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Lecture 3

NROC64H3 Lecture Notes - Lecture 3: Homonymous Hemianopsia, Hemianopsia, Quadrantanopia

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Matthias Niemeier

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NROC64H3S Sensory and Motor Systems
Lecture 3 01.27.12
- Neurons in Visual System: Neural processing resulting in perception
- Parallel Pathway serving conscious visual perception originate in
retina: Progress to LGN, 1ARY VC & higher order visual areas in
temporal and parietal lobes
- Neuronal receptive fields: Sensitive to different facets of visual input
Anatomy of Striate Cortex
Where is V1/Striate Cortex located?
- Map of visual field onto target structure (retina, LGN, S. Colliculus,
Striate Cortex) overrepresentation of Central Visual Field
- Discrete point of light = activate many cells in target structure,
overlapping RFs
WILL ALWAYS ACTIVATE>1 CELL, photoreceptor strikes many
- Perception: Based on brain’s interpretation of distributed patterns of
Layers in V1
- Lamination of Striate Cortex
Layers I-VI
Spiny Stellate Cells: Spine-covered dendrites; layer IVC
Pyramidal cells: Spines; thick apical dendrite; basal dendrites
Inhibitory neurons: Lack spines; all cortical layers, forms local connections
Inputs and Outputs
- Inputs of Striate Cortex
Magnocellular LGN neurons: Project to Layer IVCa IVB
Parvocellular LGN neurons: Project to to layer IVCb III
Koniocellular LGN axons: Bypasses layer IV Synapse in layer II & III
- Ocular Dominance Columns and Orientation Columns: LOOKS LIKE
GINERPRINT FROM AERIAL VIEW, blood can be used (oxygenated and
deoxygenated), white = right eye, black left eye
Pinwheels of orientation,
- Inputs to Striate Cortex
Layer IVC innervates superficial layers
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Radial and horizontal connections to II & III
III & IVB: Connections to all layers in V1
- Outputs of Striate Cortex
Layers II, III and IVB: Projects to other cortical areas
Layer V: Projects to S. Colliculus and pons
Layer VI: Projects back to LGN
- Cytochrome Oxidase Blob: Cytochrome oxidase is mitochondrial enzyme used for cell metabolism/ CO BLOBS
- Blobs: Cytochrome oxidase staining in cross sections of striate cortex
Physiology of Striate Cortex
Receptive Fields
- Layer IVC: Monocular; center-surround
- Layer Iva: Insensitive to wavelength
- Layer IVb: Center-surround colour opponency
- Binocularity: Layers superficial to IVC, 1st binocular
receptive fields in visual pathway, STARTS AFTER 4C
- Direction Selectivity: Neurons fire APs in response
to moving bar of light, neurons in V1
- Simple Cells: Binocular; orientation-selectively
elongated on- or off- region w/ antagonistic
flanks responds to optimally oriented bar of light,
possibility composed of 3 LGN cells axons w/
center-surround receptive fields
- Complex Cells: Binocular; ON and OFF response
to light but no distinct on-off regions
- Blob Receptive Fields:
Blob cells: Wavelength-sensitive; Monocular;
no orientation direction selectivity
Some show colour opponency like LGN cells
Others have no surround; RG/YB opponency in center
Double-opponent cells; opponent in center and surround
Pathways vs. Modules
- Parallel Pathways
- Cortical Module/Hypercolumn
Extrastriate Cortex and
How to Identify visual
areas in Human Brain
- Dorsal Stream:
Analysis of visual
motion and visual
control of action
- Ventral Stream: Perfception of visual world and
recognition of objects
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