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Primary Visual Cortex (V1, Area 17, Striate Cortex)

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Primary Visual Cortex (V1, Area 17, Striate Cortex) Primary Visual Cortex (V1, area 17, striate cortex) 1. Organization of early visual pathway 2. Circuitry of primary visual cortex a. layering, inputs, outputs b. cell types 3. RF properties of V1 neurons a. orientation selectivity b. simple cell and complex cell 4. Circuitry basis of the RFs 5. Retinotopic map 6. Functional architecture of V1 a. orientation columns b. ocular dominance columns c. hypercolumn d. horizontal connections Visual pathway from retina to V1 LGN V1 eye Circuitry -- inputs, outputs and layering 1 2/3 4A 4B 4 4Cα 4Cβ 5 6 M P (LGN) Input LGN → layer 4, layer 6 Layer 4 → layer 2/3 → layer 5 → layer 6 Output Layer 2/3, Layer 4B → other visual cortical areas Layer 5 → superior colliculus Layer 6 → LGN 1 two basic morphological types of cells Pyramidal cell Axons Stellate cell Pyramidal cells • large, pyramid shaped cell bodies • project to other areas, also connect to other local neurons • excitatory Non-pyramidal cells • small and stellate shape (spiny stellate or smooth stellate) • local interneurons • either excitatory (spiny, with many dendritic spines) or inhibitory (smooth, few spines) A top-down view diagram fixation point left visual field right visual field nasal left right nasal half half temporal half temporal half optic chiasm lateral LGN geniculate nucleus (LGN) V1 V1 axons from nasal retina cross → contralateral LGN axons from temporal retina stay → ipsilateral LGN left visual field → right LGN → right V1 right visual field → left LGN → left V1 studying RF properties of V1 neurons receptive field ---- part of the retina (visual field) in which light can evoke response from a cell. retinal ganglion cells Circular with antagonistic surround LGN cells ON or OFF center - + - + - + - + - + V1 cells ? David H. Hubel (left) and Torsten N. Wiesel 2 V1 cells have orientation selectivity orientation response Orientation tuning curve 120 80 40 0 0 30 60 90 120 150 Response (spikes/sec) Response Orientation (o) Two cell types based on response property simple cell -- separated ON and OFF regions ON ---- increase its response to light on (bright stimulus) OFF ---- increase its response to light off (dark stimulus) complex cell -- overlapping ON and OFF regions ± ± ± ± ± ±±± ± ± ± ± ± ± simple cell complex cell position sensitivity position insensitive length summation length summation width summation no width summation orientation sensitive orientation sensitive Simple cell and complex cell simple cell complex cell position (yes) (no) sensitive ± ± ±±± ± ± ± ± increase response ±±± increase ± ± response ± ± ±±± decrease response ± ± length (yes) (yes) summation ± ± ±±± little response little response ± ± ± ± ± strong response strong response ±± ± ± width (yes) (no) summation ± ± little or no ±±± Little or no response response ± ± orientation (yes) (yes) selectivity ± ± strong response ±±± strong response ± ± ± ± weak response ±±± weak response ± ± ± ± Little or no response ±±± Little or no response ± ± 3 Circuitry -- inputs, outputs and layering 1 2/3 4 5 6 (LGN) simple cells: layer 4, layer 6 complex cells: layer 2/3, layer 5, layer 6 Circuitry basis of V1 RFs (simple cell) circuitry + + + cortical simple cell LGN cells receptive field Hubel & Wiesel, 1962 cortical LGN cells simple cell 1. Simple cell is built up from many LGN cells 2. These LGN cells have the same center/surround structure 3. The centers of these LGN cells are distributed along a line * you can also add a set of OFF-centered LGN cells, with their centers along the OFF subregion Circuitry basis of V1 RFs (complex cell) circuitry receptive field + + + complex cell complex cell simple cells simple cells 1. Complex cell is built up from many simple cells 2. These simple cells have the same preferred orientation 3. These simple cells have overlapping RFs 4. These simple cells have different arrangement of subregions 4 The Nobel Prize in Physiology or Medicine 1981: Roger W.Sperry: for his discoveries concerning the functional specialization of the cerebral hemispheres David H. Hubel & Torsten N. Wiesel: for their discoveries concerning information processing in the visual system retinotopic map Retinotopic map -- neighboring cells have neighboring RF -- retinotopic map is most precise in the retina, LGN and V1, but it gets fuzzier as you move on to higher visual areas c Project orderly to b LGN and V1 a a b retina c object retinotopic map FP 123 visual field left right 3 3 2 2 retina 1 1 3 2 LGN 1 3 V2 12 V2 V1 From visual field to V1 medial visual field → lateral V1 lower visual field → anterior V1 upper visual field → posterior V1 5 Nonuniform representation of the visual field in V1 Fixation point Visual field left right V1 V1 Cortical magnification in the fovea ---- The fovea has a larger cortical representation than the peripheral. 6.
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