Gustation and Olfaction
The Senses of Taste and Smell
Why do we study taste and smell
together?
SENSORY INTERACTION: the
principle that one sense may
influence another.
The senses of taste and smell
have a very cooperative working
relationship. Many of the subtle
distinctions you may think of as
flavors really come from odors
(Much of the “taste” of an onion is
odor, not flavor).
Often, if you can’t smell the food,
you can’t taste the food (have
you tried eating when you have a
bad cold?)
Gustation – The Sense of Taste
What is the central muscle involved in
taste?
Five Distinct Tastes
Sweet
Sour
Bitter
Salty
Umami (the taste of glutamate (MSG) – savory
taste in meat and cheese)
Each of these tastes developed as survival
functions, according to evolutionary psychology.
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Sweet - energy source
Sour – potentially toxic acid
Bitter – potential poisons
Salty – sodium essential to physiological processes
Umami – proteins to grow and repair tissue
A Theory Debunked
Since 1942, tongue maps like this one were
widely published and touted as an accurate
portrayal of where certain taste receptors
were located. Wine glasses are even
designed around this idea.
The notion that the tongue is mapped into
four areas—sweet, sour, salty and bitter—is
wrong. There are five basic tastes identified
so far, and the entire tongue can sense all of
these tastes more or less equally.
The tongue map is easy enough to prove
wrong at home. Place salt on the tip of your
tongue. You'll taste salt. For reasons
unknown, scientists never bothered to
dispute this inconvenient truth until 1974,
and even today, many textbooks still publish
picures of the tongue map.
Remarkably, more is known about vision
and hearing, far more complicated senses,
than taste.
Papillae
Those bumps on our tongue
are called papillae.
Papillae help grip food while
your teeth are chewing. They
also have another special job
- they contain your taste buds
Grab a partner and identify
some papillae – how many do
you see? Count them and
write the number down.
Individuals vary in their
sensitivity to taste sensations,
a function of the density of
these papillae on the tongue.
Taste Buds
Taste (gustation) has as its
physical stimulus chemical
substances that are dissolvable in
water.
Receptors for taste are clusters of
cells found in the taste buds,
which line the trenches around
tiny bumps on the tongue.
These cells absorb chemicals,
trigger neural impulses, and send
the information throughout the
thalamus and on to the
somatosensory cortex in the
parietal lobe.
Figure 4.49: The tongue and taste.
(a) Taste buds line the trenches around tiny bumps on the tongue called papillae. There
are three types of papillae, which are distributed on the tongue as shown in (b). The
taste buds found in each type of papillae show slightly different sensitivities to the four
basic tastes, as mapped out in the graph at the top. Thus, sensitivity to the primary
tastes varies across the tongue, but these variations are small, and all four primary
tastes can be detected wherever there are taste receptors. (Data adapted from
Bartoshuck 1993a).
Other Taste Facts
Taste receptors reproduce themselves every week or
two (this is why it hardly matters if you burn your tongue
with hot food).
As you grow older, the number of taste buds decreases,
as does taste sensitivity.
As with other senses, your expectations influence your
brain’s response. If you are told something is going to
taste bad, your brain responds more negatively.
Likewise, being told that a wine costs $90 rather than its
real $10 price makes an inexpensive wine taste better
and triggers more activity in a brain area that responds
to pleasant experiences.
As happens with the pain placebo effect, the brain’s
thinking frontal lobes offer information that other brain
regions act upon.
Non-Tasters, Tasters, and
Supertasters
In 1931, a chemist named Arthur Fox was pouring some powdered PTC
(phenylthiocarbamide) into a bottle. When some of the powder accidentally blew
into the air, a colleague standing nearby complained that the dust tasted bitter.
Fox tasted nothing at all. Curious how they could be tasting the chemical
differently, they tasted it again. The results were the same. Fox had his friends
and family try the chemical then describe how it tasted. Some people tasted
nothing. Some found it intensely bitter, and still others thought it tasted only
slightly bitter.
The PTC gene, TAS2R38, was discovered in 2003. Soon after its discovery,
geneticists determined that there is an inherited component that influences how
we taste PTC. Today we know that the ability to taste PTC (or not) is conveyed
by a single gene that codes for a taste receptor on the tongue.
The ratio of tasters to non-tasters varies between populations, but every group
has some tasters and some non-tasters. On average, 75% of people can taste
PTC, while 25% cannot.
There are two common forms (or alleles) of the PTC gene, and at least five rare
forms. One of the common forms is a tasting allele, and the other is a nontasting allele. Each allele codes for a bitter taste receptor protein with a slightly
different shape. The shape of the receptor protein determines how strongly it
can bind to PTC. Since all people have two copies of every gene, combinations
of the bitter taste gene variants determine whether someone finds PTC intensely
bitter, somewhat bitter, or without taste at all.
The “PTC Gene”
The ability to taste PTC shows a dominant pattern of inheritance. A
single copy of a tasting allele (T) conveys the ability to taste PTC. Nontasters have two copies of a non-tasting allele (t).
Can you taste PTC?
Try a PTC strip yourself, and rate the taste on the Green
Scale.
Now, look back at how many papillae your partner was able
to identify in the sample area of your tongue earlier.
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Supertasters have a mean of 44
Tasters have a mean of 32
Non-tasters have a mean of 24
Does this match up with your PTC paper results?
About 25% of the world’s population are supertasters (a
higher percentage of women fall into this category), 50% are
tasters, and 25% are non-tasters.
The world is built for regular tasters that experience food as
not too sweet, bitter, salty, or sour.
Evolutionary psychologists believe that there are advantages
to being a supertaster vs. a non-taster. Super tasters would
be able to tell if a plant was poison; non-tasters evolved in
times of famine due to needing to eat tree bark, etc.
Why does this matter?
Studies indicate that individuals with the
“strong tasters” PTC gene variant were
less likely to be smokers. This may
indicate that people who find PTC bitter
are more likely than non-tasters to find the
taste of cigarettes bitter and may be less
likely to smoke.
Other studies suggest that there may be
correlations between the ability to taste
PTC and preferences for certain types of
foods. This may be why some of us think
that broccoli is just too bitter to eat.
Interestingly, supertasters and non-tasters
also respond to noise differently.
Bartoshuk finds that supertasters may rate
a particular noise level as very loud,
between a boombox and a baby crying,
while non-tasters rate it much lower,
PTC tasters may be more sensitive
than non-tasters to compounds in
between a shout and a boombox.
tobacco and vegetables in the
cabbage family.
Why does this matter? (cont.)
If you are a supertaster:
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You probably cannot stand the taste of broccoli, Brussels sprouts,
spinach, diet drinks, cauliflower, rutabaga, strong cheeses, turnips, or
bok choy (Chinese cabbage).
Caffeine also makes coffee taste bitter to tasters, but has little effect on
non-tasters.
They perceive more burn from oral irritants, like alcohol and chili
peppers. Many foods are too intense.
Vegetables are especially unpalatable and so supertasters have an
increased risk of colon cancer. The upside of being a supertaster is that
fats are also experienced as too intense. Thus, supertasters weight is
lower, their blood profile is healthier, and their risk of cardiovascular
disease is reduced.
If you are a non-taster:
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You probably do not experience the intensity of foods that others do.
Non-tasters tend to like very spicy foods, perhaps because they may be
trying to experience some strong tastes.
They do not taste the bitterness in heavily alcoholic drinks, so they may
have a higher incidence of alcoholism.
“Non-tasters live in a pastel taste world, whereas supertasters
live in a neon taste world.”
Picky Eaters by NOVA
Watch the video Picky Eaters by NOVA ScienceNOW.
http://www.pbs.org/wgbh/nova/sciencenow/0404/01.html
More on the Web!
• NOVA scienceNOW’s Tour the Tongue (10 minutes)
http://www.pbs.org/wgbh/nova/body/tongue-taste.html
Learn how taste works and why we evolved the ability to detect bitter
and sweet tastes.
• NOVA’s The Sense of Taste (4 minutes)
http://www.pbs.org/teachers/connect/resources/888/preview
Learn what happens when we lose our sense of taste and how smell
affects our experience of food.
• Howard Hughes Medical Institute’s Taste Lecture (6 minutes)
http://www.hhmi.org/lectures/webcast/ondemand/97webcast1/tast
e.html
Learn how taste receptors function. (Also check out the other
lectures listed at the bottom of this site!)
Other Cool Taste Sensations
If you decide to try these yourself at home, make sure you check with
your parents first! You should make sure to read all about them before
trying anything, because they have not necessarily been completely
studied.
Gymnemia Sylvestre – a taste modifier that selectively abolishes the
sensation of sweet, leaving all other taste modalities unchanged.
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Gymnemia is sold over the counter as a tea in Japan. Can be obtained through Best Nutrition
Products at http://www.gymnema.com/ (510-477-9116). Prepare as instructed and store in the
fridge.
The drink tastes like spinach tea, but it won’t be bad if you hold your nose. You might want to rinse
your mouth with water immediately afterward.
Taste salt (should taste normal), then sugar (will taste like melting sand on the tongue), Sweet
Tarts (will be purely sour), and finally M & M’s (will taste quite bitter).
The Miracle Fruit – a plant native to West Africa that makes things taste
sweet.
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It contains miraculin, which binds to the tongue’s taste buds when the fruit is consumed. Miraculin
acts as a sweetness inducer when it comes in contact with acids, causing bitter and sour foods to
taste sweet, temporarily. This effect usually lasts between 30 minutes and 2 hours.
These berries are being used in some places to help treat obesity and make food more appealing
to people undergoing chemotherapy.
http://www.miraclefruitusa.com/ - this website explains the fruit (watch the video about the foodtasting parties thrown in NY), and sells the berries, tablets, and plants to grow your own.
Read an article from the NY Times: http://www.nytimes.com/2008/05/28/dining/28flavor.html?_r=1
From Union County College’s Biology Dept: http://faculty.ucc.edu/biologyombrello/pow/miracle_berry.htm
Olfaction
Our Sense of Smell
How Olfaction Works
Smell (Olfaction) operates much like the sense of taste.
The physical stimuli are chemical substances carried in
the air that are dissolved in fluid, the mucus in the nose.
Pathway: Olfactory cilia -> neural impulse -> olfactory
nerve -> olfactory bulb (brain)
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Olfactory receptors are called olfactory cilia and are located in the
upper portion of the nasal passages.
The olfactory receptors synapse directly with cells in the olfactory
bulb at the base of the brain. Olfaction is the only sense,
therefore, that is not routed through the thalamus. This suggests
that smell evolved earlier than the other senses.
Odors are not easily classified, and primary odors have
not really been delineated. Humans can distinguish
among about 10,000 odors, but for some reason have a
hard time attaching names to odors quite frequently.
Figure 4.51: The olfactory system.
Odor molecules travel through the nasal
passages and stimulate olfactory cilia. An
enlargement of these hairlike olfactory
receptors is shown in the inset. The
olfactory nerves transmit neural impulses
through the olfactory bulb to the brain.
Figure 4.51 The olfactory system
Pheromones
In many animals, the sense of smell is used for
communication. For example, insects such as ants and
termites and vertebrates such as dogs and cats
communicate with each other by secreting and detecting
odorous signals called pheromones – especially to signal
sexual receptivity, danger, territorial boundaries, and food
sources.
We humans seem to use the sense of smell primarily in
conjunction with taste to seek and sample food, but some
evidence exists to suggest that people may also use sexual
pheromones as well as pheromones that help us identify
family members by smell.
For more information:
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Watch this video on PBS called “Sweaty T-Shirts and Human
Mate Choice” for an evolutionary perspective on pheromones:
http://www.pbs.org/wgbh/evolution/library/01/6/l_016_08.html
ABC News article called “Are Pheromones a Secret Weapon
for Dating?”
http://abcnews.go.com/2020/Health/story?id=1386825
CNN article called “Study Finds Proof that Humans React to
Pheromones”:
http://www.cnn.com/HEALTH/9803/11/pheromones/index.html
Fragrance Effects
Research suggests that pleasant scents may trigger pleasant moods
and give a boost to workers’ performance.
Social psychologist Robert Baron, who has studied these fragrance
effects, has patented and is marketing a device that emits pleasant
scents. Called PPS (Personal Productivity/Privacy System) it
combines fragrance release with a whitenoise generator and an air
filter.
After testing dozens of smells, Baron found that lemon and light floral
had broad appeal (pine was the least popular odor), and is marketing
discs producing these odors with the PPS.
On a much larger scale, Shimizu Corporation has also patented an
“odordelivery” for commercial buildings. For example, it pumps a
citrus odor through an office building’s ventilation ducts every two
minutes. “The fragrance sense can be fundamental to controlling
conditions for office workers,” says Junichi Yagi, a representative for
Shimizu. He cites a monthlong study of Japanese keypunchers in
which those who inhaled a lemon aroma make 54 percent fewer
errors than those who sniffed plain air. While the citrus odor seemed
to make people more alert, other smells, such as spiced apple,
seemed to aid relaxation.
Fragrance Effects (cont.)
Researchers are investigating the effects of various fragrances in
diverse settings. In some cases, they have reported dramatic
success.
For example, Susan Schiffman of Duke University has explored how
pleasant odors may influence the disposition of New York City
subway riders. In pumping scents through one subway car and not
another, she reported finding that some food odors cut shoving and
pushing by 40 percent.
She has also reported success in using an apricot scent to help
patients at a weight loss clinic to relax. Many overweight people, she
claims, eat compulsively when they’re under stress and the aroma
technique has proven beneficial.
William Redd and Sharon Manne at Memorial SloanKettering
Cancer in New York City used a vanilla scent to lessen patient
anxiety. Those who detected the scent and perceived it as pleasant
reported a drop in anxiety by as much as 65 percent.
Baron and his colleagues also found that shoppers in Crossgates
Mall in upstate New York were more likely to help a stranger if they
smelled roasting coffee or baking cookies. “There’s nothing
magical,” Baron said. “When you put people in a good mood, they
become more helpful.”
Read about the importance of
smell in marketing!
http://www.tampabay.com/features/humani
nterest/article1203774.ece