Perceptual Processes chapter 15

Interesting Tidbit

• Dixy Lee Ray suggests that if your tongue was as sensitive as radiation detectors, you could taste one drop of vermouth in five carloads of gin

Fun Facts About Taste

• Sweet foods activate the dorsal hippocampus, improving memory recall
• Eating a sweet item like dessert after a meal helps you to remember the meal better
• Artichokes contain cynarin, a chemical that temporarily blocks sweet receptors
• After eating artichokes, water tastes sweet because cynarin is removed by the water and the receptors fire
• Noise dampens sweet receptors and enhances umami receptors when flying, leading to a preference for savory foods
• A specific gene (OR26A2) causes aldehydes in cilantro to taste soapy or perfumy
• Endocannabinoids are endogenous cannabis-like chemicals that activate sweet receptors, explaining the "munchies"

What Is Taste

• Taste is the sensations evoked by solutions in the mouth, contacting receptors on the tongue and roof of the mouth.
• Flavor is the combination of true taste (sweet, salty, sour, bitter) and retronasal olfaction.
• Taste involves primarily sensations, while flavor is the combination of taste sensations and smell.

Flavor Explained

• Retronasal olfactory sensation is the sensation of an odor perceived when chewing and swallowing forces an odorant in the mouth up behind the palate into the nose.
• Odor sensations are perceived as originating from the mouth, even though the actual contact of the odorant and receptor occurs at the olfactory mucosa.
• Mouthfeel is the texture and physical sensations in the mouth produced by specific foods.

Try This Experiment

• Plug your nose tightly and chew a piece of candy to release maximum flavor and note the limited taste.
• Swallow the candy, then immediately unplug your nose, and note the difference in the complete flavor profile.
• This demonstrates the difference between basic taste and the full experience of flavor.

Taste Loss

• Damaged taste sensation, along with normal olfaction, means that you can smell lasagna, but it has no flavor
• Anesthetizing the chorda tympani with lidocaine has a similar effect
• Cranial nerve VII carries taste information from the anterior, mobile tongue
• Blueberry yogurt has a distinct scent but no flavor if taste is damaged.

Taste and Smell Connection

• Brain imaging studies show that the brain processes odors differently depending on whether they come from the nose or mouth
• This allows for compartmentalizing odors from the air versus odors from food
• Adding sugar to fruit juice intensifies the sensation of fruit
• Increased sweetness increases the perceived olfactory sensation of fruit
• Increasing volatile flavor components can allow for reducing sugar during food processing.
• Studies show volatile compounds contribute to perceived sweetness in heirloom tomatoes, strawberries, and blueberries
• There is a correlation with degree of liking in flavor studies
• These volatiles increase retronasal olfaction and may increase perceived sweetness without adding more sugar
• Certain volatile odorants strongly correlate with higher liking and sweetness ratings, but do not correlate with the amount of sugar actually present

Four Basic Tastes

• The four basic tastes are salty, sour, bitter, and sweet
• There may also be a fifth taste: Umami

Salty Taste

• Salt is composed of a cation and an anion
• The sodium cation is the component that causes the salty taste sensation
• The ability to perceive salt is not static
• Low sodium diets increase sensitivity to salty foods over time
• Liking for saltiness is not static
• Early experiences can modify salt preference
• Chloride deficiency in childhood can lead to preference for salty foods later
• Saltiness can be affected by gestational experiences

Sour Taste

• Sourness originates from acidic substances
• Produced when hydrogen ions enter ion channels
• There is an alternate mechanism allowing undissociated acid molecules to enter through the cell membrane
• Acids will damage both external and internal body tissues at high concentrations

Bitter Taste

• The taste cannot distinguish between different bitter compounds
• The main evolutionary purpose is to avoid all things that are bitter
• Many bitter substances are poisonous
• There is an ability to "turn off" bitter sensations, beneficial to liking certain vegetables
• Adenosine monophosphate (AMP) is present in breast milk to deactivate bitter receptors to make milk more palatable
• Bitter sensitivity is affected by hormone levels in women; it intensifies during pregnancy
• Protects the baby from poisons, especially early when they are most harmful
• This explains many taste aversions during early pregnancy

Sweet Taste

• Sweetness is evoked by sugar
• Many different sugars taste sweet
• Glucose is a major source of energy for most animals
• Fructose is sweeter than glucose
• Sucrose is common table sugar made of glucose and fructose
• There is a single receptor responsible for all sweet perception
• Artificial Sweeteners stimulate this receptor

Umami Taste

• Umami has been called the fifth taste
• Umami comes from monosodium glutamate (MSG)
• It's glutamate
• Glutamate is an important neurotransmitter
• There are safety issues in human consumption
• It can lead to numbness, headache, flushing, tingling, sweating, and tightness in the chest if sensitive ones consume a large amount
• MSG does not pose a problem in small doses for most

Fat Taste

• Fat is an important nutrient, like protein
• Fat molecules evoke tactile sensations like oily, viscous, and creamy
• Rats have fatty acid receptors on their tongues, and humans may as well
• If digesting fat in the gut produces conditioned preferences for the sensory properties of the food containing the fat.
• Diet foods mimic the sensations of fat but reduce the caloric intake
• This may be problematic because it disrupts normal body responses
• This is also observed in artificial sweeteners

Gustatory System

• Taste buds create neural signals conveyed to the brain by taste nerves
• Taste buds are located in structures called papillae (the bumps on the tongue)
• Taste buds contain taste receptor cells
• They send information to the brain via cranial nerves.

Kinds of Papillae

• Filiform papillae are small structures on the tongue that provide the bumpy texture, but have no taste function
• Fungiform papillae are mushroom-shaped structures on the edges of the tongue that perform the majority of tasting
• There is an average of six taste buds per papilla
• Foliate papillae are folds of tissue containing taste buds on the rear of the tongue
• They are lateral to the circumvallate papillae, where the tongue attaches to the mouth
• The circumvallate papillae are circular structures that form an inverted V on the rear of the tongue (three to five on each side)
• Circumvallate papillae are mound-like structures surrounded by a trench and are much larger than fungiform papillae

Taste Myth

• Hänig measured taste thresholds at different parts of the tongue in 1901
• Boring replotted Hänig's data and labeled it "sensitivity" instead of thresholds in 1942
• The actual variations in the thresholds are rather small, but Boring's replotting made them look big
• Sweet, sour, salty, and bitter are tasted all over the tongue, not just in the locations indicated by the tongue map

Taste Receptor Cells

• Microvilli are slender projections on the tips of some taste bud cells that extend into the taste pore
• Microvilli contain the sites that bind to taste substances, and are not tiny hairs, but extensions of the cell membrane
• There are three types of cells in a taste bud: Type I, Type II, Type III
• Type one cells have housekeeping functions
• Type II cells are the receptor cells for sweet, bitter, and amino acid stimuli
• Type III cells are excited by the sour stimuli

Taste Stimuli

• Tastant is the term for any stimulus that can be tasted.
• Tastants can be divided into two large categories
• The first consists of small, charged particles that taste salty or sour
• Small ion channels in the microvilli membranes allow some types of charged particles to enter, but not others
• The second consists of tastants perceived via G protein-coupled receptors (GPCRs) similar to those in the olfactory system
• These molecules taste sweet or bitter
• It is not yet known how to fully explain the perception of saltiness

What We Taste With Where

• Taste receptors can be found throughout the body and are not limited to the tongue
• Most of our fat-sensing receptors are located in the gut
• These are called gut receptors
• Stomach receptors are sensitive to certain bitter compounds and will slow the absorption of ingested material when activated; this helps avoid ingesting toxin
• They are bitter receptors
• Airway receptors are activated by bitter compounds and cause cilia to move

Taste & the Brain

• Cilia help clear debris and irritants from the airways
• Pancreas receptors are activated by sweet compound and help to regulate insulin
• There also testes and sperm receptors
• If taste buds go to the cranial nerves and then to the medulla and thalamus from the insular cortex
• Which is a primary cortical Processing Center for Taste
• This is the part of the cortex that first receives taste information
• Furthermore, it's critical in olfactory processing as well as in our emotional sate
• The orbitofrontal cortex is the part of the frontal lobe of the cortex that lies above the bone (orbit) containing the eyes
• It also receives projections from the insular cortex and is involved in processing of temperature, touch, smell, and taste, as well making it an integration area

Taste Processing

• Inhibition plays a vital role in processing taste information in the brain
• When activated, cranial nerves carrying taste information actually inhibit or reduce taste sensations.
• If one part of these nerves is damaged, it prevents the inhibition while increasing the activation of the taste system
• Redundant system preserves whole-mouth taste processing in case of damage
• Localized damage to the taste nerves can result in phantom taste because of the Redundant system of if one part is damaged that gets prevented then the other undamaged parts react more.
• Phantom taste is tasting flavors that are not currently present
• It is common to experience Metallic taste in the mouth during and following chemotherapy
• Inhibition helps you not to lose your entire taste sensation
• Descending inhibition from the taste cortex inhibits pain signals
• This survival value is necessary to eat even if ones mouth has been injuried

Genetic Taste Factors

• Arthur Fox discovered in 1931 that phenylthiocarbamide (PTC) tastes dramatically different to different people
• Some experience it's not better well others do
• The 1960s Started using propylthioracil instead because it is safer
• A gene for PTC / Prop receptors was discovered in 2003 Individuals can either be nontasters or tasters of PTC/PROP

Taste Genetics Described

• Individuals with two recessive genes are non-tasters of PTC/PROP
• Individuals with one or more of the genes are tasters of PTC/PROP
• Supertasters are individuals who are tasters of PTC/PROP and have a high density of fungiform papillae
• Supertyasters perceive the most intense taste sensations
• There is something called cross-modality matching and what ability to watch the intensities of sensations that come from different sensory modalities
• This is used to assess intensity of taste sensations for non-tasters medium tasters and super tasters

Taste Genes vs Experience

• Nontasters match the bitterness of PROP to the same intensity as the sound of a watch or a whisper
• Medium tasters match the bitterness of PROP to the same intensity as the smell of frying bacon or the pain of a mild headache
• Supertasters match the bitterness of PROP to the same intensity as the brightness of the sun or the most intense pain ever experienced.
• Taste Sensations tell us which foods we should or should not be consuming
• Variations in sensory properties of foods and beverages affects food preferences and therefore diet
• Supertasters are more likely to avoid some vegetables because of bitter taste, as well as high-fat foods because of bitter taste, lowering their risk for heart disease

Taste Regulation Explained

• We have sensory properties that are affected by food preferences and diet
• Examples include some vegetables have a bitter taste, therefore might be avoided by supertasters
• There are Health consequences of taste
• Super Tasters get routine colonoscopies and those who taste PROP have the worst
• PROP is very bitter, and these types avoid high fat food, which may lower their risk for heart disease
• Humans who are omnivores have to decide what to eat
• This poses omnivore's dilemma
• Modern human's need to find a healthy diet amidst dizzying choices available to us today
• How do taste and smell help us find What to eat and what not to eat.
• Taste helps us understand nutrients and antinutrients and what to choose

How We Survive With Taste

• Taste helps us regulate nutrients
• By smelling and tasting it helps determine choices by helping find what we eat and smell what we eat
• In this way we avoid eating Poison and know how to survive
• Bitter might signal poisons
• Sour is configured to test acidic solutions and might be harmful to the human bodies
• Some also survive of sweet and salty foods to survive that have sugar and sodium

Taste's Survival Value

• Infant behavior and facial expressions reveal innate preferences for certain foods
• Infants
• Infants Like the sweetness cause they are happy face and the they like to suck for nutrition
• Infants Don't like the sour because it purses them Infants react negatively to beta, and makes them want to vomit
• This affects how they react to different tastes
• Specific hunger's are also a thing that affects how to survive those things can be from salty foods and sweet foods
• These food choices affect deficiencies in substances
• There are modern theory such as learning
• The way taste is emphasized in a different way which also might or might not avoid certain foods
• Foods with positive values can transfer to other new foods as well
• We can regulate the eating intake though learned response of food flavors by hardwired tastes

Taste Theories

• There are two ways that we can process taste those are both theories
• Labeled lines are each taste fiber carries a particular taste quality for separate lines
• Also there is Pattern coding that all activity and different test neurons
• These types of coded are in other senses
• Patterns for all the faction in color that are also use pattern coding
• Hearing and touch pain are all use hearing too
• Taste adaptation and adaptations for all these

Nature of Taste Explained

• Pleasure has has retronasal effects versus orthonasal effects in that how we gather flavour information affects how we respond to eating it
• Pleasure vs olfaction happens through the nose
• Do we learn that some people like it in similar smells but others do not

Flavor and Smell

• Pleasure has retronasal versus orthonasal and that how we gather helps how we respond. Orthonasal through the nose versus how that information in a version helps you do your part
• Pleasure happens when it has it's own part
• How food and eat smell and like an important thing to the taste it helps with learning
• Examples People wouldn't eat it
• As opposed to a versions that requires it will show up well there are

More On Sensory Perception

• Chilli Peppers effect how foods taste
• Chili Peppers are also depended the of social and fluence
• Chilli Peppers have Restricting in the population in humans There is a variability on how much the are in each
• Capsaicin causes burn and has receptors
• The acquisition has had desensitization

Potential Taste Problems

• Ageusia is complete loss of the ability to taste, making it impossible to detect any flavors
• Hypogeusia is a reduced ability to make distinct, and reduced to taste
• Dysgeusia there is a distortion or nasty taste
• Phantogeusia (Phantom Taste): A persistent taste that is unpleasant