Because the maturation of the superior colliculus (SC) plays an integral role in the development of visual orientation and attention, the ontogeny of its visual cells has been subjected to a great deal of scrutiny. Because these cells are concentrated most heavily in superficial laminae, it was this population that was examined most closely. These are not, however, the cells most directly involved in these behaviors. Rather, it is the deeper laminae cells, whose axons project to motor and premotor areas, that are most relevant. Recent evidence has shown that the visual afferents involved in the elaboration of receptive field properties are different for superficial than for deep labinae cells. These may show substantially different ontogenetic time courses and have different developmental requirements reflecting their differing roles in behavior. By employing a multidisciplinary (anatomical, physiological and behavioral) approach to document the maturation of deep laminae visual cells, we can begin realizing some of the objectives that originally prompted much of the interest in this structure. Specifically, these studies will determine when deep laminae visual cells are first functional, what are their receptive field properties and how these change during maturation. In addition, data will be generated to evaluate developmental changes in the visual representation in the SC. Furthermore, since corticotectal cells (in suprasylvian cortex) are responsible for the complex properties of deep laminae visual cells they will be studied ontogenetically to evaluate at what maturational stages their properties are imposed on SC visual cells. These data are necessary if we are to understand how the brain builds the receptive field properties that play a major role in transforming visual cues into coordinated visually-guided behaviors.
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