The globus pallidus is a subcortical structure located deep within the brain, forming a key part of the basal ganglia. This intricate network of nuclei plays a fundamental role in controlling voluntary movement and various behaviors. Also known as the paleostriatum, the globus pallidus primarily exerts an inhibitory influence on movement regulation, helping to balance neural signals for smooth and coordinated actions.
Anatomical Position
The globus pallidus is situated deep within the cerebral hemispheres, medial to the putamen and lateral to the internal capsule. Together with the putamen, it forms the lentiform nucleus, which lies beneath the insula. Its Latin name, “pale globe,” references its paler appearance due to myelinated axons.
A thin sheet of white matter, the medial medullary lamina, divides the globus pallidus into two distinct segments: the globus pallidus externa (GPe) and interna (GPi). The GPe is positioned more laterally, while the GPi is more medial. Both segments are composed predominantly of inhibitory neurons that use the neurotransmitter GABA.
Role in Movement Regulation
The globus pallidus serves as a significant output nucleus of the basal ganglia, playing a central role in modulating motor commands. It helps in suppressing unwanted movements and facilitating desired ones. The globus pallidus receives its primary input from the striatum, which includes the caudate and putamen.
Information then flows through two main pathways, known as the direct and indirect pathways, which ultimately influence the activity of the GPi. The GPi acts as the main output of the basal ganglia, sending inhibitory signals to the thalamus. The thalamus, in turn, relays information to the motor cortex, which then initiates movement. The direct pathway generally promotes movement by reducing the GPi’s inhibitory effect on the thalamus, while the indirect pathway limits motor function by increasing GPi inhibition. This intricate interplay allows for the fine-tuning of motor control, posture, and coordination.
Clinical Significance
Dysfunction within the globus pallidus can lead to various neurological conditions, particularly movement disorders. In Parkinson’s disease, degeneration of dopamine-producing cells in the substantia nigra leads to GPi overactivity, with increased inhibition contributing to motor symptoms like rigidity and bradykinesia.
In Huntington’s disease, degeneration of striatal neurons projecting to the GPe plays a role in uncontrolled, involuntary movements, causing an imbalance in the direct and indirect pathways. The globus pallidus is also implicated in dystonia, where inappropriate GPi activity can lead to inadequate inhibition of thalamic inputs to the cortex.
Deep brain stimulation (DBS) targeting the GPi is an established treatment option for improving motor symptoms in Parkinson’s and for medication-refractory dystonia.
Beyond movement disorders, the globus pallidus has been linked to obsessive-compulsive disorder (OCD). Research suggests an imbalance in brain circuits involving the globus pallidus, striatum, and thalamus may contribute to OCD symptoms. Structural changes, like increased volume in the globus pallidus, have been observed in some individuals with OCD, particularly those with childhood-onset disease.