olfactory hallucination
   Also known as phantosmia, phantom smell, and hallucination of smell. The term olfactory hallucination is indebted to the Latin verb ol(e)facere, which means to smell. Using source localization as a guiding principle, olfactory hallucinations can be differentiated into * intrinsic and *extrinsic olfactory hallucinations, i.e. hallucinated smells attributed by the affected individual to a source within or outside the body. Both types of hallucination are notoriously difficult to distinguish from other *chemosensory disorders (notably * gustatory hallucinations) and real odours. The difficulty involved in establishing the presence or absence of olfactory hallucinations has to do with the fact that the quality of olfactory percepts depends on a number of factors. These include the prior presence of food or drink in the oral cavity, smoking, the use of perfume or other odorants, the use of therapeutics and illicit substances, and local or general medical conditions such as rhinitis, sinusitis, oral candidiasis, and influenza. As a consequence, it may be difficult to distinguish olfactory hallucinations from tastes and smells induced by a substance or disease. Second, the assessment of olfactory hallucinations is complicated by the close relationship between the senses of taste and smell, so that olfactory hallucinations can easily be confused with gustatory ones. A third difficulty involved in the assessment of olfactory hallucinations is the existence of various * smell disorders that are not strictly speaking classified as hallucinations. This group of smell disorders comprises five broad categories: anosmia, hyposmia, *dysosmia, *hyperosmia, and smell agnosia. Olfactory hallucinations can be experienced in a multitude of ways. As noted in 1911 by the Swiss psychiatrist Eugen Bleuler (1857-1939), "The schizophrenic hallucinations of taste and smell have no special characteristics. The patients taste sperm, blood, feces, and all sorts of poison in their food. Soap is tasted in the noodles; grease in the coffee. Something dusty and something bitter in taste is blown toward them. Bad smells and poisons are forced into their mouths so that they have no other recourse than to stuff their mouths full of wool or rags, till they turn blue. 'The meat stinks as if a golden egg had been squashed on it.' The room smells of corpses, of chloroform, of tar, of'snake-sweat'. The bed smells bad; it has been soiled by onion skins and tobacco. One patient smells his own masturbation. In ecstatic conditions, all sorts of pleasant odors appear. A female patient smells a heavenly taste in her mouth and nose when she attends the service of a certain minister." When olfactory hallucinations are experienced as emanating from the oral cavity, the term * hallucinated halitosis applies. Transient * stereotypic olfactory hallucinations that either precede an attack of migraine or an epileptic seizure, or occur without being followed by such a paroxysmal neurological event, are usually referred to as * olfactory aurae. When olfactory hallucinations or parosmia occur in conjunction with hallucinations in other sensory modalities or with alterations in the sense of familiarity, they can be designated - under certain conditions - as a *psychic aura. In clinical practice, olfactory hallucinations tend to call forth an association with epilepsy or migraine. However, empirical research indicates that their prevalence is much higher in individuals with a clinical diagnosis of depression, * schizophrenia, or * olfactory reference syndrome. Other conditions in the context of which olfactory hallucinations have been described include paraphrenia, delusional states, neurotic illness, organic brain disease, and toxic states. They can also occur in individuals without any demonstrable psychiatric or neurological illness. Pathophysiologically, olfactory hallucinations are associated primarily with aberrant neuronal discharges in the uncinate gyrus.
   References
   Bleuler, E. (1950). Dementia praecox or the group ofschizophrenias. Monograph series on schizophrenia no. 1. Translated by Zinkin, J. Madison, WI: International Universities Press
   Burstein, A. (1987). Olfactory hallucinations. Hospital and Community Psychiatry, 38, 80.
   Meats, P. (1988). Olfactory hallucinations. British Medical Journal, 296, 645.
   Pryse-Phillips, W.E.M. (1968). Olfactory hallucinations: A clinical study. M.D. Thesis, London.
   Pryse-Phillips, W. (1971). An olfactory reference syndrome. Acta Psychiatrica Scandinavica, 47, 484-509.
   Schiffman, S.S., Gatlin, C.A. (1993). Clinical physiology of taste and smell. Annual Review of Nutrition, 13, 405-436.
   Spitzer, M. (1988). Halluzinationen. Ein Beitrag zur allgemeinen und klinischen Psychopathologie. Berlin: Springer-Verlag.

Dictionary of Hallucinations. . 2010.

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