Chapter 12 - Visual Pathways Flashcards
how is the striate (primary visual) cortex organized ?
multiple processing units working together, with different layers (there are 6) doing different things
what would you find with micro-electrode penetration perpendicular to the cortical surface ?
that in that column, all the cells are pretty similar, suggesting a radial organization. have similar receptive
field properties, responding. for example, to stimulation
arising from the same region of visual space and exhibiting preferences for similar stimulus properties, such as edge orientation and direction of motion
adjacent columns have similar but
slightly shifted receptive field locations
(12.11)
what would you find with micro-electrode penetration that is oblique ?
Neurons displaced along the tangential axis of the cortex exhibit an orderly progression of receptive field
properties. Neurons encountered along the electrode penetration have receptive field centers (center panel) and orientation preferences (right panel) that shift in a progressive fashion.
(for example, in 12.11, it’s a downward slope, and for the spike rates for the preferred orientation you no longer see one bell curve but several since they all have different preferred orientations)
which eye do the neurons in the striate (primary visual) cortex respond to ?
both. most neurons there are binocular.
in the primary visual cortex, how is orientation preference mapped ?
adjacent cells have simillar preferred orientations
except at the very center, where nearby
cells exhibit nearly orthogonal orientation
preferences (fig 12.12 with colors)
over 1 mm of cortex, a different color is represented. it looks like a huge colorful quilt.
how many eyes do we need for a sense of depth (stereopsis) ?
2
what is the primary visual pathway ?
from the retina to the dorsal lateral geniculate nucleus in
the thalamus and on to the primary visual cortex
how is input from both eyes organized in the lateral geniculate nucleus ?
it’s segregated in separate layers
at the early stages of cortical processing, how is input from both eyes still segregated ?
as the axons of geniculate neurons terminate in alternating eye-specific ocular dominance column and within cortical layer 4
Beyond this point, however, signals from the two eyes converge as the axons from layer 4 neurons in adjacent monocular stripes synapse on individual neurons in other cortical layers.
how is ocular dominance cortically depicted ?
first of all, in layer 4, at the early stages of cortical processing the geniculate neurons terminate in alternating ocular dominance columns
in other layers, although they are usually binocular, they still have a preference. Cortical neurons
vary in the strength of their response to the Inputs from the two eyes, from complete domination by one eye to equal influence of the two eyes.
what does tangential electrode insertion reveal about ocular dominance mapping in the primary visual cortex
Tangential electrode penetration across the superficial cortical layers reveals a gradual shift in the strength of response to the Inputs from the two eyes, from complete domination by one eye to equal influence of the two eyes.
what are the different ways lateral geniculate cells may differ from one another ?
- size
- input-specific (which eye)
what are the three kinds of pathways and layers in the lateral geniculate nucleus ?
magnocellular
parvocellular
koniocellular
what is the ventral layer of the lateral geniculate nucleus ?
magnocellular layer
what are magnocellular cells
M cells have large-diameter cell bodies and large
dendritic fields. They supply the magnocellular layers
of the lateral geniculate nucleus.
They’re bigger and have large receptive fields- responsible for motion-specific pathway
which cells in the lateral geniculate are in charge of a motion-specific pathway ?
the magnocellular
