(Author's abstract): The long-term goal of this research project is to produce quantitative neurophysiological data in monkey and interpret the results to generate a deeper understanding of the normal operation of the human oculomotor system. Such data may also be useful in the diagnosis of certain neurological disorders with oculomotor manifestations. Among oculomotor systems the saccadic system occupies a pre-eminent position as a model system for increasing the understanding of controlled biological movements in general. Therefore, the research proposed for the next project period focuses on several, as yet unanswered, questions regarding the neural control of saccades. Specifically, the project will address the following three questions: 1) Are saccade dynamics controlled by a rostrally directed wave of neural activity in the superior colliculus? Build up neurons, a class of neuron located in the ventral intermediate layers of the colliculus with open-ended movement fields and extensive build up of activity well before saccade onset, will be studied individually with traditional serial recordings and simultaneously with multi-electrode arrays. Data will be obtained from cells evenly spaced over the entire rostral part of the colliculus using these two techniques. The data will be used to generate three-dimensional representations of the population activity in build up neurons at closely spaced temporal intervals during saccades. Nonparametric tests will be used to test the statistical evidence for a sequential activation of buildup neurons and the presence of a wave. 2) What are the physiological characteristics of the resettable neural integrator that have been hypothesized to generate the feedback signal for the saccadic control system? Redirected saccades that putatively probe the state of the integrator will be evoked by stimulation of the colliculus or the frontal eye fields net the end and shortly after preceding visually guided saccades. In order to remove confounding neuronal signals that may prevent observation of the isolated integrator, we will first truncate the previous saccade by stimulation of the rostral pole region of the colliculus or the omnipauser region in the pontine reticular formation. stimulation of either of these regions terminates residual activity in the colliculus associated with the previous saccade that could contribute, by a mechanism of spatial averaging, to the deviation measured in redirected saccades. 3) How are signals from the frontal eye fields and the superior colliculus combined at the level of the saccadic burst generator to coordinate saccadic control? Stimulation of the colliculus and the frontal eye fields in the same animal will be carried out in order to clarify how inputs from these two higher level saccadic control regions, which have very different dynamic characteristics during saccades, are combined at the level of the horizontal saccadic burst generator in the paramedian pontine reticular formation. Specifically. individual cells from each of the classes found in the burst generator will be studied for evidence of synaptic input from either or both structures. Particular attention will be paid to conducting the electrophysiological tests for input from either structure during contralateral saccades when the inhibitory influences of omnipause neurons, that may have obscured much inputs in previous experiments, are absent.
