wk3: ND - Visual development and Amblyopia Flashcards
True/False: afferent pathways from the two eyes remain segregated as they project to the visual cortex
True
Describe research by Hubel and Wiesel, 1977, that stated Monocular deprivation leads to ocular dominance shift
In cats and monkeys you have a range of monocular/binocular cells, driven by 7 categories:
group 1 = only contralateral eye, group 4 = equal input, group 7 = only ipsilateral eye
Response (total number of cells reponding) for each group of these monocular/binocular cells in area 17 were measured after monocular deprivation (suturing of an eye) and they found what the title said
In Hubel’s monocular deprivation study, how did they look at the eye?
- Adult monkey: radioactive aminoacid injected into ipsilateral eye
2 and 3. 18 month old monkeys: one eye sutured at 2 weeks
What did anatomical observation by Hubel in his monocular deprivation experiment find?
Anatomical studies show layer IV dominated by non-deprived eye, i.e., the non-deprived eye takes over most of the available cortical space
What happens when you suture both eyes shut? (Binocular deprivation)
Binocular Deprivation causes only fewer binocular cells. Receptive fields are not very abnormal! [In Nicholls, p. 560]
! !
What did Levay et al 1978 find about cat ocular dominance? How did he do this?
Found that cat ocular dominance is column dependant. He injected radioactive aminoacid into the ipsilateral eye at different postnatal days: at 2 weeks the whole of layer 4 of the striate cortex is filled with the radioactive label, whereas less and less of layer 4 is filled, as gaps start to appear as more time passes
What is interesting about LGN afferents terminating in layer 4 of the striate cortex?
they have markedly overlapping arbors
In cats and monkeys, when do distinct ocular dominance patterns become evident in layer 4 of the striate cortex?
Within about 6 weeks
Define arbor/arborization
a treelike figure or arrangement of branching parts especially : a treelike part or process (as a dendrite) of a nerve cell the terminal arborization of an axon. Comments on arborization.
What happens to geniculocortical axon arbors in the deprived eye of a cat with a deprived eye?
Much more shallow (way less branches) and much less concentrated. Barely any inputs here and the inputs are way less dense compared to the normal eye
True/False: There is competition between the geniculocorticoid inputs related to the two eyes for cortical space
True
Which vision is essential to establish normal connectivity? Form vision or Diffuse Light?
Form vision
What happens to cortical inputs in the one eye in the absence of inputs from the other eye?
Inputs increase. Inputs related to the other eye takes over the cortical space
What is the critical period for humans to be susceptible to ocular dominance shifts? Can ocular dominance shifts occur outside this period?
Few years. Yes they can, but obviously less likely
Does the extent of critical period for susceptibility for ocular dominance shifts differ between species?
Yes
