntary motor function. It was once believed that the primary function of the basal ganglia was to integrate projections from the cerebral cortex, and project information via the thalamus to the motor cortex. New research shows that the basal ganglia can be modeled as a group of components of parallel, reentrant cortico-subcortical circuits, which originate in cortical areas, traverse the basal ganglia and terminate in specific areas in the frontal lobe.  These areas are thought to control not only motor function but also oculomotor, prefrontal, associative, and limbic areas. Understanding these circuits has led to breakthroughs in understanding the disorders of the basal ganglia.
caption: Main circuits of the basal ganglia. Picture shows 2 coronal slices that have been superimposed to include the involved basal ganglia structures. + and - signs at the point of the arrows indicate respectively whether the pathway is excitatory or inhibitory in effect. Green arrows refer to excitatory glutamatergic pathways, red arrows refer to inhibitory GABAergic pathways and turquoise arrows refer to dopaminergic pathways that are excitatory on the direct pathway and inhibitory on the indirect pathway.