The globus pallidus (Latin for "pale body") is a sub-cortical structure in the brain. It is part of the lenticular nucleus (the other part being the putamen), which is the phylogenetically oldest part of the corpus striatum . In primates, the medial medullary lamina divides it into two parts—the internal and external segments, which form two of the major nuclei of the basal ganglia. In non-primates the two parts of the globus pallidus are even more distinct. The non-primate globus pallidus is usually considered homologous to the primate external segment of the globus pallidus, whereas the non-primate entopeduncular nucleus is often considered the homolog of the internal segment of the globus pallidus. The globus pallidus is traversed by numerous myelinated nerve fibres that give it the pale appearance for which it is named.

The external segment of the globus pallidus

The external segment of the globus pallidus consists mostly of neurons that send axons to the subthalamic nucleus, substantia nigra pars reticulata, and the internal segment of the globus pallidus, where they release the neurotransmitter GABA. It receives GABAergic inputs from the striatum and also a reciprocal glutamatergic projection from the subthalamic nucleus. It is sometimes used as a target for deep brain stimulation as a treatment for Parkinson's disease.

The internal segment of the globus pallidus

The internal segment of the globus pallidus is one of the output nuclei of the basal ganglia (the other being the substantia nigra pars reticulata). The GABA-containing neurons send their axons to various thalamic and brain stem nuclei.