Organisation of the visual cortex

Question 1

Organisation for function

Answer 1

retinotopic maps, magnification factor, occular dominance columns, orientation columns

Question 2

Retinotopic maps evidence

Answer 2

tootell et al 1982 macaque cortex, 2dg staining

Question 3

Spatial receptive fields in the cortex

Answer 3

1mm tangential move yields a new receptive field. Smaller in the fovea

Question 4

Cortical magnification

Answer 4

describes how manyneuronsin anareaof thevisual cortexare ‘responsible’ for processing astimulusof a given size, as a function of visual field location. In the center of the visual field, corresponding to thefoveaof theretina, a very large number of neurons process information from a small region of the visual field. If the same stimulus is seen in the periphery of the visual field (i.e. away from the center), it would be processed by a much smaller number of neurons. The reduction of the number of neurons per visual field area from foveal to peripheral representations is achieved in several steps along thevisual pathway, starting already in the retina

Question 5

Orientation columns

Answer 5

in 1mm orientation changes 180degrees. Made up of complex, simple and hypercomplex cells. are flat slabs that are parallel to each other. The slabs are perpendicular to the surface of the visual cortex and are lined up similar to slices of bread

Question 6

Occular dominance columns

Answer 6

Wiesel and Hubel (1963)
Some cells respond best to contralateral eye and others best to ipsilateral eye
 Kittens were deprived of vision in one eye from birth and unit recordings were taken from the striate cortex. It was concluded that this monocular deprivation can lead to unresponsiveness of cortical cells when the deprived eye is stimulated.
Cells in the input layer IV are strictly monocular

Question 7

Hypercolumn

Answer 7

cytochrome oxidase blobs are included. form with the orientation pinwheel. The top “slice” above the ice-cube model depicts two fundamental modules each containing a complete set of about 60,000 neurons processing all the 3 features of orientation, depth and color (400 micron * 800 micron)