Nucleus · one in each half of the brain
Internal globus pallidus (GPi)
Also called GPi, Medial globus pallidus
The basal ganglia's main exit door, and a key target for brain pacemakers.
The internal segment of the globus pallidus is where the basal ganglia's decisions leave the building. Its cells fire nonstop, keeping the movement relays of the thalamus under a steady brake. When the striatum's "go" signal briefly silences them, the brake lifts and a movement starts. Because it sits at such a central spot, doctors target it with deep brain stimulation to calm Parkinson's symptoms and dystonia.
Where it is
The innermost part of the pale globe, beside the internal capsule and close to the thalamus.
What it does
The exit door
It is the main output of the basal ganglia, sending their final verdict to the thalamus.
A steady brake
Its cells fire constantly, keeping movement relays quiet until an action is picked.
Opening the gate
When the "go" pathway briefly silences it, the thalamus is released and the chosen movement can begin.
Sharing the job
It shares the output role with the substantia nigra pars reticulata, which handles more of the eye and head movements.
Think of it as a gate guard who keeps the gate shut until the right password, the "go" signal, arrives.
Works with
- Ventral lateral nucleus of the thalamusThe motor relay it keeps under a brake, releasing it for chosen movements.
- Ventral anterior nucleus of the thalamusAnother thalamus relay that carries its verdict up to the planning areas.
- PutamenSends it the "go" signal of the direct pathway.
- Subthalamic nucleusDrives it to brake harder when an action should be stopped.
- Substantia nigra pars reticulataIts twin output station on the other side of the internal capsule.
- HabenulaSends signals to the habenula, the brain's disappointment detector.
When it goes wrong
Deep brain stimulation
Thin electrodes placed here can ease Parkinson's symptoms and the twisting cramps of dystonia. It is one of the main targets for this treatment.
Pallidotomy
Before brain pacemakers, surgeons treated severe Parkinson's by making a tiny, deliberate lesion (a small area of controlled damage) here. It is still used in some cases.
Braking too hard
In Parkinson's disease, the GPi brakes too hard, which helps explain why starting a movement can feel so difficult.
For learning only, not medical advice. If you have a health concern, talk to a doctor.
Surprising facts
- The GPi and the substantia nigra pars reticulata are thought to be one structure that got split in two by a thick highway of nerve fibers, the internal capsule.
- Surgeons treated Parkinson's with small brain lesions like this from the 1940s through the 1960s, until the drug levodopa arrived in the late 1960s and largely replaced them.
Where the name comes from
"Internal" because it sits deeper, closer to the middle of the brain than the external segment.
Quick quiz
3 questions. Your answers are saved and come back in your daily review.
Which of these is a job of the internal segment (GPi)?
Show the answer
The exit door. It is the main output of the basal ganglia, sending their final verdict to the thalamus.
The exit door. It is the main output of the basal ganglia, sending their final verdict to the thalamus.
The internal segment (GPi) is part of which larger structure?
Show the answer
Globus pallidus. It belongs to the globus pallidus.
Globus pallidus. It belongs to the globus pallidus.
Which part fits this description? "Like a gate guard who keeps the gate shut until the right password, the "go" signal, arrives."
Show the answer
Internal segment (GPi). It is the internal segment (GPi). The basal ganglia's main exit door, and a key target for brain pacemakers.
Internal segment (GPi). It is the internal segment (GPi). The basal ganglia's main exit door, and a key target for brain pacemakers.
These parts now come back in your daily review, just before you would forget them.
Practice it and its neighbors in 3DSources
- Projections from the Basal Ganglia to Other Brain Regions, Neuroscience (Purves et al.), NCBI Bookshelf
- Deep Brain Stimulation, StatPearls, NCBI Bookshelf
- Deep brain stimulation for Parkinson's disease, Lasker Foundation
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