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class+16+lecture_posted - Sensation and Perception Class...

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Sensation and Perception Class XVI: Touch & Iriki et al.
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Touch Physiology Pain Pain sensations triggered by nociceptors Responses to noxious stimuli can be moderated by anticipation, religious belief, prior experience, watching others respond, and excitement Example: Wounded soldier in battle who does not feel pain until after battle
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Touch Physiology Analgesia : Decreasing pain sensation during conscious experience Soldier in above example: Experienced effect because of endogenous opiates : chemicals released in body to block release or uptake of neurotransmitters transmitting pain sensation to brain Externally produced substances have similar effect: Morphine, heroin, codeine
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Touch Physiology Gate control theory Description of the system that transmits pain that incorporates modulating signals from the brain. Feedback circuit located in substantia gelatinosa of dorsal horn of spinal cord Gate neurons that block pain transmission can be activated by extreme pressure, cold, or other noxious stimulation applied to another site distant from the source of pain.
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Figure 12.9 Gate control theory of Melzack and Wall (1988)
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Touch Physiology Pain sensitization: Nociceptors provide signal when there is impending or ongoing damage to body’s tissue: “Nociceptive” pain Once damage has occurred, site can become more sensitive: Hyperalgesia Pain as a result of damage to or dysfunction of nervous system: Neuropathic No single pain medication will alleviate all types of pain
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Touch Physiology Cognitive aspects of pain Pain is generally a subjective experience with two components: Sensation of painful stimulus and emotion that accompanies it Areas S1 and S2 are responsible for sensory aspects of pain Recently, researchers have identified areas of brain that correspond to more cognitive aspects of painful experiences: Anterior cingulate : A region of the brain associated with the perceived unpleasantness of pain sensations Prefrontal cortex : A region of the brain concerned with cognition and executive control. May contribute to pain sensitization
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Figure 12.10 PET signals showing the effect of suggested pain (under hypnosis) on the brain, as observed by Rainville et al. (1997)
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Touch Physiology Pleasant touch Discriminative touch : The classic touch sensations of tactile, thermal, pain, and itch experiences Newly uncovered fifth component of touch : Pleasant touch Mediated by unmyelinated peripheral C fibers known as “C tactile afferents” (CT afferents) CT afferents not related to pain or itch Respond best to slowly moving, lightly applied forces (e.g., petting) Processed in orbitofrontal cortex rather than S1 or S2
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Tactile Sensitivity and Acuity How sensitive are we to mechanical pressure? Max von Frey (1852–1932): Developed an
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class+16+lecture_posted - Sensation and Perception Class...

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