The ability to coordinate movements during the performance of complex behaviors in our ever-changing environment is an essential goal of the nervous system. To accomplish this, sensory information must be integrated continuously in order to construct a representation of objects in the world. This critical function requires the ability to distinguish between self-generated and object motion, to integrate diverse sensory information, and to plan and execute simultaneous motor behaviors. The neural control of eye movements is an experimental system that has provided significant insights into the neural mechanisms mediating visual orienting behaviors. Directing the line of sight (gaze) towards interesting objects enhances our perception of the object and provides a way to construct and maintain an internal model of the world. These shifts in gaze direction are generally accomplished by coordinating movements of the eyes and head, and they provide an excellent model system for studying the neural control of orienting behavior, the coordination of multiple body segments, spatial orientation and transformation of sensory information into motor commands. By recording the activity of specific groups of neurons during performance of orienting movements it is possible to correlate neural responses with particular features of coordinated gaze shifts. The goals of the proposed research are to use these techniques to elucidate the neural computations and processes involved in eye-head coordination. Our recent experiments, recording neural activity in the brainstem of head-free monkeys, indicate that the relationships which have previously defined the rules of the oculomotor system, break down when the head and eyes move together to re-direct the line of sight (gaze). The implications of these experiments are that hypotheses of oculomotor control based on data from head restrained subjects, are a special case of a more general system. The proposed experiments are designed to identify and characterize the mechanisms of this more general control system, and will contribute directly to our understanding of the neural control of orienting movements. They also contribute to a more general understanding of the neural mechanisms involved in motor control and coordination during complex behaviors. In addition, this research will facilitate identification and treatment of spatial disorientation, saccadic and/or gaze dysmetrias, and brain stem damage resulting from trauma or disease.
