Chemical senses - smell and taste
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Chemical senses - smell and taste



Chemical senses - smell and taste, psychology 280 LECTURE 9

Chemical senses - smell and taste, psychology 280 LECTURE 9



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    Chemical senses - smell and taste Chemical senses - smell and taste Presentation Transcript

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