PSYC304 Lecture 08 - Somatosensation PDF

PSYC304: General Principles of Sensory Processing, Touch, and Pain Jay Hosking, PhD 1 Lecture outline Principles of sensory processing Types of somatosensation Pain, thermosensation, and itch 2 L...

PSYC304: General Principles of Sensory Processing, Touch, and Pain Jay Hosking, PhD 1 Lecture outline Principles of sensory processing Types of somatosensation Pain, thermosensation, and itch 2 Learning objectives 1. Differentiate sensation and perception. 2. Differentiate top-down from bottom-up sensory processes. 3. Do we have five senses? Justify your answer with evidence at the cellular level. 4. How do we determine whether incoming neural information reflects vision, or sound, or touch, etc.? What would happen if we wired the auditory neurons to the visual system, and vice versa? 5. Define the four main types of somatosensory receptors in sensory cells. How do they transduce the external energy into a neural signal? How is their information carried to the brain, including their axons and the pathways? 6. How does the brain code for intensity of a stimulus? 7. Why does our sensation diminish with constant stimulation? Why would this be a good thing? 8. Understand the concepts of a receptive field as well as centre-surround organization. 9. How does the brain organize sensory information? 10. What does it mean that the brain is plastic? How does this relate to damage or experience? 11. In biological terms, what is attention? 12. Why experience pain? Why not simply have the negative stimulus alter our behaviour? 13. Define some different types of nociceptors and thermoceptors, including the receptor types and pathways into the brain. 14. Describe some ways that pain can be managed, including their potential drawbacks. 3 Basic Concepts of Sensation and Perception (part 1) Under normal circumstances, sensation and perception are parts of one continuous process Sensation Perception Sensory principles 4  Basic Concepts of Sensation and Perception (part 2) Bottom-up processing Top-down processing Sensory principles 5 Basic Concepts of Sensation and Perception (part 3) Our senses Receive sensory stimulation, often using specialized receptor cells Transduction, often into receptor potentials (cf. PSPs) via ionotropic receptors, can also be via metabotropic Deliver the neural information to our brain Hair cell (Auditory, i.e. sound) Sensory principles 6 The five senses? + Magnetic? + More? Sensory principles 7 Sensory Receptor Organs Detect Energy or Substances Sensory systems have a restricted range of responsiveness. Sensory principles 8 Sensory principles 9 Sensory principles 10 Sensory principles 11 How can we decode action potentials, which are all the same, into separate senses? The doctrine of specific nerve energies The concept of labelled lines What happens if the lines are crossed? What happens if the lines are wired to different targets? Sensory principles 12 Receptors in the skin Touch 13  Example: the Pacinian Corpuscle (Part 1) AKA the lamellated corpuscle One type of skin receptor that detects vibration Graded potentials Action potentials Cell bodies in the dorsal root ganglia (i.e. pseudounipolar neurons) Touch 14 Example: the Pacinian Corpuscle (Part 2) Transduction via stretch receptors Similar to receptors in your muscles (for proprioception, called muscle spindles) Touch 15 Receptor potentials and APs This should look familiar! Sensory principles 16 Intensity Coding: cells with differing thresholds Sensory principles 17 Intensity Coding: summation of responses Multiple neurons act in parallel Stimulus strengthens, more neurons recruited Range fractionation Sensory principles 18  Sensory Adaptation Adaptation: Progressive loss of response to maintained stimulus Why have adaptation? Tonic receptors (slow-adapting) Phasic receptors (fast-adapting) Sensory principles 19 Receptive Fields Sensory principles 20 The four main skin receptors Touch 21 Afferent axons from skin receptors Touch 22 Pathways: The dorsal column system Touch 23  Dermatomes Related to different dorsal roots Overlap with adjacent dermatomes Touch 24 Sensory pathways Segregated pathways (i.e. “labelled lines”) Arrive via nerves to spinal cord or brain stem Most (not all) pass through thalamus Terminate in the cerebral cortex Sensory principles 25  Cortical organization of sensory information Primary somatosensory cortex (S1) Contralateral organization Somatotopic organization Secondary somatosensory cortex (S2) More sophisticated processing e.g. bilateral information Sensory principles Touch 26  -topic organization (in this case, somatotopic) The sensory homunculus Cortical magnification Touch 27 Special systems for special animals Whiskers are for whisking! The barrel cortex Touch 28 Cortical representation Receptive fields get larger, are flexible Representation is based on use Touch 29 Neuroplasticity due to damage “The brain abhors an unused neuron.” —Your teacher, last night when he was prepping these slides Touch 30 Neuroplasticity due to use Implications for your life? Touch 31 Neuroplasticity due to cortical damage Constraint-induced therapy Touch 32 Phantom limbs: a case of large-scale plasticity Touch 33  Are cortical sensory neurons specialized for their type of sensation? Yes, but wiring also seems to be an essential feature Neurons can make sense of nearly any input, even artificial As before, the brain abhors an unused neuron https://www.youtube.com/watch?v=1-0eZytv6Qk Sensory principles Xydas et al. 2008 34  The Brain that Kind of Changes Itself (but Is Mostly Inflexible Because that Inflexibility is a Good Thing) BUT rewiring/activity is limited Sensory principles 35  Attention: manipulating sensory processing An example: listening in a conversation Specifically, enhanced processing What about unattended information? Important regions: posterior parietal cortex, cingulate cortex, others (more to come!) Sensory principles 36 “Association” cortex? AKA tertiary cortex Is multimodal Comprises much of the brain Is it truly “sensory” or “motor”? Sensory principles 37 Synesthesia: cross-modal stimulation e.g. Grapheme-colour synesthesia Thought to be driven by learning rules rather than specific memories May be related to other processes that have been evolutionarily conserved e.g. bouba vs. kiki Sensory principles38 How to test if synesthesia is real (vs. malingering) Sensory principles 39 How to test if synesthesia is real (vs. malingering) Sensory principles 40 Unpleasant but Adaptive Pain: associated with tissue damage, an unpleasant experience Congenital insensitivity to pain: a voltage-gated sodium channel mutation! Pain 41 Pain serves many functions More than simply withdrawal from a source: Recuperation Learning Signal to others Pain 42 Pain is multifaceted The McGill Pain Questionnaire Pain 43 Nociceptors Sensitive to temperature, and to chemicals released by tissue damage Pain 44  Different receptors for different temperatures TRPV1 C fibres Binds to TRPM3 capsaicin! Aδ fibres CMR1 C fibres Pain Binds to menthol! 45  Different receptors for different temperatures Pain 46  Itch: a complicated sensation Some itch cells have histamine receptors, some don’t All have TRPV1 Natriuretic polypeptide B (NPPB) Pain 47 Pathways: The spinothalamic system AKA the anterolateral system Crosses the midline in the spinal cord, before ascending to the thalamus Pain 48  Phantom limb pain AKA neuropathic pain Dorsal horn neurons can become hyperexcitable after damage Pain 49  Pain isn’t a physical sensation Social rejection experienced and described as pain All pain types seem to activate the anterior cingulate cortex Painkillers can lessen the pain of social rejection See also: existential pain?!? Pain 50  Pain management Pain 51  Pain management: drugs Analgesia: the absence or reduction of pain NSAIDS: acting on a different path than we’ve discussed i.e. COX, prostaglandins Opioids (endogenous and exogenous) act at spinal cord, descending pathways, and higher brain sites Learn more in a class on drugs! Pain 52  Pain management: PAG i.e. The periaqueductal gray (PAG) In the tegmentum (midbrain) Endogenous analgesic effects Artificial stimulation Acts by blocking incoming pain signals Pain 53  Pain management: placebo Strong effects in pain Weak/no effects in other modalities Vary according to our expectations e.g. small intervention (pill) vs. large (injection) Likely mediated by endogenous opioids Pain 54