Lecture 5: Visual cortex

Question 1

Where is the primary visual cortex located?

Answer 1

at the back of the brain in the occipital lobe

Question 2

Anatomy of V1:

Magnocellular =

Answer 2

Layer 4Ca

Question 3

Anatomy of V1

Parvocellular=

Answer 3

Layer 4Cb

Question 4

Anatomy of V1

Koniocellular=

Answer 4

layer 2 and 3

Question 5

Hemisphere projections

Answer 5

**

Question 6

where do cells in layers 2, 3 and 4b project?

Answer 6

extra striate cortex

Question 7

where do cells in layer 5 project?

Answer 7

midbrain structures such as superior colliculus and pons

Question 8

where do cells in layer 6 project?

Answer 8

LGN.

• projections are highly selective
• different cells in different parts of the layers of 6 projecting to different layers in the LGN

Question 9

Anatomy of V1: Ocular dominance columns

Answer 9

a slab of cortical tissue running perpendicular to the cortical surface, in which all binocular cells share the same degree of ocular dominance

• separation of the image from each eye in LNG maintained in V1
• layers specific to either left or right eye

Question 10

Orientation columns

Answer 10

a slab of cortical tissue running perpendicular to the cortical surface, in which orientation selective cells share the same preferred orientation

• respond to different stimuli in the world of varying angles
• orientation column specific to different orientations

Question 11

Blobs

• what layers are they in
• what are they sensitive to?
• orientation?
• how were they discovered?

Answer 11

• 2,3 and V1
• brightness and colour
• monocular: are not orientation specific
• using cytochrome oxidase staining

Question 12

Blobs: circularly symmetrical receptive fields

Answer 12

Stimulation with a particular colour in the centre elicits a response, whereas stimulation of the immediate surround elicits the reverse response

Question 13

V1 receptive fields

Answer 13

• several LGN cells combine to input on a single V1 cell
• elongated receptive field and are more selective for what stimuli activates or excites them

3 main types of orientation selective cells:
– Simple cells
– Complex cells
– Hypercomplex cells

Question 14

Receptive fields in LGN

• what are they comprised of?
• how do they respond to bar of light in any orientation?

Answer 14

• ganglion cells and are circular

- light in centre calls to fire, light in the surround causes it to silence

Question 15

Complex cell

Answer 15

a cell in visual cortex with a relatively high receptive field that does not contain identifiable excitatory or inhibitory zones, but is orientation specific
-responds to a bar of a certain orientation anywhere within its receptive field

-created by grouping simple cells of the same orientation

Question 16

Simple cells

Answer 16

an orientation selective cell in visual cortex with an elongated retinal receptive field containing excitatory and inhibitory zones

Question 17

Complex cells

Motion detection

Answer 17

• some cells in V1 respond to stimuli moving in certain direction also
• approx 25-35% of V1 cells are strongly directionally selective

Question 18

Hypercomplex cells

Answer 18

-generated through summating a number of complex cells (v.large receptive field)

• activity dependent on length as well as orientation
• if bar extends outside of receptive field, stops firing

Question 19

Topography in V1

Answer 19

-cells distributed across the visual cortex so that their receptive field locations form an ordered topographic map of the visual field

Question 20

Cortical magnification factor

Answer 20

=central areas in the visual field (the fovea) have disproportionately large area of the cortex devoted to it