visual system: visual processing in the cortex (I)

Question 1

Optic radiation

Answer 1

A projection trace which allows for the output of the lateral geniculate nucleus to project to the primary visual cortex (V1)

it is a prominent white matter fiber tract

Question 2

Visual space allocation in optic radiation

Answer 2

1. ventral half of optic radiation → top half of visual space
2. dorsal half of optic radiation → bottom half of visual space

Question 3

Stroke in optic radiation section

Answer 3

A lesion in a given area of the optic radiation would correspond to an issue with the opposite part of the visual space.

→i.e., a stroke damaging the dorsal part of the optic radiation on the right side of the brain would hinder the bottom half of visual space in the left eye

Question 4

T or F: Projections from the lateral geniculate to V1 are vastly outnumbered by reciprocal projections coming back from the cortex.

Answer 4

True!

→remember: feedback projections come in very large numbers

Question 5

Where can retinal ganglion axons project to?

Answer 5

1. Lateral geniculate nucleus (90%)
2. Superior colliculus
3. Pretectum
4. Suprachiasmatic nucleus in the hypothalamus

Question 6

Superior colliculus

Answer 6

Projections to the superior colliculus are involved in saccadic eye movements (rapid switches).

Question 7

Pretectum

Answer 7

Projections to the pretectum are involved in pupillary reflexes.

Question 8

Hypothalamus: Suprachiasmatic nucleus

Answer 8

Projections to the suprachiasmatic nucleus of the hypothalamus modulate circadian rhythms (sleep-wake cycles).

→it is responsible for the brain’s internal clock

Question 9

Brodmann’s area 17

Answer 9

-found in the primary visual cortex
-most of this area is on the medial surface of the brain surrounding and within the calcarine sulcus

Question 10

Calcarine sulcus

Answer 10

Anatomical landmark located at the caudal end of the medial surface of the brain of humans and other primates

Question 11

Primary visual cortex contains a _____ map of the external visual field.

Answer 11

Retinotopic

Question 12

Explain the layout of the retinotipic map: visual field & area 17

Answer 12

1. the center (4) pertains to the fovea
   →most caudal layer in area 17
2. first outer layer (4)
   →mid layer in area 17
3. second outer layer (4)
   →most rostral layer in area 17

Question 13

Name three conserved characteristics of the retinotopic map

Answer 13

1. Visual space from one eye is represented contralaterally in area 17
   →right side of visual world maps out onto the left side of the primary visual cortex (contralateral!)
2. Visual space allocation from optic radiation is conserved
   →top half of visual world maps out onto the bottom of the primary visual cortex (flipped!)
3. The retinotopic map is distorted
   →fovea is a small part of visual world, but it takes up a large part of the primary visual cortex (distorted retinotopic map!)