Transcript Ch 14 Cutaneous Senses

Sensation & Perception
Ch. 14: The Cutaneous Senses
© Takashi Yamauchi (Dept. of Psychology, Texas A&M
University)
Main topics
Mechanoreceptors
Temporal, spatial, & frequency responses
Cortical map
Tactile acuity
Perceiving texture
Pain perception
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The Cutaneous sensations
• Sensations based on the stimulation of receptors in
the skin.
– Pressure, vibration, heating, cooling, and tissue damage.
• It is served by the somatosensory system.
• It also creates
– Proprioception (the body sense – e.g., balancing the
body)
– Kinesthesis (the sense of the position and movement)
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• Ian Waterman (a 17 year old
butcher)
– Contracted flu.
– Damaged somatosensory
cortex
– Couldn’t
– As a result, he lost the ability to
• feel skin sensation below his
neck.
• feel his body,
• adjust his body position
• grasp objects properly.
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Skin
• “monumental façade of the human body”
– (Cornel, 1953)
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2 Layers
Skin
Epidermis
dermis
Functions of Skin:
Keeps the body warm
Protects the body from
bacteria
Help maintains the
integrity inside the
body.
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Mechanoreceptors: pick up the
movement of skin
Merkel receptor
Meissner corpuscle
Ruffin cylinder
Pacinian
corpuscle
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Mechanoreceptors
• Mechanoreceptors respond to
– mechanical stimulation such as pressure, stretching, and
vibration.
• Transduction (Pacinian corpuscle)
– When the corpuscle is bent relative to the axon, the tip
of the nerve ending opens ion channels in the
membrane.
– The opening permits the entry of molecules with
positive charge, which depolarize the membrane
potential.
– (from N. R. Carlson “Physiology of Behavior”, 7th ed)
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Fig. 14-1, p. 331
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Fig. 14-2, p. 332
Pathways from skin to cortex
Skin  spinal cord 
thalamus  cortex
• 2 pathways
• Medial lemniscal pathway
– Proprioception & touch
perception
• Spinothalamic pathway
– Temperature and pain
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Cortical map
• Somatosensory cortex
– Corresponds to body locations
• Cortical magnification
factor
– Sensitive areas occupy large
cortical areas (e.g., fingers)
• These cortical areas are
plastic (can be changed by
experience)
–  e.g., trained pianists have
larger cortical representations
of fingers.
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Perceiving details (tactile acuity)
• Measuring tactile acuity
– Two-point threshold minimum separation
needed between two
points to perceive them
as two units
– Grating acuity placing a grooved
stimulus on the skin
and asking the
participant to indicate
the orientation of the
grating
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• The density of Merkel receptors and tactile acuity is
highly correlated.
– The areas that have more Merkel receptors are more
sensitive
Merkel receptors
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Perceiving vibration
• The Pacianian corpuscle is responsible.
– Sustained stimuluation  no response
– Rapid on-off stimulation  response
Merkel
receptor
Meissner
corpuscle
Ruffin
cylinder
Pacianian
corpuscle
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Perceiving texture
• Temporal cues
– The movement of a
surface generates
vibration, which gives
the perception of texture
(rough vs. fine texture)
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Perceiving objects
• Haptic perception
– Perception, in which 3D objects are explored with the
hand.
– Involves sensory, motor, and cognitive systems.
• Demonstration
–
–
–
–
–
Identifying objects
The person sitting next to you close his / her eye.
Pick up an object (e.g., an eraser)
Let him / her touch the object and identify the object.
Swap the role.
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Perceiving Objects - continued
• Psychophysical research
shows that people can
identify objects haptically in
1 to 2 sec
• people use exploratory
procedures (EPs)
– Lateral motion
– Pressure
– Enclosure
– Contour following
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The Physiology of Tactile Object Perception
- continued
• Monkey’s somatosensory cortex also shows
neurons that respond best to:
– Grasping specific objects
– Paying attention to the task
• Neurons may respond to stimulation of
the receptors, but attending to the task
increases the response
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Figure 14.19 Receptive fields of neurons in the monkey’s somatosensory cortex. (a) This neuron responds
best when a horizontally oriented edge is presented to the monkey’s hand. (b) This neuron responds best
when a stimulus moves across the fingertip from right to left. (From “Movement-Sensitive and Direction and
Orientation Selective Cutaneous Receptive Fields in the Hand Area of the Postcentral Gyrus in Monkeys,”
by L. Hyvarinen and A. Poranen, 1978, Journal of Physiology, 283,523-537, figure 3. Copyright © 1978 by
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The Physiological Society, UK. Reprinted by permission.)
Figure 14.20 The response of a neuron in a monkey’s parietal cortex that fires when the
monkey grasps a ruler but that does not fire when the monkey grasps a cylinder. (From
“Cortical Processing of Tactile Information in the First Somatosensory and Parietal
ch 14and Y. Iwamura, 1978. In G. Gordon (Ed.),
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Association Areas in the Monkey,” by H. Sakata
Active Touch, p. 61. Copyright © 1978 by Pergamon Press, Ltd. Reprinted by permission.)
Pain perception
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Pain Perception
• Pain comes from
– a sensory component and an emotional
component.
• Three types of pain:
– Nociceptive - signals impending damage
to the skin
• Types of nociceptors respond to heat,
chemicals, severe pressure, and cold
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Types of Pain
– Inflammatory pain
• caused by damage to tissues and joints that
releases chemicals that activate nociceptors
– Neuropathic pain
• caused by damage to the central nervous
system, such as:
– Brain damage caused by stroke
– Repetitive movements which cause
conditions like carpal tunnel syndrome
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Nociceptive (skin-oriented)
Inflammatory (tissue &
joints-oriented)
Neuropathic (nervoussystem-oriented)
ch 14 ways. See text for details. (Adapted from Scholz
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Figure 14.22 Pain can be created in a number of different
& Woolf, 2002.)
Brain areas for pain perception
– Subcortical areas
• hypothalamus,
limbic system,
and the thalamus
– Cortical areas
• S1 and S2 in the
somatosensory
cortex, the insula,
and the anterior
cingulate cortex
–  the pain matrix
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Figure 14.23 The perception of pain is accompanied by activation of a number of different areas
of the brain, including the somatosensory cortex,
thalamus, anterior cingulate cortex, amygdala,
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hippocampus, and thalamus. The ring-like configuration formed by the anterior cingulate cortex,
hippocampus and amygdala form the limbic system.
What does this tell?
• Cognitive control can modify pain
– Interpreting stimuli (suggestion, recognition)
– Shifting attention (think about something else)
– Expectation (e.g., placebo effect  fake
medicine can be sometimes effective)
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Cognitive and Experiential Aspects of Pain
• Expectation - when surgical patients are told
what to expect, they request less pain
medication and leave the hospital earlier
• Shifting attention - virtual reality technology
has been used to keep patients’ attention on
other stimuli than the pain-inducing
stimulation
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Cognitive and Experiential Aspects of Pain continued
• Content of emotional distraction - participants
could keep their hands in cold water longer
when pictures they were shown were positive
• Individual differences - some people report
higher levels of pain than others in response
to the same stimulus
– This could be due to experience or to
physiological differences
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Figure 14.25:
Participants kept
their hands in cold
water longer when
looking at positive
pictures than when
looking at neutral or
negative pictures.
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