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Chapter 10: Visual Integration (Lateral Geniculate Nucleus (Receptive…
Chapter 10: Visual Integration
Nonthalamic Targets of the Optic Tract
Pretectum- between thalamus and midbrain- pupillary light reflex
Superior colliculus (Retinotectal projection)- Saccades- orients eye to new stimuli
Superchiasmatic Nucleus (SCN) of the hypothalamus- involved in circadian rhythms
Visual Hemifields
Right hemifield: Left temporal & right nasal retina
Left Hemifield: Imaged on left nasal & right temporal retina
Lateral Geniculate Nucleus
6 Layers
80% of input comes from V1
Ipsilateral axons synapse to layers 2, 3, 5
Contralateral input synapses to layers 1, 4, 6
Layers 1 & 2: Magnocellular (Input from M-type)
Layers 3-6: Parvocellular LGN layers (From P-Type GCs)
Koniocellular LGN layers- nonM-nonP
Receptive Fields of LGN cells
Parvocellular LGN cells- small center-surround RFs with sustained responses- Color Opponency
Koniocellular LGN cells: Center-surround RFs; either light/dark or color opponency
Magnocellular LGN neurons: Large RF, transient busts, indifferent to wavelength
Primary Visual Cortex (Striate Cortex, V1)
Cortical Magnification: More GCs with RFs in Fovea- Central retina is overrepresented in V1
Cytoarchitecture: 6 Layers
Layer 1
Layer 2
Layer 3
Layer 4
4B
4C
4Cα
Magnocellular LGN neurons
4Cβ
Parvocellular LGN neurons
Spiny stellate cells- Pyramidal in every other layer
Primary recipient of LGN afferents
4A
Layer 5
Layer 6
Outputs: Radial Connections
Layer 4Cβ to Layers 2 and 3
Layer 4Cα to 4B
Ocular Dominance Columns- Extend through V1
Most neurons outside of V1 are binocular
Outputs from Striate Cortex
Pyramidal Cells send axons into the white matter
Layers II, III, and IVB project to other cortical areas
Layer V projects to Superior Colliculus and pons
Cytochrome Oxidase: Mitochondrial Enzyme used in metabolism: present in blobs (pillars) at full thickness in layers II thru VI
Blobs receive input from koniocellular, magno- and parvo- from layer IVC
Orientation Columns: radial columns from Layer II to VI
DIrection Selectivity
Three Parallel Pathways
Parvocellular Pathway: P-type GCs, Parvocellular LGN, IVCβ, II and III interblob- high spatial resolution tasks
Koniocellular Pathway: nonM-nonP GCs, koniocellular LGN, blobs in II and III
Magnocellular Pathway: M-Type GCs, Magnocellular LGN, IVCα, IVB; critical for high temporal resolution tasks
Dorsal Stream- Direction-Selective, large RFs; Navigation, Directing eye movements, Motion perception
Ventral Stream- Contains AREA IT: Colors, abstract shapes. May be important for visual perception & visual memory
Fusiform Face Area- prosopagnosia