Retinotopic Projections (M2)

Question 1

What relationship do waves in the prenatal retina set up?

Answer 1

relation between retina and brain

Question 2

What are albinism patients still able to do well, despite their visual deficiencies?

Answer 2

1. sports

2. reading

Question 3

What is the ability to change as a result of experience called?

Answer 3

plasticity

Question 4

Why don’t the cells in V1 sweep like waves when they respond synchronously like many of the other areas during development?

Answer 4

the V1 domains are joined with gap junctions rather than synapses

Question 5

What does the signaling molecule En2 attract? 1. What does it repel? 2

Answer 5

1. nasal axons

2. temporal axons

Question 6

What do signaling molecules at the LGN signal for the growth cones to do?

Answer 6

1. guide projection D-V-M-L

2. segregate the two eyes to appropriate levels

Question 7

What is the result of foveal immaturity seen in albinism?

Answer 7

1. poor VA
2. pendular nystagmus
3. positive angle Kappa (exodeviation)

Question 8

What is the ratio of cones to RGCs? 1. Rods to RGCs? 2

Answer 8

1. 5:1

2. 100:1

Question 9

What is the term for preserving the order of points on the retina?

Answer 9

retinotopic

Question 10

What is how the visual brain “codes” for stimulus position and makes sense of the spatial structure of the stimulus?

Answer 10

retinotopic projection

Question 11

What does the plasticity of the brain determine for the visual system?

Answer 11

1. how visual system is wired during normal development
2. how visual system is wired during amblyopic development
3. how visual system responds to optometric treatment

Question 12

What directs the projecting axons to the approximately correct location?

Answer 12

1. molecular guidance

2. spontaneous waves of activation occur and responses determine location prenatally

Question 13

Taking the RGCs into account, does the LGN represent the fovea more or less than the peripheral retina?

Answer 13

equally

Question 14

What is culling guided by?

Answer 14

visual experience

Question 15

What is the ratio of RGCs to LGN neurons?

Answer 15

1:1

Question 16

The curve of synaptic development to certain areas and then the culling off to make areas more specific is the physiological basis for what in neurological and psychological development?

Answer 16

critical periods

Question 17

What relationship do responses to stimuli in the postnatal retina set up?

Answer 17

relation between the proximal stimulus and the brain (formation of synapses and cuts out useless synapses)

Question 18

What is the result of abnormal projections from the retina to visual cortex in albinism?

Answer 18

1. stereopsis rarely present

2. saccadic eye movements not stable

Question 19

Once processes arrive at their destinations, what do they do?

Answer 19

1. synapse over a relatively large area
2. then the strongest synapses in that area “wins”
3. culling occurs so only the strongest remain

Question 20

For what disorder is it important to understand how the visual system organizes its projections during development?

Answer 20

strabismic amblyopia

Question 21

What is one of the major problems that occurs in albino patients during the retinotopic development? 1. Why does this occur? 2

Answer 21

1. systematic misrouting of the connections between the retina and the visual cortex where the projection is almost entirely crossed
2. EphB1 is not expressed in the RGCs, so ipsilateral projection does not occur

Question 22

What are the major ocular problems that occur in albinism?

Answer 22

1. foveal immaturity
2. scattered light within the eye
3. abnormal projections from retina to visual cortex

Question 23

What is the result of scattered light within in the eye seen in albinism?

Answer 23

1. transilluination of iris (diaphanous)
2. reduced contrast sensitivity
3. further reduced VA

Question 24

What is the idea that the position on the visual cortex is related to position in the visual field?

Answer 24

agreement across methods

Question 25

What is the ratio of LGN neurons to V1 cells?

Answer 25

1:200

Question 26

How can retinotopic organization of normal human cortex, in vivo be measured?

Answer 26

fMRI

Question 27

Taking the density of cones into account, do RGCs have a greater or lesser representation of the fovea?

Answer 27

greater

Question 28

What do signaling molecules at the optic chiasm signal for the growth cones to do?

Answer 28

either go ipsilateral or contralateral

Question 29

What are the principles of retinotopic refinement?

Answer 29

1. cells that are neighbors tend to respond together
2. cells that fire together, wire together
3. the great land grab for space in the visual cortex

Question 30

What is the idea that the foveal parts of areas V1, V2, and V3 all run together and are not easily distinguished called?

Answer 30

foveal confluence

Question 31

What is the pattern of light that arrives at the retina called?

Answer 31

proximal stimulus

Question 32

How do cell nuclei born locally know where to go to develop the retinotopic map?

Answer 32

projecting neurites growth cones follow chemical signals up the concentration gradient, through mechanical pathways

Question 33

Why is there not a fixed wiring system that is the same for everyone?

Answer 33

not enough genes to specify the details of a fixed scheme