PSYC post-quiz 3 content

odorant + 3 requirements

odour-inducing chemical

• small and volatile

• hydrophobic

• fat soluble

near sense (retronasal olfaction)

odorants in mouth reach receptors through throat

distance sense (orthonasal olfaction)

odorants in air reach receptors through nostrils

describe the anatomy of the nasal cavity (2) 

• septum separates right and left nasal cavities

• 3 turbinates warm and humidify air to promote olfaction

olfactory sensory neurons (3 functions)

• project (10-20) cilia into overlying mucus

• have axons (unlike neurons from other systems)

• fat-soluble molecules bind to odourant receptors

what 2 sensory systems have neurons with axons

olfactory and somatosensory

describe split of 800 odorant receptor genes in humans

• half are functional

• half are pseudogenes (present, but odorant receptors are not produced)

specific amnosia

inability to smell a specific odorant; due to absence of specific odorant receptor protein

amnosia + 3 causes

• inability to smell

• caused by infection, disease/drugs, head trauma

how is amnosia caused with COVID (3)

• support cells in olfactory epithelium are infected

• inflamed support cells blocks odorant receptor expression in OSNs

• recovery may be fast due to turnover in OSNs every 28 days

amblyopia

poor visual acuity in an otherwise healthy eye that cannot be corrected with lenses

3 causes of amblyopia

due to abnormal visual experience during development

• congenital cataract (cloudy lens)

• strabismus (misaligned eyes)

• anisometropia (unequal refractive errors in both eyes)

Fourier’s theorem and analysis + how it can describe visual stimuli

• theorem: sine wave is basic unit — makes complex patterns

• analysis: procedure for separating a complex pattern into component waves that vary over space

• with visual stimuli: complex scenes can be described as a set of component sine waves

olfactory epithelium function + components (2)

tissue lining the upper nasal cavity; senses smell

• odorant sensory neurons: project cilia into overlying mucus; have axons (unlike neurons from other systems)

• odorant receptors: protein molecules in cilia membrane; fat soluble molecules bind to them

describe steps of olfactory transduction (5)

• odorant binds with same type of odorant receptors and send their axons to the same glomerulus pair

• G protein activated

• increase in cAMP

• sodium channel opens

• neuron depolarizes (fires action potentials until odorant is swept away)

what brain regions process olfactory information

• olfactory bulb (axons of mitral and tufted cells) —> primary olfactory cortex (piriform), amygdala, etorhinal cortex —> all 3 synapse in orbitofrontal cortex

something to note about the process of olfactory information in brain

olfaction doesn’t synapse in the thalamus before cortex

connections between olfactory sensory neurons and the olfactory bulb

• Axons of OSNs form the olfactory nerve (cranial I)

• Olfactory nerve synapses with mitral and tufted cells in glomeruli in ipsilateral olfactory bulb

2 techniques for assessing vision in human infants

• forced-choice preferential-looking: show two stimuli, see what babies respond to more

• VEP (visually evoked electric potential) experiment: measure changes in brain electrical activity caused by a changing stimulus image

shape-pattern theory of odour-coding

• Each odorant may bind to several different types of odorant receptor + each receptor may bind several different odorants

• Produces specific pattern of glomerular activity in olfactory bulb

• This is how we can identify thousands of different odours with only 350 receptors

lock and key theory of odour-coding

• 7 primary odours

• Odorant receptors are keys and odorants are locks; transduction initiated when odorant molecule of correct shape binds with particular odorant receptor

• Shape determines odour perceived

vibration theory of odour-coding + example of similar vibrational frequency odours

• Every odorant has a molecular vibrational frequency; odorants with same frequency smell the same

  • E.g. all citrus odors have a similar vibrational frequency

  • Odorants with the same shape can smell different (e.g. methyl alcohol and methyl sulfide; sweet vs. rotten)

• Electron tunnelling: vibrational frequencies (not shape) of odorants activate odorant receptors 

specific anosmia + shape-pattern vs. vibration theory

• Relates to shape-pattern theory:

• 30% of people can’t smell androstenone, some smell it sweet, more smell it urinous

  • Due to genetic differences in odorant receptor (shape-pattern)

• Vibration theory does not explain this because vibrational patterns for androsterone are constant

stereoisomers + shape-pattern vs. vibration theory

• Molecules with different arrangements, but the same vibrational frequencies, smell different

  • so this doesn’t support vibration theory

what is vibration theory supported by

perfume industry (create similar smells with different molecules) and studies in fruit flies (can detect difference b/w same shape/diff frequency molecules)

how does sex affect olfactory detection

females have higher sensitivity (especially during ovulation but not during pregnancy)

• due to hormones + more neurons in olfactory bulbs

how does age affect olfactory detection

OSNs are not replaced as quickly as they die; 50% of the population becomes anosmic after 85

how does experience affect olfactory detection

can develop ability to detect androstenone with repeated exposure

how does attention affect olfactory detection

less olfactory sensitivity during demanding visual tasks

how does the specific odorant affect olfactory detection

easier to detect odorants with longer carbon chains

olfactory discirmination JND

• judge change in intensity of odorant (difficult)

• JND is 18-25%, drops to 7% if olfactometer is used (tool for proper control of stimuli)

olfactory recognition + how difficult, how long, emotion

• knowing you’ve smelled it before

• requires 3x more odorant molecules than detection

• durable up to over a year

• memory is better when initial exposure is associated with emotion

olfactory identification: sex and age factors

• females better

• peaks at 20, declines after 50

3 reasons for the disconnect between our sense of smell and language

1. olfactory processing occurs in right side of brain, language in left

2. competition between odour and language processing in brain (e.g. word recognition impaired when odorant presented at same time)

3. MEG activation differences: more activation when recognizing words without odour

self-adaptation

• Prolonged exposure to a particular odorant reduces sensitivity to, or perceived intensity of, that odorant (smell of something good or bad disappears after a while)

• Difference b/w this and cognitive habituation is this is short-term (sensation can return quick if stimulus is taken away, put back)

cross-adaptation

• Sensitivity for odorant reduced after exposure to different but similar odorant (e.g. picking out perfumes at store – same odorant receptors)

mechanisms for self and cross-adaptation

• Short-term biochemical phenomenon that occurs after continuous exposure to an odorant for 15 min

• Odorant receptor is internalised into cell body of OSN, emerges again after several min (receptor adaptation/recycling)

cognitive habituation

• After long-term exposure to an odorant, no longer able to detect that odorant or has very diminished detection ability

• E.g. going out of town, coming back to house with funny smell or smelling strong fragrance that person wearing it cannot smell

mechanism for cognitive habituation

• Odorant receptors in cell bodies may be hindered after continuous exposure, take longer to recycle

• Odorant molecules may be absorbed into bloodstream and transported to OSN via nasal capillaries, causing adaptation to continue

developmental evidence that odorant preferences are learned

• Infants and children have different preferences (e.g. infants like smell of feces)

• Preferences can come from in utero exposure (if mother eats lots of garlic, baby may like its smell)

cross-cultural evidence that odorant preferences are learned

cultural likes vs. dislikes (e.g. natto, cheese)

evolutionary evidence that odorant preferences are learned

• Innate odour responses are adaptive for special species

• Innate odour responses could be disadvantageous for general species (humans, rats, cockroaches, etc.)

• Learned taste aversions: humans and rats avoid, based on smell, substances that have been paired with gastric illness

2 caveats about odorant preferences being learned

• Potential variability in receptor genes and pseudogenes expressed across individuals may influence perceived odour intensity and therefore pleasantness 

• Trigeminally-irritating odorants (concentrated chemicals like ammonia, capsaicin) may elicit pain responses — we have an innate drive to avoid pain, so these aren’t “learned” responses

example of odorant you can feel + sensory receptors involved

• hot peppers, onions

• Stimulation of free nerve endings (dendrites of trigeminal nerve) in mouth and nose is responsible for the feeling; warning about potentially harmful substances

pheromones

chemicals for animal communication (not necessarily odorants)

• secreted through urine and sweat glands

• trigger physiological/behavioural response in another member of same species

type of pheromone: releasers

trigger immediate, specific behavioural response

• attracting mates, mother recognition, swarming

type of pheromone: primers

trigger slow physiological change

• new queen production, accelerates puberty in animals, period syncing (possibly)

neural structures involved in pheromone communication

• VNOs (vomeronasal organs): detect pheromones in many animals

• project to accessory olfactory bulbs (AOBs)

• no AOB in humans (we use olfactory epithelium)

evidence for pheromones and chemosignals

• chemosignals: chemicals emitted by humans that are detected by olfactory system

• evidence: smelling shirts of ovulating women increase testosterone levels, smelling women’s tears decreases

• evidence: body odour carries info about potential partners (gender, sex orientation)

  • groups had faster response to body odour of preferred sex

name and locate the 4 types of papillary on the tongue

• circumvallate

• foliate (more in children)

• fungiform

• filiform (only one with no taste receptors)

describe taste receptor cells

• 3000-12000 taste buds in mouth

• 50-100 TRCs per taste bud

• have microvilli that are replaced every 10 days from basal cells

• no axons, but release neurotransmitters

salty

• salts (NaCl+) dissolve into cation (Na+) and anion (CI-)

• saltiness is due to cation

• need sodium for nerve and muscle function

sour

• acidic substances dissolve into hydrogen ions

• at high concentrations, will damage both external and internal body tissues at high concentrations

bitter

• compounds contain nitrogen

• many bitter substances are poisonous for survival (bitter sensitivity increases during pregnancy)

sweet

• evoked by sugars: carbon, hydrogen, oxygen

• principle energy source

• artificial sweeteners mimic chemical structure of sugars; sometimes activate bitter receptors

umami

• some say not one of 5 taste classes because we are not born with like or dislike for it

• claimed to be nutritionally important — bodies naturally manufacture it though

• protein molecules too large to stimulate taste/odorant receptors; protein detection occurs in gut, not mouth

transduction of salty tastants

enter through cation (Na+) channel

transduction of sour tastants

enter through H+ channel or as acid (dissociates into H+ inside cell)

transduction of sweet, bitter, umami tastants

involves G-protein coupled receptors

type I taste quality

most taste bud cells, mainly housekeeping

type II taste quality

• no synapses, but depolarize in response to sweet, bitter and umami tastants

• then release ATP that acts on adjacent receptor cells or nerve fibres

type III taste quality

• depolarize in response to sour tastants

• then release serotonin

neural code for taste intensity (higher concentration = ?)

higher concentration = more neurons fire + faster

labelled line theory + 2 supports

• each taste fibre carries a particular taste quality

  • some taste fibres do seem to be tuned to specific tastes

  • sweet tastes can temporarily knocked out in humans by gymnema sylvestre (tastes nasty)

pattern-coding theory

• taste quality is carried by the firing pattern across many taste fibres (olfactory, colour vision)

• Similar across-fibre firing pattern for ammonium and potassium chloride, should taste similar 

• Different pattern for sodium chloride, should taste different 

• Study done in rats:

  • Electric shock trained rats to avoid potassium chloride, ammonium chloride also avoided (might taste the same) but did not avoid sodium chloride (might taste different)

how does temperature affect absolute threshold for taste

• sweet is sensitive at high temp

• salty/bitter is sensitive at low temp

• sour has little effect from temp

how does area affect absolute threshold for taste

larger areas of the tongue are more sensitive

how does duration affect absolute threshold for taste

longer durations of stimulation increase sensitivity

how does location affect absolute threshold for taste

• Primary taste qualities are not exclusively associated with particular tongue locations but slight variation in absolute threshold occurs for different locations

• Middle of tongue has no taste buds (even for suprathreshold concentrations)

how does substance being tasted affect sensitivity for taste

• less sensitivity for sweet tastes

• most sensitivity to bitter tastes

self-adaptation taste example

detection thresholds for salt increase during continued stimulation of tongue with same tastant

cross-adaptation taste example

when threshold for one tastant increases after exposure to a different tastant with the same quality

• e.g. adapting to NaCl raises threshold and reduces saltiness of other salty substances

modification taste example

special type of cross-adaptation; exposure to one tastant alters the quality of a different tastant (e.g. toothpaste affects taste of oranges)

PTC for nontasters vs tasters

• nontasters: no taste

• tasters: bitter

PROP for taster vs. nontaster

• bitter chemical used for taste studies

• inherited trait:

  • nontasters: have 2 recessive alleles

  • tasters: have 1 or both dominant alleles expressing specific bitter receptor

supertasters vs. medium tasters anatomy difference

supertasters have lots more fungiform papillae

health consequences for supertasters and nontasters

• supertasters: higher risk of colon cancer (avoid bitter veggies), lower risk of cardiovascular cancer (avoid fatty substances)

• nontasters: more likely to smoke/consume alcohol

supertaster

 experiences strong sensations of (all) taste, favour, texture, and oral burn

thresholds for bitterness

• Perceived intensity for suprathreshold bitter taste quality grows more slowly than for other taste qualities, but we are more sensitive to bitter at low concentrations

cross-modality matching

• match intensity of sensations that come from different sensory modalities

  • E.g. match loudness of sound to brightness of light to intensity of taste

  • Perceived bitterness increases from nontasters to medium to supertasters

taste discrimination ability

very poor compared to other sensory modalities (for all tastes)

specific hungers theory + evidence for (2) and against (2)

• ideas that a nutrient deficiency will produce a craving for that specific nutrient

• for: studies of cravings associated with sugar or salt deficiencies

• for: study of infants allowed to choose their food —- chose healthy variety

• against: BUT all food choices were healthy so they chose variety out of boredom

• against: this is only true for sugars and salt (things we have taste receptors for); study: Vitamin B deficient rats don’t seek it out without sensory cue (taste)

MMI: difference between taste and flavour

• flavour is determined by the odours stimulating smell receptors while eating (retro nasal sensations)

• that’s why flavour is reduced by illness or plugging nose

MMI: where do flavour sensations actually come from

• perceived to come from the mouth BUT transduction occurs in olfactory epithelium (mislocalization due to taste and tactile sensations from mouth when eating)

MMI: where do flavours of odorants that stimulate the trigeminal system come from + example

nose AND mouth; e.g. Wasabi

MMI: evidence that the brain knows whether odorant is for smell vs. flavour

• fMRI showed orthonasal (nostrils) vs. retronasal (mouth) delivery of food odorants (e.g. chocolate) but not non-food odorants (e.g. lavender)

• activated different brain regions

MMI: evidence that flavour is reduced without taste and touch

patient with normal olfaction, but impaired taste and oral touch, can smell lasagna but it has no flavour while eating

MMI: evidence that flavour is reduced when taste is removed

• Intensity of blueberry flavour yogurt is reduced (but still present) when taste is removed by anaesthetising chorda tympani

MMI: how can we make foods taste more sugary/salty without actually adding those tastants

• retronasal olfactory input (volatiles) can enhance sweetness/saltiness, or inhibit bitterness

analytic vs synthetic sense

• analytic: a high and low note played simultaneously can be analyzed out of the mix and perceived separately

• synthetic: if we mix red and green lights, we see yellow - cannot analyze red and green

is olfaction a synthetic or analytic sense

• both but primarily synthetic

  • we perceive odorant mixtures synthetically, but some degree of analytical perception is possible; ability varies with prior training and the odorants

  • the more odorants in the mixture, the more undistinguishable they become

  • Binaural rivalry: when two odours are presented to either nostril, we alternate in our ability to smell either one (evidence for analytic)

Describe how emotional associative learning can affect odour hedonics

• Anecdotal evidence: 

  • Methyl salicylate (wintergreen) is pleasant in north america but disliked in britain 

  • Britain: wintergreen is associated with medicine, especially analgesics in WWII 

  • United states: wintergreen is with candy which is nice and sweet 

  • Perceived odour pleasantness is a function of learned association between the odor and the emotions experienced at that time

Explain aromatherapy effects based on odour-evoked memories

• Odours can elicit emotional and intense personal memories compared to verbal or visual representations 

• Odours alter mood, performance, well-being and physiology correlates of emotion in a druglike automatic manner 

  • But mainly just due to associated emotions