The Postnatal Development of the Visual Corticopontine Projection in the Hamster
Graf, Ethan R.
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The adult mammalian cortex is divided into a number of different functionally distinct areas, each forming very specific connections with other areas of the brain. But exactly how hardwired are these connections? A major concern in the study of cortical development is how such distinct areas, including the specificity of their connections, develop. Some studies show that the developing cortex is just as differentiated as the adult while other studies reveal that early cortex is fairly uniform and becomes transformed and differentiated throughout development by the input it receives. By removing the lateral geniculate nucleus (LON) in the thalamus, visual cortical axons are forced to develop without thalamic input. A study of the visual corticopontine projection in the hamster in this situation shows a dramatic increase in the extent of arborization within the pons as compared to the normally developing corticopontine tract (M. Kingsbury, personal communication). In order to discover the role thalamic input plays in cortical development, the normal development of this tract in the hamster was studied. It was discovered that while there seems to be a period of exuberance during development, it is not as great as that observed in the thalamic lesioned brains. It appears as though developing cortex void of thalamic input fails to undergo the process of refinement while at the same time increases the amount of secondary sprouting. The exuberance in these brains, which is not found at any time during development, proves how plastic connections may be, while at the same time is likely to profoundly affect the functional capabilities of other areas.With honors.