PSYC 330: Perception

THE CHEMICAL SENSES

The Chemical Senses

• Smell and Taste– Olfaction and gustation• Odors

– Volatile molecules

• Tastes– Soluble molecules

– Trigeminal system• “tactile” sensation of some smells and taste

– temperature

Comparisons with other senses

• Evolutionarily Old• Slow• Regenerative• Ipsilateral• Not well understood

The Stimulus• Odorants

– aromatic • Volatile (airborne)• Small• Hydrophobic

• Shape-pattern theory- lock and key fit

- chemical structure

• Vibration theory - atomic vibration

Data? Most consistent with SHAPE- specific anosmia

(inability to smell ONE thing)- stereoisomers

(same atoms arranged in new shape)

Olfactory System - Hardware

Purpose of nose is to prepare air for breathingInternal shape of nose directs odorants upward towards olfactory system (turbinates)

Olfactory cleft - locationOlfactory epithelium - surface

basal cells (“stem” cells for OFS)

olfactory sensory neurons dendrites have cilia with

receptorssupporting cells

Cribriform plate – separates nose from brainOlfactory bulb – lays along surface of brain; includes glomeruli (organized by odor NOT by location)

Transduction and Early ProcessingOdorant binds to receptorAP sent along olfactory sensory neuronTravel thru cribriform plate (olfactory nerve)

into olfactory bulbSynapse at glomeruli

sorted by TYPE of receptor, not locationMitral cells…. Climb on the gypsy wagon…..

Brain Primary olfactory cortexLimbic system

amygdalahippocampus

Entorhinal cortex

An interesting aside….• Craft (2011) Transnasal insulin therapy for

Alzheimer’s patients

Coding Smells

• Buck and Axel (1991)– Genetic code for 1,000 types of olfactory

receptors– Similarity across mammal species BUT • Not all expressed (pseudogenes)• Dogs express 80% (20% pseudogenes)• Humans express 30-40%• Differences relate to smell sensitivity (not number of

odors perceived)

Pattern Theory

• Shape of odorant molecule is important• Odorant-Receptor fit– Pattern of odorant compounds fitting into various

receptor types different pattern in glomeruli activation unique smells

• Evidence– Specific anosmias– Stereoisomers

Adaptation

• Adaptation defined– Receptor-level adaptation• Receptor recycling• Cross adaptation

– Olfactory habituation• Dalton (2002) long term receptor changes• “cognitive” habituation

Hedonics

• Particularly important as it relates to taste• Learned

Durian fruit

... its odor is best described as pig-shit, turpentine and onions, garnished with a gym sock. Richard Sterling

Olfactory Memories and Emotions

• Olfactory cortex (orbitofrontal cortex)• Limbic system (amygdala)• Limbic system (hippocampus)

• Accuracy?• Memories with strong emotional

content