Sensory Systems:

• Touch, temperature, taste, smell

There

are

a variety

of touch receptors

• Touch receptors send signals to the somatosensory cortex via long axons in the spinal cord

• Signals are sent to the opposite (contralateral) side of the brain

• Wilder Penfield - Montreal Neurological Institue - 1940’s

• Found somatotopic map by stimulating brain during surgery

The

Homunculus

• Two-point discrimination threshold- How far apart do the points have to be to be perceived as two points?

Touch

Discri

mination

To Brain

Skin

Receptors

• Two-point discrimination threshold varies dramatically across the skin surface

• Where is it smallest? Where is it largest?

Touch

Discri

mination

• Two-point discrimination threshold varies dramatically across the skin surface• Where is it smallest? Where is it largest? • Best (smallest) threshold is on finger tips, tounge, and face• Worst (largest) threshold is on legs and back

Touch

Discri

mination

• Cortical representation correlates with two-point discrimination threshold

Touch

Discri

mination

• Two classes of thermoreceptors: warm and cold

Thermoception

Taste (Gustation)

Taste buds contain

chemical receptors

Taste

What are the various “tastes”?

• Multi-dimensional scaling reveals several “varieties” of tastes:

– sweet

– salt

– bitter

– sour

– umami (MSG) - protein receptor?

– fat receptor?

Taste

• What you “taste” depends critically on what you’ve recently been tasting– taste receptors adapt and reduce firing over time– for example: eating something salty reduces the perceived saltiness of subsequent foods

Taste is

Relative

• Olfactory bulb receives input from olfactory receptors which contact mucus in nasal cavity

Smell

• There are thousands of different receptors for different kinds of molecules

Smell

• Olfactory receptors use a “lock-and-key ” mechanism - only specif ic molecules will bind with a given receptor

Smell

Receptor

Odor Molecules

• Odor recognition is excellent in humans

• but odor identification (naming) is very poor

• Women tend to be (slightly) better than men at naming smells

Smell

• Smell is strongly influenced by “top-down” processes such as what you are expecting to smell

Smell

• Pheromones are not smells

• Pheromones are chemical signals sent from one animal to another

Pheromones

• Pheromones either induce a behavior in another animal or cause some physiological change

• Very common in insects...not so common in mammals...unclear role in humans

Pheromones

• For example: Alpha Androstenol, found in male pig saliva, causes a female pig to allow the male to mate with her

Fun

Facts

about

Pheremones

• Alpha androstenol is also found in the sweat of human males!

• Does alpha androstenol (or pheromones in general) affect humans?

• Design an (ethical) experiment…

Fun

Facts

about

Pheremones

• Kirk-Smith & Booth (1980) sprayed some of the seats in a dentist’s waiting room with alpha androstenol• Compared to a control condition, more women used the alpha androstenol seat

Fun

Facts

about

Pheremones

• Fewer men used the alpha androstenol seat !

Fun

Facts

about

Pheremones

• Other possible ways in which pheromones influence humans:

– synchronization of menstrual cycles

– mate selection - attraction to opposite major histocompatibility complex

Pheromones

• Pheromones do not control behavior!

• Human behavior is largely under top-down influences, but may be affected subtly by pheromones

Pheromones