The brainstem burst generator for saccadic eye movements: a modern synthesis.

In the 16 years since we last summarized the behavior of the premotor elements that control saccades, research has revealed shortcomings in previous formulations of the control mechanisms of the brainstem saccadic burst generator. Specifically, complexities in the eye movement plant, a more detailed knowledge of the behaviors of certain bursting neurons, and previously undiscovered anatomical connections have broadened our knowledge but have generated new questions that require rethinking previous concepts. Perhaps the most crucial revelations/insights have come from studies that have implicated the superior colliculus and the midline cerebellum as crucial elements of the burst generator. In summarizing these recent findings here, we have been led to conclude that the superior colliculus issues the saccadic command and receives feedback from the brainstem burst generators, but the feedback does not control saccade size. In addition, the midline cerebellum also contains a feedback path, but only as part of a more generalized circuit that serves multiple functions.