Neuroscience/Objectives/Lecture 28
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Vision II: Receptive fields and central visual pathways
Describe how color information is transduced by cones and how different types of color blindness may occur.
Understand ganglion cell receptive fields, how their properties are generated by retinal circuitry, and the general concept of opponent processing.
Describe the concept of two streams of processing from the retina to the visual cortex.
Most retinal ganglion cells can be classified as parvocellular or magnocellular. Both project topographically to the lateral geniculate nucleus (LGN). The LGN has six layers, with the most ventral being layer 1, and the most dorsal being layer 6. Layers 1 and 2 receive input from parvocellular retinal ganglion cells, while layers 3-6 receive magnocellular input. Layers 2, 3, and 5 receive inputs from the ipsilateral eye, while layers 1, 4, and 6 receive contralateral input.
Neurons of the LGN project to the the striate cortex topographically. Fibers representing superior retinal quadrants travel superiorly, wrapping around the trigone of the lateral ventricle until reaching the striate cortex. Fibers representing inferior retinal quadrants form Meyer's loop and travel through the temporal lobe before reaching the striate cortex. The visual cortex is topographically organized, with the fovea represented most posteriorly. The binocular portion of the visual field is represented just anterior to the fovea, and the monocular portion of the visual field represented most anteriorly. The fovea receives a disproportionately large representation in the visual cortex (50%). Superior visual field quadrants are represented inferiorly and inferior visual field quadrants are represented superiorly in the visual cortex.
