Globus Pallidus Internus (GPi)
Published: Jul 17, 2023
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Updated: Jul 25, 2023
Written by Oseh Mathias
Founder, SpeechFit
The Globus Pallidus Internus (GPi) is one of the key structures in the brain and is a part of the basal ganglia. It is located lateral to the thalamus and underneath the cerebral cortex[1]. The term "globus pallidus" translates to "pale globe," which refers to its appearance, while "internus" denotes its position relative to the Globus Pallidus Externus (GPe).
The GPi plays a crucial role in the regulation of voluntary movement. It is the primary output nucleus of the basal ganglia, providing a major inhibitory output to the thalamus and other areas [3].
The main input to the GPi comes from the striatum (both the putamen and the caudate nucleus), through the direct and indirect pathways [4]. In the direct pathway, the GPi is inhibited by the output of the striatum, which is modulated by dopamine from the substantia nigra pars compacta (SNc)[5]. In the indirect pathway, the striatum inhibits the GPe, which in turn inhibits the subthalamic nucleus (STN). The STN provides excitatory input to the GPi, so the net effect of the indirect pathway is to increase GPi output [6].
Additionally, the GPi receives excitatory inputs directly from the subthalamic nucleus, and inhibitory inputs from the GPe as well [7].
The GPi, along with the substantia nigra pars reticulata (SNr), serves as a primary output center of the basal ganglia. The output is mainly inhibitory, sending GABAergic projections to several areas in the brain [8]. One of the most important projections goes to the ventral anterior (VA) and ventral lateral (VL) nuclei of the thalamus, which in turn project to the motor cortex, forming a loop known as the basal ganglia-thalamocortical circuit [9]. This circuitry plays a critical role in the modulation and execution of voluntary movements [10].
The GPi also sends inhibitory output to the brainstem, specifically to the pedunculopontine nucleus (PPN), which is involved in the control of gait and postural stability [11].
Oseh is a software engineer, entrepreneur and founder of SpeechFit. Oseh is passionate about improving health and wellbeing outcomes for neurodiverse people and healthcare providers alike.
References
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