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 ’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 Discrimination To Brain Skin Receptors

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

Cortical representation correlates with two-point discrimination threshold Touch Discrimination

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 specific 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