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Slide 2 Wesner, M. F. Slide 3 Nonperceptual pathways: Retinotectal (retina to superior colliculus) Retinotectal (retina to superior colliculus) A perceptual pathway: Retinogeniculostriate (retina - thalamus - cortex) V1 or striate cortex Retinohypothalamic (retina - hypothalamus - pineal) Slide 4 Slide 5 Retinogeniculate and retinotectal projections Slide 6 Retinogeniculocortical or retinogeniculostriate pathway - mediates conscious visual perception Slide 7 Slide 8 On-Center; Off-Surround Cell in LGN Historic movie footage of early single-cell recording in the cat visual system by David Hubel and Torsten Wiesel. Slide 9 Slide 10 Slide 11 Slide 12 Slide 13 ipsilateral contralateral Slide 14 The projections of the small ganglion (PC cells) and large ganglion (MC cells) cells to the parvocellular and magnocellular layers of the LGN: Acknowledgement: Image from Webvision by Kolb, Fernandez and Nelson, courtesy of Matthew Schmolesky at Erasmus University, Rotterdam. Slide 15 Slide 16 This means that all information in the right (left) visual field projects to the left (right) cortex. This means ViSUAL INFORMATION is contralaterally represented. Slide 17 Slide 18 Slide 19 Ocular Dominance Slide 20 Slide 21 This begins to establish a retinotopic organization to the cortex. Slide 22 Slide 23 A recently recognized, anatomically & functionally distinct third subdivision of the visual pathway, called the koniocellular (KC) pathway. Slide 24 The properties of koniocellular cells have only recently been studied in anthropoid primates, and their importance for human vision is only now becoming understood, particularly with respect to S-cone operations. Slide 25 KC cells form thin layers that lie between the M and P layers..formally referred to as intercalated layers. Slide 26 Slide 27 Generally, the spatial and temporal properties of the KC cells in primates fall between the parvocellular and magnocellular spatiotemporal properties.. Slide 28 Spatially, the KC cells are species specific. Generally, however, they are tuned to spatial frequencies that are lower than the PC system but higher than the MC system. Similarly, the temporal modulation (i.e., timing) sensitivity of KC cells are higher than PC but lower than MC cells. Slide 29 The projections of the koniocellular cells to the primary visual cortex (V1) appear to be towards the cytochrome oxidase (CO) cortical blobs (i.e., cortical areas responsive to chromatic changes). KC cells are particularly responsive to blue-yellow differences (S-cone ON mediated). Slide 30 V1 The projections of the koniocellular cells to the primary visual cortex (V1) appear to be towards the cytochrome oxidase (CO) cortical blobs (i.e., cortical areas responsive to chromatic changes). KC cells are particularly responsive to blue-yellow differences (S-cone ON mediated). Slide 31 Primary visual cortex (V1)Primary visual cortex (V1) Brodmann 17Brodmann 17 Striate cortexStriate cortex Slide 32 The retinotopic organization of V1 (striate cortex) using 2-dg autoradiography Slide 33 This begins to establish a retinotopic organization to the cortex. Slide 34 Slide 35 Slide 36 Note: A retinotopic map can also be found in the superior colliculus of the mesencephalon, but more distorted than at the cortex. Slide 37 Slide 38 CORTEX: Simple Cells Slide 39 Slide 40 Slide 41 Slide 42 Slide 43 Slide 44 CORTEX: Complex Cells Slide 45 Slide 46 Slide 47 Slide 48 CORTEX (beyond V1): Hypercomplex or End-Stop Cells ? Slide 49 Slide 50 Slit Length (deg visual angle) Complex Cell End-Stop Cell Slide 51 Possible circuit for an end-stop cell - - + 3 converging complex cells. Slide 52 V1 (primary visual cortex): Orientation columns Orientation columns Slide 53 V1 Look at a gyrus of the primary visual cortex (Area #17) or V1 or striate cortex. Slide 54 Slide 55 Slide 56 2-dg treated Orientation Columns Slide 57 V1 (primary visual cortex): ocular dominance columns ocular dominance columns Slide 58 Radioactive proline injected into the eye. OCULAR DOMINANCE COLUMNS PRO* treated Slide 59 Slide 60 Margaret Wong-Riley (1979) coined the term blobs. Introduced labeled cytochrome oxidase (an enzyme used in cellular metabolism) and measured its migration to V1. Prominent blobs found in layer III of V1 cortex. Slide 61 Slide 62 Slide 63 GranularAgranular Slide 64 Slide 65 Six Layers of the Striate Cortex (V1): 1.Layer devoid of nuclei 2.Orientation, ocular dominance columns & (inter)blobs (input from 4A & 4C - PARVO) 3.Orientation, ocular dominance columns & (inter)blobs (input from 4A & 4C - PARVO) 4.Afferent Input - big sensory layer A.Input from PARVO & 4C B.Input from 4C C.Afferent Input ..from MAGNO (M x & M y cells) ..from PARVO (P cells: foveal chromatic & luminance signals) 5.Feedback to superior colliculus (visual motor) 6.Feedback to LGN (visual motor) To V2 (thin stripes & pale stripes) & V4 Slide 66 (Layers 3, 4,5, 6) ventral dorsal Slide 67 Six Layers of the Striate Cortex (V1): 1.Layer devoid of nuclei 2.Orientation, ocular dominance columns & blobs (input from 4A & 4C - PARVO) 3.Orientation, ocular dominance columns & blobs (input from 4A & 4C - PARVO) 4.Afferent Input - big sensory layer A.Input from PARVO & 4C B.Input from 4C C.Afferent Input ..from MAGNO (M x & M y cells) ..from PARVO (P cells: foveal chromatic & luminance signals) 5.Feedback to superior colliculus (visual motor) 6.Feedback to LGN (visual motor) To V2 (thick stripes), V3 & MT (V5) Slide 68 (Layers 1,2) ventral dorsal Slide 69 luminance Chromatic Chromatic or luminance responsive luminance responsive IVA Slide 70 V2 (thin stipes) interblobs V2 (pale stipes) Slide 71 ipsilateral Magno (MC) & Parvo (PC) projections V3 (movement, orientation, depth) V5 (MT) (movement, dynamic form) RIGHT LGN LEFT RIGHT V4 (form, color, constancies) Inferotemporal (high form) contralateral Slide 72 Slide 73 Parvocellular (PC) stream LGN Layers: 3, 4, 5, 6 V1: IVC , IVA V1 (layers II & III): blobs (chromatic) & interblobs (luminance) & orientation & some ocular dominance columns. V2: thin stripes (chromatic) & pale stripes (luminance) V4: (color, color constancy & form) Inferotemporal: (form & color) A quick down & dirty: extrastriate Slide 74 Koniocellular (KC) stream LGN Layers: intermediate (intercalated between all layers: 1, 2, 3, 4, 5, 6) V1: Straight into layers II & III blobs (chromatic). V2: thin stripes (chromatic) V4: (color, color constancy & form) and.. V5 (MT): (motion, dynamic form) Inferotemporal: (form & color) and.. Dorsal (movement) A quick down & dirty (cont.): extrastriate Slide 75 Magnocellular (MC) stream LGN Layers: 1, 2 V1: IVC , IVB V2: thick stripes (luminance only) V3: (motion, orientation, depth) V5 (MT): (motion, dynamic form) Dorsal (MST) (movement) A quick down & dirty (cont.): extrastriate Slide 76 (Layers 3,4,5,6) Slide 77 Slide 78 Extrastriate or Slide 79 V1 #17 WHERE WHAT 2 major visual streams: Slide 80 Cortical damage here: Akinetopsia Achromatopsia Cortical damage (occipitotemporal): Apperceptive Agnosia Cortical damage here: Blindness Cortical damage (fusiform gyrus): Apperceptive Prosopagnosia Slide 81 Slide 82 Do sensory pathways always involve such anatomical divisions of labor? NO Multisensory operations generally occur at high- level associative cortical sites in the processing heirarchy. Slide 83 Modular processing The general cortical architecture of sensory processing, according to the modularity theory. Specialized processing systems are dedicated to different sensory modalities; vision (red), audition (blue), and somatosensation (green). In each system information flow divides into two streams, one carrying what information and the other carrying where information. Multisensory processing occurs relatively late in the processing hierarchy, in the intraparietal sulcus (IP) and the superior temporal polysensory area (STP), both shown in multiple colors. Re-drawn from Schroeder, Smiley, Fu, McGinnis, OConnell, and Hackett (2003), Figure 1. Copyright Elsevier. Reproduced with permission. Slide 84 Modular processing Modular processing architecture has a number of virtues. For example, each module can be optimized for its specific function, operating with maximum speed and efficiency rather than compromised to serve several functions at once. Errors remain confined to one function, rather the propagated widely. New functions can be created by adding new modules.