The superior colliculus is a structure in the midbrain thought to mediate attention and orienting responses. This structure integrates visual, auditory and tactile sensory information that comes from lower relay centers (ascending) and from the cerebral cortex (descending). A single sensory nerve cell (neuron) often is functionally characterized by the properties of its "receptive field," which is the set of criteria for location, shape, movement or other aspects of a stimulus that cause the cell to respond. For a higher-order sensory neuron, this receptive field may be built up from the receptive fields of many separate sensory neurons that send processes to converge on that neuron. Within the superior colliculus, it is unknown which incoming (afferent) fibers converge on individual neurons, which properties of the receptive field depend on which afferents, and which receptive field properties of the output neurons are most directly involved in behavior. This project examines input to cells in the superior colliculus from neurons of the somatosensory system, responsive to touch on the face, limbs, or body surface. Preliminary studies show that somatosensory neurons in the superior colliculus receive both ascending and descending inputs. Electrophysiological stimulation and recording techniques will be used to identify the patterns of convergence of these different inputs on the collicular neurons, to determine correlations between inputs and receptive field properties, and determine which collicular neurons send output to the brain and spinal cord. This work exploits the superior colliculus as a model with a large base of information about its structure and function, to understand how the nervous system builds particular sensory receptive fields from convergent individual sensory inputs.
