Does the cerebellum preferentially control discrete and not continuous movements?

Rebecca Marie Spencer, Purdue University

Abstract

Individuals with unilateral cerebellar damage exhibit increased temporal variability on finger tapping and intermittent drawing tasks when performing with their impaired limb. Surprisingly, these individuals are unimpaired in timing of continuous circle drawing (Spencer et al., in preparation). In Experiment 1, distinctions between discrete and continuous tasks and handedness effects were examined in neurologically healthy adults. Subjects performed repetitive and discrete finger tapping and circle drawing with their dominant and non-dominant limbs. Significant correlations were observed between temporal variability on discrete tapping and discrete drawing and between temporal variability on the discrete tasks and repetitive tapping. Temporal variability on repetitive continuous drawing did not correlate with temporal variability on the other tasks. Additionally, significant correlations were present between temporal variability of the dominant and non-dominant limb within each task. In Experiment 2, underlying impairments on discrete and continuous tasks in performance by subjects with cerebellar damage were examined. Individuals with unilateral or bilateral cerebellar damage and neurologically healthy young and elderly adults performed three tasks: discrete finger tapping, discrete circle drawing, and continuous circle drawing. Increased temporal variability was observed when subjects with unilateral cerebellar damage performed the discrete tasks with the impaired limb relative to the unimpaired limb; however, these subjects exhibited no temporal impairment on the continuous drawing task. Additionally, subjects with bilateral cerebellar damage were more variable on the discrete tasks relative to control subjects, yet were not more variable on the continuous task. Temporal variability of the joint cycles paralleled the results from the endpoint: subjects with cerebellar damage exhibited increased temporal variability of joint cycles on the discrete and not the continuous drawing task. Surprisingly, coordination deficits were not observed on either drawing task. However, subjects with cerebellar damage tended to decompose movements, moving one joint at a time when possible. Together, these experiments support the hypothesis of a dichotomy in timing processes. Explicit timing utilizes the cerebellum for representation of the temporal goal. Discrete movement tasks appear to utilize such a timing process. Implicit timing is an emergent process. The trajectory and limb properties can account for temporal consistency during continuous movements.

Degree

Ph.D.

Advisors

Zelaznik, Purdue University.

Subject Area

Neurology

COinS