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The outermost layer of gray matter making up the superficial aspect of the cerebrum
Cerebral Cortex
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The lobe which has the primary function of processing, integration, interpretation, et. of vision and visual stimuli
Occipital lobe
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Cortical area V1 is AKA:
- striate cortex
- primary visual cortex
- brodmann's area 17
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V1 is approximately __ thick, has __ cell layers and a (high/low) cell density.
- 2mm
- 6
- high (250,00 cells/mm2)
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Which neurotransmitters does V1 use and are they excitatory or inhibitory?
- Glutamate - excitatory
- GABA - inhibitory
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The first site along the primary visual pathway that has truly "binocular neurons" is ____.
V1
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The right VF maps to the ____ occupital cortex
The upper VF maps to the ____ occipital cortex
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The area of the cortex from the tip of the occipital cortex along the right superior medial wall of the hemisphere represents _____.
left inferior VF
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The result of cortical magnification is that a lesion affecting 1mm of visual cortex will likely create a (larger/smaller) VF defect if it is located closer to anterior visual cortex than to the occipital pole.
larger
Seems backwards! There are more cells representing the fovea so if some are lost, there is less effect than if the same number are lost from the cells representing the periphery
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What is the cortical magnification factor?
- cortex to visual space
- mm of cortex/degree of visual angle
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What is the inverse cortical magnificataion factor?
- visual space to cortex
- degrees of visual angle/mm of cortex
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What layer of V1 does visual imput go to and what are its divisions?
- 4C
- 4Calpha (magnocellular input) and 4Cbeta (parvocellular input)
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What are the 6 layers of V1?
- 1: superficial layer
- 2, 3, 4a, 4b: supragranular layers
- 4c:granular layer
- 5, 6: infragranular layers
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Which V1 layer sends output to cortical and sub-cortical areas?
5 and 6
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Which layer of V1 is AKA the intracortical connection layer?
1
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The LGN sends most of its input to which of the Brodmann's layers of V1?
4
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Where do the magnocellular and parvocellular pathways have input into V1?
4c
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What are the main connections of primate V1 and ganglion cells?
Midget ganglion cells > parvocellular layer of LGN > layer 4Cbeta of V1
Parasol ganglion cells > magnocellular layer of LGN > layer 4Calpha of V1
Koniocelular layer > layer 3 of V1
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When are the signals from both eyes combined?
They are still separated when they synapse in V1, but after the synapse, the signals start to be put together as binocular signals
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V1 cells can be divided anatomically and functionally. List the divisions.
- Anatomical: spiny stellate, spiny pyramidal, smooth interneurons (smooth = GABA; spiny = glutamate)
- Functional: simple, comples, end-stopped (simple or complex)
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Simple cells are spatially linear cells with elongated receptive fileds that usually _____ and _____.
- show orientation specificity
- have parallel, opposing subfields
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Why can simple cells detect orientation?
because they are elongated
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Simple cell's parallel, opposing subfields can be divided into 2 types:
- 2 opposing subfields (edge detectors)
- 3 opposing subfields (bar or line detectors)
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Simple cell, edge detectors are based on ___.
movement
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Describe V1 simple cell receptive fields.
- spatially linear (elongated)
- orientation specific
- size or spacial frequency specific
- symetric or asymmetric
- open-ended or end-stopped
- monocular or binocular
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Which of the followins statements about simple cells in V1 are false?
A. Simple cells may be end-stopped
B. Simple cells demonstrate spatial-antagonism
C. A simple cell will fire to light off anywhere in its receptive field
D. Simple cells can be monocular
C is FALSE
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Describe V1 complex cells.
- spatially non-linear
- higher spontaneous activity
- more numerous than simple cells
- strong orientation specificity
- may show true direction of motion/tuning
- may be open-ended or end-stopped
- most are binocular, 70%
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What does open-ended or end-stopped refer to?
The cells may or may not be limited in stimulus length
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The response of a complex (end-stop/open-ended) cell decreases when the length of the stimulus extends into the off subfield.
end-stop
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The traditional classification of binocularity classified V1 cells into 7 categories (1-7). What does each respond to?
1 - only to stimulation of the contralateral eye
2 and 3 - mostly to the contralateral eye but will respond to theipsilateral eye a small amount
4 - equally to stimulation of either eye
5 and 6 - mostly to the ipsilateral eye but will respond to the contralateral eye a small amount
7 - only to stimulation of the ipsilateral eye
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According to the hierarchial model, the simple cell receptive field is derived by input from
several LGN cells
adding together the synapses from the LGN makes up the elongated field
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According to the hierarchial model, complex cells receive synapses from
several simple cells
this input adds together to produce a complex receptive field for the complex cell
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Problems with a strict hierarchial model
- There are simple and complex cells both receiving direct input from the LGN so, there are some complex cell receptive fields that aren't made up of simple cell synapses
- Some complex cells are tuned to faster stimulus velocities than any simple cells
- Since complex cells are spatially non-linear, their directional tuning can't be predicted from on and off portions of their receptive fields as is true of simple cells
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Which of the following observations does not support the hierarchical model of receptive fields proposed by Hubel and Wiesel?
A. some complex cells prefer faster stimulus velocities than any simple cells
B. Most simple cells receive direct input from LGN cells
C. Many complex cells receive direct input from simple cells
D. Simple cells demonstrate spatial antagonism
A does not support the model
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All visual signals necessary for conscious visual perception are processed in ____ before they are sent to other visual areas
V1
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The left and right eye segregations (until they synapse in V1) create
occular dominance columns
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Activation of V1 neurons depends completely on ______, but V1 receives many other cortical and subcortical modulatory inputs.
LGN input
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New receptive field properties are created within the circutry of V1, allowing for coding of local image features such as:
- orientation
- direction of motion
- binocular disparity
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Characteristics of cortical areas:
- homogenous pattern of connections
- similar neuron characteristics
- single retinotopic map
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An _______ is an area of VF (or retina projection) circumscribed by all receptive fields encountered on a single electrode penetration.
Aggregate receptive field
an electrode was inserted into the cortex and any receptive fields that cam into contact with the electrode are part of this aggregate of receptive fields
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Ocular dominance columns are most clear and distince in layer ___.
4c
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Which layer of V1 has the highest proportion of monocular neurons?
4C
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All cells within an ocular dominance column demonstrates ______.
same eye preference
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In adulthood, projections from each eye, via the ____ converge on columns of cells in layer ___ of visual cortex.
LGN; IV
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How can you visualize the ocular dominance colums ?
Injecting radioactive proline into one eye; detected by autoradiography
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The cortex is subdivided into slender regions of ____ orientation preference extending from surface to white matter (electrode goes perpendicular to surface)
Constant
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Which orientation colum has no orientation preference?
layer 4 (interrupts constant orientation preference)
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If an electrode is pushed thur cortex in a direction parallel to the surface, what type of sequence of changes in orientation preference occurs?
(orientation colums)
Regular sequence (all same direction)
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If the electrode is traversed (?obliquely inserted?) by 1 mm what type of orientation preference occurs?
a total shift of 180 degrees in orientation preference is recorded
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Orientation "pinwheels"
all orientations are represented across that of section V1
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Cells respond to lines at particular angles, and nearby cells respond to..
similar angles
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Orientation "pinwheels" are superimposed on
ocular dominance colums
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The centers of Orientation "pinwheels" generally occur in the middle of an
ocular dominance column
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Each Orientation "pinwheels" belongs to a ___ colums of ocular dominance
single
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A single colums will only respond to signals from ___ but it will repond to ____ for that eye
one of the eyes; to many orientations of a stimulus
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A VI hypercolumn has how many ocular dominance columns? with a full _____ range
2 (one per eye); 180 degree
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VI hypercolumn is approx __ mm per side, full thickness of cortex?
1 mm (1mm3)
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VI hypercolumn's module size (in cubic mm) is ___ throughout VI
constant
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Area of visual field represented in each VI hypercolumn increases from...
- fovea to periphery
- (inverse of cortical mag)
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VI hypercolumn = a term for organizing the cortex. Another name for a hypercolumn is a ...
module
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What is an indicator of energy consumption
Cytochrome Oxidase
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The more energy cells use....
the more Cytochrome Oxidase builds up in the brain
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Highest density of Cytochrome Oxidase...
- - throughout Layer IVC ( alpha and beta)
- - direct LGN M&P input to layer IVC
- - in segregated "blobs" centered in later IIIB, extending partially into IIIA and IIIC
- -direct LGN K input to layer III
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MOre energy consuption occured in the cells where...
lgn cells directly synapse
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Magno and parvo LGN cells synapse in
IVC, then signal is passed to other cortex layers
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Cytochrome Oxidase Blobs =
wavelength columns?
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Cytochrome Oxidase Blobs are arranged along centers of
ocular dominance stripes
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Cytochrome Oxidase blobs have a separation of what betweeen blobs?
~400mm center-center separation
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Cytochrome Oxidase blobs are most distinct in layer ? and what synapses here
III, koniocellular cells
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Koniocellular cells are thought to have something to do with?
wavelength discrimination
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Cytochrome Oxidase blobs contain what types of cells
wavelength opponent and double opponent cells
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Cytochrome Oxidase blobs contains cells with ____ receptive fields
non-oriented ( no preference for orientation)_
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Cytochrome Oxidase blobs: R/G to B/Y blobs =
3:1 (more R/G!)
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space between the blobs is called the
interblob
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Where does the color information get integrated in the cortex?
Cytochrome Oxidase blobs
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Cytochrome Oxidase blobs in VI =
special cells grouped together that integrate color information
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path of color from R/G cones...
R/G cones --> color sensitive ganglion cells ---> LGN parvo cellular cells --> CO blobs in VI
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path of color from B/Y cones...
B/Y cones --> color sensitive ganglion cells ---> LGN koniocellular cells --> CO blobs in VI
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Each ocular dominance colums contains... ( in relation to color)
a pinwheel for each colums of orientations and CO blobs that integrate the color info.
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Functional blocks of cortex that are equal in size, each contaings the processing ability available to that area
cortical modularity
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Each cortical modularity applies the processing to a different portion of the
visual field
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If you were able to test a single cortical module, you would find it could represent all the info you need to...
percieve the area of the visual field it is associated with.
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Another name for a module is a
hypercolumn
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How many organized modules do they believe there are in V1?
~2500
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stains for cyctochrome oxidase reveal how many blobs in each module?
2 (one for each eye)
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Each module contains...
one OD dominance column and one OS dominance column
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Cells within each CO blob are sensitive to ?
color and to low spatial freq info
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Outside each blob, neurons respond to ? but not to?
orientation, mvnt, spatial freq and texture. but NOT to color info
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Striate modules show?
ocular dominance, orientation columns
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Cells in a colums respond to the same orientation, adjacent cells that are shifted by 10 degrees are?
orientation columns
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Orientation colums are organized ____ to the ocular dominance columns
perpendicular (right angles)
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As one moves from V1 areas representing the fovea to those more peripheral, the size of the modules___, but each sucessive module represents ___. This is called?
- does not change
- larger are of VF
- Cortical Magnification
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Moving from areas ofo V1 from foveal to peripheral what happens to the :
1. aggregate receptive field size
2. cortical mag factor
3. size of cortical modules (& ocular dom colums, orienation colum & CO blobs)
- 1. increases
- 2. decreases
- 3. remains constant
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