1. Review Session: (1) Brain Development 3: Modification of Neural Circuits (Map Plasticity and Reorganization (Wed Apr 24 th 10 AM) (2)Somatosensory Circuitry: Touch and Proprioception (Friday Apr 26 th 8 AM) (3) Somatosensory Circuitry: Pain and Temperature (Friday Apr 26 th 10 AM) Kimberle M Jacobs kmjacobs@vcu.edu 804 827-2135 http://www.people.vcu.edu/~kmjacobs/teach.htm

2. Topographic Map Principles There is an ongoing competition for neural space (between adjacent representations) Proper formation of the topographic map during development requires normal experience Changes in the map due to alteration of sensory afferent input can be called use-dependent or experience-dependent plasticity Some aspects of topographic maps can only be altered during a “critical period” of development (thalamic input to cortical layer IV) Some aspects of topographic maps can be altered into adulthood (via intracortical connections) Presumably more cortex gives you better control over that sense or body region – blind, braille readers have greater spatial resolution in finger tips Your patient has lost their index finger – what would you advise in order for them to gain increased sensitivity in adjacent fingers? What effect would this have on cortical representations?

3. Time Course of Reorganization of Sensory Representations in Adults Digit 1 Digit 2 Digit 3 Normal Digit 1 Unresponsive Digit 3 Digit 2 Amputation Immediate Digit 1 Digit 3 Short term (hours to days) Digit 1 Digit 3 Days to years Map Reorganization time Border Shifts Adjacent representation s take over Large scale reorganization – over 10 cm in Monkey cortex Unmasking of inputs normally hidden by inhibition Synaptic Plasticity changes (LTP) Anatomical changes, sprouting, creation of additional synapses

4. Basic Plan for Somatosensory Info to Consciousness Quaternary (4 ) o Action Potential Initiation Site Outside the CNS! 1 2 3 4

5. Conscious Somatosensation Non-conscious Proprioception Spinocerebellar Tracts (IPSILATERAL) BODYHEAD Trigeminal System TouchPain SpinalPrincipal (Main) PAIN & Temp Fine Touch Lateral Spino- Thalamic Dorsal Column System Information reaching consciousness goes to the CONTRALATERAL Neocortex, Nonconscious Sensory Information goes to the IPSILATERAL Cerebellum

6. Compare ALS and Dorsal Column

7. Somatosensory Information from the Body to Consciousness

8. Trigeminal System: Touch Component

9. Gliosis and cavitation in midline of the spinal cord – CSF enters the cord. The larger the cavitation, the more tracts affected. One possible cause is a Chiari Malformation. Other causes include trauma, infection. (anything that compresses the CSF) http://www.asap4sm.com/ Symptoms: Bilateral loss of pain and temperature at the level of the lesion (segments involved). Lesions and Clinical Deficits - Syringomyelia Area of lesion

10. Lateral Medullary (Wallenberg’s) Syndrome – Symptoms include loss of pain and temperature on the ipsilateral head/face, contralateral loss of pain and temperature in the body, and ataxia. ALS (lateral spinothalamic tract) Trigeminal Nucleus Spinal Trigeminal Tract Dorsal Spinocerebellar Tract Ventral Spinocerebellar Tract Lesions and Clinical Deficits - Wallenberg’s

11. Degeneration of myelinated afferent fibers in the dorsal columns, (destroys large diameter axons), is a late stage of syphilis. Symptoms: Severe deficits in touch and position sense but often little loss of temperature perception and of nociception. Bilateral lesion = bilateral effects. Lesions and Clinical Deficits – Tabes Dorsalis Area of Lesion

12. LESIONS and Clinical Deficits – Brown-Sequard Syndrome Hemisection of the spinal cord, often in the cervical spinal cord – (it is rare for the entire hemisection to be affected, but this does occur, more often incomplete hemisection is found). DC Symptoms: a) Loss of fine discrimination touch, vibration, and position sense ipsilaterally for body regions from affected dermatome and down Arch Neurol (2001) 58: 1470. b) Loss of pain and temperature contralaterally for body regions from affected dermatome and down (small region of bilateral loss of pain and temp at level of lesion and 2 segments below) c) Motor Effects: – Ipsilateral Spasticity and Weakness