Memory-guided saccadic eye movements: effects of cerebellar disease

We compared the accuracy of oblique, memory-guided saccades if the eye is stationary or moves horizontally during the memory period. We studied 11 patients with cerebellar disease and 11 age-matched control subjects. Normal subjects showed similar accuracy of saccades for both conditions. In contrast, all patients showed greater errors if the eye moved horizontally during the memory period; however, errors of both vertical and horizontal components of memory-guided saccades were similar. Thus, inaccuracy of memory-guided saccades could not be simply attributed to failure to internally monitor change in horizontal gaze during the memory period. Instead, we propose that the greater saccadic errors which occurred when gaze changed during the memory period reflected a disruption of predictive mechanisms governing eye movements.