L12: Central Visual Pathways I Flashcards
Primary visual cortex has multiple names, such as
Area 17
striate cortex
V1
The reticulo-geniculo-striate pathway is most important for visual perception. Explain the pathway
retinal ganglion cell, optic nerve, optic chiasm, optic tract, LGN, ultimately to primary visual cortex
Due to the optics of the eye, the visual field mapping onto the retina is inverted and flipped, what does this mean?
- superior nasal field will map onto the inferior temporal retina
- inferior temporal field will map onto the superior nasal retina
The nasal hemiretinal axons that carry info from temporal visual field will cross while the temporal hemiretinal axons do not cross. When exactly does this crossing occur?
The nasal hemiretinal axons cross at the level of the optic chiasm. So visual field representations are crossed at the level of the LGN and cortex
Explain the 6 layers of the LGN
lateral geniculate nucleus is found in the thalamus. It has 6 layers (VENTRAL/Layer 1: 2 magnocellular layers and 4 parvocellular layers: DORSAL/Layer 6). These diff layers are eye-specific/will be innervated by the optic nerve but in this way: Contra, ipsi, ipsi, contra, ipsi, contra)
The output of the LGN then creates the optic radiation that provides input to V1, primarily in which layer of the neocortex?
Layer 4 gives primary visual cortex, V1 its other name as the striate cortex because it forms the macroscopically visible “stria of gennari”
The visual input into V1 is also ordered retinotopically. But far greater cortex is devoted to which parts of the eye?
To central vision -the fovea
The task of vision is divide among several receptor systems. List 3 of them
1) the rods
2) 3 cone classes - L-cones, M-cones, S-cones
3) P, M, K signalling pathways
The magnocellular system is specialized for
high temporal resolution (speed) and higher contrast gain
The parvocellular pathway is specialized for
higher visual acuity and color
The koniocellular pathway is probably also specialized for
color perception
Where do you find the koniocellular layers in the LGN?
You find the K layers in btw the 6 layers
Both retinal ganglion cells and LGN cells have what types of receptive fields?
center-surround receptive fields
The input from the two eyes are segregated until V1, forming what types of columns?
ocular dominance (eye preference) columns
Who discovered the ocular dominance columns?
Hubel and Wiesel
V1 output that goes to extrastriate cortex, such as V2 (area 18) comes from which layers of the LGN
layers 2 and 3
Layer 5 of the V1 sends output to
superior colliculus which is a different visual pathway involved in eye movements and head/attentional orientation
Layer 6 of V1 goes
back to the LGN, forming the cortico-thalamic feedback loop
V1 neurons’ receptive fields are different from retinal ganglion cells and LGN in that
VI neurons are not center-surround receptive fields; they are orientation-tuned/have oriented receptive fields
What does orientation tuning mean?
orientation tuning refers to the preference of a cell to be stimulated by an edge of light presented at a particular angle
Why does V1 want to create oriented cells?
Orientation tuning is probably the early stage of form vision anaylsis
What are the 2 color opponent signals that are created in the retinal circuitry?
1) Red vs Green
2) Blue vs Yellow
* *where yellow is red vs green