- peduncular hallucination
- Also known as peduncular hallucinosis, pedunculopontine hallucinosis, Lhermitte's hallucinosis, Lhermitte syndrome, *brainstem hallucination, and mesencephalic hallucinosis. The eponyms Lhermitte's hallucinosis and Lhermitte syndrome refer to the French psychiatrist Jean-Jacques Lhermitte (1877-1959), who is credited with being the first to describe the concomitant phenomenon in 1922. The eponym Lhermitte syndrome was introduced in or shortly before 1936 by the Swiss neurologist Georges de Morsier (1894-1982). The term peduncular hallucination is indebted to the Latin noun pedunculus,which means stalk or stem. It refers to a stalk-like connecting structure in the upper brainstem called the pedunculus cerebri. The term peduncular hallucination and its synonyms are used to denote a vivid type of hallucination, often *visual or * compound in nature, the mediation of which is attributed to aberrant neuronal discharges in or around the rostral brainstem. The term peduncular hallucination was introduced in or shortly before 1924 by the Belgian neuropathologist Ludo van Bogaert (1897-1989). In 1922, Lhermitte had published a paper on dreamlike perceptual phenomena occurring in waking subjects suffering from rostral brainstem pathology. In 1924 and 1927, van Bogaert described a series of similar cases to which he gave the name peduncular hallucination. Peduncular hallucinations have historically been envisaged as complex, lively, and often brightly coloured visual hallucinations which may last for seconds to several hours. They often consist of people (typically but not always described as walking in file), faces (i.e. *facial hallucinations), animals (i.e. *zoopsia), and landscapes. The hallucinations in question can be realistic, distorted, or fantastic in nature, and appear in a regular or a miniature format (i.e. *microptic hallucinations). Pathophysiologically, they are believed to occur as a consequence of lesions or functional aberrations within the pedunculus cerebri (previously designated as the brain's dream centre), the midbrain, pons, or diencephalon. More specifically, they are believed to correlate with a dysfunction of the third nerve nucleus, the red nucleus, the superior colliculus, the periaqueductal grey matter, the substantia nigra, and the pulvinar. Some authors suggest that peduncular hallucinations are typically accompanied by a sleep disturbance, whereas others attribute them exclusively to the neuroanatomical lesions themselves. De Morsier has been credited with expanding the scope of the notion of peduncular hallucination to include hallucinatory percepts attributed to thalamic lesions. Etiologically, peduncular hallucinations are associated with any type of pathology capable of affecting said structures, including infectious disease, vascular disease, vascular malformations, and neoplasms. They have also been reported in the context of paroxysmal neurological disorders such as migraine and epilepsy, in individuals with a clinical diagnosis of * schizophrenia or dementia, in multiple sclerosis, in the context of traumatic brain lesions, as a consequence of iatrogenic lesions caused by regional surgery or angiography, and as side effects of dopaminergic and anticholinergic medication. A type of hallucination considered closely akin to the peduncular hallucination (i.e. in a conceptual and patho-physiological sense) is known as *brainstem auditory hallucinosis. In addition, a relationship has been suggested with visual hallucinations occurring in the context of * Charles Bonnet syndrome, and with the groups of *lilliputian and * gulliverian hallucinations (i.e. visual or compound hallucinations depicting people or animals of a disproportinally small or large size). Because of its emphasis on the involvement of a specific brain structure (i.e. the pedunculus cerebri or one of its surrounding midbrain structures), the peduncular hallucinosis model may be classified as a * topological model of hallucinatory activity.Referencesffytche, D.H. (2007). Visual hallucinatory syndromes: Past, present, and future. Dialogues in Clinical Neuroscience, 9, 173-189.Leo, R.J., Stievater Ahrens, K. (1999). Visual hallucinations in mild dementia. A rare occurrence of Lhermitte's hallucinosis. Psycho-somatics, 40, 360-363.Lhermitte, J. (1922). Syndrome de la calotte du pédoncule cérébral. Les troubles psychosensoriels dans les lésions du mésocéphale. Revue Neurologique, 2, 1359-1365.Noda, S., Mizoguchi, M., Yamamoto, A. (2003). Thalamic experiential hallucinosis. Journal of Neurology, Neurosurgery and Psychiatry, 56, 1224-1226.Van Bogaert, L. (1927). L'hallucinose pédoncu-laire. Revue Neurologique, 47, 608-617.
Dictionary of Hallucinations. J.D. Blom. 2010.