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Cortical Reorganization in Somatosensory Cortex: A Biological Approach to Lost Sensory Nodes

Cortical Reorganization in Somatosensory Cortex: A Biological Approach to Lost Sensory Nodes. Dan Stiehl wdstiehl@mit.edu MAS.965. Somatosensory Maps. Each Region of Area 3b and Area 1 maps to a different body location Owl Monkey shown. Principles of Neuroscience 4 th Edition, Chapter 20.

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Cortical Reorganization in Somatosensory Cortex: A Biological Approach to Lost Sensory Nodes

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  1. Cortical Reorganization in Somatosensory Cortex:A Biological Approach to Lost Sensory Nodes Dan Stiehl wdstiehl@mit.edu MAS.965

  2. Somatosensory Maps • Each Region of Area 3b and Area 1 maps to a different body location • Owl Monkey shown Principles of Neuroscience 4th Edition, Chapter 20

  3. “Wiring” of the Sensor Network • Originally believed that all the cortical maps of the body’s surface were hard wired from birth • Recent work has shown that in fact cortical maps are very plastic and can rewire themselves based on changes in the body • Details of the topographic map vary from animal to animal thus implying differences in wiring

  4. When One Node Dominates Neighbors • Monkeys trained to touch disk with fingertips for several months • Finger tip regions expanded into proximal phalanges region • Use of fingertips strengthened connections Principles of Neuroscience 4th Edition, Chapter 20

  5. When Nodes Combine: “Cells that Fire Together, Wire Together” • Surgically connected tissue of two monkey fingers • Connected fingers are always used together • Sharp discontinuity between fingers was not seen in cortex Principles of Neuroscience 4th Edition, Chapter 20

  6. Syndactyly in Humans • Fusion of fingers together from birth • Size of the representation of the hand is less than in normal humans • No separation of fingers • Surgically separating fingers • Within weeks they show individual representations of fingertips • Hand representation expands to almost normal size (3-9 mm) Principles of Neuroscience 4th Edition, Chapter 20

  7. When a Node is Removed • Study of deafferented monkeys • The sensory nerves to the arm were severed at the upper limb • After 10 years or more, the cortical representation for the face had expanded into the cortex area for the hand • Stimulation of the face of these monkeys evoked responses in the area that normally represented the hand

  8. When a Node is Removed • Phantom Limbs • Possibly due to the rearrangement of cortical circuits • Remapping of referred sensations • Just like in the monkeys, the face and upper arm regions occupy the territory previously devoted to the hand Principles of Neuroscience 4th Edition, Chapter 20

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