Transcript Chemical senses - Department of Psychology

Psy280: Perception
Prof. Anderson
Department of Psychology
Chemical senses
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Chemical senses:
Your are what you eat (smell)
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What’s it good for?
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Olfaction (i.e., smell)
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Chemical composition of our surroundings
Distal/remote sensing
Small concentrations of airborne substances
Gustation (i.e., taste)
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Proximal/immediate sensing
Check if appropriate to enter your body
Last sense to use
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If it looks like and it smells like, it probably is it
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Comparative taste
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Not all organisms “taste” with a tongue
Moth antennae
Fly “feet”
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In good and bad taste
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Useful for the body
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Potentially harmful
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Tend to taste bad
Tend to taste bitter
Not always the case:
Influence of culture
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Tend to taste good
The burn of capsaicin
Bitterness
Compare with vision
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All dangerous things ugly?
All ugly things dangerous?
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Taste in infancy
Neonatal “liking”
responses
Sweet
 Lip smacking
 Smiles
Bitter
 Grimace
 Lip retraction
 Nose wrinkle
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Anatomy of taste: Papillae
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Filiform
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Fungiform
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Folds at sides
Circumvallate
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Mushroom shaped
Tip & sides
Foliate
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Cone shaped
All over the tongue
Give rough appearance
Flat mounds
At back
Other taste receptors
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Palate
Larynx
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Anatomy of taste: The bud
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All papillae contain taste
buds except the filiform
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Thus, centre of tongue is
“taste-blind”
Taste buds
Multiple taste cells
 Create taste pore
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Taste sensory transduction
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Different taste cell types
for different tastes
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Salt
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Specificity at receptor
level
NaCl
Na+ entry into cell
Depolarization
Sour
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H+ ions block channels
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Taste pathway
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Electrical signals carried by 3
pathways
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Chorda tympani
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Glosso-pharyngeal
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Mouth & larynx
NST (brainstem)
Gustatory thalamus
Primary taste areas
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Back
Vagus
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Front & side
Insular/opercular cortex
Secondary taste areas
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Orbitofrontal cortex
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Insular cortex and disgust
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Disgust = “bad taste”
Anterior insular cortex
is primary taste area
Viewing disgust faces
increase activation
Lesions impair
recognition of disgust
Disgust vs fear
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Taste experience
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What tastes do we taste?
4 (maybe 5) basic tastes
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Sweet (Sucrose), bitter (quinine), sour (HCl), salty
(NaCl)
And … umami (MSG)
All taste experience can be described in terms of
their combinations
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Some substances are primarily 1 taste
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Sodium chloride: Salty
Quinine: Bitter
Some are combinations
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Sodium nitrate: salty, sour, & bitter
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Neural code for taste:
Specificity
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Different taste receptors carry different dimensions of
taste?
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Salt receptors related to saltiness?
Block receptors (amiloride)—> impair salt perception
Leaves other sensations intact
Parallel between receptor morphology and taste
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E.g., circumvallate (back) = bitter?
Foliate (side) =sour?
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Neural code for taste:
Specificity
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4 different types of
fibers in chorda
tympani
Activation of
specific fiber tracts
responsible for
taste sensations
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E.g. “sweet”, “bitter”
neurons
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Problem with taste specificity
coding
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Taste neurons response are a combination of
quality (e.g. bitter) and intensity
E.g., same magnitude of response in “bitter”
neuron
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A high concentration of sucrose
low concentration of quinine
Similar to colour vision
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Neurons response a result of wavelength and
intensity
Need 2 or more receptors to resolve ambiguity
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Neural code for taste:
Distributed coding
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Across fiber patterns
Emphasize degree of
overlap between fibers
Idea: More overlap—>
greater taste similarity
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Relative to ammonium
chloride (NH4Cl)
NaCl more distinct than
KCl
Correlation between
taste and across fiber
pattern
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Tastes differ
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Taste is dynamic
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Depends upon internal state: Hunger
Adaptation/Sensory-specific satiety (SSS)
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Alliesthesia
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Peripheral
Chewing, smelling induces SSS
Sweet desserts follow savory meals
Central
Changed pleasantness that is not sensory based
Decreased pleasantness of sucrose when tubed into stomach
Animals change diet based on nutritional needs
Individual differences
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Experience: culture
Genetics: tasters and nontasters
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saccharin (bitter or tasteless)
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Flavor = Taste+smell
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Eating chocolate with a
stuffed nose
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Where’s the flavor?
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Taste Identification is
impaired without smell
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What we call taste is
really an interaction
between our chemical
senses
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Locate taste as
occurring in the mouth
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Taste nerves carry
somatosensory/texture
info as well
Like visual capture
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Distal chemical sensing:
Olfaction
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For many mammals it is
the most important sense
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Identification
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Smell “face”
localization
We are vision/hearing
dominate mammals
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Under-appreciate/underuse our sense of smell
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Olfactory epithelium
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Olfactory mucosa
Mucus!
 High in nasal cavity
 Site of transduction
 Contains olfactory
receptor neurons (ORN)
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Nose hair: Olfactory cilia
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ORN have cilia
Cilia contain
olfactory receptor
proteins
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Similar to visual
pigment
Transduction
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Odorants bind to
ORs
Change shape of
protein
Ion flow across OR
Electricity
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Smell blind
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Olfactory nerve passes through cribriform
plate (skull) to reach OB
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Smell antennae: Olfactory
bulbs
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An outcropping of
the brain
Its like a snail in
your brain!
Electrical responses
in cilia passed
through olfactory
nerve to OB
Chemotaxis
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How many receptor types are
there?
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1000 different kinds of olfactory receptors (OR)
10 million OR neurons
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10,000 of each type of OR
Each OR neuron has only one type of receptor
1000 neuronal chemical detectors
Compare to visions 4 receptor types (3 cones, 1
rod)
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Mapping onto the bulb
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Similar ORN axons go to
similar portions of the bulb
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Glomeruli (1000-2000)
Inputs mainly from 1 ORN
Thus, each glomerulus
responds to similar
compounds
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Like orientation columns in
visual cortex
Glomeruli coding
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Similar structure, not smell
Odotope maps
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Mapping of similar chemical
features
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Distributed coding of smell
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Olfactory code is a
complex pattern
Overlap across 1000 ORN
types represents smell
quality
Number of receptors would
suggest specificity coding
Millions of colours can be
perceived with 3 cones
How many odors?
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Experience and identification
of odors
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Can tell the difference between 10,000
odors
Distributed coding suggests much greater
number
Poor at identification
Vision dominates
 Get better with experience
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Of mice and men
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Rats up to 50 times more sensitive to odors than
humans
Dogs can be 10,000 times more sensitive
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Yet olfactory receptors equally sensitive
1 molecule can stimulate an olfactory receptor
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Many more receptors (1 billion compared to 10
million)
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Can’t get more sensitive than that!
Decreases # of molecules needed for neural response
Expertise
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Wine tasters don’t get more sensitive w/ their nose
Better at retrieving labels from memory
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Rebuilding your neural nose:
Olfactory neurogenesis
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Mucosa is exposed
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Not safely protected like photoreceptors or auditory
cilia
Unlike vision/audition receptors regenerate
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Every 5-7 weeks
Axons have to find way to bulb
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Create new synapses
Constant rebuilding olfactory system
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What special about neural
transmission in olfaction?
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Unlike other senses, short distance to brain
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Central destinations of olfactory information from
bulb
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Vision/audition have many synapses between retina
and brain
Primary olfactory cortex (piriform cortex)
Secondary olfactory cortex (orbitofrontal cortex)
Amygdala
Unlike other senses, no mandatory thalamic
relay
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What’s the neural code for
smell?
 How does the brain know what of hundreds of
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chemicals are entering the nose?
Don’t really know
Odor quality
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Related to physical/chemical properties?
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Similarly structured molecules smell the same?
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Not necessarily
Differently structured molecules smell different?
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e.g., structure of molecule
Odotopes in olfactory bulb (OB)
Not necessarily
Thus, not easy to relate smell with
physicochemical properties of stimulus or OB
maps
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The hedonic primacy of
olfaction
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Sensory and emotional experience
Not the same for vision/audition
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More intertwined in the chemical senses
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Seeing and feeling more distinct
Why?
Orbitofrontal cortex
Plays dual role
 Critical for emotional
experience
 Secondary sensory
cortex for olfaction
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What makes a bad smell
smell bad?
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Amygdala/pi
riform =
intensity
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Medial OFC
= good
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Lateral OFC
= bad
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The smell of attraction
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Attraction and symmetry
Symmetry associated with
immune system health, healthy development
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 Pleasant odor
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Does the world smell
different to each nostril?
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Nostrils are different sizes
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Odorants attachment to
mucosa depends on airflow
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Alternate every few hours
which is bigger!
Airflow in each nostril differs
Some better at low vs high
and vice versa
Provides two olfactory
images of the world
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Result: better olfactory acuity
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Smell constancy:
Little and big sniffs
Intensity and concentration constancy
 Do big sniffs make for more intense smells? No
 Sniff activity in piriform
Magnitude estimation for odor
cortex
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strength equal
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Olfactory subliminal
perception: Pheromones
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Odorless airborne
chemicals can powerfully
influence behavior
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Sexual behaviour
Mood
Menstrual synchronization
Bruce effect: Aborted fetus
Accessory olfactory system
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Vomeronasal organ (VNO)
Not sure if functional in
humans
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Like extrageniculostriate
visual pathway
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Nonconscious vision
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ESP
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Extrasensory perception: ESP
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The feeling of presences, being, or energy
without use of the 5 basic senses
The problem with ESP is that it is “extrasensory”
Sensory systems are the receivers of
environmental stimulation
Without a receiver there is no perception
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Tree falls in a forest
Subliminal is sensory (e.g., visual, olfactory,
auditory), but nonconscious
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Below subjective threshold for perception
Brain can discriminate thingsto which we don’t have
conscious access
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E.g., amygdala and “unseen” fear
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Why is it possible?
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What have we learned?
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All about conscious perception
Guides our own investigations
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Colour, motion, depth, pitch, smell, taste, etc.
Bias in what “phenomena” we investigate
ESP might represent sensory systems that are
functional but unknown
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Don’t represent conscious information processing
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E.g. discovery of new photoreceptor that regulates circadian
rhythms
Electromagnetic waves outside the visual spectrum
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Experiments on ESP:
Ganzfeld research
trees... buildings...
clouds...
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Target randomly
chosen
receiver
sender
reports imagery attempts to ‘psychically’
send target to receiver
All “sensory” information reduced
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Receiver in sound proof chamber with ping pong balls on eyes,
earphones w/ white noise
Reduce external sensory “noise” to enhance sensitivity to weak
signal
Progressive relaxation: Decrease internal somatic noise
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Experiments on ESP:
Ganzfeld research
At end of session…
– Receiver shown 4 pictures (3 decoys plus target)
– Must rate each picture in terms of matching imagery
– 25% chance of rating target picture highest
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Results
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1974-1997
50+ studies from 15 different labs
 Hit rate = 33.2%, significantly different from
chance (25%)
 Dynamic targets better than static (37% vs
27%)
 Higher rates when a friend versus stranger is
the sender (44% vs 26%)
 50% hit rate for “artistic” students (n=20)
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Julliard students
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Problems
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Experimenter needs to be blind to target
Sensory “leakage”
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The file drawer problem
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How many studies not showing effect unreported?
What are the limits of this perception?
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Sensory cues from use of same target
Send over telephone wire?
Reading other minds
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Would be difficult to home in on one signal
Potentially insulting too!
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Magnetoreception
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Diverse animals can use the earth’s magnetic field as
orientation cue
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North/south axis, and local magnetic fields
Magnetic map sense
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Like having an internal GPS
Homing pigeons, spiny lobsters
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Placed in novel location
Don’t monitor outward journey
Can navigate back
Know very little about the physiological mechanisms
No obvious receptors
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Accessory structures usual focus sensory stimuli on sensory surface
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Lenses: vision
Outer ear: audition
Biomaterials don’t affect magnetic field lines
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THE END
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