Visual System 2

Question 0

Which side of the brain is the left visual field processed on?

Answer 0

Right side and vice versa

Question 1

What is the human visual pathway ?

Answer 1

Retina-lateral geniculate nucleus- primary visual cortex

Ganglion cells progress dorsally in optic nerve to the optic chiasm and then become optic tract

Question 2

What is the full visual field, left/right hemifields and binocular visual field ?

Answer 2

FVF- area viewed by both eyes
L/R VF- division of the FVF into 2
BVF- area of overlap between the L/R VF

Question 3

At the optic chiasm which fibres cross ?

Answer 3

Fibres from the nasal retina

Question 4

What are perceptual disparities perceived as by the brain ?

Answer 4

Depth

Question 5

What is the retinofugal projection ?

Answer 5

Main target is the lateral geniculate nucleus
Also targets hypothalamus for circadian rhythms
Pretectum and superior colliculus for ability to looks at something suddenly when it appears in your periphery

Question 6

What does the lateral geniculate nucleus look like ?

Answer 6

Retinal inputs produce 6 segregated layers
1-2 are inputs from M type ganglion cells - 2 strips due to inputs from both eyes
3-6 are inputs from P type ganglion cells
The more lightly stained areas between the darker stained strips are the koniocellular layers which K type ganglion cells project into

Question 7

What does it mean by retinotopic projections ?

Answer 7

Neighbouring locations on the retina project to neighbouring locations in the LGN and this is preserved all the way to layer 4c of striate cortex

Question 8

What is the cytoarchitecture of the visual cortex like ?

Answer 8

6 layers
Layer 4 is split into a, b and c and receives inputs from LGN
Layer c is split into alpha and beta
Alpha receives magnocellular inputs and beta receives parvocellular inputs

Question 9

What are the cells like in the visual cortex ?

Answer 9

Spiny stellate cells with small dendritic fields in layer 4c
Pyramidal cells with large dendritic fields in layers 4b, 3, 5 and 6

Question 10

Where do layers 2,3 and 4b project?

Answer 10

These pyramidal cells project to other cortical areas

Question 11

Where does layer 5 project to ?

Answer 11

Pyramidal cells project to pons and superior colliculus

Question 12

Where does layer 6 project to ?

Answer 12

Pyramidal cells have very large projects back to the LGN

Question 13

Why is the primary visual cortex also called the striate cortex ?

Answer 13

Because of its striped appearance
Using a myelin stain you can see a stripe in laYer 3 of the cortex due to horizontal pyramidal cell connections, this is not present anywhere else on grey matter

Question 14

What layers do the K type ganglion cells terminate in the visual cortex from the LGN ?

Answer 14

Patchy patterns in layers 2 and 3 of the cortex
They come in as blobs between these 2 layers
Blobs provide specific info about colour

Question 15

Which layer of the primary visual cortex does info from both eyes from magnocellular pathways combine ?

Answer 15

Layer 4b

Question 16

Which layer of the primary visual cortex does the information from both eyes combine from parvocellular inputs ?

Answer 16

Layers 2 and 3

Question 17

What is ocular dominance ?

Answer 17

Across layer 4 of the visual cortex every 0.5mm the response from neurons switches from each eye, allowing over a 1mm distance to have information from both eyes
Then the info is combined at the next level for binocular processing

Question 18

What does ocular dominance create?

Answer 18

Creates ocular dominant columnar organisation in layer 4 of the primary visual cortex

Question 19

What information from the retina is processed at the right LGN and what is processed at the left LGN ?

Answer 19

Right- right temporal retina and left nasal retina

Left- right nasal and left temporal

Question 20

Why are layers 2 and 3 of V1 very important ?

Answer 20

Key role in visual processing, providing most of the info that leaves V1 for other cortical areas

Question 21

What did staining with cytochrome oxidase in the cortex do ?

Answer 21

Showed that it wasn’t uniformly distributed in layers 2 and 3
Appeared in a colonnade - series of pillars at regular intervals and this was also seen in layers 5 and 6

Question 22

What were the pillars rich in cytochrome oxidase in the visual cortex ?

Answer 22

Called blobs - cytochrome oxidise rich neurons
They are centred on an ocular dominance stripe in layer 4 and between them is the region called inter blobs
They receive direct inputs from the LGN from koniocellular layer cells and inputs from par ocular and mag ocular cells from layer 4c in cortex

Question 23

What do the receptive fields of blobs display ?

Answer 23

Colour opponency

Question 24

What organisation do neurons display when an electrode is advanced into V1 vertically ?

Answer 24

Same orientation specificity

Question 25

What organisation do neurons display in the cortex when an electrode is advanced obliquely ?

Answer 25

Display heterogenous orientation specificity

Question 26

Describe the parallel magnocellular pathway to the cortex

Answer 26

Info from both eyes combines in layer 4b making it binocular
They are orientation selective and many are direction sensitive but not wavelets sensitive (not detecting colour)
They have a transient response with large dendritic field and due to highest number of direction sensitive RF they analyse object motion

Question 27

Describe the parallel parvocellular pathway in the cortex

Answer 27

Info from both eyes is integrated in layers 2 and 3 for binocular vision
Interblob layer 3 cells have a simple and complex RF
Relatively insensitive to wavelength but highly orientation selective
Sustained response with small recognise fields for analysis of object shape

Question 28

Describe the parallel pathway for blobs in the cortex

Answer 28

Blobs cells have monocular rf and lack orientation selectivity
Most have circular rf- some are centre-surround colour opponent, some are colour opponent in centre only and some are colour opponent in centre and surround so double copponent
They analyse object colour

Question 29

What do the cells in the visual cortex have to respond to ?

Answer 29

Location of stimulus
Orientation of stimulus
Orientation and direction of movement of stimulus
Wavelets/ colour of stimulus

Question 30

What is ten basic cortical module ?

Answer 30

For image processing 
Each point in space is analysed by dedicated cortical module which is made up of cells of 2mm cubed - contain all the cells necessary to deco strict the info from the stimulus