ATAXIA REFLECTED IN THE SIMULATED MOVEMENTS OF PATIENTS WITH CEREBELLAR LESIONS

Previous studies demonstrated that the time required to simulate menta lly a complex movement is highly correlated with the time required to execute the same task. The purpose of this experiment was to examine w hether this relationship exists when execution times are prolonged as a consequence of the motor abnormalities exhibited by patients with su bstantial cerebellar pathology. The paradigm required subjects to alte rnate between moving a hand-held stylus horizontally on a digitizing t ablet through a four-segment template and imagining the same movement through the same template. These two modes of performance were compare d based on the times required to complete the two types of trials. Per formance using both upper extremities was assessed using templates wit h two different levels of difficulty. Difficulty was varied by interpo sing gates that narrowed the path through the template. Using a MANOVA , measurements of actual and simulated movement times were compared be tween the group of cerebellar patients and a group of age- and sex-mat ched controls. The results showed that: (1) both movement times and me ntal-simulation times were greater for cerebellar patients than for co ntrol subjects under all experimental conditions, (2) both the movemen t times and the mental-simulation times of the patients were greater o n the more-affected side than on the less-affected side, and (3) on th e 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 dysfu nction on the time required to execute a volitional movement is reflec ted in the time needed to simulate the same behavior.