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Taste versus Flavour Retronasal olfactory sensation: The sensation of an odour that is perceived when chewing and swallowing force an odourant in the mouth up behind the palate into the nose Chorda tympani: The branch of cranial nerve VII (the facial nerve) that carries taste information from the a...

Taste versus Flavour Retronasal olfactory sensation: The sensation of an odour that is perceived when chewing and swallowing force an odourant in the mouth up behind the palate into the nose Chorda tympani: The branch of cranial nerve VII (the facial nerve) that carries taste information from the anterior, mobile tongue (the part you can stick out). Connection between taste and smell Brain imaging studies: Brain processes odours differently, depending on whether they come from nose or mouth. Food industry: Adds sugar to intensify sensation of fruit juice Increase in sweetness (a pure taste sensation) increases perceived olfactory sensation of fruit. 4 KINDS OF PAPILLAE Papillae: Tiny structures on surfaces in the mouth, mainly on the tongue; three different types of 1. Filiform papillae: Small structures that give bumpy appearance. no taste function. 2. Circumvallate papillae: Circular structures that form an inverted V on the rear of the tongue (three to five on each side). Moundlike structures surrounded by a trench. 3. Foliate papillae: Folds of tissue containing taste buds on the rear of the tongue. 4. Fungiform papillae: Mushroom- shaped structures distributed densely on the edges of the tongue, esp. tip. On average, 6 taste buds per papilla are buried in the surface. Anatomy and Physiology of the Gustatory System Taste buds: Create neural signals conveyed to brain by taste nerves Embedded in Papillae (bumps on tongue) Each taste bud contains taste receptor cells Information is sent to brain via cranial nerves Taste buds and taste receptor cells Taste buds: Structures that contain taste receptor cells, within papillae in the mouth. Cilia: Slender projections on the tips of some taste bud cells that extend into the taste pore. Contain the sites that bind to taste substances Not tiny hairs (as the name implies): We now know they are extensions of the cell membrane Tastant: Any stimulus that can be tasted Tastants can be divided into two large categories: ◦ Some are made up of small, charged particles that taste salty or sour ◦ Small ion channels in microvilli membranes allow some types of charged particles to enter but not others Other tastants are perceived via G protein- coupled receptors (GPCRs) similar to that in the olfactory system. These molecules taste sweet or bitter Inhibition: Plays an important role in processing taste information in the brain. Function: To protect our whole mouth perception of taste when we have injuries to taste system. Descending inhibition from taste cortex blocks pain perception Has survival value because we need to eat even if our mouth has been injured The Four Basic Tastes 1. SALTY Salt is made up of two charged particles: Cation and anion. Ability to perceive salt is not static ◦ Low-sodium diets will increase in intensity of salty foods over time Liking for saltiness is not static ◦ Early experiences can modify salt preference. Chloride-deficiency in childhood leads to increased preference for salty foods later ◦ Gestational experiences may affect liking for saltiness 2. SOUR Comes from acidic substances (H+ ions). At high concentrations, acids will damage both external and internal body tissues. 3. BITTER Quinine: Prototypically bitter-tasting substance Cannot distinguish between tastes of different bitter compounds Many bitter substances are poisonous Ability to “turn off” bitter sensations—beneficial to liking certain vegetables Bitter sensitivity is affected by hormone levels in women, intensifies during pregnancy 4. SWEET Evoked by sugars Many different sugars that taste sweet: ◦ Glucose: Principle source of energy for most animals ◦ Fructose: Even sweeter than glucose ◦ Sucrose: Common table sugar. Combination of glucose and fructose Single receptor responsible for all sweet perception ◦ Different sweeteners stimulate different parts of receptor Artificial sweeteners stimulate this receptor as well The Fifth Taste: Umami Meaty Taste ◦ Comes from sensing glutamate (or in its salt form of monosodium glutamate). ◦ Glutamate: Important neurotransmitter Safety issues in human consumption: ◦ Can lead to numbness, headache, flushing, tingling, seating, and tightness in the chest if sensitive individuals consume a large amount ◦ For most people, MSG does not pose a problem in small doses The Perception of Flavour Flavour: The total sensory experience evoked by ingesting something; it includes the perception of the basic tastes, the perception of other attributes of tastants such as pleasantness and intensity, and other sensory properties, the most important of which is smell. trigeminal sense: The sense that signals the presence of irritants in the mouth, such as menthol and chili pepper; it contributes to much of the “mouth feel” of foods. Taste buds to brain 2 MODELS Labelled line model: Each cranial nerve fibre carries information about a single taste quality, from a single type of receptor Across-fibre pattern model: Cranial nerve fibres carry information about combinations of taste qualities, from multiple types of receptor Neural Coding of Tastes taste receptor cells (TRCs): Elongated neurons, packed within taste buds, that transduce tastants into neural signals. cell-to-cell signaling: In taste perception, signals from receptor cells to presynaptic cells, causing the presynaptic cells to release neurotransmitters in a way that carries information about sweet, umami, and bitter tastants. Representing Taste and Flavour in the Brain primary taste cortex: The first cortical areas to receive taste signals, consisting of the anterior insular cortex and the frontal operculum. The Pleasures of Taste Different flavoured foods placed on tips of infants’ tongues: Sweet food evokes a “smile-like” expression followed by sucking. Sour produced pursing and protrusion of lips. Bitter produced gaping, movements of spitting, and sometimes vomiting movements. Specific hungers theory: The idea that deficiency of a given nutrient produces craving (a specific hunger) for that nutrient Cravings for salty or for sweet are associated with deficiencies in those substances. However, the theory has not been supported for other nutrients, such as vitamins. Theory only holds for sweet and salty foods. Coding of Taste Quality Taste adaptation and cross-adaptation: All sensory systems show adaptation effects. Constant application of certain stimulus temporarily weakens subsequent perception. ◦ E.g. Adaptation to salt in saliva affects our ability to taste salt Cross-adaptation: When the taste of one food affects the taste of another E.g. A sour beverage tastes too sour after eating a sweet substance Genetic Variation in Taste Experience phenylthiocarbamide (PTC) tastes dramatically different to different people Bitter taste to some but not to others 1960s: Started using propylthioracil (PROP) instead of PTC because it is safer  Gene for PTC/PROP receptors discovered in 2003 Individuals with two recessive genes are nontasters of PTC/PROP Individuals with one or more of the genes are tasters of PTC/PROP Supertaster: Individual who is a taster of PTC/PROP and has a high density of fungiform papillae. Perceives the most intense taste sensations. Chili Peppers Acquisition of chili pepper preference depends on social influences Restriction of liking to humans Variability across individuals, depending on number of papillae Capsaicin: The chemical that produces the burn in chilis. Binds to TRPv1 receptors Health consequences of taste sensation Variations in sensory properties of foods and beverages affects food preferences and therefore diet. For instance, some vegetables have a bitter taste and so might be avoided by supertasters. fats also taste bitter to supertasters, causing them to eat fewer high- fat foods. Duffy et al (2005) showed that among men getting routine colonoscopies, those tasting PROP as the most bitter had the most colon polyps. Pleasure and retronasal versus orthonasal olfaction Orthonasal olfaction: Olfaction through the nostrils Do we learn to like or dislike smells separately for retronasal versus orthonasal olfaction? Possibly E.g. Many people like the smell of freshly cut grass, but wouldn’t want to eat it However, if an aversion is acquired retronasally, it usually shows up orthonasally as well: E.g. Becoming sick from drinking Tequila and then disliking even the smell of Tequila. Regulating Food Intake Sensory-Speci c Satiety Satiety: A reduction in appetite for food. sensory-specific satiety: A reduction in appetite specifically for foods that have been recently consumed. Individual Differences in Taste and Flavour Perception Tasters: People with a form of a gene that allows them to detect certain bitter tastants; approximately 75% of people are tasters. fi  Nontasters: People with a form of a gene that allows them to detect certain bitter tastants only at very high concentrations; approximately 25% of people are nontasters. Supertasters: Tasters who have about twice as many fungiform papillae as others and are especially sensitive to certain bitter tastants; approximately one- third of tasters are supertasters