PSY280 - 10. Chemical senses Flashcards
chemical senses
molecules floating in the air + molecules you put in your
mouth
stimulants incorporated into our body
have to take molecules in to experience perception
Chemical senses
basic purpose of life to take-in some substances & avoid others: which ones are which?
food vs toxins
to identify chemicals, help us identify which molecules are helpful
olfaction
odorant is an aromatic chemical.
Odor is the olfactory sensation.
Odorant
produce an odor, ordorant needs to be volatile & hydrophobic - There are some notable exceptions.
volatile - can become airborn
hydrophobic - repellant to water
Odorant
allows odourant to remain separate from medium, doesn’t dissolve in mucus + membrane to reach receptors
more molecules will have an odour, but not true universally
CO - byproduct of methane gas, but odourless - associate it with smell but added so we can detect it
the apparatus
2 bilateral olfactory bulb - first site of processing, two, ipsilateral
glomerulus (pl. glomeruli): with bulb organize info about odourants
cribriform plate - separates nose from brain
axons of OSN pass through tiny holes
olfactory epithelium - retina of the nose
the apparatus
olfactory mucosa: capture odourants to facilitate interaction with olfactory receptor neurons olfactory receptor (sensory) neurons: translates it to electrical signals
the apparatus
olfactory cilia: dendrites of sensory receptors - experience adult neurogenesis - regenerate every 28 days
contain receptors which interact with odourant molecules
turbinates - direct volatile molecules to olfactory epitheluim
nose - primary purpose to filter warm + humidify air before it’s passed on to lungs
the apparatus
pass through cribiform - delicate axons pass through tiny holes to synapse with olfactory bulb
olfactory bulb extension of brain - ipsilaterally organized
threshold
average, 7-8 molecules bind to one receptor to trigger an action potential & 40 action potentials are required for us to experience of odor*
detection threshold - lowest concentration of odourant that can be detected
threshold
sensitivity varies based on substance
CO2 low threshold important to detect
acetone has high threshold even though we can easily smell it
detecting odors
Dogs 30-100,000X more sensitive than people:
1 billion more ORNs, more cortex
humans .1% vs dogs 5% dedicated
not bad in detecting smells, humans can follow 10 m scent track of chocolate
Anosmia
total inability to smell, sinus infection/head trauma:
associated with depression
sensitivity declines with age
delicate sense
Anosmia
dependent on smells reaching olfactory - going through small axons
head trauma - can cut axons and may not come back
highly associated with depression: most likely has to do with adult neurogenesis - decreases in limbic system
die out faster than regeneration as we age
Olfactory receptors
analogous to visual pigments except humans have about 350 different types of receptors, not just 4
diff receptors respond to diff odourants - each of them has only 1 receptor type
will respond to range of odourants, but tend to have a preference
Olfactory receptors
1000 genes that code for olfactory receptors, but many are non-functional in humans, most are functional in rats, and dogs
Evolutionary Trade-Off?
trichromats vs dichromats
primates are trading olfaction for vision
old world - less olfactory genes, more colour vision
new world - more olfactory genes, less colour vision
Olfactory receptors
Each kind of receptor widely distributed across olfactory epithelium, but synapse on a specific glomeruli pair
glomeruli receive diff type of stimuli: organize info based on odourant in the olfactory bulb
Olfactory receptors
can receive all of signals from red and green
Molecular structure does not predict odor experience.
two diff structures can produce same odour
Ca2+ imaging
infuse odourant into fluorescent to easy visualize
CA+ enters cell during depolarization, decreasing concentration of fluorescence - means stronger activation
patterns of activation determines smell
each odourant can activate diff receptor types
at the receptors
Using Ca2+ imaging can identify odorant recognition profile - pattern of activation across multiple olfactory receptor types
similar structures can produce similar recognition profiles - not necessarily the case
in the olfactory bulb
Each odorant activates multiple glomeruli, location related to length of carbon chain for the chemical
produce pattern of activation across multiple glomeruli
carbon chain attached, but length varies
shorter chains more posterior/longer chains more anterior
location coding in olfactory bulb
in the olfactory bulb
Chemical structure matters less than the pattern of activity for determining odor
diff forms of same molecule where structure is flipped
stereoisomers smells diff, activation is also diff
similar pattern of activation, similar smell
higher-order processing
O1 & O2 have strong bi-directional connections to
limbic system, including the amygdala
piriform cortex - basic qualities related to odour are processed
orbitofrontal - analyzing odour at higher level, what they indicate - reward or punishment
higher-order processing
In olfactory bulb, evidence of placing coding (chemotopic map), but in the cortex, activation is more distributed
distributed level of activation across puriform cortex - expect odours processed synthetically
synthetic or analytic?
Audition is analytic: diff pitches activate diff parts of cochlea & we hear separate pitches
Vision is synthetic: 2 diff wavelengths of light combine to produce a singular experience of a diff color
analytic - distinct stimuli processed as seperate stimuli
synthetic - 1 experience even when contains multiple wavelengths
synthetic or analytic?
Olfaction is both, with a tendency toward synthesis: few odours that contain only 1 odourant
Analytic abilities vary with practice: depends on familiarity + practice in differentiating
synthetic or analytic
odour presented simultaneously can identify 3/5
each odour has separate odourant molecules produces distinct smell of bacon
our ability to distinguish bacon because we’ve experienced in diff contexts
identifying odors: presence vs. quality
detection/discrimination not identification
diff thresholds for each of these
identification threshold is 3x more than detection
350 olfactory receptor types to produce hundred thousands of types
the mute sense
All languages have only few words exclusively to describe smell
inability to name it even when they find it familiar
huge gap between odour and language
aromatic, redolent, stinky, fragrant, pungent
the mute sense
descriptors to odour - we talk about odour itself
floral - flowers/fruity - fruit
deep disconnection with language
not just in english
several explanations for disconnect:
resources
only sense not integrated through thalamus
damage to thalamus associated with language deficits
lateralized to right hemisphere, whereas language is in the left
several explanations for disconnect:
competition for resources - language + smell need same resources
process semantics, and present odour stimulus, changes fmri signal and ppl less likely to recall word later
can’t do both at same time
but to process non semantic processes - length - don’t get interference
olfactory hedonics
Intensity has a complex relationship with liking dimension of odor.
breaks down based on hedonic value of odourant
inverted u shape pleasant: low - neutral, peak - pleasant, high - unpleasant
negative linear unpleasant: low - neutral, high - unpleasant
both unpleasant for high intensity
olfactory hedonics
tend to like familiar odors, & to think pleasant odors are familiar.
familiarity is a top-down contribution
more semantic based top-down contributions like applying labels
olfactory hedonics
Other top-down contributions, like labels can influence same odour
told cheddar cheese/body odour
diff hedonics - diff labels: fritos and dog feet, weed and skunks
orbitofrontal - tracks reward + punishment
innate
# of diff olfactory receptors expressed by any 1 person is quite variable + probably corresponds to intensity of smell. high intensity we don’t like regardless
innate
anosmic to androstenone found
either sweet musky or urinous
clearly have some genetic component
learned
Babies don’t find either sweat or feces unpleasant
learn associations
learned
prenatal experience plays a role
Mothers who consume distinctive smelling volatiles have newborns who
show greater preference for those odors
learned
no universally unpleasant odors, but there are cultural preferences
hedonics largely dictated by experience which is cultural specific
secondary olfactory - in prefrontal cortex because it tracks reward value
Odors have an unusually retention curve
non linear
diff rates of decrease - steeper, then more stable
small decline overall
right after, still don’t have a high recognition
lost 25% accuracy in 30 seconds
what we remember after 30 seconds, close to what we remember after a week, month, year
Smell
no better than other sensory cues for recall of specific memories
reputation that it’s best cue for recall
in terms of accuracy, same as other modalities
in terms of emotionality, smell wins
in both lab induced + autobiographical - report more memory + greater intensity
Proust effect
induce recall for memory from events that happened years ago
unintentional recall of memories from pasts
Proust effect
In animals that rely on smell for survival, there are two subdivisions of the olfactory system: main & accessory olfactory bulb
main olfactory: responisble for detecting and organizing molecules that interact with epithelium
accessory: triggered by vomeronasal organ
Proust effect
vomeronasal organ evolved to detect large or aqueous molecules, primarily pheromones
detect those that can’t be detected by main olfactory
pheromones - trigger response in other species
signal - danger, reproductive
equivocal evidence that we respond
McClintock effect
menstrual synchrony
pheromones explanation
McClintock effect
Underarm sweat from different times in the cycle caused menstrual cycles to either lengthen or shorten
random cycles when viewed through small window can give appearance of synchrony that’s untrue
pheromones in humans: the evidence
exotic dancers: make more money when ovulating
men smelling t-shirts: men tshirts worn by females ovulating
on birth control make more money
pheromones in humans: the evidence
chemicals in women’s tears decrease sexual arousal in men
significant in sexual attraction, less attracted to female faces
breastfeeding women increases sexual arousal in other women especially with a sexual partner
Gustation
gatekeeper between taste quality + substance’s effect:
sweet= caloric bitter=poison salt=sodium sour=acid
discern which chemicals to ingest + spit out
Gustation
more deliberate - more important
hedonics more specific
four basic qualities + maybe 5
children avoid bitter flavours - desirableness is learned
the apparatus
papillae (bumps)
filiform - most of bumps, no taste, texture especially in trough - not directly involved in taste
fungiform - mushroom-shaped, edges of tongue especially tip
foliate - folded, sides & back of tongue
circumvallate - flat mound surrounded by trench
the apparatus
texture allow us to detect texture + spreads molecules over tongue
buds - globular clusters of
taste cells
the apparatus
taste cells - signals are conveyed through brain
each taste cells have microvilli that project through taste pore
taste receptors specialized for quality - 1 for each - can appear on any type of papillae
diff receptors on a single taste cell
taste receptors
Salty (Na+) & sour (H+) ions enter the cell through ion channels, directly increasing the potential inside the cell
to trigger depolarization.
taste receptors
salty + sour bundled - both positive ions - change drives membrane potential - triggers depolarization
encourages Ca to enter cell + triggers release of neurotransmitters
saliva breaks it down to ions
taste receptors
Sweet, bitter & umami molecules act through second messenger: activate G-protein
triggers enzyme cascade, Ca2+ released intracellularly, triggers neurotransmitter release
bind with receptors activating the G protein which triggers an enzyme cascade - intracalcium stores which in turn triggers release
taste receptors
chemotopic map (doesn’t exist)
detection threshold is similar across
bitter - back of throat highly sensitive
umami: is it or isn’t it?
quality evoked by monosodium glutamate & is described as meaty, brothy, & savory.
idea is an advertising campaign that insisted it signaled consumption of protein
but peanut butter is high in protein, yet it doesn’t have umami taste
survival advantage of protein, but some people don’t like protein
umami: is it or isn’t it?
associated with sweet receptors
in the gut
• safe for consumption
umami receptors unique combo of 3 + 2 - take off of sweet
umami: is it or isn’t it?
receptors in a way they aren’t organized
break down of protein into glutamate
associate msg with reward - only works if you swallow it
have to consume protein to develop associations
no evidence that msg is bad for you
higher-order processing
signals from the taste buds transmitted via 3 cranial nerves:
nucleus of the solitary tract
! thalamus
!insula & frontal operculum (T1) !orbitofrontal cortex
innervate tongue and throat
converge in brain stem
thalamus to insula + frontal operculum - primary cortex for taste perception
some end up in orbitofrontal cortex - reward + punishment - how taste preference is formed
distributed or specificity coding?
Reports from subjective experience in humans parallels these results.
distributed coding
sodium chloride diff activation with potassium chloride +
distributed or specificity coding?
amonium chloride
pair foot shock with KCL enough, so classical conditioning takes place
transfers to ammonium but not sodium chloride
distributed or specificity coding?
Sucrose, NaCl, HCl & QHCl are compounds that com the closest to having only one of the four basic tastes. Each tends to activates specific neurons in the chorda tympani.
shows some specificity
distributed or specificity coding?
But! Taste cells can have more than one type of taste receptor, & the nerve fibers that innervate them can synapse with more than one taste cell!
taste cells have more than one taste receptor
nerve fibers specificity - how it’s organized is a mystery
don’t know how we identify
taste perception distributed - most valid way
genetic variation in taste experience
PROP & PTC: some people taste it (tasters), some people don’t (nontasters) 1/3 taste nothing 2/3 bitter taste prop = taster PTC related compound - safer
Tasters
tend to be more finicky eaters.
Supertasters
have more fungiform papillae, and experience the most intense taste sensations.
more sensitive to bitter tastes
fewer alcoholics because of sensitivity
linked to a specific gene
supertasters more intense taste perception
some ppl report more or less intense taste - most intense oral burnings and acids - generally avoid
feel fats + thickeners more
Flavor
combination of basic tastes, retronasal olfaction, & tactile sensations
tactile critical component to our experience
preference often around texture
Flavor
When you pinch your nose, the experience of flavor is significantly diminished.
pinch nose reduces flavour
decreases identification
Flavor
Flavor is localized to the mouth, except for volatiles that activate c-fibers in the nasal cavity.
localize to mouth - where you feel + put the food
volatiles that activate c fibers can feel like burning in your nose
Flavor
Responses from taste & smell are first combined in the orbitofrontal cortex.
vison, taste, olfaction, touch converge here
place where flavour lives
directly correlates with hedonic experience
Activity in the OFC indicates hedonic qualities of flavor
pleasure varies according to OFC activity
first got it - excited
as they got more and more, monkeys no longer wanted it
similar pattern in OFC activation
tracking reward + punishment + changes in rewarding value of stimulus
Sensory-specific satiety
refers to the fact that we can be satiated for one flavor (broccoli), but still have room for apple pie.
can be satiated for one flavour but have room for another flavour
can get nutrients from diverse flavours
