110 LGN-cortex 2008

110 LGN-cortex 2008 - Lecture 4: From the retina to the...

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Lecture 4: From the retina to the primary visual cortex through the LGN Topics to be discussed: Organization rules for sensory systems The Lateral Geniculate Nucleus: Structure and Function Primary Visual Cortex Classes of cortical receptive fields within V1 Organizational rules for the cortex Organization rules for sensory systems: 1) General rule for the organization of sensory systems: Information from the periphery has to reach the cortex via the thalamus. In the case of the visual system information has to reach the visual cortex through the Lateral Geniculate Nucleus (LGN) division of the thalamus. 2) General rule for the organization of sensory and motor systems: Topographical organization. By topographical organization it is meant that neighboring areas in the periphery (e.g., retina) are directly connected to neighboring areas "upstream” (e.g., LGN, which in turn connect to neighboring areas in the cortex, etc.). Thus, an image of an object that is reflected on the retina is transmitted as one, continuous image to the LGN and beyond. In the visual system this organization is called retinotopic organization . You will encounter later other types of topographical organization in sensory systems: a tonotopic organization in the auditory system and somatotopic organization in the somatosensory system. Clinical implications: Migraine (from a Greek word meaning “half of the skull”) refers to recurrent attacks of headache that are usually localized to one side of the head; that very in severity, frequency and duration; and are often accompanied by nausea and vomiting. Migraine is perhaps the most common neurological disorder, afflicting some 5 to 20% of the population at some time in their lives, and seems to be related to problems with the blood vessels that supply the brain. People who suffer from “classical migraine” experience an “aura” that precedes the migraine and lasts 20 – 40 minutes. The aura begins as a point of flashing light that slowly enlarges over time. There is no sight in the flashing area; it becomes a blind region – scotoma – in the visual field. Due to the retinotopic organization, the scotoma affects the corresponding part of the visual world. If, for example, a person has a classical migraine attack at the cortical representation of the fovea, he will experience problems in the center of his visual field. If such a person glances around the room and his scotoma happens to “fall” on a large clock or painting on the wall, the object will disappear completely. But instead of seeing an enormous void in its place, he sees a normal-looking wall with paint or wallpaper. The region corresponding to the missing object is simply covered with the same color of paint or wallpaper due to active “filling-in”.
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3) General rule for the organization of sensory and motor systems: Crossing sides. Neuronal information from your
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This note was uploaded on 04/14/2010 for the course BIO SCI BIO N110 taught by Professor Leon,chance&parker during the Spring '09 term at UC Irvine.

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110 LGN-cortex 2008 - Lecture 4: From the retina to the...

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