functional neuro-anatomy of the visual system: a coarse course
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Functional Neuro-anatomy of the Visual System: A Coarse Course. Jay Hegdé. How to Learn (Visual) Neuroanatomy. I. Distinguish 3-D structure from connectivity. II. Keep in mind that not all structures have (known) functions – biological structures are evolved, not designed. - PowerPoint PPT PresentationTRANSCRIPT
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Functional Neuro-anatomy of the Visual System: A Coarse Course
Jay Hegdé
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How to Learn (Visual) Neuroanatomy
I. Distinguish 3-D structure from connectivity
II. Keep in mind that not all structures have (known) functions – biological structures are evolved, not designed.
III. Mind your Greek/Latin
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Section I. Anatomy of Various Visual Structures
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Developmental Bases of Neuroanatomy
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Since the early visual system is anatomically highly ordered, visual field mapping can be highly useful in neuro-ophthalmological diagnosis.
Closer view of the Optic Chiasm
Early Visual Pathway
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Clinically Important: Anatomy of Visual System Can be Highly Variable!
Diffusion Tensor Imaging (DTI) of Two Healthy Adults
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Mnemonic:“On Old Olympus' Towering Top, A Friendly Viking Grew Vines And Hops”
Optic Nerve is Fundamentally Similar to Most Other Sensory Cranial Nerves
In humans, the optic nerve contains 38% of all the axons connecting to the brain.
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Human Brain: Ventral View
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(Tortured) Mnemonic:C-I-I-C-I-C
“See I? I See, I See”
Lateral Geniculate Nucleus (LGN)
C = contralateralI = ipsilateral
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Functional Organization of Macaque Visual Cortex
Van Essen et al (1992)
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Cortex has a laminar, canonical structure
Courtesy of David Hubel
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A closer look at the laminae
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Neocortical Layers (Total thickness ~1mm)
Opercular V1Nissl stained
Courtesy ofDavid Hubel
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Probably a structure without a function
Ocular Dominance Columns in V1
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Scale bar = 2 mm
Arrow: relieving cut
Area 17 of the cat / Layers 2 & 3
Cytochrome Oxidase ‘Blobs’
Another structure without a function? (Hmm…)
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Some Facts and Figures about Macaque Visual Cortex
• Total cortical surface area: ~100 cm2
• Total surface area of visual cortex: ~ 50 cm2
• ~35 visual areas, ~25 primarily visual
• 323 known anatomical pathways; ~33% connectivity
• ~75-85% of visual cortical neurons are pyramidal cells* Glutamatergic (thought to be always excitatory)* ~104 synapses/cell
• 250,000 neurons/mm2 in V1; 100,000 neurons/mm2 elsewhere
• 10 billion axons in the white matter * ~10-20 million connect with nuclei outside the cortex * ~ 98.6% of the axons are intra-hemispheric * Corpus callosum contains ~100 million axons
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Molecular Cognitive Science is Here Already!
Molecular pathways of plasticity in the visual cortex
Daw (2004)
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Section II. Connectivity
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Felleman and Van Essen (1991)
How are visual cortical areas distinguished from each other?
FunctionAnatomyConnectivityTopography
Functional Organization of Macaque Visual Cortex
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Hegdé & Felleman (2007)
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Image
PrimalSketch
2.5DSketch
3DSketch
Marr (1982) Model of Visual Processing
Local primitives (e.g., edges)
Surface-level representation
Object-level representation
An ImageAn Image
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Early ‘Feed-forward’ Visual Pathways
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Pyramidal Cell: The Workhorse of the Cerebral Cortex (‘Relay’ Neuron)
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Stellate Cell: Most Common Interneuron (‘Crosstalk’ Neuron)
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Inputs and Outputs of Sensory (Especially Visual) Cortex
From Crick (1995) [still largely current]
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How known cortical connections join the layer 6→4 and layer 2/3 building blocks to form the entire V1/V2 laminar model.
Raizada R D S , and Grossberg S Cereb. Cortex 2003;13:100-113
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Feed-forward Connections Develop Earlier Than Feedback Pathways
Kennedy and Burkhalter (2004)
Development of Visual Connectivity in the Macaque
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Section III. Functional Organization
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Ventral PathwayArea V4
Area AIT
MTMST
7a
Area V1Dorsa
l Pathway
Macaque visual system(Human visual system is fundamentally similar)
What Happens to the Visual Information Once It Gets to the Cerebral Cortex?
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Visual Pathways in the Monkey
• A popular urban myth: The dorsal and ventral pathways are the magnocellular and parvocellular pathways, respectively. NOT TRUE!
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Olshausen & Field, 2006
There is Much that We Don’t Know
This is even more true of other visual areas.