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Phantosmia is an olfactory hallucination. A hallucination is the sensory perception of something with no basis in reality, as opposed to an olfactory illusion, which is a ''misinterpretation'' of a physical stimulus; in the case of an odor it is known as parosmia. Phantosmia is the perception of a smell in the complete ''absence'' of any physical odor. The perceived odor can range from pleasant to disgusting. Although the causes of phantosmia are uncertain, it often occurs with neurological and psychological disorders such as schizophrenia, mood disorders, Parkinsons disease, epilepsy, neuroblastoma, and frequent migraines. Galen also mentioned olfactory hallucinations in his work and stated that these hallucinations constitute the signs of an oncoming disease. Different types of phantosmia include: Unirhinal (single nostril), episodic, and recurrent, where the activation of brain's GABAergic system seems to play a role in the inhibition of the unirhinal phantosmia.〔Levy, L., & Henkin, R. (2000). Physiologically initiated and inhibited phantosmia: cyclic unirhinal, episodic, recurrent phantosmia revealed by brain fmri. Journal of computer assisted tomography, 24(4), 501-520.〕 Treatments for phantosmia range from drug therapies (e.g., venlafaxine) and brain stimulation therapies to invasive surgical procedures involving removal of the olfactory bulbs or olfactory epithelium. The word phantosmia is a noun of Greek origin. It is composed of two words: (1) ''phant''- meaning "phantom" and (2) -''osmia'' (from ''osme'') meaning "smell".〔(【引用サイトリンク】title=English Word Information )〕 ==Olfactory system== The olfactory system is connected to the limbic system and gustatory system. An example of the relation between the systems is the common cold. When an individual suffers from a cold, the abilities to smell and taste are co-affected. Furthermore, the smells of food tell people if the food item is safe to consume or not; foods with unpleasant smells may be poisonous or harmful. So the sense of smell warns them away before they taste the food, or it cautions them to taste carefully, to confirm what the smell has already told us. Although this relationship exists, the olfactory system is not affected by the gustatory system. The two systems are independent and have different neuronal pathways to the brain. It is thought that the olfactory and gustatory systems were originally one and became defined and distinct over time. Odors have a strong influence on the cerebrum where the emotions are seated; thus olfaction is also related to the limbic system. The olfactory system gave rise to the limbic system. It has also been found that the olfactory and limbic systems have evolved into two different structures known as the olfactory stratium and the corpus stratium. In a study done by Dr. Alan Hirsch, it was found that gamblers spent 33–55% more money and time gambling when they were exposed to a certain odor compared to those that were not exposed to the odor.〔{(Rhawn J.). ''The naked neuron:evolution and the languages of the body and brain''. New York : Plenum Press.〕 The limbic system structures that are responsible for memory, the hippocampus and the amygdala, are part of the rhinencephalon. The nerve fibre that connects the olfactory mucosa to the olfactory bulb ends in this region of the brain. The olfactory bulb is composed of several million neurons. All olfactory messages from the olfactory limbic system are received there and are carefully organised. After this the message or signal is transmitted to other regions of the brain. Insects do not have an olfactory bulb. The olfactory nerve is composed of nasal nerve cells. These nerves link the nose and the olfactory bulb together. Accidents, damage due to surgery, infections and brain tumors may damage or destroy the olfactory nerve; this will cause the patient to lose the ability to smell and taste. This can also occur if the olfactory bulb or olfactory tract is destroyed. The olfactory tract is composed of many axons that connect the olfactory bulb and other limbic brain regions as well as temporal lobe.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「phantosmia」の詳細全文を読む スポンサード リンク
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