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Lecture 12

PSYB51 lecture 12.docx

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Matthias Neimier

Lecture 12 Odors: Olfactory sensations – Chemical compounds that are ... • Volatile: high vapor pressure at ordinary, room-temperature conditions
 • Small
 • Hydrophobic – But not all. The human olfactory apparatus: – Nose: Small ridges (nasal cycle)-> one nostril will always be smaller than the other (it will switch back and forth because the air flow has different speeds) – Sniffing
 – olfactory cleft, olfactory epithelium – Secondary purpose of the nose: olfaction; primary purpose: breathing to survive  The olfactory epithelium: the ―retina‖ of the nose contains 3 types of cells: – 1. Supporting cells – 2. Basal cells (precursors to...) – 3. Olfactory sensory neurons (OSNs)—cilia protruding into mucus covering olfactory epithelium – Olfactory receptors (ORs): Interact with odorants  action potentials along... 
 – Olfactory nerve (cranial nerve I; thin axons, slow)  Lesions to olfactory nerve cause anosmia: – Head trauma (cribriform plate) – Infections: permanent damage and olfactory loss called anosmia – Olfactory loss can cause great suffering:  Sense of taste/flavour
 :you can‘t sense what you‘re eating and whether it‘s turned bad, etc  Danger warning – Quite common
 – Early symptom for Alzheimer‘s, Parkinson‘s  The olfactory bulb: – Ipsilateral projection – Glomeruli: spherical structures in which OSNs synapse with mitral cells and tufted cells – Chemo-topography: glomeruli sort according to ORs -> Olfactory cortex -> Amygdala-hippocampal complex -> Entorhinal cortex • The genetic basis of olfactory receptors: 
 – ~1000 different olfactory receptor genes (Each single receptor has it‘s own gene; we have 300 types of receptors), each codes for single type of OR
 – Pseudogenes: dormant, don‘t produce proteins that are necessary to create these olfactory receptors (i.e., ORs), 20% in dogs, 60-70% in humans – Trade-off between vision and olfaction? (that we rely more on vision and dogs are more olfactory) • Multisensory perception: a feel of scent: 
 – Odorants can stimulate somatosensory system (touch, pain, temperature receptors)
 – These sensations are mediated by the trigeminal nerve (cranial nerve V) – Also see taste! From Chemicals to Smells – Shape-pattern theory 
 – Odor mixtures  Shape-pattern theory: Match between shapes of odorants and odor receptors (key & lock); dominant biochemical theory  we‘re talking about 2 molecules: one is one that flows on your nose and the other one sits in and fits like a lock – Recent molecular research: Scents are detected by means of combinatorial codes – The molecules lock onto the odorous receptors in all sorts of combinations  The importance of patterns:
 – We detect a multitude of scents based on „only‟ 300-400 olfactory receptors ... how? – We can detect the pattern of activity across various 
 receptor types – Similar to metameres in colour vision: phenyl ethyl alcohol = rose  Odor mixtures: – We rarely smell ―pure odorants,‖ rather we smell 
 mixtures – How do we process the components in a mixture of odorants? – Two possibilities:
 1. Analysis (audition: hi/low pitched tones) 2. Synthesis (metameres in colour vision) Olfaction rather synthetic but can be trained  Olfactory Psychophysics
 – Differences between Detection –Discrimination – Recognition – How do we adapt to smells? – Olfactory detection thresholds: Depend on several factors, e.g., length of carbon chains (vanilla!) – Women: lower thresholds than men, depending on menstrual cycles but not pregnancy – Professionals can distinguish up to 100,000 odors (e.g., professional perfumers, wine tasters – Recognition: Smell and memory – Durability: Our recognition of smells is durable even after several days, month, or year  Identification: smell and language – Attaching verbal label to smell is not easy (few words for smell) – “Tip-of-the-nose phenomenon” – Disconnect btw. language and smell (left vs. right brain) – Patrick Süskind: The Perfume  Adaptation:
 – Sense of smell is essentially a change detector – E.g., walking into bakery, plumber
 – Odors bind to G protein-coupled receptors that indirectly open Na+ channels – Receptor adaptation: Continuous stimulation; GPCRs bury themselves inside cells so that their surface is not exposed to the outside anymore – Intermittent stimulation: e.g., wood smell at IKEA – Cross adaptation: reduced detection of odor after exposure to odors that stimulate the same ORs.  Cognitive (and other kinds of) habituation: After long-term exposure to an odorant, one has very diminished detection ability – After returning from vacation house has smell – Long-term (not necessarily cognitive) 
 1. Longer term receptor adaptation 
 2. Odorant molecules may be absorbed into bloodstream causing adaptation to continue (eg. You‘re used to the smell of garlic so you don‘t notice that you smell of garlic; you also don‘t smell your own house because you‘ve been habituated to it) 
 3. Cognitive-emotional factors
 : our ability to judge on whether something might or might not be dangerous will also influence how much we‘ll habituate  Odors believed to be harmful won‘t adapt What makes us(dis)like smells? Olfactory Hedonics – Familiarity vs. intensity – Nature vs. nurture  Odorhedonics: The liking dimension of odor perception; typically measured with scales pertaining to an odorant‘s perceived pleasantness, familiarity, and intensity – We tend to like odors we‘ve smelled many times before (nurture!) – Influence of intensity : if the intensity goes beyond that , then the same scent becomes unpleasant Anatomy and Physiology • The Five Basic Tastes
 • Taste versus Flavor  Taste buds: – Create neural signals conveyed to brain by taste nerves – Embedded in structures: Papillae (bumps on tongue) – Each taste bud contains taste receptor cells – Information is sent to brain via cranial nerves  Papillae: Four kinds – Filiform papillae: Anterior portion of tongue; without any taste function – Fungiform papillae: Resemble tiny mushrooms, on anterior part of tongue, visible – Foliate papillae: On sides of tongue, look like series of folds – Circumvallate papillae: Large circular structures 2 types of tastants: 
 • Channels for salty & sour • Gprotein-coupled receptors  Central nervous system:
 – Facial nerve/chorda tympani (VII), glossopharyngeal nerve (IX), vagus nerve (X)
 – Gustatory information travels through medulla and thalamus to cortex – Primary cortical processing area for taste: Insular cortex Orbitofrontal cortex: Receives projections from insular cortex – Some orbitofrontal neurons are multimodal Salty: – Salt made up of two particles: Cation (+ anion) – Sodium saccharine – Ability to perceive salt & liking it: not static – Gestational experiences may affect liking for saltiness: ex. when you‘re a fetus and you‘re used to eating a lot of salt Sour:

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