Brainstem
Page most recently updated 7 September 2026
This page focuses on the neuropsychiatric manifestations associated with lesions of the brainstem. Although brainstem lesions most commonly produce sensorimotor and autonomic deficits, disruption of specific brainstem and connected networks can also result in psychiatric syndromes, including peduncular hallucinosis and pseudobulbar affect.
Psychiatric, cognitive, and behavioural effects of lesions may also arise through mechanisms other than network disruption; the potential contribution of these mechanisms can be considered using the Neuropsychiatric Effects of CNS Structural Abnormalities (NECSA) classification.
On this page:
1. Rostral midbrain
2. Basis pontis
Brainstem
The brainstem viewed from the sagittal, lateral, and posterior aspects.
Image credit: Upper image adapted from Gray's Anatomy of the Human Body (20th edition, 1918). Public domain. Lower images adapted from Sobotta's Atlas of Human Anatomy, edited from the 8th German edition by J. Playfair McMurrich (1930), via the Wellcome Collection. Public Domain Mark. Composite figure created by combining and modifying images from the above sources. Title and caption modified.
Middle cerebellar peduncle
This illustration shows the middle cerebellar peduncle (coloured red), which carries pontocerebellar fibres forming part of the frontopontocerebellar pathway.
Image credit: Adapted from Gray's Anatomy of the Human Body (20th edition, 1918). Public domain.
1. Rostral midbrain → peduncular hallucinosis
Lesions affecting the rostral midbrain, particularly the tectum and adjacent tegmentum, including transient ischemic events, may cause complex visual hallucinations known as peduncular hallucinosis. Lesions involving the caudal midbrain and pontine tegmentum have also been associated with auditory hallucinations.
2. Basis pontis → pseudobulbar affect (pathological laughter and crying)
The basis pontis is the structure most consistently associated with pseudobulbar affect (pathological laughter and crying). Discrete lesions of the paramedian basis pontis, particularly following stroke, can produce involuntary episodes of laughing or crying that are disproportionate or incongruent with the patient's underlying emotional state. Similar symptoms have also been reported with cerebellopontine angle and posterior fossa tumours, multiple sclerosis, and multiple system atrophy. In addition to the basis pontis, pseudobulbar affect has also been associated with lesions affecting other components of the frontopontocerebellar pathway, including the cerebellum, cerebral peduncles, and internal capsule.
Clinical reminder: consider NECSA mechanisms
(Neuropsychiatric Effects of CNS Structural Abnormalities)
When a structural lesion is identified in a patient presenting with neuropsychiatric symptoms, consider which NECSA mechanisms may explain these symptoms:
● Network disruption
Disruption of functional networks due to the presence of the lesion
● Electrical disturbance
Ictal, preictal, postictal, or interictal effects due to epileptic activity associated with the lesion (particularly if involving or adjacent to cortex)
● Chemical (endocrine) effects
Hormone excess or deficiency caused by the lesion (particularly if involving the pituitary gland or hypothalamus)
● Side effects of treatment
Effects of medications, surgery, radiotherapy, or other interventions
● Alternative explanations
The lesion may be incidental, or symptoms may arise from another cause (e.g., psychological response to illness or a comorbid psychiatric condition)
Selected references and further reading — Lesional lens
Rohlfing T, Zahr NM, Sullivan EV, Pfefferbaum A. The SRI24 multichannel atlas of normal adult human brain structure. Hum Brain Mapp. 2010;31(5):798–819.
Clark DL, Boutros NN, Mendez MF. The brain and behavior: an introduction to behavioral neuroanatomy. 4th ed. Cambridge: Cambridge University Press; 2018.
Brazis PW, Masdeu JC, Biller J. Localization in clinical neurology. 7th ed. Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins; 2016.
Blumenfeld H. Neuroanatomy through clinical cases. 3rd ed. New York: Oxford University Press; 2021.
Hassan I. The neuropsychiatric effects of CNS structural abnormalities (NECSA) classification: an aid to differential diagnosis. Aust N Z J Psychiatry. 2015;49(10):943.
Arciniegas DB, Yudofsky SC, Hales RE, editors. The American Psychiatric Association Publishing textbook of neuropsychiatry and clinical neurosciences. 6th ed. Washington (DC): American Psychiatric Association Publishing; 2018.
Agrawal N, Faruqui R, Bodani M, editors. Oxford textbook of neuropsychiatry. Oxford: Oxford University Press; 2020.