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Maps Plasticity of maps Retinotopic map

Last Lecture. Maps Plasticity of maps Retinotopic map. Today’s Outline. More: Retinotopic Map Parallel Visual Pathways Blindsight. Visual world onto the retina. RVF Left Temporal retina Right Nasal retina. LVF Left Nasal retina Right Temporal retina. Retinotopic Map.

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Maps Plasticity of maps Retinotopic map

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  1. Last Lecture • Maps • Plasticity of maps • Retinotopic map

  2. Today’s Outline • More: Retinotopic Map • Parallel Visual Pathways • Blindsight

  3. Visual world onto the retina RVF Left Temporal retina Right Nasal retina LVF Left Nasal retina Right Temporal retina Retinotopic Map

  4. Left Eye’s View Retinotopic Map

  5. Right Eye’s view Retinotopic Map

  6. View from above Perimetric testing to Diagnose field defects Retinotopic Map

  7. Each eye’s field of View (visual field) is mapped out Can light be detected throughout the visual field? Retinotopic Map

  8. VF Left Eye VF Right Eye Combined Visual Field Right Left Retinotopic Map

  9. VF Left Eye VF Right Eye Right Combined Visual Field Left Retinotopic Map

  10. Function: Perimetric Map shows blindness in lower right quadrant of… Left Eye Right Eye Where is the damage? Retinotopic Map

  11. On the retinae? Retinotopic Map

  12. From Retina to Brain Geniculo-Striate Pathway • Optic nerve carries signals from retina. • Decussation at optic chiasm (optic tract) • Synapse at Thalamus: Lateral Geniculate Nucleus (LGN) • Optic radiations to • AREA 17; Striate Cortex, Primary visual cortex Retinotopic Map

  13. Visual World Mapped onto Cortex (via the retina) >> retinotopic map Retinotopic Map

  14. UpperBank CALCARINE FISSURE Lower Bank Hemianopia Deficit in 1/2 VF (homonymous: both eyes) Retinotopic Map

  15. Function: Perimetric Map shows blindness in lower right quadrant of… Left Eye Right Eye Where is the damage? Retinotopic Map

  16. Quadrantanopia defect affects 1/4 VF Retinotopic Map

  17. Scotoma An area of visual loss surrounded by relatively well-preserved vision. Size and shape vary. Retinotopic Map

  18. Gordon Holmes (1919) Correlated Visual Field Defects with lesion locus to identify the Retinotopic map. Retinotopic Map

  19. Sensitive areas are “magnified” Field of View Fovea Cortical Map of Visual Field Retinotopic Map

  20. Equi-visibility chart • Objects in the periphery must be Physically larger in order to beas visible as objects falling on fovea • Fovea is more sensitive • Cortical Magnification Anstis Retinotopic Map

  21. Fovea is a small portion of retina Retinotopic Map

  22. Cortical Magnification • Area 17 neurons have receptive fields in the retina • More neurons have foveal receptive fields Retinotopic Map

  23. Retinotopic map: Summary Crossed organization • Left 17 --> RVF • Right 17 --> LVF Inverted organization • Lower calcarine > Upper VF • Upper calcarine > Lower VF Fovea: Disproportional representation • cortical magnification • NOTE: Each visual cortex represents a visual field NOT an eye. Retinotopic Map

  24. VF Left Eye VF Right Eye Combined Visual Field Right Nasal Left Retinotopic Map

  25. VF Left Eye VF Right Eye Combined Visual Field Right Nasal Left Retinotopic Map

  26. VF Left Eye VF Right Eye Combined Visual Field Right Nasal Left Retinotopic Map

  27. Left Eye Nasal hemiretina- LVF- projects to right hemisphere Temporal hemiretina- RVF- projects to left hemisphere For your review: the connections LVF input to Rhem. RVF input to LHem Right Eye Nasal hemiretina- RVF- projects to left hemisphere Temporal hemiretina- LVF- projects to right hemisphere RIGHT EYE’s RETINA LEFT EYE’s RETINA nasal To cross at optic chiasm uncrossed uncrossed

  28. Outline • The Retinotopic Map • Parallel Visual Pathways • Blindsight

  29. Parallel Pathways From Retina • To primary visual cortex • To superior colliculus Path to SC Parallel Pathways

  30. extra Striate LGN Striate Vision requires Area 17…or maybe not? • Reports of residual vision in Animals with striate lesions (hamsters; monkeys): • Recovery after experimental field defects (cortical ablations) • spared light/dark discrimination • spared localization abilities • Implication: Other pathways can compensate for some geniculo-striate function. • Can this also be true in humans?? LORE of neurology until the early 70's... Parallel Pathways

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