5 - Maps & Modules in the Brain Flashcards
Why are maps important in the brain?
Minimal wiring constraint.
Brain wants to minimise length of axons so related things are wired close together
Why are there so many maps in the visual cortex?
Importance the brain places on putting information into a visual space.
What are the function of maps?
Different maps serve different functions by encoding diferent types of information (e.g. features)
Type of information encoded defines different modules in the brain.
What are features?
Physical and cognitive constructs the brain is encoding,
e.g. spatial frequency and contrast, face identity, social networks, biological motion
What is the pathway of feature encoding in the early visual pathway?
Retina; information encoding
LGN
Primary Visual Cortex (V1)
Each area represents visual information differently, emphasising different feature representations.
Explain the maps from the retina to the LGN
Locations retinal maps have corresponding locations in the LGN. Adjacency principle holds.
Explain the maps of the LGN
6 maps layered on top of one another.
Each map layer portrays different information.
Eye of Origin information and Functional information
What is a receptive field?
The region of space that drives a response from a visual neuron
Explain center surround receptive fields
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
What are Oblique penetrations of the LGN?
Same map, different locations in the retinotopic map.
What are Perpendicular penetrations of the LGN?
Different map, same locations in the retinotopic map.
Edge and motion detectors
Which eye of origin does each layer of the maps in the LGN receive information from?
Layers 2, 3 and 5 receive signals from ipsilateral eye
Layers 1, 4 and 6 receive information from contralateral eye
Which layers in the LGN maps receive information from magno and parvocellular cells?
Layers 1, 2 Magnocellular
Layers 3-6 Parvocellular
Which layers do the Midget and Parasol retinal ganglion cells project to?
Midget -> Parvocellular layers (3-6)
Parasol -> Magnocellular layers (1,2)
What is the Magno/Parasol pathway involved in?
Implicated in motion perception
Transient response
Colour blind
What is the Parvo/Midget pathways involved in?
High spatial acuity (texture, colour, form and depth perception)
Slow, sustained response
What changes in feature recognition when moving from LGN to Visual Cortex?
From centre surround to edge features.
LGN’s “dot” detectors become V1 edge detectors
Explain V1’s map
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)
What are the differences in maps with the LGN and V1?
LGN: multiple maps
V1: one constant map.
What happens as you move up the visual pathway (V2+)?
Each responds to more complex features.
Develop modules
Retinotopic coding principles are still evident
What is a module?
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)
