PowerPoint PresentationSlide 2Slide 3Slide 4Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Primary Visual Cortex(V1, area 17, striate cortex)1. Organization of early visual pathway2. Circuitry of primary visual cortexa. layering, inputs, outputsb. cell types3. RF properties of V1 neuronsa. orientation selectivityb. simple cell and complex cell4. Circuitry basis of the RFs5. Columnar Organizationa. orientation columnsb. ocular dominance columns c. hypercolumn6. Horizontal connectionsVisual pathway from retina to V1eyeLGNV1A top-down view diagramright visual fieldleft visual fieldfixation pointtemporal halfnasal halftemporal halfoptic chiasmlateral geniculate nucleus(LGN)V1axons from nasal retina cross  contralateral LGNaxons from temporal retina stay  ipsilateral LGNleft visual field  right LGN  right V1right visual field  left LGN  left V1left rightnasal halfV1LGNCircuitry -- inputs, outputs and layeringInputLGN  layer 4, layer 6Layer 4  layer 2/3  layer 5  layer 6OutputLayer 2/3, Layer 4B  other visual cortical areasLayer 5  superior colliculusLayer 6  LGN2/344A4B4C4C56MP(LGN)1two basic morphological types of cellsPyramidal cells• large, pyramid shaped cell bodies• project to other areas, also connect to other local neurons• excitatory (glutamate)Non-pyramidal cells• small and stellate shape (spiny stellate or smooth stellate)• local interneurons (smooth)• either excitatory (spiny, with many dendritic spines, glutamate) or inhibitory (smooth, few spines, GABA)Pyramidal cellAxonsStellate cellHetergeneity in the interneuron typesMorphologyPhysiology (spiking properties)Biochemistry (neuropeptide contents), Connectivity (dendrite-domain specific innervation of pyramidal cells).David Hubel (left) and Torsten WieselV1 cells have orientation selectivityorientation responseOrientation (o)Response (spikes/sec)0 30 60 90 120 15004080120Orientation tuning curvesimple cell -- separated ON and OFF regionscomplex cell -- overlapping ON and OFF regionssimple cell complex cellposition sensitivity position insensitivelength summation length summationwidth summation no width summationorientation sensitive orientation sensitiveTwo cell types based on response propertyON ---- increase its response to light on (bright stimulus)OFF ---- increase its response to light off (dark stimulus) Simple cell and complex cellsimple cell complex cellposition sensitive(yes)(no)length summation(yes)(yes)width summation(yes)(no)orientation selectivity(yes)(yes)increase responsedecrease responselittle responsestrong responseLittle or no responsestrong responseweak responseLittle or no responsestrong responseweak responseLittle or no responselittle or no responselittle responsestrong responseincrease response         Circuitry basis of V1 RFs (simple cell)1. Simple cell is built up from many LGN cells2. These LGN cells have the same center/surround structure3. 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 subregionLGN cellscortical simple cellreceptive fieldcircuitryLGN cellscortical simple cell+++Hubel & Wiesel, 1962Circuitry basis of V1 RFs (complex cell)1. Complex cell is built up from many simple cells2. These simple cells have the same preferred orientation3. These simple cells have overlapping RFs4. These simple cells have different arrangement of subregionssimple cellscomplex cellreceptive fieldcircuitrysimple cellscomplex cell+++Columnar Organization--Cells in the same column have similar properties (RF position, orientation preference, ocular dominance)(1) Orientation columnsOblique penetration in V1--preferred orientation gradually shiftsVertical penetration in V1--same preferred orientationAfferent pathways from the two eyesright eyeleft eyeLGNleft V1nasaltemporal654321CIIICCLayer 4left eyeright eyeRL2. Ocular dominance (OD) columns in V1. layer 4R L R LR L R LRlLrRlLrRlLrRlLr~ 0.5mmleft eye right eye left eye right eyeOblique penetration: cells responding to left and right eyes alternately Vertical penetration: cells responding toone eye exclusively or more stronglyEyesCorticalcellsgroups1 2 3 4 5 6 7contra- equal ipsi-Definition of Ocular Dominance GroupsOD distribution in normal adult V1 (monkey)Normal adult V1 –Binocular cells are common above & below layer 4), with each eye represented to different degrees contralateral ipsilateralEqualOD groupsNumber of cellsNormal V1Hypercolumn—An ensemble of orientation and ocular dominance (OD) columns in V1, including one set of L and R eye OD columns and a set of orientation columns for lines of all orientations. All cells within the hypercolumn have RFs that cover a similar area in the visual field.Optical imaging of intrinsic light scattering signals reveals pinwheel pattern of orientiation columnsBlobs in Layer 2/3--- Columns (blobs) revealed by cytochrome oxidase staining that are color sensitive--- Cells between the blobs (interblobs) are color insensitive, orientation sensitiveHorizontal ConnectionsCells with similar response properties in different columns (orientation, color) are linked by long-range horizontal connections made by axons of Layer 2/3C.