Visual System Pathways

Question 1

What part of the visual field does information carried in the left optic tract come from? Right optic tract?

Answer 1

Left optic tract - carries information from the right half of the visual field

Right optic tract - carries information from the left half of the visual field

Question 2

What section of the retina crosses the midline at the optic chiasm?

Answer 2

Nasal part of the retina

Question 3

What are the four primary targets of optic tract fibers in the brain?

Answer 3

Lateral geniculate nucleus

Superior colliculus

Pretectum

Hypothalamus

Question 4

Which two pathways contribute to the two major visual system pathways and what are these pathways?

Answer 4

Projection to the LGN - geniculocalcarine tract

Projection to the superior colliculus - extrageniculate tract

Question 5

Describe the topographical arrangement of the LGN

Answer 5

Contralateral and ipsilateral fibers come in alternating layers

Most of the LGN is composed of parvocellular layers, while the remainder is magnocellular

Question 6

What is the difference between parvocellular and magnocellular input?

Answer 6

Parvocelllular - color and form vision from central retina

Magnocellular - movement information from the peripheral retina

Question 7

What is the geniculocalcarine tract?

Answer 7

Primary visual pathway in the brain that connects the LGN to the primary visual cortex

Fibers known as the optic radiations, travels through the retrolenticular portion of the posterior limb of the internal capsule

Question 8

What are the two major divisions of the geniculocalcarine tract?

Answer 8

Upper division - from medial LGN, travels dorsally over the lateral ventricle to the cuneus gyrus

Lower division - from lateral LGN, travels rostrally around the inferior horn of the lateral ventricle to the lingual gyrus

*Lower division is known as Meyer’s loop

Question 9

What part of the visual field do the optic radiations in each hemisphere represent?

Answer 9

The contralateral hemifield of vision (i.e. right optic radiation represents left visual field)

Upper division represents the lower half of the visual field

Lower division represents the upper half of the visual field

Question 10

What are the two extrastriate visual pathways?

Answer 10

Dorsal - connects PVC (V1) to parieto-occipital association cortex (V5), encodes motion and spatial relationships

Ventral - connects PVC (V1), to occipitotemporal association cortex, encodes information about form (V3) and color (V4)

Both streams connect to the secondary visual cortex (V2) for further information refinement

Question 11

What is the function of the superior colliculus in vision?

Answer 11

Main player in the extrageniculate pathway

Highly sensitive to moving visual stimuli and regulates the control of saccades

Receives input via the brachium of the superior colliculus

Question 12

Where do deep layers of the superior colliculus project?

Answer 12

CNs III and VI

Upper spinal cord via the tectospinal trach

Pons/cerebellum

Pulvinar nucleus

Question 13

What is the pathway/function of the extrageniculate tract?

Answer 13

Retina -> Superior Colliculus -> Pulvinar -> extrastriate cortex

Works in parallel with the geniculocalcarine tract to assimilate different types of information

Question 14

What is the function of retinal ganglion cell projections to the pretectum?

Answer 14

Pupillary light reflex

Pretctum projects to the Edinger-Westphal nucleus

Question 15

What is the function of the suprachiasmatic nucleus of the hypothalamus?

Answer 15

Located in the anterior ventral portion of the hypothalamus

Receives input from primitive light-sensitive RGCs

Nucleus involved in linking circadian rhythm and hormonal cycles with levels of ambient light

Question 16

What is progressive encephalizaiton?

Answer 16

The shifting of devotion of visual information to higher-order association cortices instead of primary visual areas

Question 17

What is cortical blindness?

Answer 17

Loss of conscious visual perception caused by lesions of area 17/V1

Some individuals can still respond to visual stimuli - an ability known as blindsight

Question 18

What is Anton’s Syndrome?

Answer 18

Patient’s are cortically blind, even though they adamantly deny it

Perception does not occur normally

Aka Visual anosognosia

Question 19

What is prosopagnosia?

Answer 19

Face blindness; results from bialteral fusiform gyrus lestion

I.e. inferior occipitotemporal

Question 20

What is achromatopsia?

Answer 20

Disorder of color perception; caused by fusiform gyrus lesion

Differs from color agnosia/anomia in which pereptio still occurs normally but fails at the ID stage

Question 21

What is metamorphopsia?

Answer 21

Distortion of size and shape

Lesions in inferior or lateral visual association cortex

Question 22

What is Balint’s syndrome?

Answer 22

Simultanagnosia - perception of only one portion of the visual field at a time, changes randomly

Optic ataxia - lack of coordination between visual input and hand movement

Ocular apraxia - impaired gaze direction

Cause by bilateral lesions of dorsolateral parieto-occipital cortex (Dorsal “where” stream)