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Touch 2: Perception, Pain and Plasticity

Touch 2: Perception, Pain and Plasticity. Outline. Perception How we perceive texture, vibration, details Central Processing Receptive field properties in cortex Effects of attention on touch processing Pain Gate control theory Pain and cognition Plasticity

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Touch 2: Perception, Pain and Plasticity

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  1. Touch 2: Perception, Pain and Plasticity

  2. Outline • Perception • How we perceive texture, vibration, details • Central Processing • Receptive field properties in cortex • Effects of attention on touch processing • Pain • Gate control theory • Pain and cognition • Plasticity • Sensory experience and cortical organization • Phantom limbs PSY 295 - Fall 2012 - Grinnell College

  3. Perception PSY 295 - Fall 2012 - Grinnell College

  4. Fine details • Braille readers can read 100 words per minute • Which population of mechanoreceptors is useful for resolving fine spatial details like these braille patterns? PSY 295 - Fall 2012 - Grinnell College

  5. Fine details • Merkel disks (SA1 fibers) signal fine spatial details PSY 295 - Fall 2012 - Grinnell College

  6. Fine details • Areas of skin more sensitive to fine detail have denser innervation of Merkel receptors PSY 295 - Fall 2012 - Grinnell College

  7. Measuring tactile acuity • What is one confound with the two-point threshold as a means of studying tactile acuity? PSY 295 - Fall 2012 - Grinnell College

  8. Measuring tactile acuity • Thresholds for discriminating grating orientation are more controlled way of measuring tactile acuity PSY 295 - Fall 2012 - Grinnell College

  9. Vibration • Several mechanoreceptor types respond to vibratory stimuli • Put vibrating probe on hand and measure smallest vibration which can be detected by people and by sensory receptors PSY 295 - Fall 2012 - Grinnell College

  10. Vibration • Different receptor types are sensitive to different frequencies • Perception follows the most sensitive receptors • Lower envelope principle PSY 295 - Fall 2012 - Grinnell College

  11. Romo paper • Which types of neurons did Romo et al. find important for discriminating vibratory frequencies near 20 Hz? • Which kinds of neurons were ineffective? PSY 295 - Fall 2012 - Grinnell College

  12. Texture • Spatial and temporal cues are important • Temporal cues important when you actively scan fingers across surface PSY 295 - Fall 2012 - Grinnell College

  13. Mechanoreceptors and texture • Selective adaptation experiment • Pre-adapted to low-frequencies to reduce Meissner corpuscle responses (RA1) before fine texture discrimination test • Pre-adapted to high frequencies to reduce Pacinian corpuscle responses (PC) PSY 295 - Fall 2012 - Grinnell College

  14. Feeling roughness with a pen • You can determine the texture of a stimulus just by running a pen over it, i.e. without touching it • Which receptor types might be useful for this? PSY 295 - Fall 2012 - Grinnell College

  15. Central Processing PSY 295 - Fall 2012 - Grinnell College

  16. Perception and central processing PSY 295 - Fall 2012 - Grinnell College

  17. Sensory processing • Mechanoreceptor neurons have simple receptive fields • Increase firing rate with stimulation • Neurons in thalamus have center-surround receptive fields • Excited by stimuli in RF center, inhibited by surrounding stimuli PSY 295 - Fall 2012 - Grinnell College

  18. Generation of receptive fields convergent excitation surround inhibition lateral inhibition PSY 295 - Fall 2012 - Grinnell College

  19. Lateral inhibition improves perceptual discrimination PSY 295 - Fall 2012 - Grinnell College

  20. Cortical neurons • In the cortex, many neurons have complex feature sensitivity • Selective for oriented bars or movement in a given direction PSY 295 - Fall 2012 - Grinnell College

  21. Attention • Neural responses cortex are modulated by attention • Monkey trained on both visual and tactile task while recording from S1 and S2 • Find some neurons respond more when monkey is paying attention to touch stimuli PSY 295 - Fall 2012 - Grinnell College

  22. Pain PSY 295 - Fall 2012 - Grinnell College

  23. Nociceptors • Bare nerve endings in skin sensitive to harmful stimuli • Pressure, burns, chemicals, etc… PSY 295 - Fall 2012 - Grinnell College

  24. Pain is a subjective phenomenon • Responses to noxious stimuli modified by variety of factors • anticipation • prior experience • watching others • excitement • Soldiers in battle often do not feel pain until after the battle PSY 295 - Fall 2012 - Grinnell College

  25. Gate-control theory • Top-down signals from brain can block bottom-up signals from nociceptors by modulating the response of spinal cord neurons PSY 295 - Fall 2012 - Grinnell College

  26. Opiates • Body produces endogenous opiates which act in spinal cord to suppress pain – soldier in battle • Inhibit synaptic transmission in spinal cord pain pathways • Chemically similar to morphine, heroin, etc… PSY 295 - Fall 2012 - Grinnell College

  27. More analgesia • Benign stimulation (rubbing skin) near site of injury also reduces pain PSY 295 - Fall 2012 - Grinnell College

  28. Pain and cognition • Areas S1 and S2 represent the sensory aspects of pain, emotional aspects in anterior cingluatecortex • Hypnosis experiment – subjects put hands in same water, but those who were told it was worse had more activity in AC cortex, but not S1 or S2. PSY 295 - Fall 2012 - Grinnell College

  29. Pain and cognition • Subjects put hand in cold water while being shown pleasant and unpleasant pictures • Could keep hand in longer when looking at pleasant pictures PSY 295 - Fall 2012 - Grinnell College

  30. Pain and cognition • Women received shocks or their male partner received shocks • Activity in same brain regions (anterior cingulate, insular cortex) whether receiving shocks or watching shocks • More empathetic women had more brain activity PSY 295 - Fall 2012 - Grinnell College

  31. I feel your pain PSY 295 - Fall 2012 - Grinnell College

  32. Plasticity PSY 295 - Fall 2012 - Grinnell College

  33. Body is mapped on cortex • Maps are not static but change with experience PSY 295 - Fall 2012 - Grinnell College

  34. Maps change with experience • Monkey trained on task using his fingertip to make a discrimination • After several months, the cortical representation of that fingertip had expanded tremendously PSY 295 - Fall 2012 - Grinnell College

  35. Violin players • Brain imaging experiments show more cortical area for hand which fingers the violin strings than the hand which holds the bow PSY 295 - Fall 2012 - Grinnell College

  36. Digit fusion • Monkeys had two digits fused together • Region of cortex between digits responded to both digit • Multi-digit receptive fields PSY 295 - Fall 2012 - Grinnell College

  37. Digit amputation • Removed input from glabrous skin of D1, D2 • Immediately afterward saw responses to dorsal skin • Eventually also saw responses to digit D3 PSY 295 - Fall 2012 - Grinnell College

  38. Phantom limbs PSY 295 - Fall 2012 - Grinnell College

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