5. Brains and Neurons Part II (LGN, V1, Simple Cells, Complex Cells, End-stopped Cells) Flashcards
What are LGNs?
Where various parts of the brain can modulate inputs from the eyes
Segregates information from both eyes
Part of Thalamus
Specialized for visual input; receives input from the retinal ganglion cells and has input and output connections to the visual cortex
Layers of LGNs
P (Parvocellular Layers)
P
P
P
M (Magnocellular Layers)
M
P: physically smaller and receive input from P ganglion cells. They are responsible for processing details of stationary targets.
M: the bottom two neuron-containing layers of the lateral geniculate nucleus, the cells of which are physically larger than those in the top four layers. They receive input from M ganglion cells in the retina, and respond to fast movign objects
Parvocellular Layers
Top four layers of the LGN. Physically smaller and receive input from P ganglion cells. They are responsible for processing details of stationary targets.
Magnocellular Layers
The bottom two neuron-containing layers of the lateral geniculate nucleus, the cells of which are physically larger than those in the top four layers. They receive input from M ganglion cells in the retina, and respond to fast moving objects
Layers of LGNs
P
P
P
P
M
M
P Ganglion Cells
Receive excitatory input from a single-midget-bipolar cell.
Feed the parvocellular layer of the LGNs
70% in Retina
M Ganglion Cells
Receive excitatory input from diffuse bipolar cells.
Feed the magnocellular layers of the LGNs.
8-10% in Retina
Simple Cells in V1
Neurons whose receptive fields have defined excitatory (+) and inhibitory (-) regions and respond to specifically oriented bars and gratings.
- Orientation and Position Selective
- Predictable from arrangement of on and off areas.
Complex Cells in V1
Neurons whose receptive field dos not have clearly defined excitatory (+) and inhibitory regions (-); they will respond regardless of where the stripe is presented.
- Orientation Selective
- Not sensitive to absolute position
- No response to small spots or diffuse illumination
- Responds to light or dark bars.
Main difference of Simple and Complex Cells
Both prefer a particular orientation
BUT, complex cells do not have clearly defined excitatory/inhibitory regions
a complex cell will respond to a stripe presented anywhere in it’s receptive field, whereas the simple cell might respond to the stripe in only one position.
End-Stopped Cells
In visual cortex, oriented RFs Limited length for best stimulus; a neuron that is maximally responsive to a line of a certain length or to a corner of a larger stimulus. Such neurons have a reduced or absent response when the line or corner is extended beyond a certain point.
Firing rate increases when bar fills entire the receptive field.
How is the LGN connected to the retina spatially?
LGN located in between the retinal inputs and V1 (primary visual cortex)
Is the cell response (excitation or inhibition) affected by the area of the light /dark stimulus?
Not simply light vs dark. Rather, preferred vs. Non-preferred
Do complex cells receive input from simple cells?
Simple cells provide excitatory input for complex cells
Orientation vs Direction in a complex cell (review summary table)
Review summary table
