# Extrapyramidal system
The extrapyramidal system (EPS) is a clinical and historical grouping of deep brain nuclei and descending tracts, including the basal ganglia, substantia nigra, red nucleus, subthalamic nucleus, and the reticulospinal, vestibulospinal, rubrospinal, and tectospinal tracts, that modulate posture and automatic movement outside the pyramidal (corticospinal) tract[1](https://ncbi.nlm.nih.gov/books/NBK554542/). First formulated by Johann Prus in 1898, the concept remains in everyday clinical use, especially in psychopharmacology, though movement disorder specialists consider it anatomically and physiologically ill-defined and propose replacing it with specific phenomenologic terms[1](https://ncbi.nlm.nih.gov/books/NBK554542/) • [2](https://doi.org/10.1212/cpj.0000000000200308).
| Key fact | Detail |
|---|---|
| Origin | Coined after Johann Prus's 1898 finding that disturbing the pyramidal tracts failed to prevent epileptic motor activity; also ascribed to Samuel A. Kinnier Wilson for all efferent movement control outside the pyramidal tract[1](https://ncbi.nlm.nih.gov/books/NBK554542/) • [3](https://jnnp.bmj.com/content/83/10/949) |
| Nuclei included | Caudate and putamen (the neostriatum), substantia nigra, red nucleus, subthalamic nucleus of Luys; regulation also involves cortex, cerebellum, thalamus, and reticular substance[1](https://ncbi.nlm.nih.gov/books/NBK554542/) |
| Descending tracts | Reticulospinal, vestibulospinal, rubrospinal, and tectospinal tracts terminating in the spinal cord[1](https://ncbi.nlm.nih.gov/books/NBK554542/) |
| Core mechanism | Nigrostriatal dopamine: reduced signaling causes hypokinetic disorders, excess causes hyperkinetic ones; direct (D1) and indirect (D2) striatal pathways gate thalamic output[4](https://link.springer.com/article/10.1007/s40263-024-01078-z) • [5](https://journals.physiology.org/doi/full/10.1152/nips.01363.2001) |
| Lesion contrast | Pyramidal lesions: weakness, spasticity, hyperreflexia, Babinski sign; extrapyramidal dysfunction: involuntary movements, rigidity, and immobility without paralysis[6](https://www.ncbi.nlm.nih.gov/sites/books/NBK540976/) • [7](https://rcweb.dartmouth.edu/CANlab/brainstemwiki/lib/exe/fetch.php/ch43.pdf_%3B) |
| Antipsychotic EPS prevalence | Pooled prevalence 37% (31% after sensitivity analysis); parkinsonism 20%, akathisia 11%, tardive dyskinesia 7%[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC8432767/) |
| Per-drug range | 3-year cumulative EPS incidence from 7.7% (olanzapine) to 32.8% (depot typical antipsychotics); tardive dyskinesia 2.8% to 11.1% over the same drugs[9](https://pubmed.ncbi.nlm.nih.gov/20814320/) |
## Definition and anatomical scope
The term has a specific historical trigger. In 1898 Johann Prus observed that disturbing the pyramidal tracts failed to prevent epileptic motor activity, and postulated alternative "extrapyramidal tracts" that could carry motor commands[1](https://ncbi.nlm.nih.gov/books/NBK554542/). The name was later associated with Samuel A. Kinnier Wilson, the founding editor of the *Journal of Neurology, Neurosurgery, and Psychiatry*, who used it to encompass all efferent mechanisms of movement control apart from the pyramidal tract, grouping these structures as the "dark basement of the brain"[3](https://jnnp.bmj.com/content/83/10/949).
What counts as the system varies by author. StatPearls lists the caudate nucleus and putamen (together the neostriatum), the substantia nigra, the red nucleus, and the subthalamic nucleus of Luys as the nuclei, with regulation involving the cerebral cortex, cerebellum, thalamus, and reticular substance; the tracts are the reticulospinal, vestibulospinal, rubrospinal, and tectospinal tracts[1](https://ncbi.nlm.nih.gov/books/NBK554542/). The Merck Manual instead equates the extrapyramidal system with the basal ganglia, including the substantia nigra, located deep in the forebrain and rostral midbrain, directing output mainly through the thalamus to the cerebral cortex[10](https://www.merckmanuals.com/professional/neurologic-disorders/movement-and-cerebellar-disorders/overview-of-movement-and-cerebellar-disorders).
This variability is one sign that the EPS is a grouping rather than a discrete anatomical system. A peer-reviewed history of the concept describes it as "an amalgam of disparate and often conflicting ideas with a tortuous history," persisting from the late 1890s through the neuroimaging revolution of the 1980s, and argues that using "extrapyramidal" as a surrogate for the basal ganglia or for movement disorders results from unwarranted translation of animal experimentation into clinical interpretation[11](https://www.tandfonline.com/doi/abs/10.1080/0964704X.2011.595652).
## Anatomy and circuitry
The basal ganglia proper comprise the corpus striatum, the caudate nucleus and the lenticular nuclei (putamen and globus pallidus), plus the subthalamic nucleus, the substantia nigra (pars compacta and pars reticulata), and, in more recent usage, the pedunculopontine tegmental nucleus[5](https://journals.physiology.org/doi/full/10.1152/nips.01363.2001).
**Direct and indirect pathways.** Striatal neurons of the direct pathway establish a monosynaptic inhibitory (GABAergic) connection from the putamen to the internal globus pallidus and substantia nigra pars reticulata (GPi/SNr); these medium spiny neurons carry mainly D1 dopamine receptors and coexpress the peptides substance P and dynorphin. Indirect-pathway neurons carry mainly D2 dopamine receptors and the peptide enkephalin, and project GABAergic axons to the external globus pallidus, which connects through the excitatory, glutamatergic subthalamic nucleus to the GPi/SNr[5](https://journals.physiology.org/doi/full/10.1152/nips.01363.2001). Increased direct-pathway activity inhibits GPi/SNr output, disinhibiting thalamus and brainstem targets, whereas indirect-pathway activity increases subthalamic excitation of the GPi/SNr[5](https://journals.physiology.org/doi/full/10.1152/nips.01363.2001).
The nigrostriatal dopamine pathway, projecting from the substantia nigra to the dorsal striatum, is the modulator over this circuitry: decreased dopamine signaling is associated with hypokinetic movement disorders, while excessive signaling is associated with hyperkinetic disorders[4](https://link.springer.com/article/10.1007/s40263-024-01078-z). The classic two-pathway model, in which the circuits arise from distinct populations of striatal medium spiny neurons controlling voluntary actions, has been critically reappraised in the modern literature[12](https://www.nature.com/articles/nn.3743).
## Function in motor control
Functionally, the EPS is described as a complex motor-modulation system: a set of nuclei and fiber tracts that receive projections from the cerebral cortex and send projections to the brainstem and spinal cord, controlling automatic activities, posture, and the inhibition of involuntary movements (hyperkinesias)[1](https://ncbi.nlm.nih.gov/books/NBK554542/). One concrete descending element illustrates the postural role: the lateral vestibulospinal tract originates in Deiter's nucleus of the pons, descends ipsilaterally to Rexed's laminae VII and VIII, and innervates extensor muscles that oppose gravity, maintaining erect posture[1](https://ncbi.nlm.nih.gov/books/NBK554542/).
**Cerebellar interaction.** The basal ganglia and the cerebellum may be viewed as key elements in two parallel reentrant systems that receive input from, and return their influences to, the cerebral cortex through discrete and separate portions of the ventrolateral thalamus[7](https://rcweb.dartmouth.edu/CANlab/brainstemwiki/lib/exe/fetch.php/ch43.pdf_%3B). The two systems are not cleanly separable: the extrapyramidal and pyramidal systems are extensively interconnected and cooperate in the control of movement[7](https://rcweb.dartmouth.edu/CANlab/brainstemwiki/lib/exe/fetch.php/ch43.pdf_%3B).
## How it compares with the pyramidal system
The classic dichotomy distinguished the pyramidal tract syndrome, characterized by spasticity and paralysis, from the extrapyramidal syndrome, characterized by involuntary movements, muscular rigidity, and immobility without paralysis[7](https://rcweb.dartmouth.edu/CANlab/brainstemwiki/lib/exe/fetch.php/ch43.pdf_%3B). On the pyramidal side, corticospinal tract lesions produce upper motor neuron findings: hyperreflexia, weakness, spasticity, and a Babinski sign; involvement of the corticobulbar tract adds lower facial weakness and speech changes[6](https://www.ncbi.nlm.nih.gov/sites/books/NBK540976/). Regulatory training material summarizes the functional split as pyramidal pathways controlling voluntary movement impulses from the motor cortex and the extrapyramidal system responsible for involuntary reflexes and movement coordination[13](https://cpd.mhra.gov.uk/antipsychotics/CON155606_11).
The dichotomy fails anatomically. [Betz cell](https://www.edgepedia.org/betz-cell) axons account for less than 3% of the fibers that collectively form the primate pyramidal tract, and Betz fiber branches terminate on pontine, nigral, reticular, pallidal, and even striatal structures, so the two systems share cortical origins and targets[2](https://doi.org/10.1212/cpj.0000000000200308). This interconnection is one reason the simple classification is no longer considered satisfactory[7](https://rcweb.dartmouth.edu/CANlab/brainstemwiki/lib/exe/fetch.php/ch43.pdf_%3B).
## Drug-induced movement disorders
The sequelae of dopamine D2 receptor antagonism by antipsychotics have traditionally been called extrapyramidal symptoms. The principal pathogenetic mechanism is blockade of dopamine D2 receptor signaling in the striatum, and many antipsychotics bind the D2 receptor, with different affinities and receptor-binding profiles[14](https://www.nature.com/articles/s41380-023-02203-y).
Four classic syndromes follow D2 antagonism: acute dystonia, akathisia, drug-induced parkinsonism, and tardive dyskinesia[4](https://link.springer.com/article/10.1007/s40263-024-01078-z). Their timing differs sharply. In most patients acute dystonia presents within 5 days of drug initiation, at variable locations (orofacial, ocular, neck, and trunk) and with diverse severity, while tardive dyskinesia, tardive dystonia, and tardive akathisia are delayed manifestations attributed to dopamine receptor denervation supersensitivity[15](https://pmc.ncbi.nlm.nih.gov/articles/PMC6299187/).
**Quantitative rates.** A systematic review and meta-analysis of observational studies found a pooled prevalence of antipsychotic-induced extrapyramidal side effects of 37% (95% CI 18–55%) before sensitivity analysis and 31% (95% CI 19–44%) after; subtype prevalences were parkinsonism 20% (95% CI 11–28%), akathisia 11% (95% CI 6–17%), and tardive dyskinesia 7% (95% CI 4–9%)[8](https://pmc.ncbi.nlm.nih.gov/articles/PMC8432767/). In the 3-year European SOHO cohort of 7,728 patients with schizophrenia, cumulative EPS incidence ranged from 7.7% with olanzapine to 32.8% with depot typical antipsychotics, and tardive dyskinesia incidence from 2.8% to 11.1% over the same comparison, with risperidone also carrying significantly higher EPS and TD risk than olanzapine[9](https://pubmed.ncbi.nlm.nih.gov/20814320/). A multicenter French cohort of 674 patients with schizophrenia measured lower point prevalences, 13.2% for drug-induced parkinsonism and 8.3% for tardive dyskinesia[16](https://pubmed.ncbi.nlm.nih.gov/30695288/); pooled and cohort figures differ in what they measure, so both are reported here rather than merged.
Antipsychotics are not the only culprits. Antiemetics (metoclopramide, perphenazine), antiepileptics (phenytoin, valproate), selective serotonin reuptake inhibitors (sertraline, fluoxetine), and calcium channel blockers (cinnarizine, flunarizine) are also well established causes of drug-induced movement disorders[2](https://doi.org/10.1212/cpj.0000000000200308).
**Measurement.** The Abnormal Involuntary Movement Scale (AIMS) is a 12-item observer-rated scale in which seven body regions (muscles of facial expression, lips, perioral area, jaw, tongue, upper and lower extremities, and trunk) are scored for involuntary movements from 0 (none) to 4 (severe), and it is widely considered the gold standard for tardive dyskinesia screening[17](https://www.cambridge.org/core/journals/cns-spectrums/article/from-assessment-to-intervention-evidencebased-approaches-in-tardive-dyskinesia/C2BBA94D0B540DDF0DDF91ED92B7FA61). Under the 2020 [American Psychiatric Association](https://www.edgepedia.org/american-psychiatric-association) guidelines for schizophrenia, all antipsychotic-treated individuals should be evaluated for drug-induced movement disorders at every clinical encounter, with structured assessment such as the AIMS at least every 12 months, or every 6 months for patients at high risk of tardive dyskinesia, such as older patients[4](https://link.springer.com/article/10.1007/s40263-024-01078-z). The Simpson-Angus Scale (with a cutoff of ≥0.65 for parkinsonism) and AIMS with Schooler-Kane criteria were the instruments used in the FACE-SZ cohort[16](https://pubmed.ncbi.nlm.nih.gov/30695288/); the Extrapyramidal Symptom Rating Scale also assesses the movements traditionally attributed to basal ganglia dysfunction[2](https://doi.org/10.1212/cpj.0000000000200308).
## Drug-induced versus idiopathic parkinsonism
[Drug-induced parkinsonism](https://www.edgepedia.org/drug-induced-parkinsonism) can be distinguished from [Parkinson's disease](https://www.edgepedia.org/parkinsons-disease) by several clinical and investigative features: a highly symmetrical presentation, a lack of gait and balance difficulties, a negative dopamine transporter single-photon emission computed tomography (SPECT) scan, and attenuation with dose reduction or discontinuation[15](https://pmc.ncbi.nlm.nih.gov/articles/PMC6299187/).
## Terminology debate and what has changed since 2023
Criticism of the term is long-standing and has grown. As early as 1981, a psychopharmacology review argued that because the natural history, pathophysiology, and pharmacology of individual drug-induced movement disorders are distinct, the unifying term "extrapyramidal syndrome" was obsolete and a source of confusion[18](https://doi.org/10.1097/00004714-198109000-00005). A physiology review likewise describes both the "extrapyramidal system" and "extrapyramidal syndrome" as obsolete and inaccurate terms disappearing from anatomic and clinical scenarios[5](https://journals.physiology.org/doi/full/10.1152/nips.01363.2001). A 2024 position article in *Neurology Clinical Practice* proposes that the term be retired from scientific literature and that clinicians use specific phenomenologic descriptors, such as bradykinesia, tremor, dystonia, tics, myoclonus, stereotypies, and akathisia, for hypokinetic and hyperkinetic movement disorders[2](https://doi.org/10.1212/cpj.0000000000200308). An expert panel convened in a 2024 CNS Drugs update agreed that "EPS" is non-specific for antipsychotic-related movement disorders, though "extrapyramidal disorder" remains in MedDRA terminology and product labeling[4](https://link.springer.com/article/10.1007/s40263-024-01078-z). One defensible narrow use survives in the historical literature: the extrapyramidal concept is considered valid when it strictly refers to the collection of descending fibers originating in a few discrete brainstem tegmental motor nuclei that project to the spinal cord[11](https://www.tandfonline.com/doi/abs/10.1080/0964704X.2011.595652).
**Treatment has shifted most since the term was coined.** [Valbenazine](https://www.edgepedia.org/valbenazine) and deutetrabenazine, both vesicular monoamine transporter 2 (VMAT2) inhibitors, were approved by the FDA in 2017 for tardive dyskinesia in adults, and both the APA and the [American Academy of Neurology](https://www.edgepedia.org/american-academy-of-neurology) have updated their guidelines to include VMAT2 inhibitors as first-line treatment with level A evidence[17](https://www.cambridge.org/core/journals/cns-spectrums/article/from-assessment-to-intervention-evidencebased-approaches-in-tardive-dyskinesia/C2BBA94D0B540DDF0DDF91ED92B7FA61). This changes practice in a specific way: patients can continue their stable dopamine receptor blocking antipsychotic while adding a VMAT2 inhibitor, rather than stopping the antipsychotic[17](https://www.cambridge.org/core/journals/cns-spectrums/article/from-assessment-to-intervention-evidencebased-approaches-in-tardive-dyskinesia/C2BBA94D0B540DDF0DDF91ED92B7FA61). A 2024 network meta-analysis pooling 1,817 patients across 33 randomized trials comparing 23 drugs against placebo found valbenazine 80 mg most effective (SMD −1.66, 95% CI −2.55 to −0.78), with valbenazine 40 mg (SMD −1.00) and vitamin E (SMD −0.77) also significantly better than placebo, while deutetrabenazine 36 mg and reserpine were not[19](https://link.springer.com/article/10.1007/s00228-024-03722-5). Serious adverse events reported for the VMAT2 inhibitors included mainly psychiatric symptoms such as depression, worsening of schizophrenia, and suicidal ideation[19](https://link.springer.com/article/10.1007/s00228-024-03722-5).
The disagreement over the term itself remains unresolved: anatomy-oriented references still present the EPS as a defined set of nuclei and polysynaptic tracts functioning as a motor-modulation system[1](https://ncbi.nlm.nih.gov/books/NBK554542/), while movement disorder neurologists argue it was never anatomically meaningful and should be retired in favor of phenomenologic descriptors[2](https://doi.org/10.1212/cpj.0000000000200308). The term nonetheless remains in use in regulation and product labeling, where "extrapyramidal disorder" persists in MedDRA terminology[4](https://link.springer.com/article/10.1007/s40263-024-01078-z).
## References
1. [Neuroanatomy, Extrapyramidal System (StatPearls, NCBI Bookshelf)](https://ncbi.nlm.nih.gov/books/NBK554542/)
2. [Extrapyramidal System/Symptoms/Signs Should Be Retired (Neurology Clinical Practice)](https://doi.org/10.1212/cpj.0000000000200308)
3. [Movement disorders: what lies beneath? (JNNP editorial)](https://jnnp.bmj.com/content/83/10/949)
4. [An Evidence-Based Update on Anticholinergic Use for Drug-Induced Movement Disorders (CNS Drugs, 2024)](https://link.springer.com/article/10.1007/s40263-024-01078-z)
5. [The Basal Ganglia and Disorders of Movement: Pathophysiological Mechanisms (Advances in Physiology Education)](https://journals.physiology.org/doi/full/10.1152/nips.01363.2001)
6. [Neuroanatomy, Pyramidal Tract Lesions (StatPearls)](https://www.ncbi.nlm.nih.gov/sites/books/NBK540976/)
7. [Principles of Neural Science, chapter 43 (Kandel et al.), basal ganglia](https://rcweb.dartmouth.edu/CANlab/brainstemwiki/lib/exe/fetch.php/ch43.pdf_%3B)
8. [Antipsychotic-induced extrapyramidal side effects: a systematic review and meta-analysis of observational studies](https://pmc.ncbi.nlm.nih.gov/articles/PMC8432767/)
9. [Incidence of extrapyramidal symptoms and tardive dyskinesia in schizophrenia: 36-month results from the European SOHO study](https://pubmed.ncbi.nlm.nih.gov/20814320/)
10. [Overview of Movement and Cerebellar Disorders (Merck Manual Professional)](https://www.merckmanuals.com/professional/neurologic-disorders/movement-and-cerebellar-disorders/overview-of-movement-and-cerebellar-disorders)
11. [The Unbearable Lightness of the Extrapyramidal System (Journal of the History of the Neurosciences, 2012)](https://www.tandfonline.com/doi/abs/10.1080/0964704X.2011.595652)
12. [Direct and indirect pathways of basal ganglia: a critical reappraisal (Nature Neuroscience)](https://www.nature.com/articles/nn.3743)
13. [Extrapyramidal side effects: introduction (MHRA Learning Modules)](https://cpd.mhra.gov.uk/antipsychotics/CON155606_11)
14. [Antipsychotic dose, dopamine D2 receptor occupancy and extrapyramidal side-effects: a systematic review and dose-response meta-analysis (Molecular Psychiatry)](https://www.nature.com/articles/s41380-023-02203-y)
15. [Movement Disorders Associated With Antipsychotic Medication in People With Schizophrenia: Overview of Cochrane Reviews](https://pmc.ncbi.nlm.nih.gov/articles/PMC6299187/)
16. [Prevalence of and Risk Factors for Extrapyramidal Side Effects of Antipsychotics: Results From the National FACE-SZ Cohort](https://pubmed.ncbi.nlm.nih.gov/30695288/)
17. [From assessment to intervention: evidence-based approaches in tardive dyskinesia (CNS Spectrums)](https://www.cambridge.org/core/journals/cns-spectrums/article/from-assessment-to-intervention-evidencebased-approaches-in-tardive-dyskinesia/C2BBA94D0B540DDF0DDF91ED92B7FA61)
18. [Drug-Induced Extrapyramidal Disorders—A Neuropsychiatric Interface (1981)](https://doi.org/10.1097/00004714-198109000-00005)
19. [Efficacy and safety of different pharmacological interventions in the treatment of tardive dyskinesia: a systematic review and network meta-analysis (Eur J Clin Pharmacol, 2024)](https://link.springer.com/article/10.1007/s00228-024-03722-5)
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*Topic: Encyclopedia › Life and health › Human health and medicine › Human structure and function › Nervous and sensory systems › Neuroanatomy*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
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