Central Visual System Flashcards
Some axons of the optic tract that don’t go to the LGN go here to synchronize sleep and wakefulness with light-dark cycles and contribute to other biological rhythms
Hypothalamus
What happens when the input from one eye is blocked from reaching V1?
Ocular dominance columns are lost. Activity drives structure
Why do perceptual illusions occur?
Same dimensions, brain is producing a 3D interpretation of a 2D image
How many layers are in the LGN?
6
This can cause lack of perfection of motion (see the world in a series of snapshots)
Stroke
Extrastriate stream of perception and object recognition, extension of V1 Parvo-interblob and blob pathways
Ventral
Crossing over of these is completed after the optic chiasm
Retinal ganglion cell axons
Have shifted orientation selectivity
Tangential cells
How is info separated in the central visual system?
Parallel pathways for analyzing different features of input
Made of optic nerve, optic chasm, and optic tract
Retinofugal pathway
These animals were used to study the central visual system
Cat and rhesus monkey
V1 to V2 to V3 to V4 to It to other ventral areas. V2 can also communicate directly with V4
Ventral stream
These neurons exist locally in all layers of V1
Inhibitory neurons
Koniocellular LGN neurons project to these V1 areas
Layers 2 and 3
2x2 mm patch of cortex containing 2 sets of ocular dominance columns, 16 blobs, inter blobs, and all 180 degrees of orientation. These are all of the computational tools we would need to analyze a specific part of our visual field. It is a theoretical model
Cortical module
4C layer insensitive to wavelength
4C alpha
These cells project out of V1
Pyramidal cells
Located anterior to the pituitary (in front of it - towards the forehead)
Optic chiasm
Radial columns of cells through several layers have this orientation preference
The same orientation preference
Part of the tectum, involved in orienting eyes with new stimulus
Superior colliculus
Respond to activity in any one of their converging input lines (any simple cell)
Complex cells
These RGCs connect to the magnocellular LGN
M type
Layers of LGN with small center surround, center response of sustained firing
3-6 (parvocellular)
Ventral stream, receives input from Parvo-interblob and blob pathways
V4
Stimulate synchronous activity in widely separated areas
Objects
Spiny stellate cells in this V1 layer make local connections (Golgi type II)
Layer 4C
In dorsal stream, these cells have large receptive fields, transient light respons, direction selectivity
4B cells
Layers of LGN with large center surround, center response is burst firing
1 and 2 (magnocellular)
V1 V2 V3 and V4 maintain these while face and object recognition areas do not
Retinotopic maps
Simple cortical cells give input to these that respond better to moving bars
Complex cortical cells
The three channels or pathways that process visual input (the parallel pathways)
- magnocellular
- parvocellular
- blob
How do pyramidal cells from the V1 project for outputs?
Project out of the visual cortex and can branch in all layers to form local connections
Cells in the same column have this preference
Same preference
Neurons from the LGN of the thalamus project here via this
Project to cortex via optic radiation
Left and right eye inputs to alternating columns in layer 4 of V1
Ocular dominance columns
Eye inputs are kept separate here
LGN of thalamus
What is orientation selectivity?
Some neurons prefer to respond to light of a certain orientation
Parvocellular LGN neurons in layers 3-6 project to this V1 area
4C beta
Receive input from koniocellular LGN neurons directly
Layer 3 blobs
Layer 1 and 2 cells in the LGN
Larger, magnocellular
Some axons of the optic tract that don’t go to the LGN go here to control pupil size, lens, and some eye movement
Pretectum
These 3 parallel pathways mix somewhat, each channel is not completely unique in receptive field properties
- magnocellular
- parvocellular
- blob
Most neurons of the optic tract connect here
LGN of dorsal thalamus
SLIDE 21
SLIDE 21
Viewed or analyzed by the left hemisphere
Right visual hemifield
Magnocellular LGN neurons in layers 1 and 2 project to this V1 area
4C alpha
Help to control the pupillary reflex
Ciliary ganglion
Layers in the striate cortex suggest what?
Segregation of input and analysis
Extracts information and some data compression (100 mil photoreceptors to 10 mil bipolar to 1 mil ganglion) and most common features are extracted
Retina
Axons from nasal retina cross here, partial decussation
Optic chiasm
Is the LGN just a relay station?
No, input from the brain stem shows it functions in modulating responses to stimuli
Neurons sensitive to shape, color, position, movement, and binocular vision are present in this system
Central visual system
Outside of layer 4C, an axon may form synapses with pyramidal dendrites from which layers?
All layers
These RGCs connect to the parvocellular LGN
P type
Ventral stream, shape and color
V4
SLIDE 45
SLIDE 45
Respond to light beam anywhere along its path
Complex cells
V1 neurons receiving a converging input from three or more LGN cells with receptor fields that are aligned along an axis are called this
Simple cells
Good at analysis of object motion
Directionally selective neurons
Composed of everything left of the midpoint
Left hemifield
Viewed by both retinas (the center of both hemifields)
Binocular visual field
Transection of the optic tract on the right side
Loss of the complete left visual hemifield
Away from structure
Fugal pathway
The world we see can be divided into these
Visual hemifields (left and right)
V1 layer 4C neurons project radially to these two layers where left and right eye inputs mix
Layers 4B and 3
Blob pathway responds best to
Color
Magnocellular pathway responds best to
Motion
Have small center surround receptive fields
Layer 4C
All parallel pathways ultimately communicate with these
Blobs
Eye output layers that are ipsilateral in LGN and contralateral in LGN
ip - 2, 3, 5
cont - 1, 4, 6
Layer one of V1
Few neurons
These areas light up when shown a picture of a face
OFA and FFA
SLIDES 51-54!!!!!!! ESPECIALLY 54
SLIDES 51-54!!!!!!! ESPECIALLY 54
Right eye axons synapse in layers 2, 3, 5 and left eye axons in 1, 4, 6 in this part of the LGN
Right LGN
All cells of dorsal stream and directionally selective, direction of motion columns like orientation columns seen in V1. More complexity bc they respond to this
Motion
Part of LGN with input from left visual field, input from eyes in separate layers
Right LGN
How do receptive fields change in size moving from V1 to higher visual areas?
They get larger
The usual theme in the nervous system
Broad tuning and parallel processing
Layers of LGN with center-surround fields with either light/dark or color opponency
Small konicellular layers
Most of the fields in retina, LGN, and 4C are this shape and respond best to spot of light matched in size to receptive field center
Circular
SLIDE 11
SLIDE 11
What does info from both eyes drive in V1 layer 4?
Organization/structure
These are lined up with layer 4 ocular dominance columns
Blobs
There is a large variation in orientation preference in this V1 layer
3
These are dominated by one pathway but aren’t exclusive
Extrastriate streams
SLIDE 58
SLIDE 58
V1 layer 4C alpha (magnocellular) projects here
Layer 4C beta
4C layer with center surround color opponency
4C beta
Six layers, 1 is most ventral, bent stack of pancakes
LGN
These axons cross over at the optic chiasm while these do not
Nasal axons cross over while temporal axons stay on the same side
Receives input from RGCs
LGN
Sustained firing LGN layers
3-6 (input from p type)
The LGN receives input from this area with the potential function of modulating responses to stimuli
Brain stem
Senses shape, color, position, movement, binocular vision (3D view of the world)
Central visual system
Parvocellular pathway responds best to
Shape
Not yet found neurons which fire only when presented with a specific face. Would have very large receptive fields that are very selective
Perception
Receptive fields and response properties of these neurons are the same as those of RGCs that innervate them
LGN neurons
How is information from each eye kept separate when protecting to V1?
Ocular dominance colums
How many layers of cortex are in V1?
6
In dorsal stream, receives info from V2 V3 also directly innervated by 4B
MT (V5 - middle temporal)
Run under Pia along lateral (sides) of the diencephalon
Optic tracts
Each one of these receives some input from all pathways
Extrastriate streams
How many extra striate areas?
24
Theoretical model to organize our concepts of how visual info is processed. If this patch of our cortex were removed, we would lose vision over some portion of our visa space that was analyzed by these neurons
Cortical module
How does the preferred stimulus for visual system neurons change as you go higher up?
Gets more complex
The neurons that project from the LGN to V1
Optic radiation
How do we know ocular dominance columns exist?
Radioactive material injected into one eye produces a black and white striped picture that has the stripes flipped when injected in the other eye
Has a dense stripe of myelinated axons running near the surface
Striate (primary visual) cortex
Most neurons outside this layer are orientation selective
Outside 4C
Cells next to each other have this preference
Different preference
Dorsal stream, linear motion, radial motion, circular motion
MST - medial superior temporal
Major target of LGN located in the occipital lobe
Primary visual cortex
Cutting the optic chiasm
Produce a tunnel vision effect due to damage to the nasal, or crossing, axons
Neurons specialized for analysis of a shape
Orientation selective neurons
Receptive fields in this layer are similar to magnocellular and parvocellular LGN inputs
4C
Path of cortex analyzes visual input (theoretical)
Cortical module
Responsible for conscious visual perception, damage at various levels cause specific deficits
LGN to optic radiation connecting to primary visual cortex
Layers 3-6 in the LGN
Smaller, parvocellular
Get LGn input from parvocellular and magnocellular 4C neurons
Blobs
Transection of the left or right optic nerve
Loss of peripheral vision on the ipsilateral side (like having one eye closed)
Viewed or analyzed by the right hemisphere
Left visual hemifield
A subset of cells that are orientation selective that respond to direction of movement
Directionally selective neurons
Some run through layers 2, 3, 5, and 6 but are not present in layer 4
Blobs
Ventral stream, orientation and color selective
V4
The optic nerves after leaving the optic chiasm
Optic tracts
What can a point of light do due to retinotopy?
Activate many cells, overlap, peak of distribution
Alignment must be along the on centers of multiple cells. These can account for the observation that a beam of light in one location in a field can activate a cortical neuron, but in a different lightly angled position it doesnt
Simple cells
What type of path do neurons take from the LGN to V1?
Direct path via optic radiation, no crossing over
Extrastriate stream of visual control of action and motion analysis, extension of V1 magnocellular pathway
Dorsal
Where are binocular responsive cells in V1 (response to input from both eyes to get a 3D view)
Layer 3
Info from this stream is used for navigation, directing eye movements, motion perception
Dorsal stream
Can be seen in layer 4 of V1
Ocular dominance columns
How are on center and off center cells organized in the LGN?
Mixed in all layers
Also called Brodmann’s area 17, V1, and striate cortex
Primary visual cortex
These cells are local only and don’t project out of V1, found only in layer 4C
Spiny stellate cells
Binocular cells without distinct on and off regions that may receive input from several simple cells and can be stimulated by any one of them
Complex cells
Major input to the LGN is from here (80%) not here
It is from V1 and not the retina
Binocular cells that are sensitive to stimulus orientation with a range of responses for color and motion direction
Simple cells
Output to V1 by optic radiation
LGN
All the other layers of the V1 contain these neurons (Golgi type I) that have a thick apical dendrite, basal dendrites, and project to other regions
Pyramidal cells
Demonstrated the presence of ocular dominance columns by injecting radioactive amino acids
Transneuronal autoradiography
Connected to over two dozen temporal and parietal lobe areas (extrastriate areas)
Primary visual cortex
Did work on the physiology of V1
Hubel and Wiesel
V1 layer 4C beta (parvocellular) projects here
Layer 3
The projection of optic tract to the superior colliculus
Retinotectal projection
Half of V1 is used to analyze info from here which creates a distorted retiotopic map
Fovea
How do neighboring retinal cells communicate with target cells in the LGN and V1?
They communicate with neighboring cells in each to create a retinotopic map
Forms the optic chiasm
Optic nerves
What are the nerves called that leave the LGN and project to V1
Optic radiation
SLIDE 47 and 48
SLIDE 47 and 48
SLIDE 16 and 17
SLIDE 16 and 17
Blocking input to V1 from one eye
Monocular deprivation
Ventral stream, colors and abstract shapes, some respond to faces, important for visual memory, more complex than V4
Area IT
Sensitive to stimulus orientation and a range of responses to color and motion direction that aren’t simple cells
Complex cells
Role in mammals is to orient eyes in response to new stimulus (hear something and move eyes to focus on it)
Superior colliculus of the tectum
Subset of orientation selective neurons that receive input from magnocellular cells of LGN
Directionally selective neurons
Neurons which express higher levels of mitochondrial cytochrome oxidase were identified in V1 and called this
Blobs
These RGCs connect to the konicellular layers of the LGN
NonM-nonP type
This has a distorted, not exact representation, bc the central field is over represented or magnified (more ganglion cells are near the fovea)
Retinotopy
Where are binocular neurons first present?
Outside layer 4
From retina to lateral geniculate nuclear (LGN) of thalamus to primary visual cortex (area 17, V1, striate cortex)
Conscious visual perception pathway
Composed of everything right of the midpoint
Right hemifield
Cells are usually sensitive to more than one of these
Properties
Outside of this layer there is better response to more complex stimuli, but small spots of light also still work in most cortical neurons (do produce some APs)
Outside 4C
Burst firing LGN layers
1 and 2 (input from m type)
10% (100,000) of ganglion cells (axons of the optic chiasm) connect here that is the major target in nonmammalian vertebrates (fish, birds, etc)
Tectum area called the superior colliculus (called optic tectum in nonmammilian vertebrates)
Tiny neurons between main layers (between magnocelluar and parvocellular layers)
Konicellular layers
Does communication exist between columns in retinotopy?
Yes, it is needed
Cutting the optic radiation on right side
Loss of the complete left visual hemifield
MT and V4 of the extrastriate streams communicate directly with what?
Each other
V1 to V2 to V3 to MT to MST to other dorsal areas. There are other direct connections from V1, V2, V3 to MT
Dorsal stream
Major target of the optic tracts
LGN of dorsal thalamus
