5 - Maps & Modules in the Brain

Question 1

Why are maps important in the brain?

Answer 1

Minimal wiring constraint.

Brain wants to minimise length of axons so related things are wired close together

Question 2

Why are there so many maps in the visual cortex?

Answer 2

Importance the brain places on putting information into a visual space.

Question 3

What are the function of maps?

Answer 3

Different maps serve different functions by encoding diferent types of information (e.g. features)

Type of information encoded defines different modules in the brain.

Question 4

What are features?

Answer 4

Physical and cognitive constructs the brain is encoding,

e.g. spatial frequency and contrast, face identity, social networks, biological motion

Question 5

What is the pathway of feature encoding in the early visual pathway?

Answer 5

Retina; information encoding
LGN
Primary Visual Cortex (V1)

Each area represents visual information differently, emphasising different feature representations.

Question 6

Explain the maps from the retina to the LGN

Answer 6

Locations retinal maps have corresponding locations in the LGN. Adjacency principle holds.

Question 7

Explain the maps of the LGN

Answer 7

6 maps layered on top of one another.

Each map layer portrays different information.

Eye of Origin information and Functional information

Question 8

What is a receptive field?

Answer 8

The region of space that drives a response from a visual neuron

Question 9

Explain center surround receptive fields

Answer 9

Have both excitatory and inhibitory connections.

E.g. light on spot, excitation increases as it covers inner excitatory circle, once moves into inhibitory it is driven back towards baseline.

“Spot” (feature) detector

Typically found in retina and LGN

Question 10

What are Oblique penetrations of the LGN?

Answer 10

Same map, different locations in the retinotopic map.

Question 11

What are Perpendicular penetrations of the LGN?

Answer 11

Different map, same locations in the retinotopic map.

Edge and motion detectors

Question 12

Which eye of origin does each layer of the maps in the LGN receive information from?

Answer 12

Layers 2, 3 and 5 receive signals from ipsilateral eye

Layers 1, 4 and 6 receive information from contralateral eye

Question 13

Which layers in the LGN maps receive information from magno and parvocellular cells?

Answer 13

Layers 1, 2 Magnocellular

Layers 3-6 Parvocellular

Question 14

Which layers do the Midget and Parasol retinal ganglion cells project to?

Answer 14

Midget -> Parvocellular layers (3-6)

Parasol -> Magnocellular layers (1,2)

Question 15

What is the Magno/Parasol pathway involved in?

Answer 15

Implicated in motion perception
Transient response
Colour blind

Question 16

What is the Parvo/Midget pathways involved in?

Answer 16

High spatial acuity (texture, colour, form and depth perception)
Slow, sustained response

Question 17

What changes in feature recognition when moving from LGN to Visual Cortex?

Answer 17

From centre surround to edge features.

LGN’s “dot” detectors become V1 edge detectors

Question 18

Explain V1’s map

Answer 18

Layer 4 gets input from LGN.

Hubel and Weisel’s Ice Model

• Each cube is a point in retinotopic map.
• Each cube has; orientation columns (pinwheel structure), eye of origin columns and multiple layer (input and output)

Wiring constrains, this is the optimal way to represent these features (pinwheel)

Question 19

What are the differences in maps with the LGN and V1?

Answer 19

LGN: multiple maps
V1: one constant map.

Question 20

What happens as you move up the visual pathway (V2+)?

Answer 20

Each responds to more complex features.

Develop modules

Retinotopic coding principles are still evident

Question 21

What is a module?

Answer 21

Clustering of neurons with similar functional properties that is characterised by discrete regions with clear boundaries across which there is no relation in preferred stimulus values.

E.g. FFA (area around it is for objects and bodies)