SACCADIC EYE MOVEMENT STUDIES

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DESCRIPTION: The long-term objective of this research is to understand how the nervous system translates sensory information into the commands for initiation and execution of movements. The PI has used the saccadic eye movement system as a model for study because of its simple peripheral mechanics and musculature and the ease with which eye movements can be quickly and accurately recorded. Because of these advantages, the saccadic system is comparatively well understood in terms of its component neuron types, their discharge patterns, and many of their connections. Nonetheless, in contrast to the abundance of recent work on more central saccadic structures (e.g., cortex), there are a number of fundamental questions about the brainstem saccade generator that have not been addressed. The PI proposes to continue investigations of the saccade generator by examining two of these basic, important areas. First, virtually all models (i.e., hypotheses) of organization of the saccade generator require the nucleus prepositus hypoglossi (nph) to provide either eye position, eye velocity, or more complex signals to other elements in the saccade generator. The PI is testing the effect of damage to that structure on saccades and will continue these experiments in two ways. A class of nph neurons, the "burster driving neurons" has been suggested to provide an important excitatory drive to the saccade generator in the cat. To test the validity of this suggestion, in one experiment he will describe the discharge of these neurons in the trained monkey. In another series of experiment, he will expand the tests of the effects of nph damage by examining the non- saccadic eye movement deficits that result from nph lesions in order to better define the neural substrate for the oculomotor neuronal integrator, another pivotal element of the saccade generator. The second region to be studied is the rostral pons. While the superior colliculus has long been implicated in the generation of saccades, it is not essential for saccade production. Therefore, another structure must either mediate its effects or be able to substitute for it when the colliculus is damaged. An obvious candidate is the rostral pons which receives collicular as well as cortical inputs. The PI will examine the metrics of the discharge rostral pontine neurons and quantitatively correlate that discharge with the saccade and target metrics in order to discover whether these neuron might code either previously hypothesized saccade signals or new signals that must be incorporated into evolving models of saccade generation. He will also test these neurons for input from collicular or cortical areas by using electrical stimulation. These studies should provide an example of how the nervous system processes visual sensory information into saccadic motor responses. In addition, the co-localization of structures with saccadic functions and the ease with which eye movements can be accurately monitored has proven, and should continue to be very useful in the diagnosis and localization of nervous system dysfunction resulting from a wide variety of causes.