: Although pursuit eye movements are necessarily guided by visual feedback, the pursuit system must also utilize predictive control to achieve clear vision of a moving target. This is due to the large approximately 100 ms delay required to process visual information. If visual control alone were used, timing errors during pursuit should also be approximately 100 ms. In fact, the eye lags the target by no more than 4 ms during sinusoidal, circular, and more complex sum-of-sines motions. In addition, the eye can continue to track a target with little lag when the target is turned off briefly during circular or linear pursuit. Some forms of predictive control are only learned after extended repetition of a predictable target motion. For example, pursuit performance along a half-circle trajectory improves dramatically with training: large overshoot error early in training slowly disappear during approximately 1000 repetitions of the half-circle. This training produces permanent alterations in input-output processing because aftereffect errors appear when the monkey is returned to a circle trajectory that was originally pursued with high accuracy. This slow learning of a complex motion is reminiscent of the slow and repetitive learning required to master a complex motor skill or procedure. Its study may provide insight into how motor skills are acquired. The proposed experiments will study single-neuron responses in the frontal eye field (FEF) of monkeys during the performance of several of these predictive behaviors to determine their role in generating predictive pursuit. When single-neuron studies are completed in each monkey, that part of the FEF most active during pursuit will be deactivated by reversible injections of GABA agonists to study the global role of the FEF during predictive pursuit.
The specific aims are to study: FEF responses during predictable versus non-predictable pursuit, FEF timing during predictable CW-to-CCW transitions, FEF activity during the learning of predictive pursuit, and FEF involvement in maintaining pursuit when the target is turned off. These results will be compared to responses from the cerebellar flocculus and paraflocculus studied in the same paradigms to contrast the roles played by these two brain systems. This work has clinical relevance. Deficits in oculomotor control are currently used as markers for clinical disorders such as schizophrenia and Parkinson's disease that involve deficits in thinking and motor processing. The measures of predictive control being developed will allow detailed assessments of predictive disorders. In addition, an understanding of how the brain learns predictive control may lead to strategies for rehabilitating patients.
