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  1. Olfaction 2 PSY 295 – Sensation & Perception Christopher DiMattina, PhD

  2. PSY 295 - Grinnell College - Fall 2012

  3. Olfaction and vision PSY 295 - Grinnell College - Fall 2012

  4. Olfaction and vision • Many analogies between olfaction and vision • Last time we talked about the olfactory epithelium • “Retina of the nose” PSY 295 - Grinnell College - Fall 2012

  5. ORNs and photoreceptors • Different ORNs express different receptor proteins which bind different odorants (~400 in humans) • Three kinds of cones are maximally sensitive to different wavelengths PSY 295 - Grinnell College - Fall 2012

  6. Synthesis and analysis • Odors are perceived as unitary wholes – no ‘bacon’ molecule • However, people can be trained to detect components • Mostly synthetic (like color mixing) but can also be analytic PSY 295 - Grinnell College - Fall 2012

  7. Binocular Rivalry • In vision, presenting different stimuli to the two eyes results in bi-stable percept • Alternately see either a face or a house, but not both at once PSY 295 - Grinnell College - Fall 2012

  8. Binaral rivalry • Two smells presented into nose at once • Alternately perceive one of the two smells PSY 295 - Grinnell College - Fall 2012

  9. Zhou & Chen (2009) • Marker scent in one nostril, rose scent in other nostril • Same stimulus on each trial, perception alternates PSY 295 - Grinnell College - Fall 2012

  10. Zhou & Chen (2009) PSY 295 - Grinnell College - Fall 2012

  11. Visual stimuli influence smell • Binocular rivalry experiment – picture of rose and marker • Smell ambiguous mixture scent • When visually perceiving rose/marker, smell rose/marker PSY 295 - Grinnell College - Fall 2012

  12. Imagery • Brain imaging of humans during visual imagery shows activation of same areas involved in visual perception • Similar results do not hold for olfactory imagery PSY 295 - Grinnell College - Fall 2012

  13. We are visual creatures • Perhaps rats dream of smells or can imagine smells better? PSY 295 - Grinnell College - Fall 2012

  14. Center-surround organization • Inhibitory interactions between glomeruli create center-surround organization – “nearby” odors inhibit each other PSY 295 - Grinnell College - Fall 2012

  15. Olfactory Psychophysics PSY 295 - Grinnell College - Fall 2012

  16. We are sensitive to odorants • Can detect extremely small concentrations • Human ORNs can be excited by 1 molecule • Have fewer ORNs than other animals which are much more sensitive (i.e. dogs) PSY 295 - Grinnell College - Fall 2012

  17. Commonsense thresholds PSY 295 - Grinnell College - Fall 2012

  18. Declines with age • Number of ORNs regenerated is less than number that die • About 50% of population is effectively anosmic after 85 • Taste and trigeminal systems do not decline as much, which is why elderly like salty and spicy foods PSY 295 - Grinnell College - Fall 2012

  19. Odor recognition memory • Excellent retention of odor memories compared to visual memories • Does not require verbal labels PSY 295 - Grinnell College - Fall 2012

  20. Olfaction and language • Olfactory processing localized to right hemisphere • Language localized to left hemisphere • Olfactory information not integrated with thalamus • May explain lack of verbal labels for smells PSY 295 - Grinnell College - Fall 2012

  21. Adaptation • We adapt rapidly to smells • One cause is G-protein coupled receptor internalization following odorant binding PSY 295 - Grinnell College - Fall 2012

  22. Adaptation • Beneficial to be most sensitive to new smells and insensitive to constant smells • Especially useful if you live on a cow farm PSY 295 - Grinnell College - Fall 2012

  23. Cross-adaptation • Smelling odors similar to a given odorant can cause ORN adaptation (at perfume store) • Why does this make sense in terms of how ORNs work? PSY 295 - Grinnell College - Fall 2012

  24. Both central and peripheral adaptation • Adaptation plays role in olfactory rivalry • Both peripheral and central effects PSY 295 - Grinnell College - Fall 2012

  25. Zhou and Chen (2009) • Present adapting odor to one nostril • Test either that nostril or opposite nostril • See cross adaptation – cannot be due to receptor effects PSY 295 - Grinnell College - Fall 2012

  26. Olfactory Hedonics PSY 295 - Grinnell College - Fall 2012

  27. What smells good and bad? PSY 295 - Grinnell College - Fall 2012

  28. Familiar odors smell better • Subjects tested with both familiar and unfamiliar odors • Gave ratings of pleasantness, familiarity, complexity to each • People prefer familiar odors, less complex odors PSY 295 - Grinnell College - Fall 2012

  29. Intensity PSY 295 - Grinnell College - Fall 2012

  30. Cross-cultural variability • The Japanese find the smell of cheese disgusting • Westerners find smell of some Japanese foods disgusting PSY 295 - Grinnell College - Fall 2012

  31. Nature or nurture? • Infants have very different odor preferences than adults • Sometimes do not find feces disgusting • Cross-cultural variability • Some cultures use cow dung in their hair • Associative learning PSY 295 - Grinnell College - Fall 2012

  32. Learned taste aversion • We can learn an aversion to certain flavors when it has been paired with sickness • Maybe you have aversions for food or kinds of alcohol which made you sick • For a while in college I found vodka disgusting after getting sick PSY 295 - Grinnell College - Fall 2012

  33. Generalist and specialist species • Species with simpler ecology do have innate smell aversions (predators) • It makes sense for species like ours which live in a variety of habitats to be able to learn associatively which smells predict trouble PSY 295 - Grinnell College - Fall 2012

  34. Orbitofrontal cortex • Olfactory pathway projects to orbitofrontal cortex • Responsible for determining ‘value’ of stimuli PSY 295 - Grinnell College - Fall 2012

  35. Devaluation of rewards • Rats trained to associate visual conditioned stimulus with food pellets in a cup • After they learned this, the food was devalued by pairing it with injections of LiCL (induce nausea) • Normal rats stopped going to the de-valued food, OFC lesion rats did not PSY 295 - Grinnell College - Fall 2012

  36. Neural codes for expected rewards • Rats had to sniff an odor port which gave one of two odors predicting either a good reward (sucrose solution) or bad reward (quinine solution) • During learning, neurons in OFC respond differently to smells predicting sucrose and quinine solutions PSY 295 - Grinnell College - Fall 2012

  37. Odor hedonics caveats • All people find painful odors aversive • Different people express different receptors, so some people may lack receptors for unpleasant odors (can’t smell compounds in sweat) PSY 295 - Grinnell College - Fall 2012

  38. Associations differ across cultures • Americans rate wintergreen as pleasant (i.e. mints, gum, candy, etc…) • In Britain it was used to flavor medicines, so has unpleasant associations PSY 295 - Grinnell College - Fall 2012

  39. Olfaction, memory and emotion PSY 295 - Grinnell College - Fall 2012

  40. Are odors the best cue to memory? • Smells bring back memories • But are they really more reliable than memories evoked by other stimuli? PSY 295 - Grinnell College - Fall 2012

  41. Experiment – Herz (1998) • People could recall memories evoked by any cue just as well • Olfactory memories had the richest emotional content PSY 295 - Grinnell College - Fall 2012

  42. Aromatherapy • Can induce positive emotions with odors • Only works however if an odor has positive associations PSY 295 - Grinnell College - Fall 2012

  43. Neuroanatomical relationships • Orbitofrontal cortex receives projections from primary olfactory and gustatory cortex • Responsible for conscious olfactory perception and assigning hedonic value to stimuli PSY 295 - Grinnell College - Fall 2012

  44. Emotions and olfaction are analogous • Either like or dislike, approach or avoid PSY 295 - Grinnell College - Fall 2012

  45. Pheromones PSY 295 - Grinnell College - Fall 2012

  46. Vomeronasal organ • Some animals have another smell organ which detects compounds of higher molecular weight (pheromones) • Projects to accessory olfactory bulb PSY 295 - Grinnell College - Fall 2012

  47. Pheromones • Used for social communication in a variety of species • Ants and social insects • When a bee stings us, cue from stinger invites other bees to attack us! PSY 295 - Grinnell College - Fall 2012

  48. Pheromones provide sexual cues in animals • Male monkey will ignore female in heat if nose blocked • Female pig needs to be exposed to male pig pheromones to mate PSY 295 - Grinnell College - Fall 2012

  49. Humans pheromones are controversial • We do not have a vomeronasal organ or accessory olfactory system • Evidence however for some chemical signaling, mostly in a sexual context PSY 295 - Grinnell College - Fall 2012