Ataxia reflected in the simulated movements of patients with cerebellar lesions.

Previous studies demonstrated that the time required to simulate mentally a complex movement is highly correlated with the time required to execute the same task. The purpose of this experiment was to examine whether this relationship exists when execution times are prolonged as a consequence of the motor abnormalities exhibited by patients with substantial cerebellar pathology. The paradigm required subjects to alternate between moving a hand-held stylus horizontally on a digitizing tablet through a four-segment template and imagining the same movement through the same template. These two modes of performance were compared based on the times required to complete the two types of trials. Performance using both upper extremities was assessed using templates with two different levels of difficulty. Difficulty was varied by interposing gates that narrowed the path through the template. Using a MANOVA, measurements of actual and simulated movement times were compared between the group of cerebellar patients and a group of age- and sex-matched controls. The results showed that: (1) both movement times and mental-simulation times were greater for cerebellar patients than for control subjects under all experimental conditions, (2) both the movement times and the mental-simulation times of the patients were greater on the more-affected side than on the less-affected side, and (3) on the more-affected side, there was no significant difference between the patients' simulation and movement times for either the more difficult or less difficult condition. Thus, the consequence of cerebellar dysfunction on the time required to execute a volitional movement is reflected in the time needed to simulate the same behavior.