Lecture 7- Vision II: Central processing

Question 1

What are the characteristics of the M ganglion cells?

Answer 1

-magnocellular=large cells -large receptive fields -make up about 10% of ganglion cells -motion detection, flicker and analysis of gross features -can tell if sth is moving or not, not good at fine detail

Question 2

What are the characteristics of the P ganglion cells?

Answer 2

-parvocellular= small cells -more numerous (about 80% of ganglion cells) -provide fine detail (visual acuity) and colour vision

Question 3

What is this picture showing?

Answer 3

-this pic shows the AP of a P ganglion cels as reacting to different frequencies of light -one ganglion cell, it responds best to one wavaelength= black it is important for carrying info for colour

Question 4

What is the output region of the ganglion cells?

Answer 4

-many brain regions -mainly the lateral geniculate nucleus (LGN) in the thalamus

Question 5

What is the visual pathway?

Answer 5

1. Retina
2. Optic nerve
3. LGN
4. Optical radiations
5. Visual cortex
   - starts in the retina= the axons of optic nerve then synapse with the thalamus (LGN), then the LGN neurons have optic radiations (white matter) goes all the way back to the visual cortex V1

Question 6

Where is the optic chiasm and what happens there?

Answer 6

• lies at the base of the brain, anterior to the pituitary
• the fibres from right and left optic nerves combine to form the optic chasm

Question 7

What fibres cross at the optic chiasm?

Answer 7

-nasal

Question 8

What hemisphere is the right visual field “viewed” by?

Answer 8

-left

Question 9

What hemisphere is the left visual field “viewed” by?

Answer 9

-right

Question 10

Explain:

Answer 10

-the nasal fibres cross over -get information from both eyes in each hemisphere -partial crossing of the visual field

Question 11

How many layers are there in the LGN?

Answer 11

-6 -contain 2 typesof cells

Question 12

What layers do the magnocellular cells and the parvocellular cells occupy in the LGN?

Answer 12

-6 layers -Magno=1 and 2 (one layer for info from each eye) -Parvo =3,4,5,6= two of these for info from each eye

Question 13

What cells in the LGN do the the P and M ganglion cells target?

Answer 13

P ganglion= parvocellular cells M ganglion= magnocellular cells

Question 14

What is the function of the thalamus?

Answer 14

-functional relay station for sensory information -except for taste!

Question 15

Is the visual information separated or mixed in the LGN?

Answer 15

-separated, keep M and P streams of information separate, and information from each of the eyes is also kept separate

Question 16

What are the optic radiations?

Answer 16

• the axons of the magnocellular and parvocellular LGN neurons carrying information to the visual cortex
• white matter, big, enclose the ventricles

Question 17

Where do the LGN neurons project to?

Answer 17

-the primary visual cortex

Question 18

Where is the primary visual cortex located?

Answer 18

-occipital lobe, around the calcarine fissure (gap) -very far back in the brain -if you cut corpus callosum medially= then there

Question 19

What does it mean that V1 is retinotopic?

Answer 19

-whatever the retina sees= the brain will see= retinotopic map= the neurons in V1 will see the same things as the retina sees –Neighbouring cells within the retina project to neighbouring cells in the LGN & Vis Cortex.

Question 20

Where is each of the visual fields (left/right) represented in the primary visual cortex?

Answer 20

-on the contralateral visual cortex -right field of vision= left V1 -left field of vision= right V1

Question 21

Does each V1 separate which part of the visual field is presented where?

Answer 21

• yes
• central part of vision is on the outermost part of the V1
• more peripheral part of the visual field is closer to the midline

Question 22

What part of vision is the most vulnerable?

Answer 22

-central -closest to the outside in the V1

Question 23

How many layers does the visual cortex have?

Answer 23

6

Question 24

What layer of the V1 do LGN neurons input to?

Answer 24

4C -P= to layer 4Cbeta -M= to layer 4Calpha

Question 25

How are cortical (V1) neurons orientation selective?

Answer 25

-neurons respond best to bars moving in particular orientation

Question 26

What are orientation columns in the V1?

Answer 26

- the cortex is extremely ordered - in each little area the neurons in all 6 layers will respond to the same direction of the bar of light - part of the way the information is divided into different bits

Question 27

What does this picture demonstrate?

Answer 27

- each of the four pics= how different spots in the V1 will see it - deconstructing what we see - then brain has to put back together

Question 28

What are occular dominance columns?

Answer 28

- input from the LGN in the V1 segregated into small regions called occular dominance columns - section 4C - infromation from the left eye is thus still separated from the right eye - it goes: right, left, righ, left...

Question 29

What is the pathway of the P ganglion cells?

Answer 29

-feed into the parvocellular LGN cells, then via optic radiations (their axons) to the V1 into the 4C beta layer

Question 30

What is the pathway of the M ganglion cells?

Answer 30

-feed into the magnocellular LGN cells, then via optic radiations (their axons) to the the V1 into the 4C alpha layer

Question 31

Where does the mixing of visual information occur?

Answer 31

in the layer 4B and 3

Question 32

What happens to the visual information after V1?

Answer 32

- divided into two large cortical streams - DORSAL pathway - VENTRAL pathway

Question 33

What does the dorsal pathway do?

Answer 33

-the where -where in the visual field something is

Question 34

What does the ventral pathway do?

Answer 34

-the what -what am I seeing? part of information

Question 35

What is the MT area?

Answer 35

-part of the dorsal stream -middle temporal (MT) lobe is an area specialised for processing of object motion

Question 36

Where does the MT receive information from?

Answer 36

-receives retinotopic information from a number of cortical areas (V2 and V3) -receives input from cells in layer 4B of the V1 (so the M type GCs and LGN)

Question 37

What does the visual system operate on?

Answer 37

-about comparison = what is the colour next to -- red vs green -- blue vs yellow =imprtant comparison -context of the colour

Question 38

What parts are part of the ventral stream?

Answer 38

V1, V2, V4

Question 39

Where does the V4 receive input from?

Answer 39

-the blob and interblob regions of the primary visual cortex via V2

Question 40

What are the receptive fields like in V4 and what is V4 for?

Answer 40

-large -both orientation selective and colour selective -important for perception of shape and colour

Question 41

What is the area IT?

Answer 41

- inferior temporal - major output area of V4 -neurons respond to a wide variety of abstract shapes and colours - important for visual memory and perception - important for perception of faces - when see faces= neurons stimulated -the information from the whole pathway is added up here

Question 42

What was wrong with David?

Answer 42

-David cannot recognize faces, can tell people only by what their voices are like -think motion perception is off -at the periphery of his vision= can't see -couldn't recognize the prime minister on a photo -lesion affecting the fusiform gyrus (area IT) -also caused a visual field defect, must have been back of the chiasm as the effect is the same in each eye

Question 43

What was wrong with Giselle?

Answer 43

-cars appear out of nowhere, pouring coffee very difficult= appears frozen until cup overflows -visual acuity and colour vision norma -visual fields= normal -lesion in the MT -she had a tiny stroke in her middle temporal lobe= area spcialised for processing motion

Question 44

What are the blob and interblob regions?

Answer 44

- areas of 4C beta of V1 (so Parvocellular cells feed into here) - blob= colour info - interblob receive the same infor bur react to diretcion of colour