Instability of syllable repetition in patients with spinocerebellar ataxia and Parkinson's disease

Abstract

The aim of the current study was to test the hypothesis of a fundamental impairment of vocal pacing in patients with spinocerebellar ataxia and Parkinson's disease. Thirty-one patients with spinocerebellar ataxia, 42 patients with Parkinson's disease, and 43 healthy controls had to repeat a single syllable at a self-chosen isochronous pace. The coefficient of variance for interval length and the change in interval length with successive utterances were used to describe pace stability. Ataxic and parkinsonian patients both showed a significant instability of vocal pace performance. Ataxic speakers featured difficulties in keeping the pace immediately from the beginning of the task, whereas parkinsonian patients accelerated the pace in the course of the performance. The results support differential roles of cerebellar and basal ganglia pathways in motor speech performance. Cerebellar function may be required for the general precision of interval timing, whereas basal ganglia rather serve to maintain rhythm stability over time.