Introduction to Neuroscience Lecture 11: Visual System II. The Central Visual System Reading Assignment: Bear et al., Ch. 10 Introduction Neurons in the visual system Neural processing resulting in perception Parallel pathway serving conscious visual perception originate in the retina Progress to <a href="/keyword/lateral-geniculate/" >lateral geniculate</a> nucleus, primary visual cortex &amp; higher order visual areas in temporal and parietal lobes CBNS 106 2 1 The Retinofugal Projection The Optic Nerve, Optic Chiasm, and Optic Tract CBNS 106 3 The Retinofugal Projection Right and Left Visual Hemifields CBNS 106 4 2 The Retinofugal Projection Targets of the Optic Tract CBNS 106 5 The Retinofugal Projection Targets of the Optic Tract CBNS 106 6 3 The Retinofugal Projection Targets of the Optic Tract CBNS 106 7 The Retinofugal Projection Targets of the Optic Tract CBNS 106 8 4 The Retinofugal Projection Nonthalamic Targets of the Optic Tract: Hypothalamus: Biological rhythms, including sleep and wakefulness Pretectum: Size of the pupil; certain types of eye movement Superior colliculus: Orients the eyes in response to new stimuli (saccadic eye movements) CBNS 106 9 The <a href="/keyword/lateral-geniculate/" >lateral geniculate</a> Nucleus (LGN) CBNS 106 10 5 The <a href="/keyword/lateral-geniculate/" >lateral geniculate</a> Nucleus (LGN) The Segregation of Input by Eye and by CBNS Ganglion Cell Type 106 11 The <a href="/keyword/lateral-geniculate/" >lateral geniculate</a> Nucleus (LGN) Receptive Fields Receptive fields of LGN neurons: Identical to the ganglion cells that feed them Magnocellular LGN neurons: Large, monocular receptive fields with transient response Parvocellular LGN cells: Small,monocular receptive fields with sustained response CBNS 106 12 6 The <a href="/keyword/lateral-geniculate/" >lateral geniculate</a> Nucleus (LGN) Nonretinal Inputs to the LGN Retinal ganglion cells axons: Not the main source of synaptic input to the LGN Primary visual cortex: 80% of the synaptic inputs Neurons in the brain stem: Modulatory influence on neuronal activity CBNS 106 13 Anatomy of the Striate Cortex CBNS 106 14 7 Anatomy of the Striate Cortex CBNS 106 15 Anatomy of the Striate Cortex Retinotopy Map of the visual field onto a target structure (retina, LGN, superior colliculus, striate cortex) overrepresentation of central visual field Discrete point of light: Activates many cells in the target structure Perception: Based on the brain's interpretation of distributed patterns of activity CBNS 106 16 8 Anatomy of the Striate Cortex Retinotopy CBNS 106 17 Anatomy of the Striate Cortex Lamination of the Striate Cortex Layers I - VI Spiny stellate cells: Spinecovered dendrites; layer IVC Pyramidal cells: Spines; thick apical dendrite; layers III, IV, V, VI Inhibitory neurons: Lack spines; All cortical layers; Forms local connections CBNS 106 18 9 Anatomy of the Striate Cortex Inputs to the Striate Cortex Magnocellular LGN neurons: Project to layer IVC Parvocellular LGN neurons: Project to layer IVC Koniocellular LGN axons: Bypasses layer IV to make synapses in layers II and III CBNS 106 19 Anatomy of the Striate Cortex Ocular Dominance Columns CBNS 106 20 10 Anatomy of the Striate Cortex Inputs to the Striate Cortex Layer IVC innervates superficial layers CBNS 106 21 Anatomy of the Striate Cortex Outputs of the Striate Cortex: Layers II, III, and IVB: Projects to other cortical areas Layer V: Projects to the superior colliculus and pons Layer VI: Projects back to the LGN CBNS 106 22 11 Anatomy of the Striate Cortex Cytochrome Oxidase Blobs Cytochrome oxidase is a mitochondrial enzyme used for cell metabolism Blobs: Cytochrome oxidase staining in cross sections of the striate cortex CBNS 106 23 Physiology of the Striate Cortex Receptive Fields Layer IVC: Monocular; center-surround Layer IVC: Insensitive to the wavelength Layer IVC: Center-surround color opponency Binocularity Layers superficial to IVC: First binocular receptive fields in the visual pathway CBNS 106 24 12 Physiology of the Striate Cortex Receptive Fields Orientation Selectivity CBNS 106 25 Physiology of the Striate Cortex Receptive Fields Direction Selectivity Neuron fires action potentials in response to moving bar of light CBNS 106 26 13 Physiology of the Striate Cortex Receptive Fields Simple cells: Binocular; Orientationselective; Elongated on-off region with antagonistic flanks responds to optimally oriented bar of light (location in the field) Possibly composed of three LGN cell axons with center-surround receptive fields CBNS 106 27 Physiology of the Striate Cortex Receptive Fields Complex cells: Binocular; Orientationselective; ON and OFF responses to the bar of light but unlike simple cells, no distinct on-off regions CBNS 106 28 14 Physiology of the Striate Cortex Receptive Fields Blob Receptive Fields Blob cells: Wavelength-sensitive; Monocular; No orientation; direction selectivity CBNS 106 29 Physiology of the Striate Cortex Parallel Pathways: Magnocellular; Koniocellular; Parvocellular CBNS 106 30 15 Physiology of the Striate Cortex Cortical Module CBNS 106 31 Beyond Striate Cortex Dorsal stream Analysis of visual motion and the visual control of action Ventral stream Perception of the visual world and the recognition of objects CBNS 106 32 16 Beyond Striate Cortex The Dorsal Stream (V1, V2, V3, MT, MST, Other dorsal areas) Area MT (temporal lobe) Most cells: Direction-selective; Respond more to the motion of objects than their shape Beyond area MT - Three roles of cells in area MST (parietal lobe) Navigation Directing eye movements Motion perception CBNS 106 33 Beyond Striate Cortex The Ventral Stream (V1, V2, V3, V4, IT, Other ventral areas) Area V4 Achromatopsia: Clinical syndrome in humans-caused by damage to area V4; Partial or complete loss of color vision Area IT Major output of V4 Receptive fields respond to a wide variety of colors and abstract shapes prosopagnosia CBNS 106 34 17 From Single Neurons to Perception Visual perception Identifying &amp; assigning meaning to objects Hierarchy of complex receptive fields Retinal ganglion cells: Center-surround structure, Sensitive to contrast, and wavelength of light Striate cortex: Orientation selectivity, direction selectivity, and binocularity Extrastriate cortical areas: Selective responsive to complex shapes; e.g., Faces CBNS 106 35 From Single Neurons to Perception From Photoreceptors to Grandmother Cells Grandmother cells: Face-selective neurons in area IT? Probably not: Perception is not based on the activity of individual, higher order cells Parallel Processing and Perception Groups of cortical areas contribute to the perception of color,motion, and identifying object meaning CBNS 106 36 18 Concluding Remarks Vision Perception combines individually identified properties of visual objects Achieved by simultaneous, parallel processing of several visual pathways Parallel processing Like the sound produced by an orchestra of visual areas rather than the end product of an assembly line CBNS 106 37 End of Presentation 19