Flashcards in Retinotopic Projections (M2) Deck (33):
What relationship do waves in the prenatal retina set up?
relation between retina and brain
What are albinism patients still able to do well, despite their visual deficiencies?
What is the ability to change as a result of experience called?
Why don't the cells in V1 sweep like waves when they respond synchronously like many of the other areas during development?
the V1 domains are joined with gap junctions rather than synapses
What does the signaling molecule En2 attract? 1. What does it repel? 2
1. nasal axons
2. temporal axons
What do signaling molecules at the LGN signal for the growth cones to do?
1. guide projection D-V-M-L
2. segregate the two eyes to appropriate levels
What is the result of foveal immaturity seen in albinism?
1. poor VA
2. pendular nystagmus
3. positive angle Kappa (exodeviation)
What is the ratio of cones to RGCs? 1. Rods to RGCs? 2
What is the term for preserving the order of points on the retina?
What is how the visual brain "codes" for stimulus position and makes sense of the spatial structure of the stimulus?
What does the plasticity of the brain determine for the visual system?
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
What directs the projecting axons to the approximately correct location?
1. molecular guidance
2. spontaneous waves of activation occur and responses determine location prenatally
Taking the RGCs into account, does the LGN represent the fovea more or less than the peripheral retina?
What is culling guided by?
What is the ratio of RGCs to LGN neurons?
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?
What relationship do responses to stimuli in the postnatal retina set up?
relation between the proximal stimulus and the brain (formation of synapses and cuts out useless synapses)
What is the result of abnormal projections from the retina to visual cortex in albinism?
1. stereopsis rarely present
2. saccadic eye movements not stable
Once processes arrive at their destinations, what do they do?
1. synapse over a relatively large area
2. then the strongest synapses in that area "wins"
3. culling occurs so only the strongest remain
For what disorder is it important to understand how the visual system organizes its projections during development?
What is one of the major problems that occurs in albino patients during the retinotopic development? 1. Why does this occur? 2
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
What are the major ocular problems that occur in albinism?
1. foveal immaturity
2. scattered light within the eye
3. abnormal projections from retina to visual cortex
What is the result of scattered light within in the eye seen in albinism?
1. transilluination of iris (diaphanous)
2. reduced contrast sensitivity
3. further reduced VA
What is the idea that the position on the visual cortex is related to position in the visual field?
agreement across methods
What is the ratio of LGN neurons to V1 cells?
How can retinotopic organization of normal human cortex, in vivo be measured?
Taking the density of cones into account, do RGCs have a greater or lesser representation of the fovea?
What do signaling molecules at the optic chiasm signal for the growth cones to do?
either go ipsilateral or contralateral
What are the principles of retinotopic refinement?
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
What is the idea that the foveal parts of areas V1, V2, and V3 all run together and are not easily distinguished called?
What is the pattern of light that arrives at the retina called?
How do cell nuclei born locally know where to go to develop the retinotopic map?
projecting neurites growth cones follow chemical signals up the concentration gradient, through mechanical pathways