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= Lateral Globus Pallidus = The lateral globus pallidus (or external globus pallidus, GPe) combines with the medial globus pallidus to form the globus pallidus, an anatomical subset of the basal ganglia. Globus pallidus means "pale globe" in Latin, indicating its appearance. The lateral globus pallidus is the segment of the globus pallidus that is relatively further (lateral) from the midline of the brain.

The lateral globus pallidus contains GABAergic neurons, which allow for its inhibitory function. The lateral globus pallidus' GABAergic neurons extend axons to the subthalamic nucleus (in the dicencephalon), the striatum, medial globus pallidus and substantia nigra pars reticulata.

GPe is particular in comparison to the other elements of the basal ganglia by the fact that it does not work as an output base of the basal ganglia but as a main regulator of the basal ganglia system.

Function
[[File:Basal-ganglia-classic.png|thumb|Direct and indirect striatopallidal pathways: Glutamatergic pathways are red, dopaminergic are magenta and GABAergic pathways are blue. STN: Subthalamic Nucleus SNr: Substantia Nigra pars reticulata SNc: Substantia Nigra pars compacta

GPi: Medial globus pallidus ]]

Indirect Striatopallidal Pathway
The basal ganglia functions to tonically inhibit movement, mainly in the absence of motor cortex command, via GABAergic inhibition of the ventral lateral nucleus and ventral anterior nucleus of the thalamus, as well as the superior colliculus and mesopontine tegmentum of the brain stem. When movement is required, the cerebral cortex sends commands to the striatum, which directly inhibits the medial globus pallidus and substantia nigra pars reticulata, decreasing thalamus and brainstem inhibition. As the pathway from the striatum to the medial globus pallidus is monosynaptic (containing one synapse), it is called the Direct Striatopallidal Pathway.

The Indirect Striatopallidal Pathway, which contains the lateral globus pallidus and the subthalamic nucleus, functions to modulate the effects of the Direct Striatopallidal Pathway. The lateral globus pallidus acts as a inhibitory "control device", adjusting subthalamic nucleus neuronal activity via GABAergic output. .

When movement adjustment is required, striatal inhibitory GABAergic axons are sent to the lateral globus pallidus, decreasing inhibition of the subthalamic nucleus. The subthalamic nucleus' glutamatergic neurons then stimulate the Medial globus pallidus and substantia nigra pars reticulata.

This multisynaptic indirect striatopallidal pathway allows for regulated excitatory input from the subthalamic nucleus to the Medial globus pallidus and substantia nigra pars reticulata. This combines with Direct Striatopallidal Pathway inhibition in the medial globus pallidus, allowing for fine tuned basal ganglia output, and more controlled movement.

Related Pathology
Lateral globus pallidus dysfunction has been observed in the following conditions:
 * Parkinson's Disease
 * Huntington's Disease
 * Dystonia

=Medial Globus Pallidus= The medial globus pallidus (or internal, GPi) combines with the lateral globus pallidus to form the globus pallidus, an anatomical subset of the basal ganglia. Globus pallidus means "pale globe" in Latin, indicating its appearance. The medial globus pallidus is the segment of the globus pallidus that is relatively closer (medial) to the midline of the brain.

The medial globus pallidus contains GABAergic neurons, which allow for its inhibitory function. As the medial globus pallidus, along with the substantia nigra pars reticulata, forms the output of the basal ganglia, these neurons extend to the thalamus, the centromedian complex and the pedunculopontine complex.

Function
[[File:Basal-ganglia-classic.png|thumb|Direct and indirect striatopallidal pathways: Glutamatergic pathways are red, dopaminergic are magenta and GABAergic pathways are blue. STN: Subthalamic Nucleus SNr: Substantia Nigra pars reticulata SNc: Substantia Nigra pars compacta

GPe: Lateral globus pallidus ]] The medial globus pallidus acts to tonically inhibit the ventral lateral nucleus and ventral anterior nucleus of the thalamus. As these two nuclei are needed for movement planning, this inhibition restricts movement initiation and prevents unwanted movements.

The Direct Striatopallidal Pathway
The medial globus pallidus receives inhibitory GABAergic signals from the striatum when a movement requirement is signaled from the cerebral cortex. As the medial globus pallidus is one of the direct output centers of the basal ganglia, this causes disinihibtion of the thalamus, increasing overall ease of initiating and maintaining movement. As this pathway only contains one synapse (from the striatum to the medial globus pallidus), it is considered a direct pathway.

The Direct Striatopallidal Pathway is modulated by stimulation of the medial globus pallidus by the lateral globus pallidus and subthalamic nucleus, via the Indirect Striatopallidal Pathway.

Pathology
Dysfunction of the medial globus pallidus has been correlated to the following conditions:
 * Parkinson's Disease
 * Huntington's Disease
 * Tourette Syndrome
 * Tardive Dyskinesia

Deep brain stimulation
Deep brain stimulation (DBS) is a treatment by which regulated electrical pulses are sent to specifically targeted areas, and has been used on the medial globus pallidus to treat a variety of medical conditions.

DBS has been applied to patients with Tardive Dyskinesia, and the majority saw more than 50% improvement in symptoms. Tourette Syndrome patients have also benefited from this treatment, showing over 50% improvement in tic severity (compulsive disabling motor tics are symptoms of Tourette patients). The medial globus pallidus is also considered a "highly effective target for neuromodulation" when using deep brain stimulation on Parkinson's Disease patients.