Central Visual Processing II

Question 1

When LGN afferents first invade the cortex in a developing fetus are they segregated by eye of origin or no?

Answer 1

no they are unsegregated at first

Question 2

Why do children with a congenital cataract that are surgically removed too late, become functionally blind in that eye?

Answer 2

they are not receiving proper stimulus through that eye as their eye is developing

Question 3

What is the ratio of contralateral, ipislateral, and binocular distribution of ocular dominance columns in V1?

Answer 3

equal amounts of contralateral and ipsilateral

some binocular

Question 4

What occurs to ocular dominance columns in monocular deprived cats?

Answer 4

the ocular dominance bands in the deprived eye are much thinner

-there is differential pruning or strengthening of connections based on input

Question 5

What is the critical period for a kitten? for a human?

Answer 5

kitten - 6 weeks

6-8 years for a child

Question 6

What is the critical period?

Answer 6

when connections are highly susceptible to stimulus input

Question 7

With binocular deprivation what occurs to:

• critical period?
• amount of binocular cells?
• amount of monocular cells?
• thickness of OD bands?

Answer 7

• it extends the critical period
• there are few binocular cells
• lots of monocular cells
• strong OD bands

Question 8

What do the binocular deprivation experiments tell us?

Answer 8

synaptic plasticity in vision is not based on disuse, but rather on competition

-if it was disuse - there would be no cells left that are responsive

Question 9

What is strabismus?

Answer 9

peripheral disorder which involves dysfunction of the extraocular muscles

Question 10

What is ambylopia?

Answer 10

lazy eye - central disorder

- lack of visual coordination btwn two eyes during development

Question 11

In an experiment using intravitreal injections of TTX, what is the purpose of TTX?

Answer 11

silences retinal output of ganglion cells

• blocks presynaptic activity
• blocks effects of monocular deprivation effects

Question 12

In an experiment using GABA in the cortex, what is the purpose of gaba?

Answer 12

silences the cortical cells

• blocks presynaptic activity
• blocks monocular deprivation effects

Question 13

what is the effect of electrical stimulation of the optic nerves after TTX injection:
asynchronously?
synchronously?

Answer 13

asynchronously - development of OD columns (but only from that eye stimulated)

synchronously - no development of OD columns

Question 14

In normal development is there synchronous or asynchronous stimulation of the optic nerves?

Answer 14

there is both
-synchrony w/in single OD column - “wiring’ of these cells together

• asynchrony btwn neigboring OD columns which segregates OD columns
• synchrony btwn eyes - binocular cells

Question 15

How do antagonists of NMDA affect ocular dominance plasticity?

Answer 15

they reduce ocular dominance plasticity

Question 16

When does the concentration of NMDA receptors in V1 reach it’s peak?

Answer 16

during the critical period

-drops as OD columns segregate

Question 17

How does rearing in the dark affect the development of OD columns and the critical period?

Answer 17

postpones both

Question 18

Is the concentration of NMDA receptors higher in a child or an adult?

Answer 18

children

Question 19

What did they find is correlated with the time window of plasticity?

Answer 19

cell age of inhibitory neurons

Question 20

In cortical reorganization of somatotopic maps in the somatosensory cortex after a stroke or in phantom limb, what is occuring?

Answer 20

input derived cortex steals input from adjacent cortex

-the resulting maps are distorted and inappropriate