06

Question 1

Enucleation at E91 (when dark/light areas correspond to inputs from the contra/ipsilateral eyes), tells us that BOTH eyes are needed for proper development of LGN ____ even though the embryo can’t see anything

• which two LGN aspects still develop NORMALLY with enucleation?
• does this happen PRE or POST natally?

Answer 1

layers - absolutely true!! Need TWO-EYED INPUT for LGN layers to develop.

1) receptive field organization
2) overall shape

-PRENATAL. (not the “disparate info” option on test) - E=embryonic age in days

Question 2

T/F: something OTHER than vision drives the LGN to appreciate the difference in inputs from the two eyes

Answer 2

TRUE - must be!! Because this is PRENATAL; embryo can’t see!

Question 3

Since it can’t be vision, WHAT drives the formation of both: LGN into layers, and cortex into ocular dominance columns?

Answer 3

Waves of CALCIUM correlated to the intensity of action potentials - DRIVES synchronized firing of small clusters of ganglion cells
-forms coarse VF layout/LGN layers

Question 4

Autism/Down syndrome is likely the result of cortical neurons’ failure to do what?

Answer 4

• failure to separate/skew the ratio of cells that go up to form neurons vs those that stay behind to continue dividing
• Note: these cells use the same type of mvmt seen in the retina/ganglion cells (follow glial fibers to the cortex)**

Question 5

how does a migrating future neuron move to form the cortex, from bottom to top (layer 7–>2)? What does it later develop into?

-which cell type helps drag the cell along?

Answer 5

amoeboid movement along the embryological glial fiber

• later develops into a cortical column
• pseudopod (growth cones)

Question 6

What is the first layer laid down in development of the visual cortex?

Answer 6

Pyramidal cells

-subsequent cells travel IN BETWEEN layers and cause interactions of cells in a vertical column, eventually leading to the formation of a CORTICAL COLUMN

Question 7

Layer 7 - aka the CORTICAL PLATE (subplate) - fills w/ early ___ cells that start to become pyramidal cells, but are interrupted…what happens?

Answer 7

trailblazer trying to become pyramidal - progression stops d/t MASS DIE-OFF that needs to happen

Question 8

T/F: the subplate (cortical plate) receives monosynaptic input from the LGN post-natally

T/F: layer 4 (major input cortical layer) initially has a large delayed response.

Answer 8

FALSE - PRENATAL only. Monosynaptic input from the LGN only happens prenatally, during fetal development.

TRUE - b/c there’s only INDIRECT LGN input at first. Improves by day 21-25; latency decreases b/c cells are now receiving MONOSYNAPTIC LGN input

Question 9

Inhibitory interneurons: originate in the ____ and travel (vertically/horizontally) thru the cortex via amoeboid action

-where do these cells form connections?

Answer 9

striatum

horizontally

BETWEEN cortical columns; NOT within them –allows inhibition of one eye by the other! Binocular rivalry, suppression, CAUSES AMBLYOPIA!

Question 10

The VOLUME and DENSITY of synapses within area 17 of the cortex INCREASE RAPIDLY until about ___ months of age (undergoing what process), then they undergo _____ to rid the weaker connections receiving less input.

Answer 10

6 months

• SPROUTING
• PRUNING BACK

Question 11

-the critical period for amblyopia is about ___ months and is an abnormality in the pattern of what process?

Answer 11

6 months

-pruning back (in the occip cortex, area 17)

Question 12

**ocular dominance columns have clearly formed by ___ months of age - basis of binocular fxns

-how does pruning back affect the cortical columns?

Answer 12

3 months (barely visible @ 2 wks)

-pruning limits axon terminals w/i their respective column to refine the column

Question 13

In the monkey, all of the following occur PREnatally EXCEPT:

a) loss of neurons from DLGn
b) loss of optic axons
c) segregation of retinal axons in DLGn -forming visual field
d) formation of ocular dominance stripes in the cortex
e) formation of layers in the DLGn

Answer 13

D - formation of ocular dominance stripes in the cortex - only occurs POST-natal

-same thing in humans (just double the ages)

Question 14

Three key things that occur in the normal development of the central visual system [RRR]

Answer 14

1) Receptive fields - developed prenatally, refined w/ maturation
2) Responsiveness to nonspecific (NE/sero/dopa) brain inputs (at birth in humans only, not cats/lower mammals)
3) Rearing (light and dark)

Question 15

Production of which two neuromodulators parallels the critical period?

Answer 15

NE, serotonin - key elements in controlling the critical period

• released in cats w/i 3-4 wks
• released slowly in humans only once VISUAL INPUT received

(recall: NE/serotonin - midbrain, dopamine - subthalamus)

Question 16

light and dark rearing only occurs when ____ are present.

• what does the onset of LIGHT stimuli trigger?
• how about DARK stimuli?

Answer 16

neuromodulators

light: critical period for plasticity
dark: delays onset of critical period

Question 17

Three cell types in the hippocampus that develop as a result of experience [PDG]

Answer 17

Place: when rat crosses certain location (seconds)
Direction: when head is facing a specific DIRECTION (seconds)
Grid: fire @ regular, repeating GRID - takes time - ~2 days. Becomes less precise if environment expands