OlfactionOlfaction

The Sense of SmellThe Sense of Smell

Smell helps us:Smell helps us:

Avoid dangerous situations (fumes, smoke) Avoid dangerous situations (fumes, smoke)

Avoid consuming poisonous substances and Avoid consuming poisonous substances and

spoiled food (sour milk) spoiled food (sour milk)

Choose mates?Choose mates?

What are olfactory stimuli?What are olfactory stimuli?

Odorants (airborne molecules)Odorants (airborne molecules)

Odorants must be volatile (they give off Odorants must be volatile (they give off vapors)vapors)

More vapors are given off when an odorant More vapors are given off when an odorant is heated!! (warm soup smells better than is heated!! (warm soup smells better than cold soup)cold soup)

Odorants reach olfactory Odorants reach olfactory receptors by:receptors by:

1. Being inhaled through the nose.1. Being inhaled through the nose.

2. Through the mouth (vapors circulate up 2. Through the mouth (vapors circulate up through throat)through throat)

Olfaction- originates in the nasal Olfaction- originates in the nasal cavitycavity

Olfactory system structuresOlfactory system structures

Olfactory Receptor NeuronsOlfactory Receptor Neurons

Carry impulses directly to the brainCarry impulses directly to the brain

Live for 5- 8 weeks & then die.Live for 5- 8 weeks & then die.

Summary: olfactory pathwaySummary: olfactory pathway Olfactory receptor neurons detect odorants in Olfactory receptor neurons detect odorants in

mucosa.mucosa.

Signals are sent via olfactory receptor neurons to Signals are sent via olfactory receptor neurons to bulb structures (glomeruli).bulb structures (glomeruli).

Mitral and tufted cells carry signals to Mitral and tufted cells carry signals to orbitofrontal cortex, temporal lobe, and the limbic orbitofrontal cortex, temporal lobe, and the limbic system.system.

Which animal is most sensitive to Which animal is most sensitive to smell?smell?

Dogs 300-10,000 times more sensitive to Dogs 300-10,000 times more sensitive to smell than humanssmell than humans

Why? Humans have 10-40 million Why? Humans have 10-40 million olfactory receptor neurons, dogs have over olfactory receptor neurons, dogs have over a billion!!a billion!!

Odor HedonicsOdor Hedonics

What are “pleasant” and “unpleasant” What are “pleasant” and “unpleasant” odors? Variability is high.odors? Variability is high.

Most universally-rated “pleasant” odorant is Most universally-rated “pleasant” odorant is vanilla.vanilla.

How is perception affected by How is perception affected by odor?odor?

Odor enhances our experience of the world Odor enhances our experience of the world (food, surroundings, people).(food, surroundings, people).

We associate memories with certain We associate memories with certain odorants.odorants.

We lose the ability to experience “flavors” We lose the ability to experience “flavors” if our sense of smell is impaired.if our sense of smell is impaired.

AnosmiaAnosmia: loss of : loss of sensesense of smell of smell

May be to May be to specificspecific odors or odors or allall odors. odors.

Caused by infection to nasal cavity or brain Caused by infection to nasal cavity or brain injury (frontal lobe).injury (frontal lobe).

About 2 million people in US are anosmic.About 2 million people in US are anosmic.

Olfaction and behaviorOlfaction and behavior

A. Infant perception & attachmentA. Infant perception & attachment

Babies enthusiastically “orient” to pleasant Babies enthusiastically “orient” to pleasant odors (banana, vanilla) and cry/grimace to odors (banana, vanilla) and cry/grimace to unpleasant odors (shrimp; rotten eggs).unpleasant odors (shrimp; rotten eggs).

Babies can discriminate their mother’s scent Babies can discriminate their mother’s scent from other women (Macfarlane, 1975).from other women (Macfarlane, 1975).

Olfaction and BehaviorOlfaction and Behavior

B. Smell may alter hormonal activity B. Smell may alter hormonal activity

McClintock Effect: women’s menstrual McClintock Effect: women’s menstrual cycles synchronize when they live together cycles synchronize when they live together (dorms).(dorms).

Olfaction and behaviorOlfaction and behavior

CC. Mate Selection. Mate Selection

Females rate males with immunity profiles more Females rate males with immunity profiles more dissimilar to their own (Wederkind et al., 1995) as dissimilar to their own (Wederkind et al., 1995) as smelling “more pleasant.” Males with very smelling “more pleasant.” Males with very similar immunity profiles are rated as smelling similar immunity profiles are rated as smelling “less pleasant.” “less pleasant.”

What is the current theory underlying this What is the current theory underlying this finding?finding?

Smell may provide a clue about Smell may provide a clue about our suitability as a mate?our suitability as a mate?

It’s possible that choosing a mate with an It’s possible that choosing a mate with an immunity profile very similar to our own, immunity profile very similar to our own, may result in the expression of unwanted may result in the expression of unwanted recessive genes in our offspring.recessive genes in our offspring.

Smell may provide us with a “cue” in which Smell may provide us with a “cue” in which we can detect suitable mates who will we can detect suitable mates who will produce healthy viable offspring.produce healthy viable offspring.