The Primary Visual Pathway and Cortex

Question 1

What does the lateral geniculate nucleus connect?

Answer 1

The retina and the cortex

Question 2

What doe dLGN receptive fields resemble?

Answer 2

Retinal ganglion cells

Question 3

How do dLGN receptive fields resemble retinal ganglion receptive fields?

Answer 3

• Retinal ganglion cell axons make big, powerful ionotropic synapses
• They are predominantly on proximal dendrites
• Single RGCs make multiple connections with single LGN cells which will be activated synchronously each time the RGC fires

Question 4

What percentage of RGCs make the terminal boutons in the LGN?

Answer 4

7%

Question 5

What do the brainstem inputs do?

Answer 5

• Controls state of a system including the sleep-wake cycle
• These inputs send the thalamus to sleep
• Also switch up the gain of responses in the LGN

Question 6

What are the 2 primary types of ganglion cell receptive fields?

Answer 6

• ON centre/OFF surround:
• flashing bright spot in the centre subregion increases the cell’s response. Flashing bright annulus in the surround subregion inhibits the cell’s response. There is little to no response to a large spot of light that covers both the centre and the surround = lateral inhibition
• OFF centre/ON surround:
• gets inhibition form a small spot of light in the centre and excitation from an annulus in the surround

Question 7

What type of cells can be found in the primary visual cortex?

Answer 7

Simple and complex cells

Question 8

What are simple cells?

Answer 8

• Cells which have separate zones that respond to light or dark
• The do not respond to flashing spots but will respond to an elongated bar
• If you flash on and off in some places, you get an on response but in other places, you get an off response

Question 9

What are complex cells?

Answer 9

• On and off response wherever you flash bar

Question 10

How are V1 cells classically described?

Answer 10

• Unresponsive to flashing spots
• Prefer elongated stimuli
• Orientation tuned - orientation of elongation matters
• Direction tune - might respond in one direction but not another
• Velocity tuned - might prefer slower or faster stimuli
• Length tuned - means the cell will only respond to a very short stimulus

Question 11

What are the benefits of binocular vision?

Answer 11

• Allows 3D vision
• Increased depth perception
• Able to use only one eye in case other one is damaged or blinded

Question 12

What is the hypercolumn

Answer 12

A therotecial cube of cortex containing a full det of orientaiton and ocular dominance columns and function as a unit that enables us to see one specific portion of the visual field