Lecture 28 - Taste and Flavor Perception Flashcards
Five basic taste qualities:
detection of molecules in liquids and solids
– Salty – Sour (how much acid is present - lemons) – Sweet – Bitter (poison detector) – Umami (meety, brothy, savory: cheese)
all have a diff receptor that responds to these elements in the environment
Fat
is not currently recognized as a basic taste, but it may have it’s own dedicated receptors.
6th hypothesized taste
no single receptor that responds to it
fat in oils or animal products has its own sensation
basic tastes are like the basic colors
Using magnitude estimation, most taste experiences can be described as comprised of
the five elements.
example: things can be salty and sweet and bitter
These taste qualities are associated
with
stimulation of different detectors on
the tongue.
There are four types of tongue papillae
(surface projections):
NOT taste buds!!!
within these are the taste buds
filiform
only ones located in the center of the tongue
- shaped like cones and located over entire surface
fungiform
if you get sick they swell up
- shaped like mushrooms and found on sides and tip
have 3-5 taste buds each
foliate
- series of folds on back and sides
have more than 100 taste buds
circumvallate
- shaped like flat mounds in a trench located at back
have more than 100 taste buds
The tongue contains approximately
10,000 taste buds.
distribution is not equal
Taste buds are located in all
papillae except
for filiform.
taste buds composed of
taste cells (close together but not one unit - like bananas)
Only filiform papillae are located
in
the center, so we don’t have
direct taste sensations there.
taste pore
where the molecules of food or liquid are making contact
transduction takes places
when the molecule comes in and makes contact with the tips of the receptor sites
Each taste bud has a variety of
taste cells and receptor types.
The taste bud is composed of
50-100 taste cells with tips that
extend into the TASTE PORE
Transduction occurs when
chemicals contact the receptor sites on the tips (gustatory hairs).
sites on the tips of receptors where chemicals have contact
gustatory hairs
there are numerous receptors types
for different tastes
e.g. there are more than 20 ‘bitter’ receptor
types
Taste sensitivity may vary
according to the number of
fungiform papillae on the tongue
experiment measuring sensitivity
– Blue food coloring is placed on the
tongue.
– Papillae will not take up the dye and will stand out as pink.
– Count the papillae within a specified region to get density.
– You can distinguish three groups of people: nontasters, tasters, and supertasters.
IDEA: nontasters: have very few papillae and if you have a lot (high density) you’re a SuperTaster
A recent (2014) crowdsourced
study of papillae density suggests
that the differences are not due to
the number of taste buds.
– Visitors to a museum (n>3,000) volunteered to have their papillae counted.
– Additionally, they tested their sensitivity to bitter chemicals (e.g. PTC).
– Finally, they had genetic testing for a taste receptor gene (TAS2R38) believed to play a part in bitterness detection.
– Variations in the receptor gene were more predictive of supertasters than density!
suggests that density theory is all wrong
Behaviorally, there are different individual responses to the
bitter taste of phenylthiocarbamide (PTC) and to 6-npropylthiouracil
(PROP):
– Normal Tasters have specialized receptors for PTC and PROP and detect their presence.
– Nontasters lack these receptors, have fewer taste buds (?), and do not detect PTC.
– Supertasters are especially sensitive to PROP (and PTC) and respond to bitter substances much more strongly than tasters.
Signals from taste cells travel along a number of pathways
– Chorda tympani nerve from front and sides of tongue
– Glossopharyngeal nerve from back of tongue
– Vagus nerve from mouth and throat
– Superficial petronasal nerve from soft palate
four separable pathways from the tongue
Chorda tympani nerve
from front and sides of tongue
front of the tongue = best access to
Taste pathways that the taste signal travels down
make connections in the nucleus of the solitary tract in the spinal cord.
• Signals then travels up to the thalamus (just like everything else except for odor)
• From there the signals go to cortical
areas:
– Insula (primary area): heavily involved in disgust responses = SPIT IT OUT
– Frontal operculum cortex (primary)
– Orbitofrontal cortex (secondary): one of the earliest areas that odor goes to: quality, qualitative element of some odor
structure
receptors in cells in taste bud in papillai
Flavor
isn’t as nearly determined by taste
qualitative element has more to do with odor than the taste
is a complex construction: multi-model: associations with other things
is the subjective experience associated with ingesting food or drink.
– Combination of smell, taste, touch
and other sensations (such as
‘burning’ of hot peppers and alcohol –
nociceptors).
– Odor stimuli from food in the mouth
reaches the olfactory mucosa through
the retronasal route.
Getting to know your coffee
– “The beans are hand-picked at the peak of harvest, fully washed then sun-dried on patios. The result is a sweet aroma, smooth texture; notes of almond, milk chocolate and cherry with a lingering finish.”
– Scales of ‘body” (medium to very
full) and ‘liveliness’ (smooth to bright) provide some measures for comparison.
– Note how tastes, smells, and textures are mixed together.
why is odor so important for flavor?
Odor stimuli from food in the mouth
reaches the olfactory mucosa through
the retronasal route.
air travels through the back of the throat and the molecules in gaseous form can go up to the olfactory mucosa
odor associated with what’s happening on the tongue
If flavor has a strong olfactory component, why do we experience it in our mouths?
• Flavor begins with spatial information: things are mapped on the tongue have a large representation in the cortex (it’s very sensitive)
• Tactile receptors in the mouth localize other
sensory components to place flavor in the oral
cavity.
• This is known as the oral capture illusion.
you’re smelling something but you think it’s coming from the tongue because the tongue is very sensitive and has good sensory info whereas the nose does not
Taste tests with the nose open and closed reveal that most
flavors are strongly affected by olfaction.
A few, such as MSG are not (umami taste).
meaty or brothy occurs whether the nose is closed or not
How is flavor constructed?
Responses from taste and smell
are first combined in the
orbitofrontal cortex (OFC).
OFC
orbitofrontal cortex
also receives input from the primary somatosensory cortex and the inferotemporal cortex in the visual what pathway.
– Bimodal neurons in OFC respond to taste and smell, as well as taste and vision.
– Firing of these neurons is also affected by the level of hunger of the animal for a specific food
(firing increases with how hungry you are).
this whole experience of flavor is being rated by OFC
convergence! all these diff associations activity the flavor representation
Common themes
perception is an active process: not just receiving info and it’s continually happening
perception is studied at multiple levels: Marr’s levels as a scaffolding
perception is a hard problem: how do we filter and make sense and transduce and make sense of all this sensory information and faithfully represent what’s going on
Perception is a hard problem, with lots of sources of stimulus ambiguity or signal variation.
- Transduction uses different mechanisms, but we seem to use similar transmission and processing strategies (e.g. hierarchical processing).
- Perception is shaped and altered through experience dependent plasticity.
• We segregate information during initial processing, but combine it for identification and action (e.g. from streams of
processing to multisensory interaction to categorization).
computational level
What problems does the system solve? How is the
output related to the input?
algorithmic level
How does it solve these problems? What steps does
it take? What representations does it use?
implementational level
How is this instantiated in the brain or system?
most concrete
perception can be manipulated
heuristics: quick and dirty solutions to make estimates about what we’re dealing with
so senses can be tricked
This can be done within a sense or between senses.
perception is affected by knowledge
Studying perception has changed your brain. This also means you have changed your perceptual abilities.
perception is fading…
Presbycusis
Changes in touch and pain sensitivity
Presbyosmia
