Central Pathways Slides Flashcards
The visual pathway from the eye to the primary visual cortex (also known as the striate cortex) in the human brain.
Visual pathway from retina to striate cortex. The right visual field projects to the left hemisphere and the left visual field projects to the right hemsphere.
What are the effects of lesions at different places along the visual pathway?
The cut at each different location gives a different kind of visual field defect.
What is this?
Cross section of the lateral geniculate nucleus (LGN) also known as the geniculate body. The upper four layers are the P zone, and the lower two layers are the M zone.
The lateral geniculate nucleus (LGN) is divided into layers. The upper layers (P zone) receive projections from the parvo (midget) ganglion cells in the retina. The lower (M zone) receive projections from the mango (parasol) ganglion cells. The smaller K layers receive input from ganglion cells coding responses from the blue (S) cones. (Green layers receive projections from the contralateral eyee, brown from the ipsilateral eye).
Effects on visual performance of lesions in the P and M zones of the LGN.
Effects on visual performance of lesions in the P and theM zones of the LGN. P cells: spatial pattern, color. M cells: motion (rapid changes in the retinal image over time.)
What is this?
Visual areas in the visual cortex of the macaque monkey.
What is this?
Major connections between visual cortical areas. The width of the connection is proportional to the number of axon fibers. The top side (warm colors) is the so-called “where pathway” and the bottom side (cool colors) is the so called “what pathway”
Major Discoveries
Cell Types in V1
Functional oranization of V1 (Maps and columns)
Torsten Weisel and David Hubel
What is this?
An electrode next to a single visual cortex neuron.
Receptive field properties of a simple cell. The cell is orientation selective and position/phase selective.
Stiumuls, Repsonse, and Tuning Curve
Direction Selective Cells
Response Properties of V1 Neurons
Simple cells:
- Low spontaneous activity (quiet when not stimulated)
- Receptive fields are elongated (not circular) and are also divided into excitatory (+) and inhibitory (-) regions.
- The (+) and (-) regions do not form a center and a surround but form alternating stripes (rectangular regions) –edge detectors, slit detectors, line detectors
- They are “position or phase” selective
- They are “orientation” selective
- They are “size” selective
- They are often “direction selective”
- They are often “disparity selective”
What are the gray squares in these boxes?
Receptive field properties of a complex cell. The gray square shows the location of the “classical” receptive field. The cell is orientation selective, but not position/phase selective.
In summary, retinal ganglion cells and LGN cells have center-surround receptive fields. Simple and complex cells in the visual cortex have quite different receptive fields making them selective to orientation, spatial frequency (size), direction of motion and binocular disparity.
Model of neural circuit for simple cells.
model of neural circuit for complex cells
Within the area of binocular overlap, the relative sensitivity of cortical neurons to left and right eye stimulation (the “ocular dominance”) alternates spatially across the primary and visual cortex. This alternating structure of ocular dominance is the so-called “ocular dominance columns” of the primary visual cortex.
The orientation selectivity of cortical neurons also varies spatially in a systematically fashion across the primary visual cortex. This spatial structure is the so-called “orientation cloumns” of primary visual cortex.
Structure and connections to and from a “hyper coumn” in primary visual cortex (V1).
