The superior colliculus is a brain region that is involved in the processing of visumotor information. Because the inputs and outputs of the superior colliculus are clearly defined, and its neurons are organized into well-defined layers, the superior colliculus presents a unique opportunity for understanding brain information processing mechanisms. The goal of this project is to use powerful patch-clamp recording methods in slices of superior colliculus to study synaptic connections between neurons in different layers of the colliculus. Such connections probably make important contributions to collicular function, but the nature of these interactions is not known because previous methods used to study collicular physiology were not sufficiently sensitive to detect such interactions. To assess the synaptic connections between superficial gray layer cells and premotor cells of the intermediate gray layer, we will record responses of the premotor cells to stimulation of neurons in the superficial layers. The two specific hypotheses to be tested with these experiments are that: 1) the descending intracollicular projections sharpen the spatial distribution of collicular activity by first exciting and then, through feedback interneurons, inhibiting underlying premotor cells and 2) these projections focus the temporal distribution of collicular activity by having the horizontal projects of interneurons inhibit premotor neurons in the surrounding regions.
