The human brain is an intricate organ, orchestrating every thought, emotion, and action. Deep within its complex structure lies the globus pallidus, a small but significant component that plays a fundamental role in various brain functions. Its proper operation is important for the body’s ability to interact with its surroundings, helping to manage coordinated activity.
Its Place in the Brain
The globus pallidus is a subcortical structure located deep within the brain. It forms a central part of the basal ganglia, a group of interconnected nuclei that help regulate movement and other functions. The globus pallidus sits medially to the putamen and is bordered by the internal capsule.
This structure is divided into two distinct segments: the globus pallidus externa (GPe) and the globus pallidus interna (GPi). These two segments are separated by a thin layer of white matter known as the medial medullary lamina. The GPe is positioned more laterally, while the GPi lies medially. Both segments are composed of neurons that have an inhibitory effect on their targets.
How It Controls Movement
The globus pallidus is involved in the regulation of voluntary movement, acting as a component of the brain’s motor circuit. It primarily exerts an inhibitory influence, functioning like a “brake” or “filter” to ensure movements are smooth and coordinated. This inhibitory action balances excitatory signals from other brain regions, enabling precise motor control.
Signals from the striatum are sent to the globus pallidus. The GPi, in particular, serves as a primary output for the basal ganglia, transmitting inhibitory signals to the thalamus. The thalamus then relays information to the motor cortex, which is responsible for initiating and directing movement. This pathway ensures that only desired movements are expressed, contributing to the fluidity of everyday actions.
Disorders Linked to the Globus Pallidus
Dysfunction within the globus pallidus can contribute to several movement disorders. In Parkinson’s disease, abnormal activity in the GPi plays a role in symptoms such as tremor, rigidity, and slowed movement (bradykinesia). Deep brain stimulation (DBS) targeting the GPi is a common surgical treatment for advanced Parkinson’s disease, alleviating these motor symptoms.
The globus pallidus is also implicated in dystonia, a condition characterized by involuntary, sustained muscle contractions that lead to twisting and repetitive movements or abnormal postures. Abnormal low activity in the GPi contributes to these involuntary movements, and GPi DBS is effective in treating severe cases of dystonia. Dyskinesias, which are uncontrolled, involuntary movements often seen as a side effect of long-term Parkinson’s medication, are also influenced by globus pallidus activity. DBS targeting the GPi can help reduce these medication-induced dyskinesias.