This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Saccadic eye movements, which rapidly shift our direction of gaze from one interesting object to another, remain accurate throughout life despite the problems brought on by growth, injury and aging. Therefore, the oculomotor system must be capable of motor adaptation or learning. Evidence from our lab and others indicates that the oculomotor part of the cerebellum is required for saccade learning. We have begun to investigate the neuronal mechanism(s) that underlie this learning. To engage the adaptation mechanism without actually damaging the brain, we deceive monkeys into thinking their saccades are inaccurate, as they would be after brain injury, by displacing the target they are following with their eyes just as a saccade is launched toward it. Gradually, the oculomotor system alters the amplitude of the saccade to reduce its landing error so that the eye eventually falls directly on the displaced target. In a first experiment, we have discovered that the activity of complex spikes in the oculomotor cerebellar vermis changes dramatically according to the 'sign' of the landing error, i.e., over- vs. undershooting. Therefore, this part of the cerebellum receives an error signal, which could drive the gradual adjustment of saccade amplitude that occurs in this behavioral adaptation paradigm. In a second experiment, we studied whether inputs to the cerebellum already reflect the adaptation process. When we examined the activity of neurons in the nucleus reticularis tegmenti pontis (NRTP), a major cerebellar input of saccade-related signals, we found that almost half changed their discharge patterns as adaptation ensued. The change was most consistent when the saccade was required to decrease in amplitude. These latter data suggest that the sites of saccadic motor learning may be distributed throughout the oculomotor system and just not be confined to the cerebellum.
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