Neuro: 2.06 - Visual System 3 - Central Pathways

Front 1

What are the two major visual pathways?

Back 1

- Geniculo-Striate System (red)
- Retino-Tectal System (green)

Front 2

What is the function of the geniculo-striate system?

Back 2

Conscious Visual Perception

Front 3

What is the function of the retino-tectal system?

Back 3

Directing eye movements and visual attention

Front 4

What is the pathway of fibers through the geniculo-striate system?

Back 4

- Retina (via optic n., optic chiasm, and optic tract)
- Lateral Geniculate Nucleus (LGN) (via Meyer's loop)
- Striate Cortex
- Extrastriate Cortex

Front 5

What is the pathway of fibers through the retino-tectal system?

Back 5

- Retina
- Superior Colliculus
- Pulvinar
- Extrastriate Cortex

Front 6

If you hear a loud noise and respond to it, which visual system are you using?

Back 6

Retino-tectal system (directs eye movements and visual attention)

Front 7

What is the name of the primary visual cortex?

Back 7

Striate cortex

Front 8

What is the pathway from the lateral geniculate nucleus to the striate cortex?

Back 8

Optic radiations (Myer's Loop)

Front 9

How can damage to the temporal lobe affect vision?

Back 9

- Can damage Myer's loop (part of the optic radiations)
- Would lead to a restricted visual field defect

Front 10

What is a common side effect of temporal lobectomies? Why would this procedure be done?

Back 10

- Damage to Myer's Loop (leads to restricted visual field defect)
- Used to relieve temporal lobe epilepsy

Front 11

Retinal signals controlling pupillary constrictor muscles travel through what structures?

Back 11

- Receptor in retina detects light (optic n. --> optic chiasm --> optic tract)
- Fibers synapse at pregeniculate body
- Fibers continue to pretectal area and some cross to opposite side on posterior commissure (to get consensual response)
- Fibers synapse at Edinger-Westphal Nucleus in midbrain
- Travel back to ciliary ganglion on CN III
- Synapse at ciliary ganglion
- Fibers innervate pupillary constrictor m.

Front 12

What structure is responsible for the consensual pupil response?

Back 12

Some fibers cross to other side of midbrain via Posterior Commissure (in pretectal area)

Front 13

If there is damage to the midbrain that cuts the posterior commissure, what is the effect?

Back 13

No consensual light reflex response

Front 14

What is the pathway for dilating the pupil?

Back 14

- Retinal receptors respond to decrease in light (CN II --> optic chiasm --> optic tract)
- Fibers synapse at pregeniculate body
- Fibers continue to Midbrain Reticular Formation
- Fibers descend to thoracic spinal cord
- Head to sympathetic chain and synapse at Superior Cervical Ganglion
- Fibers innervate Pupillary Dilator m.

Front 15

What does emotion do to the pupils?

Back 15

Can cause dilation via the sympathetic autonomic system

Front 16

What is accommodation?

Back 16

Focusing the eye

Front 17

What is the pathway of fibers for accommodation?

Back 17

- Retinal ganglion cells (CN II --> optic chiasm --> optic tract)
- Synapse at Lateral Geniculate Nucleus (LGN)
- Fibers go to visual cortex
- Pass through pretectal area and synapse at Edinger Westphal Nucleus
- Fibers continue back to ciliary body, synapsing at ciliary ganglion

Front 18

What muscles are responsible for accommodating the eye?

Back 18

Ciliary body muscle

Front 19

When the ciliary muscle contracts, what happens to the lens?

Back 19

Lens thickens - increased optical power (see better nearby)

Front 20

What happens when the ciliary muscle relaxes?

Back 20

Lens flattens

Front 21

What three things happen when attention is directed to nearby objects?

Back 21

1. Convergence of the 2 eyes
2. Contraction of the ciliary muscle to thicken the lens
3. Pupillary constriction

Front 22

What is the effect of the lens thickening?

Back 22

Increases optical power so that you can see up close

Front 23

Why do old people have to wear bifocals?

Back 23

Accommodation fails (ciliary muscle doesn't contract as well to thicken the lens)

Front 24

Why does pupillary constriction help you to see objects up close?

Back 24

- Increases depth of field (increases range over which image is focused)
- If you look through a small hole your vision will be sharper even without glasses

Front 25

How is accommodation different from the pupillary reflex?

Back 25

- Can be voluntarily controlled
- Regulated by a negative feedback mechanism that automatically adjusts the focal power of the lens
- Pathway includes cerebral cortex, only such reflex pathway

Front 26

Why is the visual cortex needed for the accommodation reflex and not pupillary reflexes?

Back 26

Cortex is needed for analysis to determine if the image is blurry (out of focus)

Front 27

What happens to the topography of the receptor array (retina) as the signal is transmitted through the rest of the brain?

Back 27

Retinotopy is preserved

Front 28

What is the difference between the visual field and the image on the retina?

Back 28

Reversed (left is right) and Upside-down (top is bottom)

Front 29

How is the retintopy preserved?

Back 29

Fibers in adjacent ganglion cells in each hemiretina stay together

Front 30

What happens to fibers from the nasal half of the retina (nasal hemiretina)?

Back 30

Cross in the optic chiasm so that fibers from the same visual field in each eye travel together

Front 31

What happens to fibers from the temporal half of the retina (temporal hemiretina)?

Back 31

Do not cross via the optic chiasm - stay on the same side

Front 32

The fovea has what kind of distribution?

Back 32

Greatly expanded (green) relative to the periphery

Front 33

The R half of the retina sees what part of the visual field? Which side of the brain does it project to?

Back 33

- R half of retina on each eye sees L visual field
- R half of retina projects to R side of brain
(follow black quadrant or red dot)

Front 34

The L half of the retina sees what part of the visual field? Which side of the brain does it project to?

Back 34

- L half of retina on each eye sees R visual field
- L half of retina projects to L side of brain (no black quadrant in LGN or cortex)

Front 35

If you lesion the L LGN, what will the deficit be?

Back 35

Lose R half of visual field from each eye

Front 36

If you lesion the R LGN, what will the deficit be?

Back 36

Lose L half of visual field from each eye

Front 37

Why is there a cortical over-representation of the fovea?

Back 37

- Enhanced acuity at center of gaze
- Fovea contains more ganglion cells than the periphery --> more fibers and cells --> more corteical area

Front 38

What is the benefit to having a cortical over-representation of the fovea and under-representation of the periphery?

Back 38

- Greatest detail and information from center of gaze
- Wide coverage and less detail of periphery

Front 39

Lesions of visual cortex that affect the fovea lead to what deficits?

Back 39

Severe deficits

Front 40

Lesions of visual cortex that affect the periphery lead to what deficits?

Back 40

Can go unnoticed (unless the physician is alert enough to test this in detail)

Front 41

What would be a possible reason for mapping the human visual cortex with a fMRI?

Back 41

Pre-surgical planning:
- Tumor (gray) near visual cortex (colored pixels)
- Want to remove tumor without damaging vision if possible

Front 42

What do the colors represent on this fMRI?

Back 42

- Red/orange represent the center of the gaze
- Blue/green represents periphery

Front 43

How come you can see the afferent visual pathways in this fMRI?

Back 43

Diffusion Tensor Imaging (DTI) identified the white matter tracts

Front 44

How can you see the tumor (gray)?

Back 44

Fluid Attenuated Inversion Recovery MRI (FLAIR)

Front 45

What does the white line/circle around the tumor represent?

Back 45

5 mm distance - high likelhood of being damaged if tumor is fully resected during surgery

Front 46

What is the most critical thing to be aware of when resecting this tumor (gray)? What could happen?

Back 46

- The proximity of the optic radiation (green fiber track) near the lateral border of the tumor (within the 5 mm boundary / white outline) is the most concerning
- If this is cut would lead to complete hemianopia (loss of vision in a hemifield)

Front 47

What is a hemianopia?

Back 47

Loss of vision in a hemifield

Front 48

What is a quadrantanopia?

Back 48

Loss of vision in a quadrant

Front 49

What does the term homonymous mean?

Back 49

Corresponding loss in each eye

Front 50

What does the term heteronomous mean?

Back 50

- Non-corresponding loss in each eye
- A loss of vision in either both nasal halves (binasal hemianopia) or both temporal halves of the visual field (bitemporal hemianopia)

Front 51

What would a lesion of the optic nerve on the right side cause?

Back 51

Total Blindness in right eye

Front 52

What would a lesion of the R optic nerve near the optic chiasm cause?

Back 52

- Total blindness in R eye
- Left Superior Quadrantanopia

Front 53

What would a lesion of the optic chiasm cause?

Back 53

Bitemporal hemianopia (heteronomous hemianopia)

Front 54

What would a lesion of the R optic tract cause?

Back 54

Left Homonymous Hemianopia

Front 55

What would a lesion of the Meyer's Loop (half of the optic radiations) on the R side cause?

Back 55

L Homonymous Superior Quadrantanopia

Front 56

What would a lesion of all of the fibers going to the striate cortex / visual cortex on the R side cause?

Back 56

Left Homonymous Hemianopia (macula spared?)

Front 57

What does a photoreceptor signal?

Back 57

The intensity of light at a small point:
- Position (x,y)
- Wavelength
- Time
- Eye (R vs L)

Front 58

If a photoreceptor only tells us intensity (position, wavelength, time, and which eye), how does the visual system figure out everything else that it is seeing?

Back 58

- Many intervening stages --> hierarchy of visual areas
- Multiple pathways --> "parallel" processing streams

Front 59

Lesions to the extrastriate cortex, will show what kind of deficits?

Back 59

- More functionally specific
- Selective loss of function (agnosias) rather than blindness

Front 60

What is an agnosia?

Back 60

- Loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss
- Associated w/ brain injury or neurological illness

Front 61

What are the inferred attributes of vision from the retinal images and sensory cues regarding "what" you are seeing?

Back 61

- 3D form (shape, size, rigidity)
- Surface properties (color - brightness/hue/saturation, visual texture, specular reflectance, transparency - shadows/highlights)

Front 62

What are the inferred attributes of vision from the retinal images and sensory cues regarding "where" things are that you are seeing?

Back 62

- 3D spatial relationships (relative positions, 3D orientation in space)
- 3D movement (trajectory, rotation)

Front 63

What cortical area surrounds the calcarine fissure?

Back 63

V1 - Primary visual cortex

Front 64

What is CoS (to left of blue area)? POS (above purple)

Back 64

CoS - Collateral Sulcus
POS - parieto-occipital sulcus

Front 65

What surrounds the Primary Visual Cortex (V1)?

Back 65

Second Visual Area V2d and V2v (dorsal/ventral)

Front 66

What are the components of the higher-level extra-striate visual area?

Back 66

V3, VP, V3A, V4, V8

Front 67

The extrastriate visual areas are organized into what two specialized systems? Functions?

Back 67

- Temporal Lobe Pathways (ventral pathway) - recognition of objects ("what is it?"
- Parietal Lobe Pathways (dorsal pathway) - localization of objects ("where is it?")

Front 68

Which special system pathway is involved in directing visual attention to an object of interest?

Back 68

Parietal Lobe Pathways for localization

Front 69

What are the visual implications of a lesion to the temporal lobe?

Back 69

Impairs recognition

Front 70

What are the visual implications of a lesion to the parietal lobe?

Back 70

Impairs allocation of attention, "attentional neglect"

Front 71

The parietal lobe pathway / dorsal pathway has also been termed what? Why?

Back 71

"Action" Pathway - emphasizes its role in how visual information is used

Front 72

The ability to navigate the world using a mental "map" involves what parts of the brain?

Back 72

Medial Temporal Lobe
Hippocampus

Front 73

Lesions of what parts of the brain produce blindness?

Back 73

Up to and including V1 (and probably V2)

Front 74

Deficits in visual areas beyond V1 can cause what issues?

Back 74

Selectively impair different aspects of visual perception without causing complete blindness

Front 75

What is hMT+? What does a lesion of this area cause?

Back 75

- Human Middle Temporal visual area plus surrounding motion sensitive areas
- Selective loss of motion perception (just see flashes of stillframes, not a smooth progression)

Front 76

What are V4/V8 a part of? What does a lesion of this area cause?

Back 76

- Components of higher-level extrastriate visual areas
- Cerebral achromatopsia (caused by damage to the cerebral cortex of the brain, rather than abnormalities in the cells of the eye's retina)

Front 77

What is FFA? What does a lesion of this area cause?

Back 77

- Fusiform Face Area
- Prosopagnosia - inability to recognize familiar faces
- Often accompanies cerebral achromatopsia (lesion of V4/V8)

Front 78

What is PVA? What does a lesion of this area cause?

Back 78

- Complex of an unknown number of parietal visual areas
- Primarily on R side, lesions cause attentional neglect

Front 79

What is achromatopsia? What causes it?

Back 79

- Loss of color vision due to cerebral cortex injury
- Lesion of V4/V8

Front 80

What is prosopagnosia? What causes it?

Back 80

- Inability to recognize familiar faces
- Lesion of FFA (fusiform face area)