The ballad of flavor, or Why my mother smells funny

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When I say my mother smells funny, I don't mean that she has an odor or can sniff out humor, but that her senses have been altered. A number of years ago, my mother slipped on a bathroom floor and hit her head. The displacement of her brain stunned her seventh nerve and severed her olfactory bulb, which convey taste and smell, respectively. For several weeks the experience of eating was like chewing textured cardboard. Her sense of texture was intact, but if she closed her eyes she couldn’t tell the difference between biting into a fresh apple and biting into a raw potato. Luckily, her taste recovered (debatable), but her smell hasn’t.

Source photograph courtesy of Pusczcynski, reformatting and alteration preformed by author.

Source photograph courtesy of Pusczcynski, reformatting and alteration preformed by author.

My mom enjoys cooking, but getting her recipes just right requires patience and volunteers (me). Even with taste, spicing is still a challenge; only the interplay of taste and smell reveals how much fresh basil, oregano and garlic properly flavors a fresh batch of tomato sauce.

Fig. 2 Not all odors become smells. Nasal odors are interpreted as smell, odors inhaled through the throat are associated with taste. Photo courtesy of Amanda Greene.

Fig. 2 Not all odors become smells. Nasal odors are interpreted as smell, odors inhaled through the throat are associated with taste. Photo courtesy of Amanda Greene.

The mouth’s taste receptors only detect 5 types of flavor: salty, sweet, sour, bitter, and savory. This paltry variety of taste buds serves as a fail- safe for rejecting contaminated foods and provides a source of satisfaction while eating1,4. When activated by chemicals in food, these receptors send signals through nerves to the brain stem. The proportion of the five types of taste receptors activated determines the perceived taste5.

Smell is considerably more complicated, with a repertoire of receptors able to distinguish a feast of 5,000 different molecules ranging from vanillin (the smell of cookies), to dimethylsulfide, a compound responsible for the “smell of the ocean”1,2. This amazing range of perception is a product of an evolutionary drive to distinguish chemicals associated with poisons, predators, people, and the palatable4.

Have you ever smelled an aroma so delicious you could almost taste it? You probably did. When you bite into food, aromatic compounds that imbue that food with its particular taste are aerosolized and inhaled though the nose from the throat1. In this instance you are smelling retronasally (through your throat, retro - backwards), and your brain associates this with taste. If you smell something orthonasally (through your nose, ortho – upright), your brain registers this as an odor1. Smell receptors, located in the roof of the nose, send signals through fragile nerves that pass through a collection of bony tunnels in the skull, called the cribriform plate, to the olfactory bulb5,6. During an impact like my mom’s, these nerves can be sheared off at the cribriform plate, thus severing the transmission of information. Signals are then compiled by the olfactory bulb and sent to the gustatory complex, the part of the brain that identifies flavor7.

The gustatory complex processes data derived from taste, the trigeminal nerve (texture), and smell, to reach a verdict on what is consumed 7,6 . My mother recalls that for several weeks after her accident, she perceived all food as textured cardboard. Her gustatory complex was receiving input only from the trigeminal nerve, only texture. To her brain nothing tasted nor smelled distinct, only bland and monotonous. She likened the cup of fresh brewed coffee she drank a few hours after her accident to drinking hot tap water. An unpleasant experience with a disappointing lack of flavor and aroma. She has since recovered her seventh nerve and with it taste, but has not reveled in the subtleties of smell, in over twenty years.

Smell enriches our sense of taste, providing flavorful context and depth to the 5 basic types of data the tongue provides. Without smell’s 5,000 distinct options, all flavors would be a combination of sweet, sour, salty, bitter, and savory. An extremely limited palette for a culinary artist like my mother.

Sources:

[1] Greene, A. (2014, March 12). The Anatomy of Flavor. http://www.decodingdelicious.com/the-anatomy-of-flavor/

[2] Agree, T., & Heinrich, A. (2004, June 26). Flavornet, http://www.flavornet.org/flavornet.html

[3] Breslin, P. (2013). An Evolutionary Perspective on Food and Human Taste. Current Biology, 23(9). doi:10.1016/j.cub.2013.04.010

[4] Evolution accounts for taste. (2014, September).  http://evolution.berkeley.edu/evolibrary/news/ 140903_hummingbirds

[5] Brody, J. E. (1992, August 03). How the Taste Bud Translates Between Tongue and Brain. http:// www.nytimes.com/1992/08/04/science/how-the-taste-bud-translates- between-tongue-and-brain.html?pagewanted=all

[6] Taste and Smell. (2012, April 1). www.brainfacts.org/sensing-thinking-behaving/senses-and-perception/ articles/2012/taste-and-smell/

[7] Araujo, I. E., & Simon, S. A. (2009). The gustatory cortex and multisensory integration. International Journal of Obesity, 33. doi:10.1038/ ijo.2009.70

[8] Puszczynski, K. (n.d.). Spaghetti [Digital image]. https://www.pexels.com/photo/food-dinner-pasta-