Chapter 15: Taste

1. Chapter 15: Taste Taste or gustation: refers to sensations produced when substances dissolved in saliva stimulate taste receptors on the tongue and in the mouth. Flavor: includes smell, texture, temperature, and consistency (not just taste). To be tasted something must be soluble, which means dissolvable in saliva (which is a substance similar to salt water).

2. Classifying tastes “Classic” four taste categories (from Hans Henning – same guy who did smells) 1) Sour: whose threshold sensitivity is lowest at the sides of the tongue  2) Salty: whose thresh. sens. is lowest at the tip of tongue  3) Sweet: whose thresh. sens. is lowest at the tip also  4) Bitter: whose thresh. sens. is lowest at the back of tongue Umami (recently accepted 5th taste category: associated with savory, protein-rich food experiences – think cheesy, meaty pizza.

3. Anatomy of taste Some 10,000 taste buds reside in the tongue (though not in the center of tongue) housed within the columns of visible bumps or papillae and in certain parts of mouth and throat. Each bud is actually a collection of receptor cells, clumped together like a clove of garlic. 

4. Anatomy of Taste From the receptor cells small threadlike substances (microvillae) extend upward and make contact with the substances dissolving in saliva in mouth.  The responses of the microvillaeare then propagated down the receptor cell, and out nerve fibers in the tongue to the brain.  It appears that certain areas of the Parietal cortex are taste centers, where tastes are identified  It also appears that certain centers in the limbic system are simultaneously registering the affective quality of the dissolving substances.

5. Taste pathways Sensory cortex: texture, temperature aspects of flavor Insula: primary gustatory cortex OFC: secondary gustatory cortex It also appears that certain centers in the limbic system (hypothalamus, amygdala) are simultaneously registering the affective quality of the dissolving substances.

6. Primary/Secondary Gustatory Cortices Primary: found in insula, taste identification and intensity. Damage can lead to inability to identify taste experiences Secondary: OFC; has more to do with reward value of taste experience; affected by recent past food intake

7. Taste processing over time in the PGC Epoch 1: as food is first put into mouth and chewed; PGC receptors extract information about texture, temperature, consistency and other somatosensory information (not so much about actual taste). Epoch 2: 1/5 of a second later: info about taste qualities begin to be extracted Epoch 3: one second into chewing: info about palatability (is food dangerous?) is extracted.

8. Tasters and non-tasters There appear to be genetically determined differences in some taste perceptions, such as bitter. Tasters find two chemical substances (PROP and PTC) very bitter (about 2/3 of us); non-tasters have little taste experience. Key difference appears to be density of taste buds.

9. Taste adaptation and modification Adaptation: prior exposure weakens taste experience (too much chocolate cake!) Cross-adaption: can happen but usually with substances that have the same basic taste profile (sour pickles and reduce sensitivity to other basically sour foods). One exception appears to be bitter; where sour appears capable of producing an adaptation effect. Modification: prior taste alters experience of current taste (I just brushed my teeth!). Artichokes can make water taste sweet – taste aftereffects or taste illusions Taste suppression: taste of one substance is reduced because of addition of another taste. Sugar masks bitter taste of coffee

10. Role of smell in taste Aids significantly in taste identification