Chemical senses - smell and taste
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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
    Chemotaxis
  • 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