Outline: LGN & Visual Cortex

Basic visual neuroanatomy

Primary visual pathway:

Eye -> optic nerve -> optic chiasm -> optic tract -> lateral geniculate nucleus (LGN) -> optic radiations -> cortical area V1 or striate cortex

Other pathways lead to superior colliculus (SC) and other brain regions
Nasal retinae cross at the chiasm
Thus, right visual hemifield is represented in the left half of the brain (and vice versa)
Retinotopic maps throughout
Magnified foveal representation throughout

LGN

6 layers
2,3,5 represent ipsilateral visual field; 1,4,6 are contralateral
1,2 = magnocellular layers, 3-6 = parvocellular layers
Parvo: linear, small cells and receptive fields, sustained, slow

conduction velocity, poor contrast gain/sensitivity, show
color opponency, project to V1 layers 4A and 4Cβ

Magno: linear or nonlinear, small and large RFs, transient, fast

conduction velocity, large contrast gain and then saturate,
tend not to be color opponent, project to V1 layer 4Cα

relates to eye movement generation, foveation, "attention"
includes visual and motor (i.e., saccade-related) cells in different layers

Cortex

Layered (input, processing and output layers)
RF types

Simple
Linear

Can be mapped with spots
Respond to edges and lines, that is, are orientation-selective

Complex

Can't be mapped with spots
Respond to edges and lines anywhere in the RF
Hence, nonlinear
More likely to be motion selective

Hypercomplex

Length-tuned/end-stopped
Not a separate category
Selective for line curvature

Models of how they are constructed
Binocularity and overlapping RFs from the two eyes

Architecture

Retinotopy
V1

Orientation columns
Ocular dominance columns
Blobs

Thin and thick stripes

Development, deprivation, and critical period
Higher areas

Specializations: color, movement, stereo, etc.
Streams/parallel pathways

Magno vs. parvo
Dorsal vs. ventral
Where vs. what
Vision vs. action