Week 3 Gustation

Question 1

gustatory system cranial nerves

Answer 1

VII- facial nerve
IX- glossopharyngeal
X- vagus

Question 2

gustatory system synapse

Answer 2

brainstem neurons - project to thalamus - project to primary taste
cortex in the insula

Question 3

Gustatory stimuli

Answer 3

Tastants are chemicals that are water soluble in saliva (hydrophilic)

• 1 tastant activates 1 tastant receptor
• If sufficient concentration can elicit sensation of taste

Question 4

Process of taste

Answer 4

1. Tastants from food dissolve into saliva
2. Saliva (filled with tastants) bathes papillae on tongue
   o Papillae house the taste buds either on top or on sides of tongue
   o Papillae aren’t the taste buds, they are housing structures
3. Saliva (with tastants) fills papillary trenches, bathes taste buds
   o Taste receptor neurons contained within taste buds – tastants delivered to the receptors by saliva
4. Tastant receptors activated – signal transduction occurs
5. Signal passed to primary afferent neurons, travels to brain via
   cranial nerves
   o And chemosensory input being sent through cranial nerve V, trigeminal nerve
   o Different cranial nerves for different parts of the tongue
6. Signal passed to neurons in brain stem
7. Signal passed to neurons in thalamus
   o And smaller relays to hypothalamus and amygdala
8. Thalamus relays to primary taste cortex (insula-fO) and secondary taste cortex
   (Orbitofrontal cortex/OFC)
   o Most of processing in insula

Question 5

Taste buds

Answer 5

5000 – 10,000 taste buds
o Increase in number from birth to ~age 40, then decline
- 90% on tongue papillae, remainder throughout mouth
o Not all animals taste buds are on the tongue – some on feet, etc.
- Taste receptor neurons within taste buds project microvilli into papillary trench
o Signal transduction in cell in response to tastant
o Receptors are located on the tip of the cell
o There is one type of receptor for the cell – a cell is responsive to one type of
taste only, on all of its microvilli
The tip of taste receptor neuron contains tastant receptors
o Activation of the receptor initiates signal transduction in that neuron
o Chemicalstimulusneuralpotential
o Release serotonin onto next neuron – its axon bundle to form cranial nerve 7,
9 or 10

Question 6

taste bud 3 cell types

Answer 6

Taste receptor neuron + support cells + stem cells
o Taste receptor neurons continually turn over – shorter rate than ORNs
 About 10 days
o Basal stem cells constantly divide – allow damaged cells to be replaced

Question 7

tip of taste receptor neuron contains tastant receptors

Answer 7

Activation of the receptor initiates signal transduction in that neuron
Chemical stimulus- neural potential
Release serotonin onto next neuron – its axon bundle to form cranial nerve 7,
9 or 10

Question 8

Smell also activates OFC

Answer 8

Sometimes called the flavour cortex but it is actually in relation to preferences
OFC has bimodal neurons – two senses
OFC neurons exhibit satiety – sensitivity
Damage to the OFC impairs choice preference tasks and time-delay tasks
Information goes to the primary cortices first and then on to the OFC

Question 9

Taste preferences

Answer 9

Hedonic assessments are highly individualised

• Innate?
• Learned?
• Based on physiology?
• Influenced by satiety?
• Influenced by flavour?

Question 10

Innate taste preference?

Answer 10

Essentially, the 5 submodalities represent innate preferences
Generally, umami and sweet = good
Bitter and sour = bad
Capsaicin = dangerous
Chemical senses unique in having somewhat generalised hedonic spectrum
Nowadays we tend to override some of these innate perceptual indicators

Question 11

Learned taste preference

Answer 11

Familiarity balance with novelty

+/- reinforcement during exposure

Question 12

Physiology based taste preference

-Genetics

Answer 12

-Dictate number of papillae/taste receptors
-Dictate number of free nerve endings
-Dictate types of taste receptors
-Variants of genes
-Different combinations of receptors means the taste is different or not
at all
-Chemosensory contributions to flavour

Question 13

Physiology based taste preference

Answer 13

• Genetics
• Age
• Sex
• Activity level

Question 14

Physiology based taste preference

Activity level

Answer 14

• Picky eaters
• Satiety-based taste preference
• Taste perception – particularly hedonic assessment- can be influenced by satiety
• Flavour based taste preference
• The hedonic assessment of taste may be strongly influenced by other components of flavour, and by expectation

Question 15

Functions of taste

Answer 15

• Indicate safety of food
• Indicate nutritional value of food
• Reinforce eating behaviour

Question 16

Taste and Dopamine

Answer 16

Taste causes DA release in the brain (or ) – indicates importance
-Reinforcement pathway
-If negative – reinforced to avoid
-If positive – reinforced to approach
Evolutionarily adaptive, reinforces that eating is a useful activity – important for
homeostatic feeding
Perhaps instead of helping us, this taste-DA relationship is actually hurting us as we
shift to hedonic feeding

Question 17

DA and the hedonic treadmill

Answer 17

When positive experiences cause DA release, the degree of dopaminergic
activity often correlates to the degree of pleasure or satisfaction felt o In hypothetical relation to taste:
-Good taste = 1 x DA = pleasure
-Great taste = 2 x DA = 2x pleasure
-Superb taste = 3 x DA = 3x pleasure
-Pleasurable things often exhibit hedonic treadmill effects
We seek out things that give us more and more DA – over time we want to keep increasing it and can develop tolerance
-Treadmill effect – we want to increase the DA activity but it stays the same even though we eat more
Want the DA release associated with intense taste again – have another slice of cake, have ice cream with it – add more stuff to get the release

Question 18

Could this taste-DA relationship explain some instances of obesity?

Answer 18

Researchers argue that obesity results from abnormalities in the dopaminergic system
Studies suggest obese individuals innately have fewer DA receptors so they eat more to achieve the same level of pleasure
Stice et al., 2011 suggest obesity itself leads to a blunted DA response to food, so obese individuals don’tget the initial rush, and eat more to try and get it

Question 19

Taste technology: additives

Answer 19

• Certain chemicals produce intense ‘tastes’
• When we frequently eat food items containing these chemicals, two things can
  happen: We find normal tastants less intense, We get the taste but we don’t get the satiety
• Taste modifiers: Certain chemicals can mask/alter the tastes of tastants

Question 20

Taste detection

Answer 20

-Can you taste something – Y/N
- A number of factors influence taste detection – psychological as well as physical
influences to threshold tests
-Absolute threshold values for taste depend on submodality
-Difference threshold/JND for taste ranges from 15-25% up towards original Weber
value of 33%
-Temperature: change temp- sub modality detection changes, absolute threshold values change
-Expectation
-Sex
-Age
-Genetics

Question 21

Taste identification

Answer 21

• What is it that you taste – we can often detect a tastant but have difficulty identifying it
• Confound of semantic recall: What we ask of humans is to name stuff which tests memory, Need language skills to do this – semantic demand
• Confound of flavour: ow do you test taste by itself? – need to remove other components of taste

Question 22

Alterations in gustation

Answer 22

Because taste (i.e. flavour) is interlinked to other modalities, changes in taste may go
unnoticed
In theory, you could be very hypogeusic yet still really like and enjoy food
Can use the other components of taste to get enjoyment out of food

Question 23

Ageusia

Answer 23

-Absence of taste perception
-Rare
-Specific or complete – loss of one or all submodalities
-Transient or permanent
Causes: congenital, oral trauma, nerve trauma/infection, CNS damage, Transient ageusia (chemotherapy)
-Common effects:Loss of interest in food, however less than anosmia, Forgetting to eat

Question 24

Hypogeusia

Answer 24

• reduced taste perception; reduced sensitivity to tastants
• Commonly associated with medications
• Xerostomia – dry mouth
• Part of natural aging
• Natural drop in number of buds, saliva, energy needs
• Hypogeusia can be confounded by hyposmia

Question 25

Hypergeusia

Answer 25

-heightened taste perception
-Rarely reported… in medicine
-Would have to show in all submodalities that they had a very high adbolute
threshold
-Some chefs might be, without knowing

Question 26

Dysgeusia

Answer 26

• distortions in taste perception
• Usually unpleasant distortions
• Dysgeusia due to a purulent nasopharyngeal infection
• Bacteria activate receptors
• Dysgeusia due to chemical interactions in mouth
• Cacogeusia – foul taste in the mouth, +/- tastants present
• Phantogeusia – unique taste percept, no tastants present, only perceptual
• As long as primary taste cortex is active you can get that perception