Transcript Chapter 15: Taste

Chapter 15: Taste
Taste or gustation: refers to
sensations produced when
substances dissolved in
saliva stimulate taste
receptors on the tongue and
in the mouth.
Flavor: includes smell,
texture, temperature, and
consistency (not just taste).
To be tasted something
must be soluble, which
means dissolvable in saliva
(which is a substance similar
to salt water).
Classifying tastes
“Classic” four taste categories (from Hans Henning – same guy who did smells)
1) Sour: whose threshold sensitivity is lowest at the sides of the tongue
2) Salty: whose thresh. sens. is lowest at the tip of tongue
3) Sweet: whose thresh. sens. is lowest at the tip also
4) Bitter: whose thresh. sens. is lowest at the back of tongue
Umami (recently accepted 5th taste category: associated with savory, protein-rich
food experiences – think cheesy, meaty pizza.
Anatomy of taste
Some 10,000 taste
buds reside in the
tongue (though not
in the center of
tongue) housed
within the columns
of visible bumps or
papillae and in
certain parts of
mouth and throat.
Each bud is actually a
collection of
receptor cells,
clumped together
like a clove of garlic.
Anatomy of Taste
From the receptor cells small threadlike
substances (microvillae) extend upward and
make contact with the substances dissolving in
saliva in mouth.
The responses of the microvillae are then
propagated down the receptor cell, and out
nerve fibers in the tongue to the brain.
It appears that certain areas of the Parietal
cortex are taste centers, where tastes are
identified
It also appears that certain centers in the limbic
system are simultaneously registering the
affective quality of the dissolving substances.
Taste pathways
Sensory cortex:
texture,
temperature
aspects of flavor
Insula: primary
gustatory cortex
OFC: secondary
gustatory cortex
It also appears that
certain centers in
the limbic system
(hypothalamus,
amygdala) are
simultaneously
registering the
affective quality of
the dissolving
substances.
Primary/Secondary Gustatory Cortices
Primary: found in insula, taste
identification and intensity.
Damage can lead to inability to
identify taste experiences
Secondary: OFC; has more to do
with reward value of taste
experience; affected by recent
past food intake
Taste processing over time in the PGC
Epoch 1: as food is first put into mouth and
chewed; PGC receptors extract information
about texture, temperature, consistency and
other somatosensory information (not so
much about actual taste).
Epoch 2: 1/5 of a second later: info about taste
qualities begin to be extracted
Epoch 3: one second into chewing: info about
palatability (is food dangerous?) is extracted.
Tasters and non-tasters
There appear to be genetically determined differences in some taste
perceptions, such as bitter. Tasters find two chemical substances (PROP
and PTC) very bitter (about 2/3 of us); non-tasters have little taste
experience. Key difference appears to be density of taste buds.
Taste adaptation and modification
Adaptation: prior exposure weakens taste experience
(too much chocolate cake!)
Cross-adaption: can happen but usually with substances
that have the same basic taste profile (sour pickles and
reduce sensitivity to other basically sour foods). One
exception appears to be bitter; where sour appears
capable of producing an adaptation effect.
Modification: prior taste alters experience of current
taste (I just brushed my teeth!). Artichokes can make
water taste sweet – taste aftereffects or taste illusions
Taste suppression: taste of one substance is reduced
because of addition of another taste. Sugar masks
bitter taste of coffee
Role of smell in taste
Aids significantly in taste identification