Sensory Systems:

1
Sensory Systems

• Touch, temperature, taste, smell

2
There are a variety of touch receptors
3

• 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

4
The Homunculus

• Wilder Penfield - Montreal Neurological Institue
  - 1940s
• Found somatotopic map by stimulating brain during
  surgery

5
Touch Discrimination

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

Skin
Receptors
To Brain
6
Touch Discrimination

• Two-point discrimination threshold varies
  dramatically across the skin surface
• Where is it smallest? Where is it largest?

7
Touch Discrimination

• 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

8
Touch Discrimination

• Cortical representation correlates with two-point
  discrimination threshold

9
Thermoception

• Two classes of thermoreceptors warm and cold

10
Taste (Gustation)
Taste buds contain chemical receptors
11
Taste
What are the various tastes?
12
Taste

• Multi-dimensional scaling reveals several
  varieties of tastes
• sweet
• salt
• bitter
• sour
• umami (MSG) - protein receptor?
• fat receptor?

13
Taste is Relative

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

14
Smell

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

15
Smell

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

16
Smell

• Olfactory receptors use a lock-and-key
  mechanism - only specific molecules will bind
  with a given receptor

Odor Molecules
Receptor
17
Smell

• Odor recognition is excellent in humans
• but odor identification (naming) is very poor
• Women tend to be (slightly) better than men at
  naming smells

18
Smell

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

19
Pheromones

• Pheromones are not smells
• Pheromones are chemical signals sent from one
  animal to another

20
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

21
Fun Facts about Pheremones

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

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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

23
Fun Facts about Pheremones

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

24
Fun Facts about Pheremones

• Fewer men used the alpha androstenol seat !

25
Pheromones

• Other possible ways in which pheromones influence
  humans
• synchronization of menstrual cycles
• mate selection - attraction to opposite major
  histocompatibility complex

26
Pheromones

• Pheromones do not control behavior!
• Human behavior is largely under top-down
  influences, but may be affected subtly by
  pheromones