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Chemosensory Malingering
Published in Alan R. Hirsch, Neurological Malingering, 2018
It is important to reiterate that the complaint of absent taste in the presence of true taste, but the absence of retronasal smell is not malingering taste loss—it just represents the confusion of physiologic synesthesia, whereby retronasal smell is interpreted as taste (Gruss and Hirsch, 2015).
Retronasal Olfaction
Published in Alan R. Hirsch, Nutrition and Sensation, 2023
Jason J. Gruss, Alan R. Hirsch
Traditionally, retronasal smell has been considered equivalent to orthonasal smell, just coming from a different direction (Wolfe et al. 2006; Voirol and Daget 1986). However, the validity of such an assumption has come under question. Retronasal olfaction has been demonstrated to evoke different sensations when odors were presented orthonasally (Frasnelli, Ungermann, and Hummel 2008). Olfactory thresholds are different: orthonasal detection threshold is lower than retronasal detection threshold. (Melzner, Bitter, Guntinas-Lichius, Gottschall, Walther, and Gudziol 2011). Projections of retronasal smell have been found to proceed to different areas of the brain than orthonasal smell (Small, Gerber, Mak, and Hummel 2005). The reason for such differences has been postulated to be due to different olfactory epithelium stimulation with orthonasal as opposed to retronasal smell, or due to different time sequences of activation (Engen 1982). Retronasal smell enhances the identification of intraoral flavor as well as intensity (Puttanniah and Halpern 2001). Such intensification has been demonstrated to have additive or superadditive influence (White and Prescott 2007). On the other hand, taste may be inhibited by retronasal smell, as has been suggested with sweet pineapple smell and its impact on bitter taste (Isogai and Wise 2013). While retronasal smell has acted to increase the perceived taste of a flavor, taste has similarly been shown to enhance the perceived retronasal olfactory component (Welge-Lüssen, Husner, Wolfensberger, and Hummel 2009). This may be through taste inhibition of retronasal olfactory adaptation (Veldhuizen, Nachtigal, Teulings, Gitelman, and Small 2010). In the above examples, congruency between taste and smell has been a major factor in retronasal smell’s impact (Labbe and Martin 2009). Retronasal smell has been shown to decrease intraoral trigeminal stimulation (Frasnelli, Heilmann, and Hummel 2004). On the other hand, retronasal smell can increase the perceived texture of food. For instance, cream odor presented retronasally increased assessment of creaminess and thickness of milk-like foods (Bult, deWijk, and Hummel 2007). However, referral of retronasal smells to the mouth occur in the absence of tastants or gustatory stimulation. For instance, if one was to inhale the aroma of vanilla or soy through a straw, and exhale through the nose, the aromas are localized to the oral cavity (Lim and Johnson 2011). Alternatively, trigeminal stimuli can act to increase retronasal smell (Dragich and Halpern 2005). The extent of retronasal smell can even impact upon true taste perception (Fujimaru and Lim 2013). Alternatively, chorda tympani anesthetization blocking taste reduces retronasal smell by 50% (Stamps and Bartoshuk 2010).
Individual Differences in Chemosensory Perception Amongst Cancer Patients Undergoing Chemotherapy: A Narrative Review
Published in Nutrition and Cancer, 2022
Alba Ruiz-Ceamanos, Charles Spence, Jordi Navarra
Smell can be experienced in one of two importantly different ways: orthonasal and retronasal (23, 24). Orthonasal olfaction occurs when we smell external aromas from the environment, while retronasal olfaction occurs when volatile aromatic odor molecules are pulsed out of from the back of the nose, especially when we swallow (e.g., when we eat or drink; see 25, 26). In the latter case, one may note that smell and taste are activated at more or less the same time, thus hindering people’s ability to distinguish between the respective inputs that are attributable to each of the senses. On the other hand, taste (gustation) refers exclusively to what can be distinguished from the stimulation of sensory receptors in the oral cavity that code for basic tastes including bitter, sour, sweet, salt, and umami. These sensations appear when a substance activates certain receptors located in the mouth (though see also 27). Finally, flavor refers to a multisensory perception of food or drink involving not only taste, but also retronasal smell (see 28) and, on occasion, the trigeminal nerve (the nerve responsible for the face and motor functions that provides sensations such as temperature, astringency, or pungency; 29) as well.