Visual System IV

Question 1

How does output from lgn project to v1

Answer 1

Through optic radiation

Question 2

where is v1

Answer 2

Medial surface occipital lobe

Question 3

describe optic radiation

Answer 3

Goes forwards then sweeps back ventrally and dorsally
Ventrally = top half of world
Dorsally = bottom half of world

Question 4

ex = stroke damage ventral part left lgn

Answer 4

Left lgn = from right side fo world
= top half right side contralateral visual field = damage = pie in the sky

Question 5

compare projections from lgn —> v1 vs v1–>lgn

Answer 5

Projections from lgn to v1 «_space;projections from v1 to lgn (reciprocal projections)
Projections from layer 6 v1- feedback, lot more than feed forward
Not driver tho = gpcr/metabotropic = modulate physiology = regulate flow of info through thalamus

Question 6

where do most of retinal ganglion axons project to

Answer 6

90% of retinal ganglion axons project to lgn
= mainly involved in seeing

Question 7

where do remaining of retinal ganglion axons project to

Answer 7

Remaining 10% project to the superior colliclus, pretectum and hypothalamus
(Retina —> other parts brain)

Question 8

describe projection to superior colliculus

Answer 8

Projections to superior colliculus involved in saccadic eye movements = rapid movements fo eyes, Orient you to novel stimuli, also head movements, 2 way connections with cortex

Question 9

describe projections to pretectum

Answer 9

Involved in pupillary reflexes
In dark = pupils dilate, also anything that surprises you or evokes emotion
Bright = pupils constrict

Question 10

describe projections to suprachiasmatic neurons

Answer 10

Projections to suprachiasmatic nucleus of hypothalamus modulate circadian rhythms
- daily rhythms, sleep/wake, built in clock in brain 24 hr, inputs from retina reset clock

Question 11

describe specifically where v1 is

Answer 11

Brodmanns area 17
Most on medial surface of brain surround and within calcarine sulcus (bisects v1, v1 = inside groove)

Question 12

what does v1 contain

Answer 12

Retinotopic map of external visual field
Regions of v1 dedicated to each part of visual field

Question 13

describe features of primary visual cortex = 3

Answer 13

Left v1 sees right side world, right v1 sees left side visual space of both eyes
Dorsal/bottom = 4,8,12, ventral/top=3,7,1
Fovea = small part visual space but disproportionally represented in v1 = way more ganglion cells coming from retina - high res vision, much more inputs

Question 14

Describe v1 cortex layer 4

Answer 14

Layer 4 = main recipient of afferent inputs from thalamus =
HUGE

Question 15

where do lgn neurons project to mainly

Answer 15

Layer 4c of v1
(Many sub regions of layer 4)

Question 16

what happens to m p and k pathways in v1

Answer 16

Integrated in diff layers of v1

Question 17

describe outputs from v1 = gen

Answer 17

Form separate dorsal (where) and ventral (what) channels

Question 18

describe p patwhay in v1

Answer 18

Midget ganglion cells= colour and high precision vision, layers 3,4,5,6 lgn
Axons in midget cells terminate in lgn —> continue to v1
End in sub layer of layer 4 = in v1 layer 4cbeta
Neurons in layer 4cbeta = stellate —> axons project to layers 2 and= diff sublayers =to blobs and interblobs

Question 19

describe m patwhay in v1

Answer 19

Start with parasol cells - motion, larger rfs, brightness, end in lgn layers 1 and 2
End in layer 4calpha —> project to 4b —> blobs and interblobs

Question 20

describe k patwhay in v1

Answer 20

Bistratifie, between layers to lgn
Projections do not end in layer 4 = project to layers 2 and 3 and end in blobs

Question 21

descibe ventral outputs of v1

Answer 21

ventral stream= what, colour vision, seeing, identifying, recognition
Get input from k m and p pathways
Temporal lobe

Question 22

describe dorsal outputs of v1

Answer 22

M patwhay - directly from layer 4b = dorsal stream
Detect where things are - visual motion and use vision to guide action
Parietal lobe

Question 23

what is blob

Answer 23

Integrate all 3 pathways
Colour vision

Question 24

what is inter blob

Answer 24

Imrpoatnt for shape discrimination
P and m patwhay

Question 25

What do simple cells in v1 respond best to

Answer 25

Bars of light at specific orientations

Question 26

how are v1 simple cells rfs built

Answer 26

Convergent input of many layer 4 cells with roughly circular rfs —> elongated rfs of simple cells = cells in lgn have same rfs as ganglion cells, but then converge on neuron = rf of simple cell specifically to bar of light at specific orientation

Question 27

describe orientation selective simple cells

Answer 27

Can be on center off surround (convergence on center off surround cells) Or off center on surround (inhibited by bar of light in cneter= convernce off center on surround)

Question 28

describe Hubble and Wiesel exp

Answer 28

Cats = stick electrode and shine light and map rf Slide projector = created edge = edge creates response in neuron Exp showed that neurons respond to bars of light at specific orientations

Question 29

Describe outputs of v1 = specifically

Answer 29

Outputs from blobs and interblobs = send to higher level in visual procession Outputs = down into cortical white matter