CHARLES D. GILBERT & TORSTEN N. WIESEL GROUP B6 MARGARITA BLAJEVA CAITLIN H. CHEONG PARI CHOWDHARY WISSAM A. SAMAD BROOKE THORNTON Receptive Field Dynamics in Adult Primary Visual Cortex

Presentation Outline Background Critiques Related Study: Macular Degeneration Other Areas of Interest Pari

Research Issue Does the primary visual cortex reorganize its cortical topography as a result of changes to its afferent input? Are these results applicable to humans? Pari

Experimental Method & Hypothesis Methods -Lesion: Focal Binocular retinal lesions. (Parafoveal, 8 mm wide) -Testing: Vertical Electrode penetrations into V1 & LGN. (Before lesion, immediately after, and months later) Hypothesis - Removing afferent input through a retinal lesion results in a rearrangement of cortical and subcortical topography. Pari

Empirical Evidence and Theoretical Conculsions  Cortical rearrangement around edges of retinal scotoma  Recovery of silenced areas months later.  Silent region remained in LGN (Does NOT support hypothesis) Theoretical assumption: Horizontal cortical connections responsible for topographic reorganization. Pari

Lateral Geniculate Nucleas - Located in thalamus - Main organized relay pathway to V1. - Study: indicates no topographical rearrangement. - Anatomical study? - Geniculocortical afferents insufficient to account for cortical recovery. Wissam Adapted from Ullal, G. (2008). Lecture 6: Vision and Retinal Processing [Power Point Slides]. Retrieved from McMaster Learnlink.

What did the anatomical studies yield?  Deafferentation or Wallerian Degeneration?  New axon sprouting? Wissam Adapted from Newell, K. (2008). Lecture 9: Visial System [PDF]. Retrieved from SOLS Wollongong University (Australia).

What About the many connections of the LGN? Other LGN connections - To brainstem - Massively overweigh retinal input. Necessary LGN organization - Change is not good? Wissam Adapted from Derrington, A. (2001). The lateral geniculate nucleus. Current Biology, 11 (16), pp. R635-7.

Horizontal Cells Horizontal Connections arise in pyramidal cells cortical cell communication Horizontal Cells vs. Connections ● present in the retina ● lateral inhibition Margarita Adapted from Ullal, G. (2008). Lecture 6: Vision and Retinal Processing [Power Point Slides]. Retrieved from McMaster Learnlink.

Further Research by Gilbert et al. (1994) Cellular Mechanisms of Cortical Reorganization FOCUS: o Intracortical axonal sprouting in the horizontally projecting plexus of cortical neurons Reorganized vs. Normal cortex RESULTS:  Very abundant terminal branching  Denser axon fibres in reorganized cortex Margarita

Further Research by Gilbert et al. (1995) Visual Pathway Reorganization Loci FOCUS: Determine reorganization loci Comparing topographic alterations in the Primary Visual Cortex and dorsal LGN Thalamocortical afferents involvement? Margarita

Age-Related Macular Degeneration (McManus et al., 2008) Computational model displayed that topographic reorganization occurs in humans with age-related macular degeneration (AMD) - Human subjects with macular degeneration do not receive visual input from damaged portions of their retinae yet their vision is complete and continuous Caitlin Adapted from McManus, J. N., Ulmann, S., & Gibert, C. D. (2008). A computational model of perceptual fill-in following retinal degeneration. Journal of Neurophysiology, 99 (5),

Impressive Methodology Eliminated bias by choosing receptive fields unaffected by simple eye movement Caitlin

Could the reverse be true for the retina in terms of cellular reorganization and plasticity if the cortex was lesioned? Wissam & Margarita Area MT (V5)?

References Bear, M. F., Connors, B., & Pardiso, M. (2006). Neuroscience: exploring the brain (3rd Edition ed.). Philadelphia: Lippincott Williams & Wilkins. Buonomano, D. V., & Merzenich, M. M. (1998). Cortical plasticity: from synapses to maps. Annual Review of Neuroscience, 21, Darian-Smith, C., & Gilbert, C. D. (1994). Axonal sprouting accompanies functional reorganization in adult cat striate cortex. Letters to Nature, 368, Darian-Smith, C., & Gilbert, C. D. (1995). Topographic reorganization in the striate cortex of the adult cat and monkey is cortically mediated. The Journal of Neuroscience, 15 (3), Derrington, A. (2001). The lateral geniculate nucleus. Current Biology, 11 (16), pp. R Gilbert, C. D. (1998). Adult Cortical Dynamics. Physiological Reviews, 78, Gilbert, C.D., Das, A., Ito, M., Kapadia, M., & Westheimer, G. (1996). Spatial integration and cortical dynamics. Proceedings of the National Academy of Sciences, 93, Gilbert, C. D., & Wiesel, T. N. (1992). Receptive field dynamics in adult primary visual cortex. Letters to Nature, 356, McManus, J. N., Ulmann, S., & Gibert, C. D. (2008). A computational model of perceptual fill-in following retinal degeneration. Journal of Neurophysiology, 99 (5),

Other Areas of Interest Limiting Visual Input to One Eye (Gilbert, 1998) VPA Rat Study and Horizontal Connections (Personal Communication, Dr. D. Day, 2008) Area MT  perception of movement and visuospatial behaviour (Gilbert, 1998) Margarita