SACCADIC EYE MOVEMENT STUDIES

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The long-term objective of this research is to understand how the nervous system translates sensory information into the commands for the initiation and execution of saccadic eye movements. The saccadic system is comparatively well understood because of its simple peripheral mechanics and musculature, because saccade-related brainstem neurons are accessible, and because it is easy to accurately measure eye movements. We know the neuron types,k their discharge patterns, and may of the connections of the neural saccade generator. Our understanding is incomplete, however, so it has been supplemented with reasonable, neurophysiological assumptions to yield working hypotheses, in the form of models,, that simulate a functioning saccade generator. We will perform three sets of experiments to more completely characterize the saccade generation process. The first experiment will test two popular current models. Those two models make distinctly different predictions about the saccades that will result following damage to the oculomotor neural integrator. Therefore we will lesion the putative integrator and record the changes in saccades. This experiment will show that the model that correctly forecasts the resulting saccades most accurate describes the saccade generator. In the second set of experiments we will record from putative inputs to the saccade generator. We will concentrate on saccade-related neurons located in regions of the mesencephalon known to project to the saccade generator. The parameters of the discharge will be quantitatively compared to the saccade and target metrics in order to discover whether these neurons code previously hypothesized saccade signals or new signals that must be incorporated into evolving models of saccade generation. Finally, we will study the connections of mesencephalic saccade-related neurons t neurons in the saccade generator as well as their connections with other saccade-related structures. We will use peri-spike histograms in alert trained animals to assess the functional connections between neurons. The description of discharge characteristics and the demonstration of connections of functionally identified types of neurons will help us to understand how signals originating more centrally produce saccadic eye movements. These studies should further our understanding of how the nervous system transforms visual sensory information to generate saccadic motor responses. In addition, our data and that of other has been, and should continue to be, very useful in the diagnosis and localization of nervous system dysfunction resulting from a wide variety of causes.