Neural control of foveal pursuit versus saccadic eye movements in primates — Single-unit data and models

摘要

The design and implementation of electromechanical devices to pursue maneuvering visual targets or to direct their optical axis quickly towards a briefly presented stationary target present formidable challenges to engineers. Yet the primate oculomotor system performs both tasks superbly, using different strategies and different sets of neural elements to acquire the appropriate information from the retina and to generate the required neural control signals for the oculomotor motoneurons. A framework for these two oculomotor subsystems, the pursuit system and the saccadic system, is proposed on the basis of neurophysiological findings in alert monkeys. This model is arranged into a sequence of spatiotemporal translation, motor program generation, and neural integration. For the purpose of foveal pursuit movements, an eye velocity signal must be internally generated and updated according to the current position error on the retina. This design probably involves a recently discovered class of pursuit neurons. Saccadic eye movements are probably controlled by burst neurons. Based on striking similarities between the neural activity of these recently analyzed burst neurons and Renshaw cells, a detailed quantitative model for the generation of preprogrammed saccades, the Renshaw model, is proposed. Open and controversial questions in the literature concerning various strategies being used by the primate oculomotor system are mentioned.