1. Receptive Field Dynamics in Adult Primary Visual Cortex Charles D. Gilbert & Torsten N. Wiesel Psych 3FA3E Neurobiology of Learning and Memory Dr. Hong-jin Sun Tuesday, October 7 2008 Abdullah Mayo Barbara Fenesi Charles Schandl Charmaine Silveira Da Graca Costa Margaret Cronyn Sarah Babcock Barbara GROUP B3:

2. Schedule  Aims Key Terms  Methods Initial Preparation Experimental Procedures  Results Cortical Sites (Short-term and Long-term effects) LGN  Conclusions Horizontal Connections  Related Studies Barbara

3. Aims  In spite of a Scotoma, the cortical representations of damaged cells in the visual cortex form new connections Scotoma: An area of loss or impairment of visual acuity surrounded by a field of normal or relatively well-preserved vision Barbara

4. Aims  Primary visual cortex is capable of cortical topographic reorganization Topographic Mapping: Mapping of the organization of the cells in the visual cortex corresponds to the organization in the spatial field Barbara

5. Aims  Horizontal connections increase plasticity, and improve cortical input Horizontal connections – pyramidal cells that link columns with shared orientation preference;allow cells to integrate visual information from outside their receptive fields Barbara

6. Aims  Topographical reorganization occurs within superficial layers of the visual cortex and not in earlier visual pathway structures such as the LGN LGN (Lateral Geniculate Nucleus) - Located in the thalamus; receives information from the retina and sends projections directly to the primary visual cortex Barbara

7. Aims  Receptive field structure changes may occur continuously during normal vision well past adulthood Receptive Field - A small restricted spatial region of the sensory field Barbara

8. Methods  Initial Preparation Electrophysiology and lesions were carried out on retina of anesthetized, paralyzed cats and monkeys Receptive Field Map - show ‘minimum response’ fields for cells in the superficial layers Abdullah

9. Methods  Procedure The lesions were made in the parafoveal retina Destroyed outer retinal cells Positions of receptive fields relative to the lesions were determined Initial lesions followed by lesions after 2 months Parafoveal Vision Abdullah

10. Methods Receptive field maps generated by mapping electrode activity in Cortex and LGN Horseley-Clarke coordinates to map LGN Retrograde tracers in the cortex on either side of the cortical scotoma Cortex and LGN compared Horseley-Clarke - Apparatus helps make 3-D map of brain in Cartesian coordinates (x, y, and z) Abdullah

11. Results  Cortex Short-term  greater expansion of receptive fields originally located near the boundary of the lesion  shift in receptive field position Charles

12. Results Long-term  for 2 month results after lesion  Receptive field size was not as great when compared to receptive field size immediately after lesion  Large shifts in field position  Receptive fields of cells shifted from the lesioned part of the retina to positions immediately surrounding it Charles

13. Results  Additional characteristics of recovered cortex - overrepresentation of perilesion retina, enlarged fields at the edge of the scotoma, bipartite fields Charles

14. Results  Lateral Geniculate Nucleus (LGN) 1mm silent area remained after 2 months None of the characteristics of recovered cortex observed Charles

15. Conclusions  Horizontal Connections Transmission of visual information (immediate and long term) may be mediated by the long-range horizontal connections Extent of long-range horizontal connections approximated that of the area of reorganization Overall orientation map stays the same Charles

16. Related Studies  A quantitative measure for short-term cortical plasticity in human vision (MK Kapadia, CD Gilbert, and G Westheimer) 1994 Dynamics of vision studied in humans, using artificial scotoma Similar conclusions about horizontal connections  Future implications Plasticity of neuronal mechanisms Progress in Visual degenerative disorders Abdullah

17. The End  Questions or Comments? Abdullah

18. References  Gilbert C.D. and Wiesel T.N. (1992). Receptive field dynamics in adult primary visual cortex. Nature 356: 150– 52. Retrived from: http://dx.doi.org/10.1038/356150a0  Kapadia, M.K., Gilbert, C.D., and Westheimer, G. (1994). A quantitative measure for short-term cortical plasticity in human vision. J. Neurosci. 14, 451-457. Retrieved from: http://www.jneurosci.org/cgi/reprint/14/1/451