The Globus Pallidus External Segment (GPe) is a major component of the basal ganglia indirect pathway and plays critical roles in movement control, motor learning, and the pathophysiology of movement disorders including Parkinson's disease, Huntington's disease, and dystonia. The GPe serves as a central hub integrating information from the striatum and sending outputs to the subthalamic nucleus (STN) and striatum, making it essential for proper motor function[1][2].
The GPe is composed primarily of GABAergic projection neurons that inhibit their target structures. These neurons exhibit characteristic firing patterns that change in disease states, providing insights into basal ganglia dysfunction and serving as targets for therapeutic interventions including deep brain stimulation[3][4].
The basal ganglia constitute a group of subcortical nuclei that play crucial roles in motor control, procedural learning, and habit formation. The GPe occupies a pivotal position in the indirect pathway:
Cortex → Striatum (D2) → GPe → STN → GPi/SNr → Thalamus → Cortex
↑ ↓
└──────────────────────────────────────────────┘
Direct Pathway (D1)
The indirect pathway through the GPe regulates movement inhibition[5][6]:
The balance between direct (facilitating movement) and indirect (suppressing movement) pathways determines motor output. GPe dysfunction disrupts this balance, leading to movement disorders.
GPe neurons are predominantly GABAergic, using gamma-aminobutyric acid as their primary neurotransmitter[7]:
| Property | Characteristic |
|---|---|
| Neurotransmitter | GABA |
| Receptors | GABA-A, GABA-B on targets |
| Vesicular transporter | VGAT |
| Synthesis enzyme | GAD65/67 |
| Firing pattern | High baseline (tonic) |
GPe neurons co-release neuropeptides that modulate their effects[8]:
GPe neurons exhibit characteristic firing patterns that can be classified into[4:1][9]:
Parkinsonian GPe shows altered firing patterns[10][11]:
| Property | Normal | Parkinson's |
|---|---|---|
| Firing rate | 50-70 Hz | 30-50 Hz |
| Pattern | Regular | Irregular, bursts |
| Oscillations | Low | Beta oscillations |
| Synchrony | Low | High |
| Response to input | Normal | Reduced |
The decreased GPe activity in PD due to increased striatal inhibition results in reduced inhibition of the subthalamic nucleus, leading to excessive STN and GPi output, which drives the hypokinetic features of Parkinson's disease.
The GPe receives input from several brain regions[6:1][12]:
GPe sends projections to several targets[12:1][13]:
Recent research has revealed diversity within the GPe neuron population[14]:
GPe dysfunction is central to PD pathophysiology[10:1]:
GPe neurons are affected in HD[15]:
GPe plays a complex role in dystonia[16]:
The GPe is a target for deep brain stimulation in several conditions[18]:
The Globus Pallidus External Segment represents a critical node in the basal ganglia motor circuit. GPe neurons integrate inhibitory input from the striatum and send GABAergic projections to the subthalamic nucleus and striatum, playing essential roles in movement control and action selection. Understanding GPe physiology and its alterations in disease states provides insights into the pathophysiology of movement disorders and informs therapeutic strategies.
Albin RL, et al. The anatomy of basal ganglia disorders. Trends Neurosci. 1989. ↩︎
DeLong MR, Wichmann T. Circuits and circuit disorders of the basal ganglia. Arch Neurol. 2007. ↩︎
Grafton ST, Turner RS. The role of the globus pallidus in movement disorders. Adv Neurol. 2014. ↩︎
Kita H, et al. Firing activity of globus pallidus externa neurons in normal and Parkinsonian conditions. J Neurophysiol. 2006. ↩︎ ↩︎
Kravitz AV, et al. Regulation of movement by the basal ganglia. Nat Rev Neurosci. 2010. ↩︎
Parent A, Hazrati LN. Functional anatomy of the basal ganglia. II. The place of the striatopallidal segments. Brain Res Rev. 1993. ↩︎ ↩︎
Kita H. Neuropeptides in the globus pallidus. Prog Brain Res. 2007. ↩︎
Kawaguchi Y, et al. Parvalbumin and somatostatin in the globus pallidus. J Comp Neurol. 1993. ↩︎
Raz A, et al. Neuronal firing pattern of the external segment of the globus pallidus in parkinsonism. J Neurophysiol. 2000. ↩︎
Blandini F, et al. Functional anatomy of the basal ganglia in Parkinson's disease. Mov Disord. 2000. ↩︎ ↩︎
Tachibana Y, et al. Gamma oscillations in the globus pallidus external segment. Brain. 2011. ↩︎
Nambu A, et al. Extrapyramidal motor functions of the basal ganglia. Front Neuroanat. 2011. ↩︎ ↩︎
Beurrier C, et al. Subthalamic nucleus receives input from the globus pallidus. Eur J Neurosci. 2006. ↩︎
Mallet N, et al. Diverse population of neurons in the external globus pallidus. Nat Neurosci. 2012. ↩︎
Bird M, et al. Globus pallidus neurons in Huntington's disease. Exp Neurol. 2014. ↩︎
Guehl D, et al. Neuronal activity in the globus pallidus in dystonia. Mov Disord. 2016. ↩︎
Hutchison WD, et al. Neuronal oscillations in the globus pallidus in essential tremor. Brain. 2014. ↩︎
Vitek JL, et al. Deep brain stimulation of the globus pallidus for Parkinson's disease. Neurosurgery. 2011. ↩︎