Functional Neuro-anatomy of the Visual System: A Coarse Course

1. Functional Neuro-anatomy of the Visual System: A Coarse Course Jay Hegdé

2. 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

3. Section I. Anatomy of Various Visual Structures

4. Developmental Bases of Neuroanatomy

5. 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

6. Clinically Important: Anatomy of Visual System Can be Highly Variable! Diffusion Tensor Imaging (DTI) of Two Healthy Adults

7. 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. Mnemonic: “On Old Olympus' Towering Top, AFriendly Viking Grew Vines And Hops”

8. Human Brain: Ventral View

9. Lateral Geniculate Nucleus (LGN) (Tortured) Mnemonic: C-I-I-C-I-C “See I? ISee, ISee” C = contralateral I = ipsilateral

10. Functional Organization of Macaque Visual Cortex Van Essen et al (1992)

11. Cortex has a laminar, canonical structure Courtesy of David Hubel

12. A closer look at the laminae

13. Neocortical Layers (Total thickness ~1mm) Opercular V1 Nissl stained Courtesy of David Hubel

14. Ocular Dominance Columns in V1 Probably a structure without a function

15. Cytochrome Oxidase ‘Blobs’ Area 17 of the cat / Layers 2 & 3 Scale bar = 2 mm Arrow: relieving cut Another structure without a function? (Hmm…)

16. 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

17. Molecular Cognitive Science is Here Already! Molecular pathways of plasticity in the visual cortex Daw (2004)

18. Section II. Connectivity

19. Functional Organization of Macaque Visual Cortex How are visual cortical areas distinguished from each other? Function Anatomy Connectivity Topography Felleman and Van Essen (1991)

20. Hegdé & Felleman (2007)

21. Marr (1982) Model of Visual Processing Object-level representation Surface-level representation Local primitives (e.g., edges)

22. Early ‘Feed-forward’ Visual Pathways

23. Pyramidal Cell: The Workhorse of the Cerebral Cortex (‘Relay’ Neuron)

24. Stellate Cell: Most Common Interneuron (‘Crosstalk’ Neuron)

25. Inputs and Outputs of Sensory (Especially Visual) Cortex From Crick (1995) [still largely current]

26. 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

27. Development of Visual Connectivity in the Macaque Feed-forward Connections Develop Earlier Than Feedback Pathways Kennedy and Burkhalter (2004)

28. Section III. Functional Organization

29. What Happens to the Visual Information Once It Gets to the Cerebral Cortex? Dorsal Pathway 7a MST MT Area V1 Ventral Pathway Area V4 Area AIT Macaque visual system (Human visual system is fundamentally similar)

30. Visual Pathways in the Monkey • A popular urban myth: The dorsal and ventral pathways are the magnocellular and parvocellular pathways, respectively. NOT TRUE!

31. There is Much that We Don’t Know Olshausen & Field, 2006 This is even more true of other visual areas.