110 cortex and beyond 2008

110 cortex and beyond 2008 - Lecture 5: Primary Visual...

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Lecture 5: Primary Visual Cortex (con't), and beyond. Topics to be discussed: The columnar organization of cortex Visual cortex beyond V1- general outlook, functional streams and relevant clinical cases The columnar organization of cortex: General rule for the functional organization of cortex: Neurons with similarly preferred response properties are grouped together, typically in vertical "columns" or slabs extending through the thickness of the cortex. Examples for V1: Neurons that have overlapping receptive fields for a perpendicular electrode penetration, ocular-dominance columns, and orientation columns are all organized across layers of the cortex. Ocular Dominance columns: In V1, at layers above and below layer 4 (in the cat) or 4C (in the monkey), inputs from both eyes mix for the first time. The cells that receive input from both eyes are known as binocular cells. The mixing is typically very precise: for a given binocular neuron one finds that identical receptive field characteristics (i.e., same location, same orientation preference, being simple or complex, etc.) can be recorded separately for after stimulating each eye. The only difference that can be detected is in the magnitude of the response (the firing rate) induced by stimulation of each eye. Typically, one eye's stimulation induces a response that is stronger than the other eye's stimulation. This phenomenon is known as ‘ ocular dominance ’. After recording from many binocular cells, H & W created 7 classes of ocular dominance, where class #4 stands for equal response for both eyes (no dominance) and classes #1 and #7 stand for complete monopoly of response for the contra lateral (opposite side) and ipsi lateral (same side) eye, respectively. All other classes represent various degree of dominance. Surprisingly, neurons in the cortex are organized in vertical
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110 cortex and beyond 2008 - Lecture 5: Primary Visual...

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